ERE5.5 | Coupled thermo-hydro-mechanical-chemical (THMC) processes in geological media
EDI
Coupled thermo-hydro-mechanical-chemical (THMC) processes in geological media
Co-organized by EMRP1
Convener: Silvia De Simone | Co-conveners: Tuanny CajuhiECSECS, Monia Procesi, Iman Rahimzadeh Kivi, Keita Yoshioka, Franco Tassi, Victor Vilarrasa
Orals
| Mon, 24 Apr, 08:30–12:30 (CEST)
 
Room -2.16
Posters on site
| Attendance Mon, 24 Apr, 14:00–15:45 (CEST)
 
Hall X4
Posters virtual
| Attendance Mon, 24 Apr, 14:00–15:45 (CEST)
 
vHall ERE
Orals |
Mon, 08:30
Mon, 14:00
Mon, 14:00
Geological media are a strategic resource for the forthcoming energy transition and constitute an important ally in the fight to mitigate the adverse effects of climate change. Several energy and environmental processes in the subsurface involve multi-physical interactions between the porous and fractured rock, and the fluids filling the voids: changes in pore pressure and temperature, rock deformation and chemical reactions occur simultaneously and impact each other. This characteristic has profound implications on the energy production and the waste storage. Forecasts are bounded to the adequate understanding of field data associated with thermo-hydro-mechanical-chemical (THMC) processes and predictive capabilities heavily rely on the quality of the integration between the input data (laboratory and field evidence) and the mathematical models describing the evolution of the multi-physical systems. This session is dedicated to studies investigating all or part of these THMC interactions by means of experimental, analytical, numerical, multi-scale, data-driven and artificial intelligence methods, as well as studies focused on laboratory characterization and on gathering and interpreting in-situ geological and geophysical evidence of the multi-physical behavior of rocks. Welcomed contributions include approaches covering applications of carbon capture and storage (CCS), geothermal systems, gas storage, energy storage, mining, reservoir management, reservoir stimulation, fluid injection-induced seismicity and radioactive waste storage.

Orals: Mon, 24 Apr | Room -2.16

Chairpersons: Monia Procesi, Tuanny Cajuhi
Experimental observations of coupled THMC processes
08:30–08:35
08:35–08:45
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EGU23-11330
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ECS
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On-site presentation
Eko Pramudyo, Ryota Goto, Kiyotoshi Sakaguchi, and Noriaki Watanabe

Previous studies showed that cloud-fracture networks (CFNs), networks of permeable microfractures densely distributed over rock body, formed in granite at superhot geothermal conditions (> ~400 °C) through the stimulation of pre-existing microfractures by low-viscosity water near and above its critical temperature. The CFNs were also shown to form in granite at conventional (~150 – 300 °C) and superhot geothermal conditions by injection of low-viscosity CO2, through the same mechanism as that by low-viscosity water at superhot geothermal conditions. The stimulation of pre-existing microfractures by the low-viscosity CO2 implied that CFNs may be formed in the matrix (i.e., unfractured rock) of naturally-fractured conventional and superhot geothermal environments, where conventional bi-winged hydraulic fractures are known to be difficult to be achieved by injection of cold water. The present study illustrates the possibility of CFN formations in naturally-fractured geothermal environments, along with the shear-slip of the natural fractures, through CO2-injection experiments into cylindrical granite samples, each contained a sawcut (representing a natural fracture) inclined from the sample axis, under geothermal conditions. The experiments show that CO2 injection induced a larger cumulative shear displacement on the sawcut at conventional geothermal condition than at superhot geothermal condition. CFNs were formed at conventional and superhot geothermal conditions; nonetheless, the fracture-apertures were thinner for the CFN formed at conventional geothermal condition. The results imply that CFNs may be formed in naturally fractured geothermal environments, and may provide additional fluid-flow paths between the stimulated natural fractures.

How to cite: Pramudyo, E., Goto, R., Sakaguchi, K., and Watanabe, N.: Shear-slip and Complex Fracturing by CO2 Injection in Naturally Fractured Granite at Geothermal Conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11330, https://doi.org/10.5194/egusphere-egu23-11330, 2023.

08:45–08:55
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EGU23-15956
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ECS
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On-site presentation
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Marco Fazio and Martin Sauter

Studying the mechanical and hydraulic behaviour of rocks at different depths is crucial to understand their potential as georeservoirs. In particular, permeability and porosity are affected by changing conditions and their values measured at surface do not represent the real value at a certain depth. Mostly rocks with low or intermediate permeability have been tested in this regard. Here, instead, we focus on a highly porous and permeable rock (approximately 25% and 1000 mD respectively): Bentheim sandstone.

Because of its petrophysical properties Bentheim sandstone is regarded as a reference rock material in laboratory experiments of rock mechanics: it is quasi monocrystalline (quartz up to 97%), with a well-sorted grain size distribution and well-connected pores, showing lateral continuity and homogeneous geometric, hydraulic and mechanical properties at the block scale.

Unsurprisingly, Bentheim sandstone, as a georeservoir, has been extensively tested in triaxial conditions for a variety of purposes, from oil and gas exploitation to geothermal energy and carbon storage and sequestration projects. In fact Bentheim sandstone is taken into consideration as a potential warm aquifer for low-cost geothermal energy and for studying anhydrite cementification in georeservoirs. Since Bentheim sandstone can be found at more than 2 km deep and has been previously buried down to 3.5 km, it is important to fully understand its behaviour at different pressure, temperature, hydraulic and stress-hystory conditions.

Previous laboratory studies have shown how the permeability of Bentheim sandstone is affected by effective confining pressure, bedding orientations and axial strain. In particular, it has been observed that an increase in effective pressure, corresponding to an increase in depth, does not influence the permeability of this sandstone. In reservoir geomechanics, this is a crucial finding. However, rocks at depths also experience different temperature and fluid pressure conditions, as well as different types of historic stress evolution. Although, general relationships between permeability and these parameters do exist, their specific effect on Bentheim sandstone has never been investigated in detail.

Based on triaxial experiments in a state-of-the-art apparatus, we demonstrate on large cylindrical samples the behaviour of Bentheim sandstone for quasi reservoir conditions. Our goal is to fill in the gap in understanding the hydromechanical behaviour of this highly-permeable rock and concomitant permeability changes at different georeservoir conditions, where a suite of geomechanical parameters is investigated.

How to cite: Fazio, M. and Sauter, M.: Simulation of different georeservoir conditions on a highly-permeable sandstone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15956, https://doi.org/10.5194/egusphere-egu23-15956, 2023.

08:55–09:05
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EGU23-13703
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ECS
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On-site presentation
Angel Ramirez, Pham Tien Hung, Leandra Weydt, and Ingo Sass

Matrix acidification is one of the most popular stimulation techniques to increase the porosity and permeability of reservoir systems. Usually, the thermal-hydro-mechanical properties of reservoir rocks affected by the matrix acidification process are studied using flow-through tests or autoclave experiments. In this study, a novel acidification approach was tested using a thermal triaxial device at the TU Darmstadt laboratory. Thereby, hydrochloric acid 0.0375% (HCl pH=2) was flushed continuously through a total of five Remlinger sandstone samples under reservoir conditions (90oC temperature, s1=25 MPa, and s3=23MPa). Changes in matrix permeability and other petrophysical parameters due to the chemical reaction between the rock sample and HCl were recorded before, during, and after the reactive experiments. In addition, outflow fluid samples were collected and the pH was subsequently measured. After approximately 30 days of continuous flow for each sample, the permeability increased for all the samples, with a maximum increase of 300%. Likewise, porosity increased from 13.2% to 14.5%. In contrast, P- and -S-wave velocities decreased from 2608 to 2189 m‧s-1 and from 1540 to 1380 m‧s‑1, respectively. Test results provide important information for reservoir stimulation and can be used to benchmark THMC models.

How to cite: Ramirez, A., Hung, P. T., Weydt, L., and Sass, I.: Long-term matrix acidification experiments under reservoir conditions using the Thermo-Triaxial device, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13703, https://doi.org/10.5194/egusphere-egu23-13703, 2023.

