EMRP1.6 | Petrophysics and rock physics across the scales: integrating models, laboratory experiments and field geophysical studies
EDI
Petrophysics and rock physics across the scales: integrating models, laboratory experiments and field geophysical studies
Co-organized by ESSI1
Convener: Chi Zhang | Co-conveners: Lucas Pimienta, Ludovic Bodet
Orals
| Tue, 25 Apr, 16:15–17:55 (CEST)
 
Room -2.21
Posters on site
| Attendance Wed, 26 Apr, 10:45–12:30 (CEST)
 
Hall X2
Posters virtual
| Attendance Wed, 26 Apr, 10:45–12:30 (CEST)
 
vHall TS/EMRP
Orals |
Tue, 16:15
Wed, 10:45
Wed, 10:45
Geophysical methods have great potential for the characterization of subsurface properties and processes to inform geological, reservoir, hydrological, and biogeochemical studies. In these contexts, the classically used geophysical tools only provide indirect information about the characteristics and heterogeneities of subsurface rocks and their associated processes (e.g., flow, transport, biogeochemical reactions). Petrophysical relationships hence have to be developed to provide links between physical properties (e.g. electrical conductivity, seismic velocity, or attenuation) and the intrinsic parameters of interest (e.g. fluid content, hydraulic properties, pressure conditions). In addition, geophysical methods are increasingly deployed in increasingly complex environments for time-lapse, continuous, and distributed monitoring. Here again, there is a great need for accurate and efficient physical relationships such that geophysical data can be correctly interpreted (e.g., included in fully coupled inversions). Establishing such petrophysical models requires multidisciplinary approaches and diverse theoretical frameworks. While each physical property has its own intrinsic dependence on pore-scale interfacial, geometrical, and biogeochemical properties or on external conditions such as pressure or temperature, each associated geophysical method also has its own specific investigation depth and spatial resolution. Such complexity poses great challenges in combining theoretical developments with laboratory validations and scaling laboratory observations to field practices. This session consequently invites contributions from various communities to share their models, their experiments, or their field tests and data in order to discuss multidisciplinary ways to advance petrophysical relationship development and to improve our knowledge of complex processes in the subsurface.

Orals: Tue, 25 Apr | Room -2.21

Chairpersons: Chi Zhang, Lucas Pimienta, Damien Jougnot
16:15–16:35
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EGU23-1838
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ECS
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solicited
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On-site presentation
Cora Strobel, Manuel Dörrich, Olaf A. Cirpka, Johan A. Huisman, and Adrian Mellage

Solid organic matter (SOM) is an important component of natural sediments and plays a crucial role in providing substrate for microbial reactions and the degradation of contaminants in soil and groundwater. Knowledge about its distribution in the subsurface is crucial for the delineation of potential hotspots of microbial activity. The subsurface is, however, difficult to access, limiting our ability to reliably delineate the spatially heterogeneous distribution of SOM. Recently, the geophysical method induced polarization (IP) has been shown to be a potentially promising mapping tool, able to detect the presence of SOM. However, the mechanisms controlling IP signals in the presence of SOM are not (yet) well understood, with a handful of studies highlighting inconclusive results (Katona et al., 2021; Mellage et al., 2022; Ponziani et al., 2012; Schwartz & Furman, 2014). Moreover, a non-negligible contribution of polarization from the organic matrix can yield signals that may cause misinterpretation of other petro-physical relationships in unconsolidated sediments.

In this study, we measured the spectral IP (SIP) response of aquifer sediment cores (2 – 8 m depth) collected from an alluvial floodplain aquifer in southwest Germany. The total organic carbon (TOC) content in the cores and the cation exchange capacity (CEC) exhibit a positive correlation with the magnitude of polarization (i.e. imaginary conductivity). In addition, strong differences in the frequency dependence of the IP measurements as a function of TOC fraction were observed for the otherwise calcareous matrix devoid of other strongly polarizing mineral phases (e.g. pyrite or clay minerals). While the CEC at the site is strongly dominated by the amount of SOM, polarization is more strongly linked to SOM than CEC. We hypothesize that the weaker correlation between SOM and CEC highlights the contribution of poorly understood charge storage mechanisms within the polydisperse organic matrix that differ from polarization at mineral surfaces. Ongoing experiments with artificial soil mixtures of calcitic sand and varying fractions of peat, under controlled conditions (i.e. constant electrical conductivity of the pore fluid), will help to shed light on the controls behind our field-derived relationships. We expect that our combined field and laboratory investigations will provide insights into the petro-, or rather, organo-physical relationship between SOM and the imaginary conductivity, and thus contribute to a conceptualization of the underlying polarization mechanisms in organic matrices.

 

References

Katona, T., Gilfedder, B. S., Frei, S., Bücker, M., & Flores Orozco, A. (2021). High-resolution induced polarization imaging of biogeochemical carbon-turnover hot spots in a peatland. Biogeosciences, 18(13), 4039–4058.

Mellage, A., Zakai, G., Efrati, B., Pagel, H., & Schwartz, N. (2022). Paraquat sorption- and organic matter-induced modifications of soil spectral induced polarization (SIP) signals. Geophysical Journal International, 229(2), 1422–1433. https://doi.org/10.1093/gji/ggab531

Ponziani, M., Slob, E. C., Vanhala, H., & Ngan-Tillard, D. (2012). Influence of physical and chemical properties on the low-frequency complex conductivity of peat. Near Surface Geophysics, 10(6), 491–501. https://doi.org/10.3997/1873-0604.2011037

Schwartz, N., & Furman, A. (2014). On the spectral induced polarization signature of soil organic matter. Geophysical Journal International, 200(1), 589–595. https://doi.org/10.1093/gji/ggu410

 

How to cite: Strobel, C., Dörrich, M., Cirpka, O. A., Huisman, J. A., and Mellage, A.: Organic matter matters - The imaginary conductivity of sediments rich in solid organic carbon, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1838, https://doi.org/10.5194/egusphere-egu23-1838, 2023.

