Displays

Currently, the integration of seismic and "non-seismic" geophysical research methods is increasingly demanded by the practice of exploration. Further improvement of the efficiency of the complex of seismometry and gravimetry, its wide introduction into practice, requires both the creation of recommendations on the methodology of joint interpretation of these methods, and the determination of limitations on the scale of surveying and the specifics of the considered cross-sections, affecting the effectiveness of the methods of the studied geological structures. The aim of the presented work is to identify the main factors that determine the limits of applicability of seismic-gravity modeling.

The possibilities of seismic-gravity modeling in conditions of different physical and geological structure of the considered environment, scale, level and quality of the initial data were investigated on real objects. It is shown that it is impossible to totally formalize a single approach (algorithmize) to the creation of a seismic-gravity model. The modeling technique inevitably changes, adapts to the physical and geological situation and the completeness and detail of a priori information. Against the background of numerous positive examples of use, the situations difficult for seismic-gravity modeling are given and analyzed carefully and the reasons for the low efficiency of the method are revealed.

The experience of practical research has shown that the effectiveness of seismic-gravity modeling is primarily influence by such features of geological structure as the extent of compartmentalization of the reflector horizons’ geometry, contrast and depth of the density boundaries, the accordance of seismic and gravity exploration (both field survey and target exploration intervals), the intricacy of the geological history of the region.

The findings are important at the design stage of field work to compile a set of geophysical methods, the most effective for this area of study.

How to cite: Shirokova, T., Lygin, I., and Sokolova, T.: The major factors of seismic-gravity modeling limits of applicability determination, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-850, https://doi.org/10.5194/egusphere-egu2020-850, 2020.

This paper presents an integrated seismic and aeromagnetic approach applied in the geological complex area of the Cagliari Gulf in the southern Sardinian margin (Western Mediterranean). The investigated area represents the southern extreme part of the main branch of the Sardinian Rift (SR) (Western Mediterranean) that is made up here of a sub-basin bounded by approximately NW faults. The study was also integrated by complementary information deduced from the GNSS network in southern Sardinia.

The aim of this study was to give a contribution on the knowledge of the tectonic evolution and volcanism of the investigated area. For this purpose we used an integrated interpretation of two-dimensional reflection seismic sections and aeromagnetic data. In the same area a well drilled for oil prospection was used for calibrating the seismic interpretation up to approximately 1.8 sec.. It is worth noting that the interpretation of the seismic data can be problematic in structurally complex areas where volcanic formations occur, but it can be assisted effectively by magnetic interpretation. An interesting magnetic pattern represented by a strong, well-localized positive magnetic anomaly extending N-S for approximately 35 km is present in the western part of the Gulf. Its width in the W-E direction is of almost 20 km. The anomaly seems to be linked with the magnetic anomalies that characterize the southern Sardinian Rift in correspondence to the Campidano Graben. In fact, a set of localized high-gradient anomalies generally corresponding to the Oligo-Miocene andesitic calc-alkaline complexes is present in this Graben. The aeromagnetic interpretation was carried out to explain the origin of the above strong elongated magnetic anomaly that has never been quantitatively interpreted. In this work, this anomaly has been interpreted by means of Euler deconvolution, the analytical signal and by a delineation technique based on the maxima of the radial horizontal derivative of the total magnetic field. The geological knowledge of the area by means of earlier studies also on land contributed to give a petrographic meaning to the magnetic sources, while by the magnetic and seismic integrated interpretation it was possible to carry out a spatial reconstruction of the volcanic source body and to give an useful contribution to the knowledge on the volcano-tectonic evolution of the area. Recently the area of the Gulf of Cagliari was affected in its western sector by a weak earthquake with hypocenter at around 10 km of depth, localized by Istituto Nazionale di Geofisica e Vulcanologia (INGV). The results of this study also provided new elements of knowledge which have contributed to understand this seismic event.