09:05–09:15
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EGU23-7185
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ECS
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Virtual presentation
Chen Zhao, Qinhong Hu, Qiming Wang, Majie Fan, Jan Ilavsky, and Min Wang

Shale has been focused because of its potentials in fossil fuel as unconventional reservoirs and in carbon storage as cap rocks. Fluid rock interaction is important for shale study. Because hydraulic fracturing in unconventional oil and gas development and the sealing ability of cap rock are all related to the fluid-rock interaction. The fluid-rock interactions,  such as the spontaneous imbibition (SI), were studied on Wolfcamp Shale core samples in Midland Basin, west Texas in this work. Multiple experiments including X-ray diffraction (XRD), contact angle measurement, scanning electronic microscopy (SEM), and (ultra-) small angle X-ray scattering [(U)SAXS] were performed to characterize the mineralogy, wettability, and pore structure to assist the analysis of the SI data in Wolfcamp Shale. XRD results indicated the Wolfcamp Shale samples were dominated by carbonate and siliciclastics with different sample depths, which is concordant with the well-logging data. The SI experiments were conducted in hydrophilic de-ionized water (DIW) and hydrophobic D2T (a mixture of two parts of decane and one part of toluene). Most samples have layer structure, therefore, the SI experiments were performed in directions that parallel to the layer (P direction) and transverse to the layer (T direction) on each sample. The fitting slopes of SI results show that samples have better pore connectivity in hydrophobic D2T than DIW in both directions. In P direction, the imbibed volume of DIW and D2T are very close to each other, which indicate the Wolfcamp Shale could be more oil wet. (U)SAXS results provided the pore diameter distribution (PDD) of the samples, which separates the samples into two groups. Associated with mineralogy, group 1 is dominated by siliciclastic with pores at 10 nm and 50 nm, and group 2 is dominated by carbonate with pores at 100 nm and 600 nm. Coupled with PDD and mineralogy, the fitting slopes in group 2 in DIW P direction decrease and then increase with clay content with the turning-point at 30%. The micro-fractures and well-aligned clay minerals in SEM images in samples with more clay content could help to form fluid pathways during the DIW imbibition. Such a positive relationship in fitting slopes and clay content also appeared in D2T P direction imbibition. In summary, the experiments conducted on the Wolfcamp Shale in west Texas including SI, XRD, SEM, and (U)SAXS could investigate fluid transport mechanisms in shale to support the studies for unconventional reservoir development and carbon storage.

How to cite: Zhao, C., Hu, Q., Wang, Q., Fan, M., Ilavsky, J., and Wang, M.: Fluid-rock interaction of Wolfcamp Shale: the effects of pore structure and mineralogy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7185, https://doi.org/10.5194/egusphere-egu23-7185, 2023.

09:15–09:25
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EGU23-3131
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ECS
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On-site presentation
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Luis Salalá, Jonathan Argueta, Noriaki Watanabe, and Noriyoshi Tsuchiya

The use of Enhanced Geothermal Systems (EGS) has been recognized as a viable source of renewable energy in regions with high geothermal temperatures. Nevertheless, geothermal reservoirs may experience reduced permeability during exploration or operation. Research on chelating agents in geothermal environments has been widely disseminated as a complementary method to conventional methods such as hydraulic and chemical stimulation. Previous studies reported fast and significant improvements in permeability in granitic and volcanic rocks using aqueous solutions of glutamic L-diacetate acid (GLDA) under acidic conditions. However, no studies have been conducted with chelating agents applied to volcanic rocks at different pH conditions, since pH determines the ionic species in the solution, and thus, the chemical interactions taking place in a system. Furthermore, the dissolution of minerals in these conditions was not quantified for modeling purposes. In the present study, an aqueous solution of the chelating agent GLDA at various pH conditions (2-10) was applied to improve the permeability of single-fractured intermediate to basic volcanic rocks. According to the results, permeability increases about up 4.3-fold under weak acid (pH 4) conditions, while it increases about 36-fold under alkaline (pH 10) conditions, due primarily to the formation of voids caused by mineral dissolution or groundmass dissolution, respectively. Moreover, channeled samples with mirror-conditions revealed that the formation of voids at acidic conditions was as deep as 135 µm by the selective dissolution of hematite, whereas an average of 4-µm dissolution of quartz was promoted at alkaline conditions. Although the depth of voids formed in alkaline conditions is less than the case of acidic, quartz composes the matrix that surrounds the phenocrysts of volcanic rocks, promoting a preferential fluid path that improved the permeability further at alkaline conditions. This study is the first step in spreading the use of this chemical stimulation technique to different volcanic-rock geothermal systems.

Keywords: EGS, chelating agents, permeability enhancement, andesitic rock, selective dissolution of minerals.

How to cite: Salalá, L., Argueta, J., Watanabe, N., and Tsuchiya, N.: pH dependence of mineral dissolution and permeability enhancement of intermediate to basic volcanic rocks by chelating agent flooding under geothermal conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3131, https://doi.org/10.5194/egusphere-egu23-3131, 2023.

09:25–09:35
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EGU23-13900
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On-site presentation
Giancarlo Tamburello, Giovanni Chiodini, Giancarlo Ciotoli, Monia Procesi, Dmitri Rouwet, and Laura Sandri

In the last decades, the enormous potential for direct geothermal heat from aquifers attracted special attention, particularly toward those thermal springs indicating areas in which exploitation of geothermal energy might be economically feasible for indirect uses such as electrical power production. The availability of geochemical data besides the location of thermal spring areas assumes particular importance, especially in the first stages of a geothermal exploration program. In this work, we present a digitised format of the literature review of Gerald Ashley Waring on the geothermal springs of the world. This unprecedented dataset contains geographical coordinates (from georeferentiation) of ~6,000 geothermal spring areas, including complementary data such as temperatures, flow rates, total dissolved solids content (TDS, expressed in ppm), and quantitative chemical analysis of major elements (only for a few hundred sites). Using temperature and flow rate, we derive the heat discharged from 1483 thermal spring areas (between ~10-5 and ~103 MW, with a median value of ~0.5 MW and ~8300 MW in total). We complement this information with geological data sets currently available in the literature and analyse them using statistical and geospatial tools and a supervised machine-learning algorithm. We show that terrestrial heat flow, topography, volcanism, and extensional tectonic play a key role in the occurrence of thermal waters around the globe. These results can also be beneficial to address the geothermal interest towards specific and less studied areas and significantly drive the first steps of the geothermal surveys and detailed investigations. Finally, this data set in electronic format will be beneficial for future research on the spatial distribution of thermalism at a small scale and the variation of temperature and flow rate of several thermal springs in the last decades in certain regions.

How to cite: Tamburello, G., Chiodini, G., Ciotoli, G., Procesi, M., Rouwet, D., and Sandri, L.: Global thermal spring distribution and relationship to endogenous and exogenous factors, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13900, https://doi.org/10.5194/egusphere-egu23-13900, 2023.

09:35–09:45
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EGU23-10601
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ECS
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Virtual presentation
Liangwei Xu, Lei Chen, Hao Wei, and Keji Yang

Shale is an unconventional oil and gas reservoir with both generation and storage characteristics. Diagenesis has an important impact on its organic petrological characteristics, reservoir physical properties, pore system structure characteristics, mineral component content and transformation. Diagenesis is of great significance for its porosity and permeability analysis, reservoir comprehensive evaluation and shale gas productivity. At present, the researches on diagenesis and diagenetic evolution mainly focus on conventional sandstone reservoir. Because the application of conventional oil and gas reservoir characterization technology to shale reservoir is limited, and the diagenetic characteristics of shale reservoir are difficult to identify, the researches on diagenetic evolution of shale reservoir are relatively weak, and the comprehensive researches on diagenesis and diagenetic evolution of shale reservoir are relatively scarce.