16:35–16:45
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EGU23-6640
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On-site presentation
Philippe Leroy, Alexis Maineult, Aida Mendieta, and Damien Jougnot

Clays are sedimentary minerals that are ubiquitous in the Earth’s continental crust. They have remarkable adsorption, catalytic and containment properties due to their high surface charge and very large specific surface area. However, their microstructural and electrochemical properties are not completely understood. In this study, we have developed a new petrophysical model to interpret laboratory spectral induced polarization measurements on kaolinite, illite and montmorillonite muds when salinity increases (from around 0.01 mol L-1 to 1 mol L-1 NaCl initially). Our model considers electrical conduction in the bulk and diffuse layer waters as well as polarization of the Stern layers of illite aggregates and Stern layers and interlayer spaces of Na-montmorillonite aggregates with different shapes and sizes. Maxwell-Wagner polarization was considered as well. By fitting predicted to measured SIP spectra, we found that the basal surface of clays controls Stern layer polarization and that the interlayer space of Na-montmorillonite may polarize in the mHz to kHz frequency range. Our study is a step forward to better understand the high surface conductivity response of clays inferred from resistivity and induced polarization measurements.

How to cite: Leroy, P., Maineult, A., Mendieta, A., and Jougnot, D.: A petrophysical model for the spectral induced polarization of clays, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6640, https://doi.org/10.5194/egusphere-egu23-6640, 2023.

16:45–16:55
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EGU23-3097
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ECS
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On-site presentation
Abdoul Nasser Yacouba, Céline Mallet, Jacques Deparis, Phlippe Leroy, Gautier Laurent, Mohamed Azaoural, and Damien Jougnot

In a context of energy transition and water resources crisis, studying the fluid flow in the critical zone appears to be a major issue. The O-ZNS (Observatory of transfers in the Vadose Zone, Orleans, France) site has been designed for the development of innovative tools that can characterize and monitor the dynamics of the vadose zone (VZ). The geological structure of this VZ is composed mainly by a lacustrine limestone formation located between 10 and 20 m-deep, characterized by multiscale heterogeneities (facies variations, presence of cracks, fractures, pores, cavities and karstification). In order to predict fluid flow, heat transfer, and aquifer recharge through this VZ, the limestone heterogeneities have to be integrated into geological concepts and numerical models.

This study is a key part of the O-ZNS project, as it aims at (i) understanding and classifying the microstructural and petrophysical properties at laboratory scale; (ii) predicting these properties through quantitative geophysical parameters and; (iii) developing new geophysical interpretations through coupled approaches.

From well logs analysis of O-ZNS site, we collected limestone samples from four main facies (with four samples per facies). We performed a state-of-the-art petrophysical characterization including connected and total porosity, density, and permeability measurements. Then we carried out acoustic measurements on dry and water-saturated plugs (2.5 and 4 cm diameter) with P- and S-waves at two frequencies 0.5 and 1 MHz.

The measurement results show a large dispersion of the petrophysical properties. For example, connected porosity ranges from 4 to 12 %, and density from 2,3 to 2,5 g/cm3. This dispersion of petrophysical properties is interpreted in terms of heterogeneity of the type of porosity (micro to cm pore size, presence of cracks and fracture) and mineralogy. However, it appears that the deepest facies (located at the aquifer level) is more homogenous and shows the highest porosity. This is consistent with directly observed (micro)structure from 3D sample and well scans.

Acoustic velocity results show coherent values for fractured limestone rocks. The different facies show dispersion, such as Vp varying from 4950 to 5600 m/s for the shallowest facies at 9 m-deep. Here also, the deepest facies appears to be the most homogeneous with the lowest velocities (around 4875 m/s). Thus, velocities are consistent with the petrophysical measurements and one can draw a simple relationship between the porosity, density and acoustic velocities. However, other petroacoustic relationships are necessary to better discriminate between each facies and therefore predict their microstructure and transport properties.

The following step of this work is to add electric measurements and develop petro-acoustico-electrical models and enhance our capacity to upscale these properties from the laboratory to the field.

How to cite: Yacouba, A. N., Mallet, C., Deparis, J., Leroy, P., Laurent, G., Azaoural, M., and Jougnot, D.: Petroacoustic characterization of fractured and weathered limestone from the O-ZNS Critical Zone Observatory, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3097, https://doi.org/10.5194/egusphere-egu23-3097, 2023.

16:55–17:05
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EGU23-6657
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On-site presentation
Damien Jougnot, Luis Guarracino, Mariangeles Soldi, Flore Rembert, Haoliang Luo, Santiago Solazzi, and Luong Duy Thanh

Since the great paradigmatic revolution initiated by Mandelbrot, we know that fractals are ubiquitous in nature. From coastlines to plant growth, fractal mathematics help us to describe and quantify many of nature’s properties. In the same way, the fractal theory can be applied to porous and fractured media. In recent decades, numerous research studies have shown that fractal theory provides a solid framework to describe the properties of geological media. Based on advanced physical knowledge at the microscale, it is possible to use fractal patterns to describe transport properties in porous and fractured media. Fractal laws can be applied to describe the size distribution of pores and fractures, fracture widths, and pore irregularities, but also to relate these pore sizes to pore tortuosities. In this contribution, we review the significant advances that have been made in the field of petrophysics by applying fractal mathematics to describe fundamental petrophysical properties such as porosity, permeability, electrical conductivity, thermal conductivity, and electrokinetic and electroosmotic coupling coefficients. These new petrophysical models are based on the upscaling procedure applied to different fractal objects such as the Sierpinski carpet, Koch curves, Pigeon holes, and Menger sponge, among others. Among the interesting results obtained by means of fractal-based petrophysics, one can derive transport properties of saturated or partially saturated media, above and below freezing temperature, and considering hysteretic behavior and reactive media dissolution/precipitation processes. Integrating these fractal-based petrophysical relationships into the laboratory or field-scale, numerical simulations are now opening a wide range of potential avenues for progress in near-surface and reservoir geophysics.

How to cite: Jougnot, D., Guarracino, L., Soldi, M., Rembert, F., Luo, H., Solazzi, S., and Thanh, L. D.: Predicting transport properties in porous and fractured media, how fractal-based models can help petrophysicists?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6657, https://doi.org/10.5194/egusphere-egu23-6657, 2023.