Acknowledgements: This work was partially supported by FIR (Fondi integrativi per la Ricerca) funded by the University of Cagliari (Italy) and by RAS/FBS (grant number: F71/17000190002) grants for funding.

How to cite: Fais, S., Klingele, E. E., Tocco, R., and Casula, G.: Integrated interpretation of reflection seismic and aeromagnetic data in a marine geological complex area: a case study., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1226, https://doi.org/10.5194/egusphere-egu2020-1226, 2020.

Advances in seismic imaging technology can discourage the integration of outcrop data into modern interpretation workflows. Yet, instigation of hydrocarbon exploration still requires the use of legacy seismic data, especially within mature petroleum provinces. Typical exploration workflows include expensive pre-stack seismic reprocessing, to better resolve exploration targets. This is a resourceful but timely process that can be enhanced by using structural geological analogues. The inner Bristol Channel has extensive outcrop: to the east the Severn Estuary, to the north the South Wales Coalfield and Vale of Glamorgan and to the south along the Somerset, Devon and Cornish coastlines. These sources of prolific data, combined with legacy exploration refraction, reflection and earthquake seismology, make the inner Bristol Channel an ideal natural laboratory to integrate analogues with seismic information and to produce realistic interpretations and explanations of complex structural heterogeneities especially in places concealed by Mesozoic and Quaternary cover, marine waters and estuarine sediments typical of the inlet. Successful structural analysis is always reliant on well-processed pre-stack seismic data. It is demonstrated however that numerous known structural inversion events also necessitate the best choice of analogues to resolve the geometry and kinematics of any major faults offshore accurately enough to reach a reliable understanding of the petroleum system. Here, in response to the Department of Energy and Climate Change (DECC) 2016 data release and the 31st licensing round, we use case studies from the inner Bristol Channel to demonstrate the value of structural geological analogues by integrating them into 1985 2D legacy seismic data at an early stage in the seismic interpretation process. With suitably chosen analogues, structural dissection and reconstruction are carried out to generate geometric and kinematic models. The wider waters of the Bristol Channel are situated in quad 105; in which investigation was instigated in the 1970’s by major exploration companies. Currently, an interest in reliable structural analogues is made more relevant by the fourteen exploration licenses held onshore in south west England and South Wales. Thence our study augments the extensive field work carried out over at least three decades of academic research by generations of scholars. The targeted investigations conducted along the southern coast of Wales and the north coast of Somerset, Devon and Cornwall lead to revised syntheses, to better extrapolate, predict and model the structural architecture beneath the inner Bristol Channel. Exemplary Welsh field analogues are accounted in detail, measured, restored and integrated into an interpretation of the 2D 1985 Western-Geco dataset (WG85 2D 2001). The analogues include Trwyn-yr-Wrach, the Cold Knap, St Mary’s Well and Sully Island, among many others. In conclusion, the practical methodology exemplifies the geometric WNW-ESE lateral changes in structure and the effects of numerous kinematic phases and recent seismicity upon the architecture of the inner Bristol Channel basin as well as its relic-fabric. This demonstration of analogues improves immensely the geological understanding of seismic reflection projects whether legacy data, reflection, refraction or seismology and should remain relevant for many more crucial and modern acquisitions.

How to cite: Miliorizos, M. N., Reiss, N., and Melis, N. S.: A demonstration of the tectonic evolution of the inner Bristol Channel UK: application of structural geological analogues to interpretation of legacy and new seismic data., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3178, https://doi.org/10.5194/egusphere-egu2020-3178, 2020.