At present, there are mainly two kinds of research methods on the dual effects of thermal evolution and diagenesis of shale: the first is the direct observation method, which uses high-resolution equipment to analyze shale samples with different maturity and diagenesis to determine the characteristics and development differences of diagenesis. However, this method ignores the heterogeneity and regional differences of samples, and cannot show all the evolution characteristics of shale in the diagenesis process. The second is the physical simulation method, that is, the sample of low maturity is selected, the temperature series is set, and the generation of diagenesis process is induced by heating. This method reduces the heterogeneity of samples and the influence of regional differences on the experimental results to a certain extent. It has strong comparability and can provide the overall characteristics in the process of diagenesis. However, the disadvantage is that it lacks intuitive characterization and cannot clearly and intuitively display the diagenetic evolution characteristics of minerals in the same area.

In view of the above problems, the diagenesis and diagenetic evolution of low-mature organic-rich Marine type II shale in the Middle Proterozoic Xiamalin Formation in Zhangjiakou area of Hebei Province were studied by using the method of high temperature and high pressure physical simulation. The characteristics of diagenesis were observed and characterized in the simulated samples, and the types of diagenesis in the simulated products were identified. A conceptual model of shale diagenetic evolution sequence based on physical simulation is established. In addition, this study also uses direct observation method to characterize the diagenetic characteristics of natural marine shales of Xiamaling Formation in this area. Five diagenetic types including compaction, cementation, dissolution, hydrocarbon generation of organic matter and clay mineral transformation are identified, and diagenetic stages of Xiamaling Formation shales are divided. Furthermore, the marine diagenetic evolution sequence and diagenetic evolution model of the Mesoproterozoic Xiamalin Formation in Zhangjiakou area of Hebei Province are established (Fig.1). This study makes up for the deficiency in the study of shale diagenetic evolution, and has important reference and indicative significance for the development of other high-over-mature Marine shale gas reservoirs in China and the world.


Fig. 1. Diagenetic evolution sequence of the Mesoproterozoic Xiamaling marine shale in Zhangjiakou, Hebei.

How to cite: Xu, L., Chen, L., Wei, H., and Yang, K.: Diagenesis characteristics and diagenetic evolution of organic-rich marine shale, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10601, https://doi.org/10.5194/egusphere-egu23-10601, 2023.

09:45–09:55
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EGU23-16878
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On-site presentation
Carbon dioxide soil emission monitoring as a tool for the assessment of environmental impact of geothermal plants
(withdrawn)
Alessandro Lenzi, Marcello Cinci, Annalisa Alemanni, Nicoletta Mazzuca, Pierre De Terrasson, Luigi Parisi, Alessandro Sbrana, Michele Sbrana, Selena Sironi, and Marzio Invernizzi
09:55–10:05
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EGU23-14038
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On-site presentation
Alessandra Ariano, Francesco Frondini, Carlo Cardellini, Giovanni Chiodini, Maurizio Petrelli, Marino Vetuschi Zuccolini, and Giorgio Virgili

In the central part of Tuscany region (Italy), is located the Larderello – Travale geothermal system which is a large-scale steam dominated system with reservoir temperatures that can exceed 350°C (Bellani et al. 2004). The characteristic high heat flow in this particular area is due to the presence of a thermal anomaly caused by the intrusion of a big Pliocene batholith into the upper crust (Musumeci et al. 2002). This work is aimed at investigating the relationships between carbon emissions and heat, particularly to analyse the distribution of CO2, CH4 and soil temperatures in the Monterotondo Marittimo and Sasso Pisano areas. Three hundred measurements of gas fluxes from the soil have been performed using the accumulation chamber method. CO2 fluxes range from 0.1 gm-2d-1 to about 20,000 gm-2d-1, while CH4 fluxes, available for a lower number of points, vary between 0 and 637 gm-2d-1. Soil temperatures were also measured at each location and ranges from 8.0 °C to 100 °C, with an average of 39.8 °C.

CO2 fluxes show a polymodal statistical distribution with (i) a background population characterised by an average CO2 flux in the order of 16.0 g m-2 d-1 and (ii) anomalous populations with an average CO2 flux of 400 g m-2 d-1 and 1600 g m-2 d-1   for Sasso Pisano and Monterotondo Marittimo respectively. Not null CH4 fluxes were measured only at points with a CO2 flux in the range of the anomalous CO2 flux population. The statistical distribution of the CH4 resulted more complex with two populations characterized by an average value of 0.8 g m-2d-1 and 174 g m-2d-1 respectively, probably reflecting differences in the gas transport mechanism in the soil and/or soil permeability, which is largely variable in the areas with anomalous flux.

The areas characterized by anomalous soil gas fluxes, show also an evident soil temperature anomaly (reaching values close to 100 °C), suggesting that soil degassing is accompanied by a significant process of steam condensation. In the anomalous areas, the CO₂/CH₄ ratios by weight vary between 1.6 x 10-4 to 1.0 x 10-1 and fall in the range of variation observed for the geothermal fluids of the Larderello-Travale region (Truesdell & Nehring, 1978; Chiodini et al., 1991; Chiodini & Marini, 1998).

Assuming that the soil is heated by steam condensation, a thermal energy release associated to the degassing process of about 200 MW is estimated for Monterotondo Marittimo, an energy release >15 MW is estimated for Sasso Pisano, where the measurements are still in progress.

How to cite: Ariano, A., Frondini, F., Cardellini, C., Chiodini, G., Petrelli, M., Vetuschi Zuccolini, M., and Virgili, G.: Carbon dioxide, methane and heat emissions of the Monterotondo Marittimo and Sasso Pisano geothermal areas (Tuscany, Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14038, https://doi.org/10.5194/egusphere-egu23-14038, 2023.

10:05–10:15
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EGU23-2037
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Virtual presentation
Füsun Tut Haklıdır and Raziye Şengün Çetin

The Kızıldere geothermal field, located in the eastern part of the Büyük Menderes Graben, is one of the most productive geothermal systems in Western Anatolia (Türkiye). Electricity production in the field, which began in 1984, is still ongoing with three flash type geothermal power plants.

Four geothermal reservoirs with different rock compositions and geochemical characteristics have been identified in Kızıldere geothermal system. Steam production has changed over time from a shallow reservoir to the hottest deep reservoirs in the system. In the steam phase, CO2 is the dominant gas type in the Kızıldere geothermal system, with concentrations ranging from 98% to 99%. The 13C analyses revealed that the primary source of CO2 is Paleozoic aged metamorphics and that the origin of CO2 is primarily reservoir carbonate dissolution. The deep reservoir contains sulfate, sulfide minerals, dissolved sulfate, dissolved sulfide (HS-), H2S gas, and organic sulfur compounds. Sulfate in thermal waters could be caused by gypsum dissolution or the oxidation of sulfides such as pyrite and pyrrhotite.

In this study, the possibilities of reducing H2S and CO2 emissions by chemical and biological methods were investigated, taking into account the characteristics of the Kızıldere geothermal system. For this purpose, field tests were carried out with 6 different solutions  and the selected bacteria to examine the reduction of non-condensable gases in the Kızıldere geothermal field.

How to cite: Tut Haklıdır, F. and Şengün Çetin, R.: Geochemical Characteristics of the Kızıldere Geothermal System (Turkey) and a Case Study for Emission Reduction in the Kızıldere Geothermal Field, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2037, https://doi.org/10.5194/egusphere-egu23-2037, 2023.

Coffee break
Chairpersons: Silvia De Simone, Keita Yoshioka, Victor Vilarrasa
Numerical modeling of coupled THMC processes
10:45–10:50
10:50–11:10
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EGU23-3770
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ECS
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solicited
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On-site presentation
Qinghua Lei

Fractures such as joints and faults are widely present in crustal rocks. These discontinuity structures often form complex networks and dominate the bulk behaviour of geological media. Thus, understanding how fracture networks affect multiphysical processes and phenomena in subsurface rock formations is highly relevant to many geoenergy and geoengineering applications. However, the large-scale behaviour of fractured rocks consisting of many fractures cannot be derived by simple applications of the knowledge of single fractures, due to the hierarchy of scales, heterogeneities, and physical mechanisms as well as the possible emergence of qualitatively different macroscopic properties. In other words, macroscopic phenomena in fractured media arise from the many-body effects of numerous interacting fractures, such that the emergent properties at the fracture network scale are much richer and often surprising compared to the behaviour of each individual fracture. So, more is different!