17:05–17:15
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EGU23-2834
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ECS
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On-site presentation
Richard Wessels and Ronald Pijnenburg

Access to top research equipment facilitates top research. However, the research equipment needed may not always be available within individual institutes, while access to external facilities may not in all cases be affordable. This restricts the research that any individual can do and hampers scientific breakthroughs, particularly across disciplines. To overcome this limitation, a collaborative infrastructure network was initiated: EPOS-NL (European Plate Observing System- Netherlands). EPOS-NL provides free-of-charge access to geophysical labs at Utrecht University and Delft University of Technology, both in the Netherlands, for research within rock physics, analogue modelling of tectonic processes, X-ray tomography and microscopy. These labs include capabilities for among others: A) Mechanical and transport testing at crustal stress, temperature and chemistry conditions; B) Analogue tectonic modelling, including dynamic model imaging in 2D and 3D; C) X-ray tomography at sub-µm resolution; and D) A correlative workflow for imaging and microchemical mapping, down to nm resolution. As such, these labs can provide you with the means and expertise for your research into the physical behavior of the Earth’s crust and upper mantle.

Access to EPOS-NL can be requested by applying to a bi-annual call, posted on www.EPOS-NL.nl. This involves submitting a short (1-2 page) research proposal. Research proposals are reviewed on the basis of feasibility and excellence, but generally have a high chance of success (~80% in previous rounds). Interested? Have a look on the EPOS-NL website – and apply!

How to cite: Wessels, R. and Pijnenburg, R.: Access for free: How to get free-of-charge access to Dutch Earth scientific research labs through EPOS-NL, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2834, https://doi.org/10.5194/egusphere-egu23-2834, 2023.

17:15–17:25
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EGU23-3376
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On-site presentation
Michele Fondriest, Maurizio Vassallo, Stéphane Garambois, Thomas M. Mitchell, Di Giulio Giuseppe, Mai-Linh Doan, and Christophe Voisin

Field geological studies have revealed the heterogeneous structure of fault zones down to the sub-metric scale due to the juxtaposition of rocks presenting distinct deformation intensity and physical-transport properties. However, such internal variability is not generally resolved by most seismic tomography techniques due to spatial resolution limits. Quantifying the heterogeneous internal structure of fault zones is fundamental to understand their mechanical and hydrological characteristics. In this sense, determining seismic wave velocities and related physical properties (elastic moduli, porosity and fracture intensity) within fault zones, at different observational scales, is crucial.

Here, the near-surface velocity structure of two active seismogenic fault zones located in the Central Apennines of Italy was quantified at different length scales, from laboratory measurements of ultrasonic velocities (rock samples of few centimeters, 1 MHz source) to high-resolution first-arrival seismic tomography (spatial resolution of few meters). Detailed structural mapping was conducted within the Vado di Corno and Monte Marine fault zones, two NW-SE trending structures with length of ~ 15 km and up to 1.5 km of extensional displacement. Distinct structural units separated by fault strands were recognized in the fault zone footwall blocks cutting Mesozoic dolomitic carbonates: (i) fault core cataclastic units, (ii) breccia unit, (iii) high-strain damage zone, (iv) low-strain damage zone. The single units were systematically sampled along transects orthogonal to the average strike of the faults and characterized in the laboratory in terms of directional P and S ultrasonic wave velocities, porosity and microstructures. The fault core cataclastic units were significantly “slower” (VP = 4.5±0.4 kms-1, VS = 2.7±0.2 kms-1) compared to the damage zone units (VP = 5.6±0.6 kms-1, VS = 3.2±0.3 kms-1) at short length scales (i.e. few centimeters). A general negative correlation between ultrasonic velocity and porosity was observed, with some variability within the fault core mostly related to the textural maturity (clast/matrix volume ratio) of the fault rocks and the degree of pore space sealing by calcite cements.

Multiple P- and S-wave high-resolution seismic profiles (length 90-116 m, geophone spacing 1-1.5 m) were acquired across the two fault zones at different structural sites, moving from the principal fault surface into the outer damage zone. The derived first-arrival tomography models highlighted fault-bounded rock bodies with distinct velocities and characterized by geometries which well compared with those deduced from the structural mapping. At the larger length scale investigated by the active seismic survey, relatively “fast” fault core units (VP ≤ 3.0 kms-1, VS ≤ 1.8 kms-1) and very “slow” high-strain damage zones (VP < 1.6 kms-1, VS < 1 kms-1) were recognized. These velocity ranges were significantly different from those determined in the laboratory on small samples. This apparent discrepancy could be reconciled using an effective medium approach, considering the effect of mesoscale fractures density and size distributions affecting each structural unit.

This combined study highlighted the high petrophysical variability of carbonate-hosted fault zones, with structural units characterized by sharp contacts and different velocity scaling. In particular, the persistence of compliant high-strain damage zones at shallow depth might strongly affect near-surface deformation.

How to cite: Fondriest, M., Vassallo, M., Garambois, S., Mitchell, T. M., Giuseppe, D. G., Doan, M.-L., and Voisin, C.: The heterogeneous near-surface velocity structure of carbonate-hosted seismogenic fault zones investigated at different length scales: from ultrasonic measurements to subsurface seismic tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3376, https://doi.org/10.5194/egusphere-egu23-3376, 2023.