South Yellow Sea was a component of the circum-Pacific continental margin active belt, developing on the marine basement during pre-Paleozoic and mid-Paleozoic. The lack of detail in the offshore seismic model in the crustal levels means that the deep structure remains ambiguous. We processed the offshore wide-angle seismic data from 30 sections that were acquired in 2013 in order to achieve a continuous 2-D velocity and interface model using Rayinvr. The final velocity/interface model along the survey lineshows significant horizontal and vertical variations. The moho depth achieved in this paper (32-36 km) is consistent with those from previous studies, without a root. Two faults mark the gradient locations in the velocity and the changes in the interfaces that separate this high-velocity anomaly from low-velocity bodies. The three velocity bodies correlate well with the regional geological structures (Qianliyan Uplift, Northern Depression, Central Uplift) that are projected onto our model.

Beneath the Northern Depression, the Permian and Triassic strata such as the Qinglong Formation are denuded on a large scale combining velocity model and multi-channel seismic data. Jurassic and Cretaceous strata rest unconformably on the marine residual strata in the Mesozoic and Paleozoic. However, the Triassic strata (Qinglong Formation) and Permian strata (Dalong and Longtan Formations) are preserved in the Central Uplift. In other words, the uplift and denudation in the orogeny generally appear stronger in the north than in the south.

Previous geological and geophysical studies have suggested that abundant normal faults with NE-SW trend played an important role in the tectonic evolution of the South Yellow Sea. More specifically, investigations reveal that the Jiashan-Xiangshui-Qianliyan fault is the boundary between the Qianliyan Uplift and Northern Depression in the sedimentary formations. We suggest that normal faults terminate at the upper crust after passing through the sedimentary layers. Marked velocity changes and interface fluctuations are observed in the middle and lower crust beneath the northern South Yellow Sea, where we infer a NW-dipping fault. In other words, the deep NW-dipping fault is the deep footprint of fault system in the South Yellow Sea and appears a normal fault from the velocity feature. This finding indicates that shallow faults in the northern South Yellow Sea could converge towards the deeper crust.

How to cite: zhao, W., wu, Z., shi, H., and xie, H.: Crustal structure from offshore wide-angle seismic data: Application to South Yellow Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3304, https://doi.org/10.5194/egusphere-egu2020-3304, 2020.

Besides the carrier bed, faults and unconformities are important migration pathways for the 3-D petroleum migration and accumulation simulation. The fault is often ignored or used only as simulated grid boundaries in the traditional 3-D geological modeling, so that the transport function of faults is neglected or weakened.

In view of the fact that the traditional geological modeling method cannot establish the interrelation of carrier-system (the carrier bed, fault, unconformity, etc.), we propose a hybrid-dimensional mesh modeling technology consisting of body (stratum), surfaces (faults and unconformities), lines and points. The stratum mesh cut by a fault consists of stratum body A, stratum body B and fault surface C. There are two methods: (1) The fault is neglected in the modeling of the geological body, in other words, the mesh form and volume remain unchanged; and (2) The fault is considered in the modeling of the geological body, and the geological body on the two sides of the fault are divided into two parts for modeling. We propose the third processing method. The fault is considered in the modeling of the geological body, and the geological bodies on the two sides of the fault are divided into two parts for modeling, forming stratum meshes. In addition, the fault surface is taken as the third mesh, i.e. surface mesh. At this point, the mesh system is not the original single stratum mesh (3D body mesh) any more, and it also contains the surface mesh (2D surface mesh), therefore it is called a hybrid-dimensional mesh system (hybrid mesh system).

Based on new hybrid-dimensional mesh of the carrier-system, a special 3-D invasion percolation model (3-DIP) is proposed. The fault transport ability can also be determined by shale gouge ratio (SGR) in the 3-DIP model.

The new method is applied to the Luliang uplift in Junggar Basin, China, with an area of 3502 km². The strata are composed of Permian - Cretaceous, which are divided into 15 simulated layers. Key simulation parameters of the study area include 2884 plane simulation meshes, 59 faults and 1 unconformity. The total number of formed meshes is 54406, including 45972 body meshes, 7884 surface meshes, 549 line meshes and 1 point mesh.