To study this problem, I have developed a novel physics-based discrete fracture network modelling framework to simulate seismo-thermo-hydro-mechanical-chemical processes in fractured rocks. This modelling approach faithfully honours the discontinuous nature of geological media via explicit representations of fracture populations in rock and numerically computes multiphysics processes by solving the governing equations of fundamental mechanics. No a priori assumption about the representative elementary volume is needed, rendering this approach as an appropriate tool to study hierarchical crustal rocks that may have no characteristic length scale. Using this modelling paradigm, diverse macroscopic phenomena are spontaneously captured as emergent properties physically arising from the collective behaviour of a large population of existing/growing fractures in rock.

In this presentation, I will illustrate the richness of collective phenomena in fractured media and elucidate the underlying multiscale, multiphysical mechanisms that drive their emergence. I will also show some application examples of using this fractured media simulation framework to address subsurface engineering problems such as underground excavation, injection-induced seismicity, and nuclear waste disposal. The modelling framework established and research findings obtained have important implications for safe and sustainable development of geoenergy and geoengineering.

How to cite: Lei, Q.: More is different: On the emergence of collective phenomena in fractured geological media, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3770, https://doi.org/10.5194/egusphere-egu23-3770, 2023.

11:10–11:20
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EGU23-1111
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ECS
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On-site presentation
Santiago Pena Clavijo, Mouadh Addassi, Thomas Finkbeiner, and Hussein Hoteit

Understanding fracture propagation in chemically active rock formations is of interest to several engineering and science disciplines. Fracture nucleation and growth governed by in-situ chemo-poro-mechanical processes is crucial, for instance, during the transformation of CO2 into solid carbonate rock. The process consists of injecting a non-resident mixed fluid phase of CO2 in water which dissolves parts of the fracture-porous medium system and precipitates secondary minerals, altering the solid’s porosity and permeability. Hence, dissolution/precipitation processes and concomitant solid weakening alter physico-chemical properties in the system, which in the presence of pore pressure changes, may facilitate and enhance fracture nucleation and growth. More importantly, the evolution of fracture networks in the rock determines fluid flow, which is crucial for progressing chemical processes such as ionic advection and diffusion. This study focuses on the complex chemo-hydro-mechanical responses in naturally fractured rock formations subject to acidic carbon water injection. We use a recently developed framework to incorporate the mechanisms of reactive transport, fluid flow and transport in porous media, and fracture propagation in poroelastic media. Due to the complexity of such coupled phenomena, few numerical modeling and experimental studies have been published in this area. Existing models often oversimplify the chemical interactions by using simplistic fitting functions. Contrary to these conventional approaches, the considered framework uses PHREEQC to estimate the localized chemical interactions for a general system. A key novelty of this study is in applying the considered framework to study CO2 injection into complex naturally fractured basalt formations.

How to cite: Pena Clavijo, S., Addassi, M., Finkbeiner, T., and Hoteit, H.: Reaction-assisted fracture propagation: An application to carbon storage, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1111, https://doi.org/10.5194/egusphere-egu23-1111, 2023.

11:20–11:30
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EGU23-8356
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ECS
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Virtual presentation
Rubén Vidal and Maarten W. Saaltink

Changes in temperature can modify the geochemistry of groundwater. This effect is very relevant not only for natural geothermal phenomena, but also for geothermal energy systems and Underground Thermal Energy Storage (UTES) systems. We propose a novel method that can be used to verify sophisticated numerical models and understand the thermo-hydro-chemical (THC) processes more clearly. The method decouples the chemistry from the thermo-hydraulic (TH) processes. The chemistry is obtained from geochemical batch calculation by PHREEQC and the TH processes from the finite element code CODE_BRIGHT. The method has been applied to a UTES pilot project near Bern, Switzerland, and compared with the THC coupled code RETRASO. The good agreement between the presented method and RETRASO verifies the correct implementation of our method. Moreover, the results provide information about the dominant reactive transport processes, mineral reaction rates and porosity changes.

Acknowledgements: This work was financed by the ERANET project HEATSTORE (170153-4401). This project has been subsidized through the ERANET cofund GEOTHERMICA (Project n. 731117), from the European Commission, RVO (the Netherlands), DETEC (Switzerland), FZJ-PTJ (Germany), ADEME (France), EUDP (Denmark), Rannis (Iceland), VEA (Belgium), FRCT (Portugal), and MINECO (Spain). Also, the first author is supported by a grant from the Department of Research and Universities of the Generalitat de Catalunya (2022 FI_B1 00208).

How to cite: Vidal, R. and Saaltink, M. W.: Decoupling thermo-hydraulic processes from chemical reactions to understand the effect of heat on chemical reactions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8356, https://doi.org/10.5194/egusphere-egu23-8356, 2023.

11:30–11:40
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EGU23-1120
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ECS
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On-site presentation
Reza Taherdangkoo, Najib Mahfuzh Abdallah, and Christoph Butscher

Swelling of clay-sulfate rocks is a serious problem in geotechnical projects. In Staufen (a city in Baden-Württemberg, Germany), the heave of the land surface occurred as a result of clay-sulfate rock swelling, triggered by water inflow in Triassic Grabfeld Formation (formerly Gipskeuper = “Gypsum Keuper”). Clay-sulfate swelling is controlled by clay swelling due to osmotic processes, combined with chemical swelling due to the transformation of anhydrite into gypsum, associated with a volume increase. Previous studies showed that hydro-mechanical (HM) models can be employed to determine the mechanical behavior of swelling rocks with an accuracy sufficient for planning remedial measures. In such models, a constitutive relation between swelling pressure (stress) and swelling deformation (strain) must be defined (“swelling law”). In the present study, we developed coupled HM models to reproduce the heave observed at the Staufen site. We implemented different swelling laws, namely linear, semi-logarithmic, and sigmoidal constitutive relations between stress and strain. We compared the model calculations with the measured long-term heave records at the study site. We then analyzed the errors associated with each modeling approach to evaluate its effectiveness. This contribution provides insights about the performance of three existing swelling laws to estimate the long-term mechanical behavior of clay-sulfate rocks.

How to cite: Taherdangkoo, R., Mahfuzh Abdallah, N., and Butscher, C.: Hydro-mechanical modeling of swelling processes in clay–sulfate rocks: comparison of swelling laws, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1120, https://doi.org/10.5194/egusphere-egu23-1120, 2023.

11:40–11:50
|
EGU23-1958
|
ECS
|
On-site presentation
Erik Toller and Otto Strack

Understanding the behavior of hydro-mechanical processes is a challenging task, and groundwater plays an important role in these. We separate the effect of groundwater into two main parts: the pore pressure and the seepage force. Our interest is in the latter part, where we develop a model that incorporates analytically seepage forces in a linear elastic model. This is work in progress; we present our latest developments, focusing on both the theoretical framework and application.

The approach is a further development of the Analytic Element Method, which, was recently extended to linear elasticity. We link a groundwater analytic element to a linearly elastic one, including the seepage forces directly in the equation of the linear elastic model. We initially limit the model to one-way coupling and exclude the effect of stresses and strains on the hydraulic conductivity.

We present an application where we isolate the impact of the seepage force on the mechanical model focusing on situations where we expect a large pressure gradient.

How to cite: Toller, E. and Strack, O.: A Hydro-Mechanical Analytic Element Model for Seepage Forces, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1958, https://doi.org/10.5194/egusphere-egu23-1958, 2023.

11:50–12:00
|
EGU23-4700
|
ECS
|
On-site presentation
Hyun Chul Yoon and Jihoon Kim

When CO2 is injected into the saline aquifer or depleted reservoir for geological carbon storage, physical processes are tightly coupled, affecting CO2 flooding and its trapping mechanisms.