17:25–17:35
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EGU23-1059
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ECS
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On-site presentation
Edith Sotelo, J. German Rubino, Nicolas D. Barbosa, Santiago G. Solazzi, and Klaus Holliger

Fractures are ubiquitous through out the Earth's upper crust and dominate the mechanical and hydraulic properties of the affected rock masses. Indeed, open fractures act as fluid conduits and, commonly, flow is controlled by larger fractures, which are, in turn, likely to be connected to smaller ones. Therefore, fracture characterization is of paramount importance for many pertinent applications, such as geothermal energy production, CO2 sequestration, nuclear waste storage, and hydrocarbon exploration. Seismic reflection methods are useful tools for fracture characterization due to the generally high reflectivity that large fractures exhibit as a consequence of their strong mechanical contrast with the embedding intact background. The magnitude of this mechanical contrast is known to be strongly affected by fracture-to-background wave-induced fluid pressure diffusion (FPD). Conversely, the FPD effects associated with secondary connected fractures remain so far unexplored. We investigate the influence of FPD on the normal compliance and on the vertical incidence PP reflectivity of a large fracture that is hydraulically connected to smaller fractures. To this end, we use several models that consist of an infinite horizontal main fracture connected to multiple vertical secondary fractures of finite length. This fracture system is embedded in impermeable background. The individual models differ only with regard to the geometrical (e.g., length and aperture), and physical properties (e.g., permeability and bulk modulus) of the secondary fractures. For comparison, we also calculate the normal compliance and the reflectivity of an isolated infinite horizontal fracture. To assess the changes of fracture compliance due to FPD, we perform a vertical compressional oscillatory test over samples of the aforementioned models that include part of the fracture system and the embedding background. This test simulates the FPD effects that a vertically propagating P-wave generates between the main and secondary fractures. Specifically, the wave produces a pressure increase in the horizontal fracture that equilibrates as fluid flows into the secondary vertical fractures. Based on this oscillatory test, we compute the average of the vertical components of strain and stress over the main fracture, which we use to estimate its normal compliance. We then proceed to calculate the PP reflectivity at normal incidence using its inferred P-wave modulus. Our results show that both the compliance and the PP reflectivity of the main fracture increase as much as two-orders of magnitude in response to the presence of secondary fractures. We also find that the physical and geometrical properties of the secondary connected fractures have an influence on the normal compliance and reflectivity of the main fracture.

How to cite: Sotelo, E., Rubino, J. G., Barbosa, N. D., Solazzi, S. G., and Holliger, K.: Seismic reflectivity of fractures: the impact of secondary connected fractures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1059, https://doi.org/10.5194/egusphere-egu23-1059, 2023.

17:35–17:45
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EGU23-8860
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ECS
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On-site presentation
Gabriel Quiroga, Santiago Solazzi, Nicolás Barbosa, J. Germán Rubino, Marco Favino, and Klaus Holliger

The seismic characterization of fractured geological formations is of importance for a wide range of applications throughout the Earth, environmental and engineering sciences, such as, for example, hydrocarbon exploration and production, CO­­2 sequestration, monitoring of enhanced geothermal reservoirs, nuclear waste storage, and tunneling operations. Seismic methods are indirect in nature, and, hence, comprehensive modelling techniques are required to translate corresponding observations into rock physical properties. In this regard, numerous works have employed the theoretical framework of poroelasticity in order to explore the seismic response of particularly complex and elusive parameters of fluid-saturated fracture networks, such as their fracture density and interconnectivity. This is motivated by the fact that poroelasticity allows to account for fluid pressure diffusion effects between connected fractures as well as between fractures and their embedding background. Fluid pressure diffusion prevails when zones of contrasting compliance are traversed by a seismic wave, as this results in pressure gradients, which induce oscillatory fluid flow and, consequently, energy dissipation. This form of energy dissipation has a significant impact on seismic velocity dispersion, attenuation, and anisotropic characteristics, which are key seismic observables. While a wide range of approximations are employed to represent fracture properties in order to compute the seismic response of formations, they do tend to inherently ignore the complex interrelationships between the lengths, compliances, apertures, and permeabilities of fractures remains, as of yet, unaccounted for. In this work, we seek to alleviate this in combination with a poroelastic modelling approach to explore how length-dependent fracture scaling characteristics affect the effective seismic properties of fractured rocks. We start by revisiting canonical models with two orthogonally intersecting fractures of different lengths to analyze the interactions occurring when fractures are affected by a seismic wavefield. We then proceed to explore how scaling relations affect these results. Finally, we consider fracture networks with realistic stochastic length distributions, for which we compare the effective seismic response with and without the proposed length-dependent scaling of the fracture characteristics. Our results demonstrate that the scaling of fracture properties does indeed have a significant effect on the seismic response, as it dramatically reduces the contribution of smaller fractures to fluid pressure diffusion between connected fractures, which, in turn, affects the overall seismic characteristics of the formation.

How to cite: Quiroga, G., Solazzi, S., Barbosa, N., Rubino, J. G., Favino, M., and Holliger, K.: Effective seismic properties of fractured rocks: the role played by fracture scaling characteristics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8860, https://doi.org/10.5194/egusphere-egu23-8860, 2023.

17:45–17:55
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EGU23-11037
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On-site presentation
Sarada Prasad Pradhan and Krishna Chandra Sundli

Quantifying in-situ stress is crucial for predicting drilling-induced tensile fractures, wellbore failures, proper well placement, hydro-fracture treatment optimization and sand production. A comprehensive mechanical earth model incorporating pore pressure, stress state, and rock mechanical properties enable us to study the cause of failure observed in the well. The study is focused on a petroleum reservoir in Western Offshore India. In this study, an attempt is made to estimate in-situ stresses present in the field. Well-log data calibrated with available direct pressure measurements viz. Modular Dynamic Test (MDT) and Leak Off Test (LOT) data are used to predict the pore pressure and minimum horizontal stress. Vertical stress is estimated by extrapolating the density log; for minimum and maximum horizontal stress, the poroelastic approach is adopted. Key rock strength parameters were estimated using standard correlations and regional studies. Wellbore stability analysis was carried out, and the results were calibrated with the actual mud weight used. Natural fractures present in the reservoir are sensitive to stress distribution which in turn is sensitive to changes in pore pressure distribution. Many exploratory and development wells have been drilled in the area, but very few have recorded DSI (Dipole Shear Sonic Image) and FMI (Formation Micro-Scanner Image) logs. With the available log data, the study was carried out to quantify the rock mechanical parameters and the stress magnitudes of the field. The study aims to model the study area's geomechanical aspect for better prediction of drilling-induced challenges, thereby reducing NPT and optimizing drainage.

How to cite: Pradhan, S. P. and Sundli, K. C.: Mechanical Earth Modelling for Petroleum Reservoir in Western Offshore India: Tensile Failure Study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11037, https://doi.org/10.5194/egusphere-egu23-11037, 2023.

