Interpretation Of 3D Seismic Data Research Articles

Structural inheritance through 3D reservoir modeling and ant-tracking attribute implications for structural configuration of Upper Cretaceous Pab Sandstone, Kirthar Fold Belt, Pakistan

This research presents a comprehensive investigation to enhance understanding of subsurface structural complexities within the Upper Cretaceous Pab Sandstone reservoir level in a gas-producing field within the Kirthar Fold Belt of the Southern Indus Basin, Pakistan. The seismic interpretation for accurate structural delineation and characterization of intricate fault systems is often challenging in Fold and Thrust Belt settings. The 3D structural maps of Upper Cretaceous Pab Sandstone at the reservoir level and the application of the ant-tracking attribute for fault extraction improve the structural understanding of the gas-producing field in the Kirthar Fold Belt in the Southern Indus Basin, Pakistan. Attribute-assisted 3D seismic interpretation has revealed several subsurface structure elements, including a large thrusted anticline extended towards the north-south, the pattern of north-south oblique ramp thrusts on the southeastern flank, and a combination of easterly vergent thrusts with a counter-back thrust creating a local pop-up structure in the area. A 3D structural model at the reservoir level was generated using horizon and fault framework volume-based modeling approach, serving as a structural model for Pab sandstone. The structural smoothing, variance and ant-tracking attribute were applied iteratively to get the best results and correlated with manual interpretation. 3D seismic interpretation and application of ant-tracking for fault extraction identifies discrete structural styles and revealed that all thrusting occurred due to compressional tectonics of the Plio-Pleistocene period. The apparent different styles result from the reactivation of earlier extensional fault systems and probably during phased periods of compression. The resulting 3D reservoir model can be used as an input to populate petrophysical properties and results can be extended for future field development plans. Integration of well and 3D seismic data interpretation and the application of automatic fault extraction techniques are highly recommended in structurally complex areas and have an equal implication for worldwide basins with similar conditions for reliable structural interpretation in Fold and Thrust Belts with structural complexity.

Sedimentary characteristics, lithofacies, and paleogeography of the Middle–Lower Cambrian in the Tarim Basin, NW China

The Cambrian pre-salt dolomite sequence in the Tarim Basin is a target zone of great strategic significance for hydrocarbon exploration in the basin. Using the results of the interpretation of 3D seismic data from Lunnan and 2D seismic data covering the whole basin, and based on a synthesis of outcrop data, drilling data, well logs, core data, and thin-section data, and the findings from previous studies, this paper studies the characteristics of the facies of the Middle–Lower Cambrian in the platform area in the Tarim Basin, the formation and evolution of platform margins, and the sedimentary characteristics, lithofacies, and paleogeographic characteristics of the Middle–Lower Cambrian series. Based on the types of lithofacies and the seismic facies analysis, the sedimentary facies of the Middle–Lower Cambrian strata can be classified into the five types. From bottom to top, the Middle–Lower Cambrian have experienced several development stages, including the deposition of continental shelf sediments of the Yuertusi Formation, gently sloping non-rimmed platform margin sediments of the Xiaoerbulake Formation, weakly rimmed platform margin sediments of the Wusongger and Shayilike formations, and strongly rimmed platform margin sediments of the Awatage Formation. In each stage, the platform margin shifted further east relative to its location in the previous stage. Based on these results and previous studies, the lithofacies and paleogeography maps of the Middle–Lower Cambrian in the Tarim Basin are modified, and the implications for hydrocarbon exploration in this area are discussed.

Introduction of new attributes: Scaling Exponent and its double derivatives for better land seismic volume interpretation

For the first time, we propose to study the behavior of the correlation (scaling) exponent and its second order with prestack seismic data. For our research, we have chosen Dibrugarh prestack 3D seismic data from the Assam-Arakan Basin, India. We have improved the calculation process so that it is possible to read amplitude values directly from SEG-Y file and collect data from the entire chosen in- or cross-line. As a result, we can now study significant amount of data within less amount of time. After completing the analysis, we could identify the main stratigraphic layers, basement, and the zones of weak and prominent amplitudes from the survey. Strong amplitude zones correlate with low scaling exponent values. Weak amplitudes reflect as high scaling exponent zones. New attributes introduced give a scope to automatize the interpretation of 3D seismic data without learning.

Structural Restorations of the Complete Conjugate US‐Mexico Eastern Gulf of Mexico Margin