For example, injection induces pore pressure build-up and dilation of pore space, which can uplift the ground surface or tensile/shear failure of the caprock which may result in the leakage of CO2. Thus, rigorous analyses of coupled flow and geomechanics are necessary to predict the long-term security of geological carbon storage. In this study, we focus on two irreversible (path-dependent) processes that are coupled through flow and geomechanics: hysteretic capillary pressure in flow and elastoplasticity in geomechanics. Hysteresis in capillary pressure during drainage and imbibition processes can be seen as mechanical energy dissipation. We employ our previously proposed numerical model based on the 1D elastoplasticity algorithm for constitutive relation of the hysteretic capillary pressure in two-phase flow, i.e., capillary pressure and irreducible water saturation. In particular, we model the irreducible (plastic) water saturation being attributed to the part from the hysteretic capillary pressure, which yields a mathematically well-posed problem. We implement the irreversible flow and geomechanics simulation, calculating the residual saturations and plastic strain from each iteration of flow and geomechanics, as we employ the fixed-stress sequential method solving coupled flow and geomechanics.

From the numerical experiments, we find robust computations of the coupled processes, highlighting the coupled effects of capillary hysteresis and elastoplasticity. As residual/capillary and structural trappings are major trapping mechanisms for CO2 geological storage, the proposed constitutive relation and algorithm for coupled path-dependent processes can predict flooding and trapping of CO2 underground more accurately.  

How to cite: Yoon, H. C. and Kim, J.: Numerical Modeling of Capillary Hysteresis and Coupled Elastoplasticity for Geological Carbon Storage, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4700, https://doi.org/10.5194/egusphere-egu23-4700, 2023.

12:00–12:10
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EGU23-1338
|
Virtual presentation
|
christine Detournay, Zorica Radakovic-Guzina, and Branko Damjanac

Heat extraction by circulating a cold fluid in a hot fractured rock mass at depth is the central topic of study in geothermal engineering. Typical reservoir rocks have a low thermal conductivity, and heat exchange between rock and fluid occurs in a thin region, adjacent to the fracture, where the temperature gradient is very high. Capturing this effect is important for accurate predictions of transient fluid temperatures — a critical aspect of geothermal power systems.

The model assumes a temperature jump at the rock/fracture-fluid contact (collapsed boundary layer), and Newton’s law of cooling

qcv = h (Trock -Tfluid )                                                                                                                            (1)

is used to express the heat exchanged by forced convection between media. The heat transfer coefficient, h has a significant impact on the results of EGS numerical modeling. A pragmatic expression is proposed whereby h is proportional to the rock thermal conductivity, kr and inversely proportional to the square root of the product of rock diffusivity, κ, and fluid injection time, t (Detournay C. et al., 2022):

     h = kr / (β√κt)                                                                                                                                (2)

The novelty is that h is primarily a function of rock thermal properties and only indirectly dependent of fracture fluid velocity. Also, Eq. (1) combined with Eq. (2) is the thermal equivalent of Carter’s equation for 1D leak-off flow. The logic, combined with heat advection-forced convection, is implemented in the commercial hydraulic fracturing code XSite and coupled with mechanical, fracture flow, and heat conduction.

Borehole injection of cold water in a penny-shaped pre-existing fracture with a 100 m diameter is simulated. Fluid extraction occurs at constant downhole pressure. Fluid-thermo-mechanical coupling is considered.


 Figure 1. Fluid temperature contour (°C) at 1 year.

Fluid temperature contours in Figure 1 show an oval cooled-off region surrounding the injection well and a “dead zone” near the producing well where the fluid temperature stays close to the warm original (rock) value. The warm fluid, initially present in the thin fracture, is produced and rapidly replaced by the injected fluid. The fluid temperature gradient between wells is caused by the migration of heat from rock to fluid.

REFERENCE

Detournay C., Damjanac B., Torres M., Cundall P., Ligocki L., Gil, I., 2022. Heat advection and forced convection in a lattice code – Implementation and geothermal applications. Rock mechanics Bulletin I (2022) 100004.

 

How to cite: Detournay, C., Radakovic-Guzina, Z., and Damjanac, B.: A new functional form of the heat transfer coefficient for use in simulating EGS processes at the field scale., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1338, https://doi.org/10.5194/egusphere-egu23-1338, 2023.

12:10–12:20
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EGU23-7515
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On-site presentation
Adriana Paluszny, Lior Suchoy, Maria Cristina Saceanu, and Robert W. Zimmerman

Understanding the mechanisms that control the development of fractures in complex thermally deformed media, as well as how they interact with smaller-scale and larger-scale heterogeneiies in material properties, is relevant to a number of natural and engineered processes. In this study, we investigate the results of numerical simulations of thermal shock and the resultant fracturing of brittle rock slabs in the context of a fracture growth benchmark. The benchmark, based on multiple laboratory experiments, induces the non-planar formation of multiple fractures due to thermal shock on ceramic mm-scale slabs. The benchmark experiment tracks fracture geometries for a series of shock temperatures and is used to directly validate our numerical approach, which utilises a three-dimensional in-house finite element code to simulate thermo-mechanical deformation. The ensuing damage and spatially variable fracture apertures are quantified, as well as the resulting fracture network patterns. In our approach, fractures are represented as NURBS surfaces, which are discretised using quadrilaterals and triangles. The matrix is discretised using isoparametric tetrahedral and hexahedral elements. We show in our results how thermal shock affects the fracture aperture distributions, and how these aperture distributions depend on the initial heterogeneities in the modelled slab. We discuss how the simulated fracture interactions are self-organising, and compare well to the proposed multi-fracture benchmark. Additionally, we discuss the manner in which geometry, scale, and heterogeneity influence the resulting fracture pattern and aperture distribution. 

How to cite: Paluszny, A., Suchoy, L., Saceanu, M. C., and Zimmerman, R. W.: Coupled thermo-mechanical growth of multiple fractures in brittle heterogeneous rocks during thermal shock and resulting aperture distributions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7515, https://doi.org/10.5194/egusphere-egu23-7515, 2023.

12:20–12:30
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EGU23-11566
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Virtual presentation
Tymofiy Gerasimov, Dmitrii Naumov, Thomas Nagel, Olaf Kolditz, and Haibing Shao

In the context of shallow subsurface ice storage, low temperature coolant fluid is circulated through multiple borehole heat exchangers (BHEs) to form ice in the surrounding soil. This can be used later on in building cooling applications. To evaluate the environmental impact of freezing and thawing cycles, we extended the classical Thermal-Hydro-Mechanical model in the OpenGeoSys software platform to simulate the aforementioned phase change scenarios.

The new feature development and verification is divided into several subsequent steps. In the model verification, the Stefan problem of slab melting is employed as the benchmark case: the numerical results from OpenGeoSys is verified against the available analytical solution. In the subsequent code verification, the concept of manufactured solution is adopted, in which the numerical outcome is compared with the reference data to show accurate agreement. Following that, the ultimate verification is conducted by comparing results from OpenGeoSys and the open source package like FreeFEM++.

For the application of the extended numerical model, we simulate the ice formation around the four BHEs in 3 dimensions for a quarter of the test field setup and over a period of 30 days. With -15 oC temperature imposed on the lower section of the BHE wall and the considered material data, the numerical simulation suggests an up to 50 cm thick layer of frozen soil surrounding the borehole. In the model results, major volumetric deformation of soil is observed in the close vicinity of the BHEs where the ice grows, also triggering small vertical surface elevation. Current on-going work is focusing on the coupling effect between thermal conductivity of soil, mechanical deformation and hydrology, where one of the envisioned impacts is the groundwater flow deviation due to the ice formed.

How to cite: Gerasimov, T., Naumov, D., Nagel, T., Kolditz, O., and Shao, H.: Numerical modelling of ice forming and thawing in a subsurface energy storage application, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11566, https://doi.org/10.5194/egusphere-egu23-11566, 2023.

Posters on site: Mon, 24 Apr, 14:00–15:45 | Hall X4

Chairpersons: Silvia De Simone, Monia Procesi, Tuanny Cajuhi
X4.138
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EGU23-3513
Muntasir Shehab, Reza Taherdangkoo, and Christoph Butscher

Bentonite and bentonite mixtures are used as buffer material for deep geological radioactive waste repositories. The swelling behavior of bentonite is an important property influencing the long-term safety of the barrier system by its self-sealing effect. The proper determination of bentonite swelling pressure is vital to ensure that geological repositories remain intact. In this study, a total of 305 data samples on bentonite swelling pressure was collected from the literature. Corresponding soil properties were montmorillonite content, liquid limit, plastic limit, plasticity index, initial water content, and dry density. We employed various machine learning algorithms, namely feed-forward and cascade forward neural networks, regression tree, regression tree ensembles, Gaussian process regression, and support vector machines to determine the maximum swelling pressure of unsaturated bentonite and its mixtures. The cascade-forward neural network (CFNN) produced the best overall performance, i.e. the lowest modeling deviations from the experimental swelling pressure values. Furthermore, we present two simplified CFNN models that depend on two (montmorillonite content and initial dry density) and three (montmorillonite content, initial dry density, and plasticity index) variables to estimate bentonite swelling pressures. These simplified models can to be used as alternatives in instances of limited data availability.