Posters on site: Wed, 26 Apr, 10:45–12:30 | Hall X2

Chairpersons: Lucas Pimienta, Damien Jougnot, Ludovic Bodet
X2.244
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EGU23-3347
Zhenya Zhou, Eva Caspari, Nicolás D Barbosa, Marco Favino, and Klaus Holliger

Fractures are ubiquitous throughout the Earth’s upper crust and represent localized zones of mechanical weakness as well as preferential pathways for fluid flow. Correspondingly, their detection and characterization is vital for a wide range of pertinent applications in geological, civil, and environmental engineering, hydrocarbon exploration, nuclear waste and carbon dioxide storage, as well as geothermal energy production. Particularly important mechanical characteristics of fractures are their normal and shear compliances, which relate the displacement perpendicular and parallel to the fracture plane, respectively, to the corresponding components of the prevailing stress tensor. Based on the linear slip model, previous works developed a phase delay method to estimate the normal compliance of individual fractures using the P-wave first-arrivals in full-waveform sonic (FWS) log data. This approach is viable for a quasi-normal incidence scenario of the sonic wavefield. However, the conditions under which this technique remains valid at oblique P- and S-wave incidence angles as well as the role played by the combined effects of the normal and shear compliances remains enigmatic. To alleviate this problem, we have extended the phase delay technique to allow for non-normally-incident P- and S-waves. In addition to improving the accuracy of the normal compliance estimates with respect to the results computed under a normal incidence assumption, this method allows for a simultaneous estimation of the normal and shear compliances. The proposed approach has been validated through analytical tests and numerical simulations of wave propagation in a hard-rock-type borehole environment intersected by a single fracture with dip angles of 0, 30, and 40 degrees with regard to the horizontal. For fracture compliance values typical of mesoscale fractures (10-14 to 10-12 m/Pa), the effects associated with oblique incidence become significant for dip angles larger than 50 and 30 degrees for P- and S-waves, respectively. However, our results also demonstrate that the normal incidence assumption can produce similar errors at even lower fracture dip angles in the presence of larger fracture compliance values and/or shear-to-normal compliance ratios. Finally, we apply the method to observed FWS data acquired in granitic rocks where the considered boreholes intersect fractures at a range of oblique angles. Direct in-situ estimates of compliances for discrete individual fractures are scarce, but essential to bridge the scale gap between laboratory estimates and input data for reservoir scale models. While recent studies show the feasibility of estimating normal compliances from FWS data, this study aims to explore whether and to what extent this approach can be practically extended to shear compliances and to the corresponding shear-to-normal compliance ratios.

How to cite: Zhou, Z., Caspari, E., Barbosa, N. D., Favino, M., and Holliger, K.: Estimation of normal and shear compliance for inclined fractures from full-waveform sonic log data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3347, https://doi.org/10.5194/egusphere-egu23-3347, 2023.

X2.245
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EGU23-3630
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ECS
gang lin, Samuel Chapman, Jérôme Fortin, and Alexandre Schubnel

Pore pressure has a major influence on the effective stress and thus on the mechanical behaviour and the physical (elastic and transport) properties of microcracked rocks. In the field, in-situ measurements of pore-pressure is difficult outside of local measurements around boreholes. Yet, fluid migration is observed ubiquitously in the continental crust, whether in fault zones or in volcanic geothermal areas. In particular, pore pressure perturbations change the effective stress, which may lead to microseismic activity. This may also occur in conventional reservoirs, the storage of CO2 or deep geothermal energy extraction.

 

In this study, we focus -in the laboratory- on the hydro-mechanical behavior of thermally treated Westerly granite and naturally microcracked Etna basalt samples (40 mm in diameter and 80 mm in length). The goal is to determine the pore pressure distribution and diffusion laws under different pore pressure gradients. First, classical (constant flow method) permeability measurements under small pore pressure gradient (1 MPa over the length of the sample) were carried out as a function of increasing confining pressures Pc (up to 70 MPa). The results show that permeability of samples varies exponentially with effective pressure, which is expected for cracks-porous rocks. The pressure sensitivity factor for permeability was then deduced to be of the order of 0.011~0.057 MPa-1.

 

In a second step, permeability was measured at high (70 MPa) confining pressure, under large pore-pressure gradients (up to 60 MPa). During this part of the experiments, pore pressure was measured along the sample using newly developed fluid pressure sensors (with an absolute accuracy of +/-1MPa). Under small pore pressure gradient (2.5 MPa), our results show that the pore pressure varies linearly over the length of the sample, as expected from Darcy’s law and a constant permeability. However, with increasing pore pressure gradient (up to 60 MPa), the linearity is lost, as the permeability can no longer be assumed constant along the sample.

 

To interpret our results, we solved the diffusion equation, assuming that permeability varies exponentially with effective pressure. For steady state flow conditions, our observations of the pore pressure distribution in the samples are consistent with the theoretical predictions. In particular, we show that the shape of the pore-pressure distribution at steady-sate does not depend on permeability itself, but rather on the permeability pressure sensitivity factor: the larger the latter, the more non-linear the pore pressure in the samples.

How to cite: lin, G., Chapman, S., Fortin, J., and Schubnel, A.: Fluid diffusion and pore-pressure distribution in microcracked rocks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3630, https://doi.org/10.5194/egusphere-egu23-3630, 2023.

X2.246
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EGU23-4452
Pauline Kessouri, Clémence Ryckebusch, Alejandro Fernandez-Visentini, and Lee D. Slater

Past metallurgical sites and deposits account for a significant proportion of potentially contaminated sites in the European Union (EU):  about 100,000 have been identified only in the North West regions of the EU. While recent wastes from sites still in operation are commonly recovered, this is not the case for old aggregated materials with a high content of ferrous (and other) metals, white and black slag, etc., which are considered to be sources of pollution and are costly to manage or dispose of. These sites could be considered as opportunities to recover large volumes of resources (metals, materials and land) using urban mining techniques if they were better characterized.

The induced polarization (IP) method is a geophysical method known to be sensitive to the presence of various metallic particles disseminated in the soil layers. If qualitative interpretation of the measured IP parameters in the field (i.e. resistivity and chargeability) are widespread, quantitative interpretation in terms of concentrations of different metallic particles is yet to be developed.