The migration pathway of oil is traced by 3-DIP, and the oil accumulation and wax content of crude oil are simulated. By comparing the simulated wax content with the measured wax content, the results are consistent with each other. It is shown that the model is reliable and the results are credible.

Key words: geological modeling, migration pathway, hybrid mesh, invasion percolation model, petroleum migration and accumulation simulation, Junggar Basin.

How to cite: Guo, Q., Wu, N., Liu, J., and Chen, N.: A 3-D geological modeling method and its application to petroleum migration and accumulation simulation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3896, https://doi.org/10.5194/egusphere-egu2020-3896, 2020.

Abstract:The Dawangzhuang area as one of the favorable exploration areas for buried hills in the Jiyang Depression, experienced the complicated accumulation process. Based on the fluid properties and regional tectonic background, it can be briefly discussed oil migration and accumulation process in the Dawangzhuang paleozoic buried hill fields using the petrographic observation, microthermometry and abundance of hydrocarbon inclusions. The result shows that the Dawangzhuang area mainly experienced two stages of crude oil charging from the late Dongying Formation (27-25Ma) and the end of Guantao Formation (5Ma) to now. Moreover, the last charging is the most important in the Dawangzhuang buried hill field. The first charging occurred in the Ordovician in the end of Dongying formation, but was quickly destroyed and adjusted by fault activities. In the end of Guantao formation, crude oil migrated on a large scale and accumulated lately in the Ordovician and Carboniferous-Permian systems respectively when they entered buried hills through Da 1 fault from source center, forming the current oil distribution pattern.

Keywords：Chezhen sag; Paleozoic; buried hill field; fluid inclusion; accumulation process

How to cite: Zhang, Z.: Hydrocarbon Accumulation Process in the Dawangzhuang Paleozoic Buried Hill Fields in the Jiyang Depression, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5078, https://doi.org/10.5194/egusphere-egu2020-5078, 2020.

In the study of Gulf of Mexico and its adjacent areas, the faults are kinds of important structures in the plate tectonics, oceanic-continental distribution and sedimentary basin structure. Based on the normalized vertical derivative of total horizontal derivative (NVDR-THDR) of Bouguer gravity anomaly and the minimum curvature field separation method, the distribution characteristics of the faults and the relating geological effects are studied. Because of the interaction between the plates, at the plate margin, the maximum values in the map of NVDR-THDR of Bouguer gravity anomaly are characterized by stable and continuous strikes. The maximum values in the map of NVDR-THDR of Bouguer gravity anomaly of intraplate region are macroscopically consistent and locally discontinuous. The faults in NWW and EW-NEE directions are mostly related to plate movement. In NE-NEE directions, arc faults are related to oceanic crust expansion. The faults in NE and NW are related to late Jurassic rift activities, or simply showing the boundaries of Yucatan and Chortis old landmass. The faults in nearly SN direction are less than that of we have talked above. In the Gulf of Mexico, there are four kinds of faults: the transition faults and mid-ocean ridge faults in the middle of central deep-sea area, the ocean-crust boundary faults in the north and south side of the central deep-sea area, the faults of thinning continental crust in the north and south of the Gulf of Mexico and the strike slip faults in the west of the Gulf of Mexico. Our research can contribute to regional geological researches and natural resources evaluations.

How to cite: Ma, J., Wang, W., Du, X., Cai, W., Ji, X., Yang, M., Luo, X., and Wang, D.: Study on distribution features of faults based on gravity data in the Gulf of Mexico and its adjacent areas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6611, https://doi.org/10.5194/egusphere-egu2020-6611, 2020.