How to cite: Shehab, M., Taherdangkoo, R., and Butscher, C.: Predicting swelling pressure of bentonite and bentonite mixtures using various machine learning approaches, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3513, https://doi.org/10.5194/egusphere-egu23-3513, 2023.

X4.139
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EGU23-4965
Taewoong Ahn, Young-ju Seo, Changhyup Park, hyunjoong Lim, and Dong Hyun Kim

Shale is attracting more attention than ever because it can act as a cap rock for CO2 storage as well as a source rock for hydrocarbon resources known as shale gas. In particular, it has been known that the enhanced gas recovery (EGR) technology that enhances the recovery of CH4 by injecting CO2 can be applied to shale gas production. Gas in shale is known to exist in phases of free gas and adsorbed gas, and the adsorption tendency of CO2 is higher than that of CH4. Because of these unique characteristics, CO2 injected into shale induces desorption of CH4 (natural gas production) and remains in adsorbed phase (CO2 storage) at the same time. In other words, shale can also serve as a CO2 storage site. Since shale has a complicated pore structure and a very small pore size, research on the fluid flow or CO2-CH4 adsorption-desorption mechanism within shale has not been well investigated yet.

In this experimental study, Low-field NMR was used to analyze the characteristics of NMR signals of gases present in shale and how they change according to various gas pressures. In addition, the CO2-CH4 adsorption-desorption mechanism was analyzed by observing how the signal characteristics due to adsorption and desorption change as CO2 was injected into a shale sample saturated with CH4 gas. Through this study, it was confirmed that the NMR signal obtained from shale sufficiently reflects the phase and amount of gas, and that the progress of the adsorption-desorption reaction can be quantitatively analyzed. The results of this experiment can be used as important analytical data to understand the behavior of gas in shale, which is essential for shale gas recovery enhancement and CO2 storage.

How to cite: Ahn, T., Seo, Y., Park, C., Lim, H., and Kim, D. H.: Experimental study of CO2/CH4 distribution in shale rock samples during adsorption/desorption reaction by low-field NMR, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4965, https://doi.org/10.5194/egusphere-egu23-4965, 2023.

X4.140
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EGU23-6711
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ECS
Le Zhang, Thomas Hermans, Alexandros Daniilidis, and Anne-Catherine Dieudonné

With the increasing demand for mineral and alternative energy resources, as well as the gradual depletion of shallow resources, the exploitation and utilization of mineral resources and geothermal energy in deep strata is an effective way to solve the problem of resource shortage. In recent years, as a new type of resource mining mode, the co-mining of deep mineral and geothermal energy has developed rapidly. This method is effective in solving the of deep mines and can also provide convenience for geothermal exploitation with the help of the original equipment of the mine. However, in deep mines, the interaction of high temperature, high geomechanical stress and high-water pressure might lead to rock failure because of the co-mining of mineral and geothermal resources. The huge uncertainty of underground parameters also makes the engineering environment difficult to predict.

We have established a Thermal-hydraulic-mechanical coupling framework of co-mining of deep mineral and geothermal energy considering uncertainty in the model parameters including porosity, rock permeability, thermal parameters (heat capacity and heat conductivity), Young's modulus and their spatial heterogeneity, as well as boundary condition. 500 samples were generated within the prior uncertainty ranges, by means of Monte Carlo simulations, and simulated the spatial and temporal distribution of the temperature, pressure and principal stresses field for each sample with COMSOL. Using the distance-based global sensitivity analysis, the most sensitive parameters for deep mining are identified, and the heat storage capacity of the system is evaluated, including uncertainty.

How to cite: Zhang, L., Hermans, T., Daniilidis, A., and Dieudonné, A.-C.: Sensitivity analysis of model parameters for geothermal energy applications in deep mines of thermal-hydraulic-mechanical coupling of spatially heterogeneous settings, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6711, https://doi.org/10.5194/egusphere-egu23-6711, 2023.

X4.141
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EGU23-7705
Deirdre Clark, Kjartan Marteinsson, Gunnar Þorgilsson, Iwona Galeczka, Helga Helgadóttir, Sandra Snæbjörnsdóttir, Bergur Sigfusson, and Sveinborg Gunnarsdóttir

The Nesjavellir high-temperature geothermal field in Iceland was chosen as part of the GECO H2020 project to further demonstrate the Carbfix method of carbon mineralization. In this method, geothermal power plant emissions of CO2 and H2S are captured using condensed steam, and subsequently co-injected with separated geothermal water into the subsurface where they mineralize in the form of carbonate and sulfide minerals. This technology has already been successfully shown to be a safe and cost-effective approach to reduce gas emissions from the nearby Hellisheiði geothermal power plant in SW Iceland.

An integration of geology, reservoir and geochemical models were used to evaluate the future injection of CO2 and H2S at the Nesjavellir site. These models include reservoir parameters such as the relative permeability and porosity of different stratigraphic layers as well as the locations of feedzones. Tracer tests and well temperature and pressure logs were used to calibrate single porosity and dual porosity TOUGH2 flow models. A 1-D flow reactive transport model was then created using TOUGHREACT and the parameters from the flow models and calibrated using chemical compositions of the reservoir background fluid and separated water, the proposed gas injection fluid chemistry and available bulk rock chemistry and lithological data from borehole reports. Results from this integrated approach offer possible controls on the flow, impacts of the CO2-H2S injection, and estimate the potential storage capacity of carbon mineralization within the Nesjavellir geothermal reservoir.

How to cite: Clark, D., Marteinsson, K., Þorgilsson, G., Galeczka, I., Helgadóttir, H., Snæbjörnsdóttir, S., Sigfusson, B., and Gunnarsdóttir, S.: Assessing carbon mineralization using an integrated approach at the Nesjavellir geothermal field, Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7705, https://doi.org/10.5194/egusphere-egu23-7705, 2023.

X4.142
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EGU23-6040
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ECS
Multi-Phase Coupled THMC Modeling of Gas Extraction from Hydrate Reservoirs
(withdrawn)
Sahil wani, Rahul Samala, Ramesh Kannan Kandasami, and Abhijit Chaudhri
X4.143
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EGU23-13696
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ECS
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Xiangyun Shi, David Misch, Stanislav Zak, Megan Cordill, and Daniel Kiener