AbstractWe present the first sequential structural restoration with flexural backstripping of the Gulf of Mexico US‐Mexico conjugate margin salt basin. We construct four large‐scale (100s of km) balanced, sequential structural restorations to investigate spatio‐temporal patterns of subsidence, geometry of the original salt basin, feedbacks between post‐salt structural and stratigraphic evolution, paleo‐bathymetry, and crustal configurations. The restorations are based on interpretations of 2D and 3D seismic data, and include sequential sedimentary decompaction, flexural isostatic backstripping, and thermal isostatic corrections. The spatially variable crustal thinning factor is directly measured from seismic data, and lithologic parameters are determined by well penetrations. We present a model for the original salt basin and discuss evidence for and implications of a deep water salt basin setting for the GoM. Our analysis suggests a salt basin that contained ∼1–2 km thick salt in a basin 175–390 km across with ∼1 km of bathymetry after salt deposition. The base of salt is mostly smooth with <1 km of local relief in the form of normal faults that disrupt a pre‐salt sedimentary section. We find that supra‐salt extension and shortening are not balanced, with measurable extension exceeding shortening by 18–30 km on each cross‐section. Our subsidence analysis reveals anomalous subsidence totaling 1–2 km during Late Jurassic and Early Cretaceous times that may reflect dynamic topography or depth‐dependent thinning. We offer an interpretation of crustal breakup invoking pre‐salt clastic sedimentation, salt deposition in a deep water syn‐thinning basin, and post‐salt lower‐crustal exhumation.

Unravelling Cenozoic carbonate platform fluid expulsion: Deciphering pockmark morphologies and genesis in the Tanintharyi shelf of the Andaman Sea as promising hydrocarbon reservoirs

Pockmarks, intriguing seafloor geological and geomorphological features, are commonly observed in marginal basins with hydrocarbon potential. As a Cenozoic marginal sea, the Andaman Sea is known for its significant petroleum reserves, and exploring its back-arc continental margin has revealed favourable conditions for petroleum occurrences. This study focuses on the Tanintharyi passive continental margin in the Andaman Sea, employing extensive stratigraphic and morphological analyses based on 2D and 3D seismic data interpretation techniques. Specifically, sub-seafloor characteristics of the Tanintharyi shelf region were investigated, focusing on comprehensively understanding pockmark morphologies, including their generation, evolution, migration, preservation, and the complete process leading to seabed leakage. This study revealed the potential of the Oligocene/Early Miocene carbonate platform in the Tanintharyi shelf region as a significant hydrocarbon reservoir for the upwelling buoyant fluids from the deep East Andaman Basin. Besides reservoir function, this carbonate platform serves as a passageway for the migration of fluids from the deep-sea area to the shallow-sea area, thereby playing a pivotal role in supporting fluid expulsion mechanisms in shaping a pockmark train adjacent to truncated sedimentary formations surrounding a geomorphological high on the contemporary seafloor. Additionally, the study examines the influence of changes in sedimentary facies and the tectonic setting of the Andaman Sea on pockmark evolutions, with a specific emphasis on the role of the uppermost shallow marine shale beds in developing sub-seafloor overpressure systems due to their impermeable seal rock properties. The article presents substantial evidence for the initiation of pockmark fields during the Middle Miocene period, followed by their transformation into pockmark trains on the present-day seafloor, attributed to the triggering effect of sub-seafloor overpressure systems due to changes in sedimentary dynamics in the Andaman Sea.

Recognition of small faults in coal fields based on multi-scale seismic curvature attributes fusion

In order to meet the needs of intelligent development of coal mines in China for transparency of geological conditions, identifying small faults with a drop of about 3 m has become one of the important geological tasks in structural interpretation. However, the accuracy of conventional 3D seismic exploration data interpretation methods for detecting small faults is still low. On the basis of introducing the basic principles of S-transform time-frequency analysis, principal component analysis, and RGB fusion, this paper proposes a method for identifying small faults in coal fields using multi-scale seismic curvature attribute fusion. The method uses S-transform to perform time frequency analysis to obtain seismic data volumes with multiple frequencies and seismic data volumes at different frequencies correspond to different scales of underground geological information portrayal. Perform spectral analysis on seismic data, determine parameters such as the dominant frequency and frequency bandwidth of seismic signals, and extract the maximum positive curvature attributes of seismic data volumes at different frequencies. Then the principal component analysis (PCA) method is used to analyze the seismic attributes of different frequency seismic data, the GRB fusion method is used to fuse the first three principal components. The application results of actual seismic data show that the results of multi-scale seismic curvature attribute fusion have obvious advantages in identifying small faults, and can improve the accuracy and interpretation accuracy of small faults in seismic data.

Structural attributes, evolution and petroleum geological significances of the Tongnan negative structure in the central Sichuan Basin, SW China

The Tongnan secondary negative structure in central Sichuan Basin has controls and influences on the structural framework and petroleum geological conditions in the Gaoshiti-Moxi area. To clarify the controls and influences, the deformation characteristics, structural attributes and evolution process of the Tongnan negative structure were investigated through a series of qualitative and quantitative methods such as balanced profile restoration, area-depth-strain (ADS) analysis, and structural geometric forward numerical simulation, after comprehensive structural interpretation of high-precision 3D seismic data. The results are obtained in three aspects. First, above and below the P/AnP (Permian/pre-Permian) unconformity, the Tongnan negative structure demonstrates vertical differential structural deformation. It experiences two stages of structural stacking and reworking: extensional depression (from the Sinian Dengying Formation to the Permian), and compressional syncline deformation (after the Jurassic). The multi-phase trishear deformation of the preexisting deep normal faults dominated the extensional depression. The primary depression episodes occurred in the periods from the end of Late Proterozoic to the deposition of the 1st–2nd members of the Dengying Formation, and from the deposition of Lower Cambrian Longwangmiao Formation–Middle–Upper Cambrian until the Ordovician. Second, the multi-stage evolution process of the Tongnan negative structure controlled the oil and gas migration and adjustment and present-day differential gas and water distribution between the Tongnan negative structure and the Gaoshiti and Moxi-Longnüsi structural highs. Third, the Ordovician, which is limitedly distributed in the Tongnan negative structure and is truncated by the P/AnP unconformity on the top, has basic geological conditions for the formation of weathering karst carbonate reservoirs. It is a new petroleum target deserving attention.