The example of the Pompey field site (FR), investigated as part of the NWE-REGENERATIS project (https://www.nweurope.eu/projects/project-search/nwe-regeneratis-regeneration-of-past-metallurgical-sites-and-deposits-through-innovative-circularity-for-raw-materials/), is used in this study to present the interest in using time domain IP (TDIP) field measurements to characterize metallurgical past deposits. Several paths are explored to convert resistivity and chargeability TDIP tomographies into quantitative interpretation of metallic element concentrations: (1) extraction of frequency data from TDIP field measurements; and (2) upscaling of lab results through numerical simulations.

Regarding (1), TDIP measurement were made with different time windows (different frequencies), giving us access to spectral IP (SIP) processing and interpretation at 5 frequencies. These new frequency interpretations of the TDIP can be compared to lab measurements and facilitate the upscaling of the found petrophysical relationships.

Regarding (2), in order to interpret the TDIP results in terms of concentration of metallic particles, known petrophysical relationships and geochemical measurements obtained at the lab scale need to be interpreted at the field scale. We propose to use a Bayesian framework for inferring field-scale metallic particles concentrations, taking into account heterogeneity and anisotropy within the inversion schemes. This work is ongoing.

For both (1) and (2), it is crucial to find the best petrophysical relationships linking the IP parameters to concentration and size of metallic particles. Wong (1979) developed a physics-based electrochemical model that is still used today. We further investigate the Wong model to explore the role of the background porous medium itself in determining the IP signature of disseminated metallic particles and discuss the sensitivity of the model to estimate metallic grains concentration.

All these different research paths lead to a better understanding of metallic particles IP signature at a small scale, as well as discussions on how to use these findings to better characterize and reevaluate past metallurgical sites and deposits.

This study was funded by the North West Europe (NWE) Interreg project called NWE-REGENERATIS that aims at the regeneration of past metallurgic sites and deposits through innovative circularity for raw materials, and by Schlumberger-Doll Research Center (USA, MA).

How to cite: Kessouri, P., Ryckebusch, C., Fernandez-Visentini, A., and Slater, L. D.: IP signature of metallic particles: lessons learnt from field and laboratory experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4452, https://doi.org/10.5194/egusphere-egu23-4452, 2023.

X2.247
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EGU23-6941
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ECS
Francisca Soto Bravo, Chi Zhang, and Lin Jia

Low-field nuclear magnetic resonance (NMR) is a minimally-invasive geophysical method often used to characterize pore spaces, water content, and fluid transport and distribution in geologic materials. NMR measurements are based on the magnetization and relaxation behavior of the spin magnetic moment of hydrogen atoms in external magnetic fields. These measurements can be taken in the field, such as from a borehole or the surface of the Earth, or in the laboratory using a bench-top apparatus. Numerical simulations of NMR signals are great tools to better understand the relaxation behavior of pore water under different scenarios, explore the effect of changes in the composition or geochemical characteristics of the geologic material, verify experimental findings, and improve the interpretation of field measurements. They can also be used to examine situations where traditional interpretation of NMR signals fails, such as in complex, heterogeneous geometries with pore coupling effects. In a pore coupled system, significant magnetization exchange between pores of different sizes occurs during the measurement time, which makes it difficult to independently characterize the pore environments. Using numerical simulations, it is possible to explore the factors that control pore coupling, such as surface relaxivity, pore-network connectivity and other pore-network characteristics, can be explored independently in a controlled setting. In this work, we introduce common numerical modelling approaches used for simulating NMR responses in geologic materials, along with their limitations and traditional workflows. We present two specific examples: a Random Walk (RW) simulation to test the effect of different pore-network connectivity features on pore coupling in a simplified pore geometry, and a Finite Element Method (FEM) simulation approach to visualize the distribution of magnetization density within a single pore. NMR is a promising hydrogeophysics tool gaining popularity and finding new applications for near-surface exploration. A better understanding of the NMR signals in diverse and complex scenarios is essential for the adequate design of experiments and field campaigns and for the correct interpretation of NMR measurements at different scales. The use of numerical modelling strategies can help improve this understanding, leading to more accurate and reliable measurements and interpretations.

How to cite: Soto Bravo, F., Zhang, C., and Jia, L.: Reviewing numerical simulation methods of nuclear magnetic resonance signals in porous media., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6941, https://doi.org/10.5194/egusphere-egu23-6941, 2023.

X2.248
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EGU23-5997
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ECS
Hadiseh Mansouri, Virginia Toy, Kevin Klimm, Nikolai Bagdassarov, Mattia Pistone, Andrew Greenwood, and György Hetényi

Electrical resistivity tomography and electromagnetic inverse modelling are particularly useful to explore orogenic systems because the most important conductive components of rock masses are economically-significant minerals (semi-metals like graphite, and semi-conducting minerals like sulphides), as well as certain clays and permeating saline fluids. Despite the efficiency of electrical measurements, anisotropic properties of the crust, which affect almost all acquired data, may lead to serious misinterpretation of the subsurface geology if they are ignored during data analysis. Understanding the geological causes of electrical anisotropy and heterogeneity, and considering their influence in field-scale electrical measurements, can provide crucial information on the crustal architecture, pore fluid network, as well as revealing the internal structure of fault zones, and increasing the accuracy of location of critical mineral deposits. To this end, we aim to quantify the electrical properties of mid- to lower-crustal metamorphic and magmatic lithologies based on their micro- to macrostructures, conductive components and fluid contents as measured by laboratory methods. Our research also contributes to, and advances, the likely outcomes of the ICDP-supported project DIVE (Drilling the Ivrea-Verbano ZonE). DIVE is currently exploring the hidden portions of the continental lower crust and crust-to-mantle transition zone of the Ivrea-Verbano Zone (Western Alps, Italy) in two boreholes at the sites of Megolo (DT-1a) and Ornavasso (DT-1b), separated by  7 km distance in Val d’Ossola. The first DIVE borehole, DT-1b, was completed in December 2022, reaching a depth of 578.5 metres, and rock cores of metapelite, gneiss, amphibolite, migmatite, and pegmatite were recovered. Some drillcores contained a range of potentially conductive lithologies, including sulphide- and graphite-bearing metapelites. In this research we are measuring electrical conductivity on a representative benchmark suite of bedrock outcrop samples from the region around the DIVE boreholes at elevated pressure and temperature. We are currently characterising the microstructural arrangement and distribution of conductive phases within these samples by electron beam methods. To properly understand electrical property measurements of the natural samples we determine the contributions of each key conductive phase (graphite and sulphides). The bulk resistivity of a mixture of quartz+10% graphite, which was synthesized in a solid–medium piston-cylinder apparatus, at temperature of 22.5 °C and pressure of 0.5 GPa, was found to be 1 Ω.m. No change in bulk resistivity was observed with increasing temperature up to 1000 °C. We will present the results of additional tests to be undertaken between January and April 2023 at this conference. Our data will be employed in interpretation of wireline electrical logs and borehole-to-surface electrical surveys from DT-1a and DT-1b.