Mudstones and shales are fine-grained sedimentary rocks that can serve as top seals of geological reservoirs in various geoenergy applications. Apart from traditional oil and gas exploration, the urgent need for underground storage of energy carriers (e.g., H2) and climate-relevant gases (e.g., CO2) facilitated extensive research on pore structural and mechanical parameters and their influence on the seal capacity of these rocks. The fracture behaviour of mudstone seal rocks controls the risk of seal failure due to microfracturing as a response to various geological processes (e.g., buoyancy pressure from the reservoir). In this contribution, the high-speed nanoindentation mapping approach was carried out for a proven mudstone top seal sample (~1629 m; quartz 31%, clay mineral 39%) from a Vienna Basin oil field. The nanoindentation results were then post-processed with machine learning-based tools to obtain representative mechanical parameters of the clay matrix. k-means clustering analysis was performed using three input features including hardness (H), reduced elastic modulus (Er), and the elastic-plastic deformation ratio based on the obtained load-displacement curves. In addition, broad ion beam-scanning electron microscopy (BIB-SEM) maps were taken before and after the nanoindentation to correlate the indentation results with direct imaging information and to verify the k-means clustering results. A total of 8 indentation map arrays (7 × 7 indents) were placed to test the sensitivity of different tips to indentation depth and load rate. The comparison of BIB-SEM image data and k-means clustering showed that decisions on phase assignment can be significantly improved and performed in a shorter time by k-means clustering analysis, still showing an overall good agreement with manual selections. For the studied mudstone sample, the resulting average Er and H values of the clay matrix range at 17.58 ± 6.89 GPa and 0.63 ± 0.76 GPa (n=30), respectively for the Berkovich tip and at 15.03 ± 4.79 GPa and 0.38 ± 0.23 GPa (n=62), respectively for the Cube Corner tip. The testing with both tips shows that despite the strongly heterogeneous microstructure of the indented clay matrix the obtained mechanical parameters are not sensitive to indentation depths and hence representative values can be determined from minimum volumes with statistical significance. Nevertheless, compared with the Berkovich tip, the Cube Corner tip sampled deeper depths (58-443 nm for the Berkovich tip and 412-1747 nm for the Cube Corner tip) and introduced more surface damage. By increasing the load rate from 1000 to 6000 μN s−1, the indentation testing tended to be unstable and the surface showed strong damage at the highest load rate. In conclusion, this contribution represents an important methodological step towards the implementation of combined high-speed nanoindentation mapping and machine learning data analysis as a feasible high throughput tool for the mechanical characterization of mudstones and similar fine-grained sedimentary rocks. The presented approach is planned to be applied to an extensive set of mudstone samples from the Vienna Basin with the purpose to link mechanical property changes to burial diagenesis.

How to cite: Shi, X., Misch, D., Zak, S., Cordill, M., and Kiener, D.: Determining representative mechanical parameters of clay matrix in mudstones using nanoindentation mapping and machine learning data analysis: a novel top seal characterization approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13696, https://doi.org/10.5194/egusphere-egu23-13696, 2023.

X4.144
|
EGU23-14784
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ECS
Kalliopi Tzoufka, Daniela Pfrang, Daniel Bohnsack, and Kai Zosseder

High-temperature aquifer thermal energy storage (HT-ATES) can contribute in balancing the spatiotemporal mismatch that arises between periods of excess energy supply in contrast to phases of high energy demand. Excess energy can be stored under the form of thermal energy in the subsurface by utilizing methods stemming from geothermal engineering applications. In order to increase the efficiency of operating geothermal systems at the German Molasse Basin, such concepts are currently considered for the storage of high-temperature fluids in the Upper Jurassic Reservoir (Malm) of the North Alpine Foreland Basin. The karstified and fractured Malm aquifer comprises a site of extensive and continuously increasing investigation and implementation of geothermal projects. Nevertheless, the suitability of this reservoir for the development of ATES systems has not been yet considerably investigated. In this work we present our initial approach to evaluate the potential for thermal energy storage application in the Upper Jurassic reservoir.

Due to the high structural and geological heterogeneity of the Malm aquifer, a subset of this reservoir, with favourable temperatures for heat storage, is investigated here that corresponds to segments governed by karst-dominated fluid flow. The numerical analysis builds upon three currently operating geothermal systems that exhibit such a characteristic karst-controlled fluid flow in depths of ca. 2000–3000 m TVD. In fact, a comprehensive analysis of borehole log data shows that several stratigraphic units contribute as inflow zones in those systems, however the main proportion of inflow results from the karstified zones. The model domain is, therefore, subdivided into three homogeneous units with the shallower layer representing a karstified unit, while the deeper units correspond to the less productive limestone and dolostone sequences of the Malm reservoir. Thermal and hydraulic properties are deciphered by field tests performed in the considered geothermal systems, their respective well logs as well as investigations of rock cores from two wells penetrating into the Malm reservoir (Bohnsack et al., 2020).

While those enhanced-permeability reservoirs may represent good candidates for subsurface heat storage due to high injectivity, they simultaneously enable high fluid fluxes that may in turn induce considerable thermal losses. A numerical analysis is performed here to capture and describe the governing physical processes, and to assess the potential of HT-ATES application in such reservoirs. Synthetic numerical models are hence developed that are based on the three considered geothermal systems of the Upper Jurassic reservoir. This approach enables to quantify thermal and hydraulic effects of heat storage, to identify potential hydraulic and thermal interference between injection and production, and to assess developing advective heat fluxes which may trigger heat losses and thus impede long-term sustainable operation of HT-ATES systems. Numerical results contribute into a better understanding of the reservoir behaviour and further into prediction of the system response under different background conditions.

 

References

Bohnsack, D., Potten, M., Pfrang, D., Wolpert, P., Zosseder, K. Porosity–permeability relationship derived from Upper Jurassic carbonate rock cores to assess the regional hydraulic matrix properties of the Malm reservoir in the South German Molasse Basin. Geothermal Energy 8, 12 (2020).

How to cite: Tzoufka, K., Pfrang, D., Bohnsack, D., and Zosseder, K.: Numerical modelling of high-temperature aquifer thermal energy storage (HT-ATES) in the Upper Jurassic reservoir of the German Molasse Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14784, https://doi.org/10.5194/egusphere-egu23-14784, 2023.

X4.145
|
EGU23-11202
Tuanny Cajuhi, Gesa Ziefle, Jobst Maßmann, and Keita Yoshioka

Opalinus Clay (OPA) has been one of the main focuses of international geoscientific research due to its potential use as a host rock for the storage of heat-generating radioactive waste. In-situ experiments taking place in the Mont Terri Rock Laboratory in Switzerland provide valuable insights into the material properties and behavior of OPA. The Cyclic Deformation (CD-A) experiment has been conducted since October 2019 in the rock laboratory to investigate hydro-mechanical effects through long-term direct and indirect measurements such as resistivity, water content, suction, and crack development. Desaturation effects due to variations in relative air humidity induced by ventilation and seasonal changes, drive the formation of desiccation cracks at the walls of the CD-A niches.

We use a mathematical model based on a macroscopic poromechanical and on the phase-field approaches to compute desiccation. The formulation consists of the balance equations of the solid and liquid phases and of the crack phase-field evolution equation. Within this combined framework, we are able to account for the drying of the niche and for desiccation cracks. Our solution scheme is implemented in the open-source finite element software OpenGeoSys (OGS 6).

In this contribution, we discuss the practical steps for applying the poromechanical phase-field approach at in-situ scale. The basic steps consist of determining the material properties and computing the fracture energy and characteristic length. Moreover, we use field data concerning the crack aperture to deduce the crack resolution for the simulations. The model setup consists of a quarter cross-section of a CD-A niche. We compare the modeled crack response with the monitored cracks at field scale and evaluate whether they initiate and propagate according to the monitored relative air humidity range. Furthermore, we assess the impact of randomly distributed material properties, e.g. fracture energy, and changes in permeability due to cracking.

How to cite: Cajuhi, T., Ziefle, G., Maßmann, J., and Yoshioka, K.: Exploring and modeling the formation of desiccation cracks in Opalinus Clay at field scale, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11202, https://doi.org/10.5194/egusphere-egu23-11202, 2023.

X4.146
|
EGU23-10929
|
Chan-Hee Jang, HyunNa Kim, and Byung-Dal So

Subsurface fluid injection of environmental (e.g., carbon capture storage) and industrial (e.g., enhanced geothermal system) projects change pore pressure and underground stress which may induce fault slip. The temperature of injected fluid controls pore pressure and underground stress by thermo-poroelastic effect of fluid injection, that explains the interaction between pore fluid flow and elastic deformation in a porous medium. Since the perturbed subsurface stress distribution increases seismic uncertainty, a numerical modeling for varying injection conditions (e.g., injection scenario and fluid temperature) is helpful for understanding thermo-poroelastic behavior before the fluid injection. In this study, we build 2-dimensional finite element fluid injection models that simulate thermo-poromechanical processes using a COMSOL Multiphysics®. The thermal equation (Fourier’s Law) is coupled with the poroelastic theory to investigate the role of thermohydraulic-convection and -stress in a porous medium. We confirm that these injection conditions may change pore pressure, subsurface stress, and surface displacement, which supports the necessity of monitoring during/after fluid injection.