Based on outcrop investigations, 3D seismic interpretations, drilling data and results from physical simulation experiment, the structural deformation characteristics of the Puguang area in the Sichuan Basin were studied. Our results show that there are three main detachment layers at different depths in the Puguang area. The lower detachment layer, which is composed of middle Cambrian gypsum-salt rock, controlled the deep structural deformation system (∈_2-3-S). The mudstone at the bottom of the Silurian acts as the central detachment layer, separated while influencing both the bottom and the central structural deformation system (S-T₁j). The Triassic Jialingjiang Formation gypsum-salt rock forms the upper detachment layer, which mainly controls the shallow structural deformation system (T₂l-K). Different structural deformation systems have different degrees of structural deformation and relatively independent deformation styles. The deformation degree of the deep structural deformation system is relatively high, faults of this system cut through the Cambrian to the Silurian strata, forming a series of low amplitude thrust anticline; the central structural deformation system, which is sandwiched by two gypsum-salt rock layers, mainly brittle ductile shear zone, is characterized by high dipping thrust faulted anticlines with relatively larger amplitudes; the deformation degree of the shallow structural deformation system is relatively low, with narrow detachment anticlines and wide synclines developed, while a series of small pop-up structures superimposing on the overlying Jurassic sequences, and asymmetric highs and steep anticlines formed in local areas. Balanced cross section and physical simulation experiments show that the Puguang area suffered from superimposed compressional deformations originated from two directions, northeast and southeast.They represent the compressive stresses transmitted from the Dabashan orogenic belt in the northern margin of the Sichuan Basin and the compressive stresses transmitted from the Xuefengshan orogenic belt in the eastern margin, respectively.In addition, the rheological properties and the thickness of the detachment layer have important influence on the structural style.

How to cite: huang, H., he, D., and zhang, W.: Constraints of multiple detachment layers on structural deformation patterns in the basin: insight from 3D geological structure model in the Puguang area, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8698, https://doi.org/10.5194/egusphere-egu2020-8698, 2020.

Research of Eastern Siberia began after the discovery of hydrocarbons. At the same time, ton the territory of a platform there is the largest trap province in the world - the Siberian province with ubiquitous magmatic bodies of the main composition, which complicate the upper part of the section assessment.

To construct geological sections, borehole data are most often used to determine the power and structure of magmatic complexes. However, drilling cannot provide sufficient details.

Magmatic formations are distinguished by large variations in magnetic properties (from 100 to 1000 * 10^-5 SI) and density (from 2.65 to 2.95 g/cm³). They create local gravitational anomalies up to 5-10 mGal, and magnetic ones - from dozens to the first hundreds of nanotests.

With the usage of geological sections as the starting model framework, 2D modeling and selection of the physical properties and geometry of the trap bodies was done. The magnetic field along the profile is set according to the digital model EMAG2 (2009). The gravitational effect was calculated based on the final models, which were assigned density properties.

Modeling of typical sections makes the shape of anomalous sources and supply channels positions more precise. This approach allows to restore the upper part of the section, saturated with trap intrusions.

How to cite: Gvozdik, S., Arutyunyan, D., and Lygin, I.: Assessment of gravity and magnetic effects of trap formations in Eastern Siberia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16792, https://doi.org/10.5194/egusphere-egu2020-16792, 2020.

Volcanic rocks have been known to be reservoirs for more than a century but due to their often complex geological settings, they are commonly avoided.

The North Atlantic Igneous Province (NAIP) is one of the largest igneous provinces in the world. Large ranges of rock types comprise the NAIP, including tholeiitic and alkali basalts, nepheline- and quartz-syenites, nephelinites and carbonatites. The province is Paleocene in age and covers large parts of the North Atlantic region today. Parts of the NAIP outcrop onshore the Faroe Islands, on the western and the eastern side of Greenland, on Iceland and on the British islands.

In the Faroe Islands region volcanic settings serve as shallow geothermal energy systems, shallow groundwater aquifers and hydrocarbon reservoirs. These settings have been studied by core data and wire-line logs and examples will be presented. The aim of this study is to examine the key important parameters governing the reservoir properties and occurrences.

In all settings microfractures are important as porosity and permeability enhancers and are often linked to lava emplacement pathways and specific lava types such as subaqueous hyaloclastites and pillow lavas.