How to cite: Mansouri, H., Toy, V., Klimm, K., Bagdassarov, N., Pistone, M., Greenwood, A., and Hetényi, G.: Quantification of electrical properties of deep crustal rocks based on their mineral modal proportion, fabric, and pressure-temperature conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5997, https://doi.org/10.5194/egusphere-egu23-5997, 2023.

X2.249
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EGU23-7902
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ECS
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Arne Marvin Mansfeld and Andreas Kemna

Interactions between mineral phases and fluids in the subsurface inevitably lead to mineral precipitation reactions and dissolution. While these processes are the major drive behind many geochemical changes in aquifer systems, their detection, monitoring and characterization is difficult. Geoelectrical methods provide potential to investigate precipitation and dissolution reactions in rocks non-invasively. However, with the measurement of the DC electrical conductivity alone, changes in pore water salinity, mineralogy, or pore space characteristics can hardly be differentiated. The ambiguity in the identification of these processes can be reduced by also measuring the spectral induced polarization (SIP) response, i.e., the frequency-dependent complex electrical conductivity, given the sensitivity of especially the imaginary component to textural and chemical characteristics. In order to assess the capability of this approach, we conducted multiple laboratory experiments on quartz-rich sandstone samples in which different precipitation scenarios were provoked under controlled conditions while monitored with SIP. The experimental setup consists of two reactant solutions in contact with both sides of the sample, leading to a reaction within the sample as diffusion from each side into the rock goes on. We used reactant solutions of NaHCO3and CaCl2in varying molality, the mixing of which in the sample’s pore space results in CaCO3formation. By varying samples and solutions, three different components contributing to the complex conductivity response during the ongoing precipitation could be identified. The onset of the chemical reaction is clearly visible in the temporal evolution of imaginary conductivity at relatively low frequencies. The observed temporal peak can be associated with changes in the pH value due to the infiltration of the reactant at earlier times and the reduction in pH with calcite precipitation. This explanation is supported by additional experiments performed on a similar sample, where pH was altered by infiltration of NaHCO3only. A second spectral high-frequency peak shows up at later stages of the experiments, suggesting that here the main changes of the pore surfaces in response to the precipitation are occurring. This phenomenon could not be recreated by using the infiltration of a pure electrolyte solution or the infiltration of NaHCO3. The last component in the complex conductivity response is the continuous increase of the real component due to the increasing salinity of the pore water, which also could be reproduced in comparative measurements. Our results show the potential of complex conductivity measurements for precipitation monitoring in rocks, including improved textural and chemical characterization. Given the applicability of complex conductivity imaging at the field scale, the method thus holds promise for monitoring tasks in the context of, for example, carbon capture and storage, enhanced geothermal energy, soil stabilization, and capture of dissolved contaminants, which are of increasing societal relevance.

How to cite: Mansfeld, A. M. and Kemna, A.: Impact of chemical subprocesses during calcite precipitation in sandstones on the measured SIP response and their identification, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7902, https://doi.org/10.5194/egusphere-egu23-7902, 2023.

X2.250
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EGU23-16816
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ECS
Anamika Sahu, Sandeep Singh, Narendra Kumar Samadhiya, and Anand Joshi

Seismic wave velocities (both P and S waves) measurements have been carried out for carbonate rock samples collected from Lesser Himalayan deposits exposed along Alaknanda valley between Rudraprayag to Helang village in Uttarakhand, India. This study has been carried out to evaluate the effect of the petrophysical and the mechanical properties of rocks on seismic wave velocities. On the core samples, petrophysical and mechanical measurements were performed where porosity, density, water absorption, and seismic wave velocities were first determined, followed by measuring the uniaxial compressive strength (UCS), and Brazilian tensile strength (BTS). Thin sections were prepared to measure the petrographic parameters (textural properties and mineralogical composition). This study focuses mainly on grain size and mineral composition. Petrographic investigation and X-ray diffraction (XRD) analysis were done to identify their mineralogy. Both petrographic and XRD analysis revealed that the main constituting minerals are dolomite, and in minor amounts, calcite, quartz, and opaque minerals are present. Interrelationships between seismic wave velocities and porosity, density, mineral constituents, grain size, uniaxial compressive strength, and Brazilian tensile strength were obtained using regression analysis. It has been concluded that there are significant positive correlations between compressional wave velocity and uniaxial compressive strength (r2 = 0.82), Brazilian tensile strength (r2 = 0.67). Similarly, strong to moderate correlations were found between shear wave velocity and uniaxial compressive strength (r2 = 0.73), Brazilian tensile strength (r2 = 0.68). Weak to moderate negative correlations were found between seismic wave velocities and porosity. Moderate positive correlations have been found between seismic wave velocities and dry density. There is moderate negative correlation has been found between uniaxial compressive strength and grain size. Furthermore, it has also been concluded that the influence of grain size on rock strength was more important than mineral content.

How to cite: Sahu, A., Singh, S., Kumar Samadhiya, N., and Joshi, A.: Correlating Seismic Wave Velocities with the Physicomechanical Properties of Carbonate Rocks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16816, https://doi.org/10.5194/egusphere-egu23-16816, 2023.