How to cite: Jang, C.-H., Kim, H., and So, B.-D.: A thermo-poroelastic finite element analysis of fluid injection depending on fluid temperature and injection scenarios, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10929, https://doi.org/10.5194/egusphere-egu23-10929, 2023.

Posters virtual: Mon, 24 Apr, 14:00–15:45 | vHall ERE

Chairpersons: Iman Rahimzadeh Kivi, Victor Vilarrasa
vERE.1
|
EGU23-42
Keshun Liu, Jiangxiu Qu, Ming Zha, and Xiujian Ding

Abstract: The Junggar basin is sandwiched between the Siberian plate, the Kazakhstan plate and the Tarim plate, and is an important part of the Central Asian orogenic belt. Based on the comprehensive analysis of the characteristics of the natural gas composition,carbon isotope, light hydrocarbons and source rocks in the eastern belt around Penyijingxi Sag, Junggar Basin, i.e., our studied area, the genesis and origins of natural gas in this area are discussed. The natural gases in the eastern belt around Penyijingxi Sag, are dominated by alkane gases, and have relatively low contents of heavy hydrocarbons and non-hydrocarbons. Methane is dominant in alkane gas, with volume fraction varies from 70.36% to 93.34%. In non-hydrocarbon gas, the volume fraction of nitrogen varies from 0.69% to 11.95%, and the volume fraction of carbon dioxide varies from 0 to 1.49%. The values of δ13methane(C1), δ13ethane(C2), δ13propane(C3) and δ13butane(C4) of natural gas are in the ranges from −45.57‰ to −31.19‰, −31.69‰ to −24.66‰, −28.76‰ to −23.56‰, −27.96‰ to −23.64‰, respectively. The overall carbon isotopic composition of the alkanes shows a trend as δ13C1 < δ13C2 < δ13C3 < δ13C4, and all δ13C1 values are ≤ -30‰, which are typical of gases of organic origin. The methane and ethane isotopic compositions and the characteristics of light hydrocarbons show that the natural gases in the studied area are dominated by coal-type gas and contain a small amount of oil-type gas. Specifically, the coal-type gas is from the mature to highly mature source rocks of the Lower Urho Formation, and the oil-type gas is from the mature to highly mature source rocks of the Fengcheng Formation. Analysis of gas migration parameters show that, while there was no significant lateral migration of natural gas in the studied area, natural gases once migrated vertically and resulted in the mixing of oil- and coal-type gases as well as the mixing of alkane gases of the same genetic type formed at different stages, which should be the cause of observed reversed carbon isotopic series. The diffusion and migration of carboniferous oil and gas after reservoir formation have led to differences in gas geochemical characteristics among gas wells in this area, which may provide important information for oil and gas exploration in the central Junggar Basin.

Keywords: Junggar Basin; geochemistry; natural gas genesis; carbon isotopes; light hydrocarbons

How to cite: Liu, K., Qu, J., Zha, M., and Ding, X.: Genesis and Origins of Natural Gas in Eastern Belt around Penyijingxi Sag in Junggar Basin, NW China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-42, https://doi.org/10.5194/egusphere-egu23-42, 2023.

vERE.2
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EGU23-6889
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ECS
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Philip Salter, Katherine Dobson, James Minto, and Jay Warnett

Biomineralization, through microbially, thermally, or enzyme induced carbonate precipitation (MICP/TICP/EICP), is a naturally occurring and inexpensive cementation process that can seal microfractures and pore throats that are inaccessible to cement and chemical based grouts. The porosity, permeability and thermal conductivity of porous geomaterials can therefore be controlled.

This project aims to determine the optimal compositional and injection parameters for biomineralization fluids in a range of subsurface applications relating to the low carbon energy transition. These include, improving the subsurface storage integrity of CO2 and H2 by reducing permeability around poorly sealed legacy wells, enhancing mineral trapping of geo-sequestered CO2, and improving the thermal performance of well casings and ground around low-high geothermal and thermal energy storage systems. We also assess the real time response of bio-cemented samples to harsh environmental conditions representative of those in the subsurface.

Understanding the interactions between geochemical reactions and the transport properties of fluid at the reservoir scale first requires biomineralization experiments to be carried out at the pore (micron) scale. These studies are essential for understanding principles of crystal formation, growth and hydrodynamic feedback mechanisms. Using real-time in situ x-ray computed tomography, the complex and synergistic factors involved in the biomineralization process can be better understood. Correlation of microstructural and macroscopic properties during repeated precipitation and dissolution events will allow refinement of larger scale reactive transport models that assess the suitability of different injection strategies.

Carbon Capture and Storage: The ability to create large, and spatially targeted low permeability regions could be a key tool in preventing leakage of geo-sequestered CO2 (and H2), as well as improving/restoring CO2 injectability and sweep efficiency. During 2-phase EICP a poor choice of injection angle and flow rate can inhibit the mixing of precipitation fluids, and therefore the efficiency of permeability reduction within a porous medium. The challenge of getting 2 fluids to mix uniformly in a tight pore space is only likely to get worse in high pressure, low permeability real world systems. We explore single-phase thermally-delayed, and pulsed EICP injection strategies that encourage better mixing within heterogeneous real-world systems. Injection cycles are repeated multiple times to target the larger (order of magnitude) reductions in permeability required to alter the flow behaviour of CO2 and other gases.

Thermal: Cement and bentonite based grouts typically have low thermal conductivities (<1 W/m K), which is detrimental to subsurface heat exchange. They often form a poor seal at the host rock/soil interface which can increase interfacial resistance. Minerals formed by MICP at the contacts between soil grains can greatly increase the thermal conductivity of the ground, particularly in unsaturated conditions. We explore enhancing this effect further with inclusion of highly conductive additives. For thermal energy storage applications specific heat capacity can also be increased with integration of phase change materials. By developing these specialized geothermal grouts/backfill, shallower boreholes may be required, greatly reducing cost.

The findings of this project have profound implications on the commercialization of engineered biomineralization, and its role in the subsurface energy transition.

How to cite: Salter, P., Dobson, K., Minto, J., and Warnett, J.: Exploiting induced carbonate precipitation to improve reservoir storage integrity and geothermal system efficiency, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6889, https://doi.org/10.5194/egusphere-egu23-6889, 2023.

vERE.3
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EGU23-11711
Victor Vilarrasa, Haris Raza, Iman Rahimzadeh Kivi, and George Sand França

Reservoir impoundment is usually accompanied by induced/triggered seismicity. The rise in the number of planned hydropower plants requires improving the understanding of the causes of this induced/triggered seismicity, which eventually could serve to propose mitigation measures to reduce the induced/triggered-seismicity risk. We investigate the case of reservoir-triggered seismicity at Nova Ponte, Brazil, where triggered seismicity started shortly after reservoir impoundment, with the maximum magnitude of M3.5 when reaching the highest water level on the dam, and followed by delayed seismicity, with the largest earthquake being a M4.0 about 4.5 years after impoundment. We have built a hydro-mechanical fully-coupled numerical model reproducing the T shape of the reservoir and including the three geological layers placed below the reservoir down to 10 km depth. Simulation results serve to identify the nodal plane, from the two nodal planes of the proposed focal mechanism, which nucleated the seismicity of the M3.5 earthquake: a vertical, E-W-oriented strike-slip fault with a reverse-displacement component. The initial seismicity was triggered by the undrained response of the subsurface to the loading of the reservoir. We also find that the delayed seismicity was triggered by pore pressure diffusion, bringing a critically oriented vertical fault to failure conditions. The vertical permeability to allow the pore pressure perturbation to reach the depth of the M4.0 earthquake, i.e., 3 km depth, in 4.5 years is 6.6·10-15 m2, two to three orders of magnitude higher than the expected permeability of the host rock, a low-permeability mica-schist. We contend that hydro-mechanical models are a useful tool to understand the triggering mechanisms of reservoir-triggered seismicity.

How to cite: Vilarrasa, V., Raza, H., Kivi, I. R., and França, G. S.: Understanding the triggering mechanisms of reservoir-triggered seismicity at Nova Ponte, Brazil, through hydro-mechanical modeling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11711, https://doi.org/10.5194/egusphere-egu23-11711, 2023.