Studies on water movement from onshore the Faroe Islands on the islands of Streymoy have shown that the water in the volcanic settings in the area is being transported through large fractures and weathered flow tops and bases. This has also been seen in e.g. similar large igneous volcanic provinces such as the Columbia River Basalt Group, USA, and the Deccan Traps, India. Six influx zones were identified in the three approximately 200 meter deep geothermal holes on Streymoy, the Faroe Islands. Three with visible macrofractures striking north-south dipping east, two through weathered units, while the sixth influx zone did not show any visible fractures or weathered zones (Eidesgaard et al., 2019).

Reference: Eidesgaard, Ó.R., Schovsbo, N.H., Boldreel, L.O. and Ólavsdóttir, J. 2019 Shalllow geothermal energy system in fractured basalt: a case study from Kollafjørður, Faroe Islands, NE-Atlantic Ocean. Geothermic vol. 82, p. 296-314.

How to cite: Eidesgaard, Ó. R., Boldreel, L. O., Schovsbo, N. H., and Ólavsdóttir, J.: Volcanic sequences as reservoir rocks. Importance of natural fracture systems - a case study from the Faroe Islands area - North Atlantic Igneous Province (NAIP), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18484, https://doi.org/10.5194/egusphere-egu2020-18484, 2020.

The paper presents the results of a novel integrated solution of formation water content and salinity determination of the low permeability reservoir rock of Bazhenov formation (West Siberia, Russia) for petrophysical characterization. The workflow is based on three techniques: evaporation method (EM) with isotopic composition analysis, analysis of water extracts, and cation exchange capacity (CEC) study. The EM offers a fast, efficient, and accurate measurement of the residual water content with breakdown to free and loosely clay-bound types. The isotopic composition reveals the origin and genesis of pore water. The chemical analysis of water extracts delivers a lower bound salinity in terms of NaCl. CEC describes rock-fluid interactions. The two methods of cation exchange capacity (CEC) measurement were applied – alcoholic NH₄Cl ((NH₄Cl)Alc) and hexammnninecobalt(III) chloride (CoHex) method. Both showed similar results. CEC varies from 2.87 to 5.82 meq/kg by ((NH₄Cl)Alc method and from 2.87 to 6.38 cmol/kg by CoHex method and depends on the clay content. Ca, Na, Mg, K form exchange complex of all studied core samples. According to interrelation (rNa+rK)>rCa the exchange complex type is marine and was inherited from the composition of the paleobasin seawater.

The target rock samples contained the residual formation water 0.11–4.27 wt.%, including free 0.04–3.92 wt.% and loosely clay-bound water 0.09–0.96 wt.%. The loosely bound water content correlates well to the clay mineral fraction. The amount of chemically bound water fell in a range of 0–6.40 wt.% and exceeds that of free and loosely bound water.

We found that water extract composition depends on the core mineral content, except chlorine and bromine, which originates from the pore water. Using the thermodynamic modelling in PHREEQC program, next ratio of cations in pore water was found - Na (up to 91%), Mg (up to 5.6%), Ca (up to 2.6 %) and K (up to 0.8%). According to the calculation using the water extracts results, the pore water salinity as NaCl changes from 1.23 to 21.96 g/L. The corresponding isotopic composition indicated the deep formation genesis and generally correlated to that of the deep stratal waters of the West Siberia. Isotopic composition proved the formation origin of extracted pore water samples.

The study made a qualitative step up towards the quantitative characterization of formation water in shale reservoir rocks with the initial water content of less than 1 wt.%.

This work was supported by the Russian Science Foundation (grant No. 17-77-20120).

How to cite: Kazak, E., Kazak, A., and Bilek, F.: Formation Water Characterization of the Shale Reservoir Rocks Using Integrated Workflow, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20251, https://doi.org/10.5194/egusphere-egu2020-20251, 2020.