Posters virtual: Wed, 26 Apr, 10:45–12:30 | vHall TS/EMRP

Chairpersons: Chi Zhang, Lucas Pimienta, Ludovic Bodet
vTE.9
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EGU23-1115
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ECS
hao yuan Li

AbstractThe bauxite reservoir of the new type Taiyuan Formation in Zhengning area, southwest of Ordos Basin, is affected by the karst palaeogeomorphology, and its thickness varies greatly.In order to systematically study bauxite, a new type of reservoir, based on core observation, microscopic thin section, high-pressure mercury injection, low-temperature nitrogen adsorption and other experimental methods, the petrological characteristics and pore structure characteristics of bauxite reservoir were studied, which further verified the significance of reservoir exploration.The results show that: (1) the upper and lower parts of the reservoir are bauxite mudstones, and the middle part is argillaceous bauxite. The relatively developed dissolution pores are the main storage space of bauxite; (2) The bauxite minerals of Taiyuan Formation are mainly composed of aluminum minerals and clay minerals. The main minerals are diaspore, kaolinite, illite and chlorite; (3) Bauxite reservoir space is mainly composed of intragranular dissolved pores, matrix dissolved pores, intergranular dissolved pores, intergranular pores and microcracks, with the pore size mainly between 20 and 200 μm; The pore diameter of the main throat of the reservoir is 150 nm~4μm. The pore structure is good, mercury removal efficiency is high, and the overall pore throat is mainly submicron to micrometer; The average physical porosity of the reservoir is 10.6%, and the average permeability is 4.04×10-3μm. Greater than 0.3×10-3μm 36% of them are above m, and the reservoir conditions are good.The research results provide a basis for bauxite gas exploration in Ordos Basin.

How to cite: Li, H. Y.: Bauxite Reservoir Characteristics of Taiyuan Formation in Zhengning Area of Southwest Ordos Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1115, https://doi.org/10.5194/egusphere-egu23-1115, 2023.

vTE.10
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EGU23-1152
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ECS
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Na Yin

The capillary force shows great potential to improve the recovery of shale oil and gas reservoirs through spontaneous imbibition. However, the mechanism of capillary force on shale oil migration and its controlling factors are still unclear. By NMR, low-temperature nitrogen adsorption, high-pressure mercury injection and other experimental means, this work attempts to investigate the role of capillary force in improving shale oil recovery. The results show that the nuclear magnetic resonance T2 spectra obtained through spontaneous imbibition can be divided into three types, and the shale oil recovery can reach 38.72% - 65.52%, which is mainly contributed by the first peak (P1). The water imbibition and oil imbibition experiments were carried out on samples of the same size, and the dynamic wettability index of the samples with the spontaneous imbibition time was calculated. It was found that type 1 shale is mainly lipophilic, type 2 and type 3 samples are mainly hydrophilic, the P1 of three types of shale is hydrophilic to neutral, and the water imbibition volume of the three samples was greater than the oil imbibition volume. In addition, by comparing the relationship between pore throats and pores and combining the structural characteristics of samples, three typical types of pore throats are summarized. Finally, through a comprehensive study on the wettability, pore structure of shale and shale oil recovery , it is concluded that water can drive oil droplets in micropores or pore throats (P1) to enter the mesopore (P2), and then the mesopore (P2) transmits the oil to the fractures by transfering pressure difference, and the oil-water distribution pattern before and after spontaneous imbibition under the effect of capillary force is summarized to provide theoretical basis for shale oil exploration. and development.

How to cite: Yin, N.: Shale oil mobility and pore size-associated wettability under capillary pressures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1152, https://doi.org/10.5194/egusphere-egu23-1152, 2023.

vTE.11
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EGU23-8629
Shaolong Zhang, Jingong Cai, Jianping Yan, Xiaojun Zhu, and Min Wang

Oil saturation is important for shale reservior to identify favorable sections and mapping the geological sweet spot. Current oil saturation evaluation methods, including experiments and empirical formulas, are not suitable for shale reservoir because of the complex mineral, fluid components and pore structure characteristics. To establish the shale oil saturation calculation model, X-ray diffraction, one-dimension and two-dimension nuclear magnetic resonance (NMR), and oil-water two-phase displacement experiments were employed on shale samples collected in the upper sub-member of the fourth member of the Eocene Shahejie Formation in the Dongying sag, Jiyang Depression, Bohai Bay Basin. After data analysis, the reason for whether oil is produced in the displacement experiments were explained, distribution characteristics of different shale components in the NMR T1-T2 map were analyzed, and a new shale oil saturation calculation method was proposed using NMR T2 sensitive parameters that reflected the changes of NMR T2 spectrum morphological characteristics with different oil saturation calibrated by NMR T1-T2 map at different displacement stage. The results indicated that the pore structure of shale samples is complex and show strong heterogeneity according to the NMR T2 spectrum, and the distribution of shale pore size is the main factor determining whether there is oil in the volumetric cylinder in the displacement experiment under the premise of the slight difference of wettability. NMR T1-T2 map is an effective way to identify different components (kerogen and solid bitumen, adsorbed oil, free oil, structural and adsorbed water, free water) of shale samples, and usually, kerogen and solid bitumen distributed in the top left of the T1-T2 map with T1>10 ms, T2<0.1 ms. Based on this, T2 threshold for free oil and adsorbed oil are 2 and 0.2 ms, and the corresponding threshold of pore radius are 40 and 4 nm according to the NMR theory. As NMR T2 spectrum sensitive parameters, geometric mean and interval porosity corresponding to the first peak are positively and negatively correlated with oil saturation respectively. With understanding this, oil saturation calculation method is established using the above two parameters and the Root Mean Square Error (RESM) between the measure oil saturation and the calculated results is 5.78%, which reflecting the accuracy and validity of the method. In general, this method allows the shale oil saturation to be accurately calculated and provides a parameter basis for the determination of favorable sections and evaluation of resource of shale oil reservoir. Moreover, it also offers a new idea for the oil saturation predication by NMR logging.

How to cite: Zhang, S., Cai, J., Yan, J., Zhu, X., and Wang, M.: Oil saturation quantitative evaluation in lacustrine shale: A novel insight from NMR T1-T2 experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8629, https://doi.org/10.5194/egusphere-egu23-8629, 2023.