Petroleum geology of marl in Triassic Leikoupo Formation and discovery significance of Well Chongtan1 in central Sichuan Basin, SW China

In 2022, the risk exploration well Chongtan1 (CT1) in the Sichuan Basin revealed commercial oil and gas flow during test in a new zone – the marl of the second submember of the third member of Leikoupo Formation (Lei-32) of Middle Triassic, recording a significant discovery. However, the hydrocarbon accumulation in marl remains unclear, which restricts the selection and deployment of exploration area. Focusing on Well CT1, the hydrocarbon accumulation characteristics of Lei-32 marl are analyzed to clarify the potential zones for exploration. The following findings are obtained. First, according to the geochemical analysis of petroleum and source rocks, oil and gas in the Lei-32 marl of Well CT1 are originated from the same marl. The marl acts as both source rock and reservoir rock. Second, the Lei-32 marl in central Sichuan Basin is of lagoonal facies, with a thickness of 40–130 m, an area of about 40 000 km2, a hydrocarbon generation intensity of (4–12)×108 m3/km2, and an estimated quantity of generated hydrocarbons of 25×1012 m3. Third, the lagoonal marl reservoirs are widely distributed in central Sichuan Basin. Typically, in Xichong–Yilong, Ziyang–Jianyang and Moxi South, the reservoirs are 20–60 m thick and cover an area of 7500 km2. Fourth, hydrocarbons in the lagoonal marl are generated and stored in the Lei-32 marl, which means that marl serves as both source rock and reservoir rock. They represent a new type of unconventional resource, which is worthy of exploring. Fifth, based on the interpretation of 2D and 3D seismic data from central Sichuan Basin, Xichong and Suining are defined as favorable prospects with estimated resources of (2000–3000)×108 m3.

Detailed study of geology of the lower parts of Pliocene in Kurovdagh area by use of 3D seismic survey

The article is devoted to the study of the geological structure of the lower parts of the Productive Series of the Lower Pliocene of the Kurovdagh field.
 It consists of an introduction, problem statement, research questions, research methodology, results, conclusion and list of references. The introduction provides basic information about the field under study, its geographical location, the history of geological and geophysical studies, the lithology of the section, the structure of the Kyurovdag fold and the oil and gas potential of the field.
 Oil and gas presence inthefield is related to the Absheron stage of Pleistocene, Akchagyl stage and Productive Series (horizons PS01—PS23) of Neogene. Despite the long-term production from the field, the lower parts of the Productive Series and underlying sediments have not been recovered and sufficiently studied by deep drilling due to the complicated surface and deepseismo-geological environment. It has been recommended to carry out a 3D seismic survey due to a high level of lateral one-fold reflections on seismic records.
 The major goals of the 3D seismic survey were studyingthe Kurovdagh field's geologic setting, obtaining characteristics previously unknown to geoscientists, and providing detailed research on velocity section to derive prognostic time-depth dependence.
 It was noted that thePetroalliance Services Company Limited geophysical company has performed a field seismic survey on request «The Caspian Energy Group» company. Processing of the acquired data used the FOCUS 5.4 software package manufactured by Paradigm Geophysical.
 For repeated interpretation of 3D seismic survey data, the 3D CDP data acquired from the field were used. The kinematic analysis by use of the 3 D cubes revealed the difference by the time shift, frequency spectrum, and amplitude range. The 3 D cubes were brought to a single formby time, phase, and amplitude. The further kinematic interpretation displayed the good quality of the data acquired from Kurovdagh area. The study applied PANGEYA® software for a multi-attribute geological and geophysical data analysis and the standard interpretation.
 For volumetric modeling of the productive layers of the Kurovdagh oil field, we used the PETREL.10.2 software package. The study targets included complex, lithologically, and tectonically sealed deposits of Productive Series PS01—PS09 and Akchagyl stage (AKCH). Productive layers are attributed to Neogene's Pliocene stage within the Caspian basin's limits.
 It is represented by a thick series of continental, coastal, and marine sediments (sand, clay, coarsely fragmented depositions) of 1600 m thickness and is unconformity laying over the Pontian stage and covered by the Akchagyl layers in a transgressive form. The Akchagyl stage is one of the stages of the Upper Pliocene which is made of clay, limestone, marl, sandstone, sand, and conglomerates.
 It became clear that the Kurovdagh field is characterized by a block type structure across the geological section. Block sizes are almost unchanged, evidencing conformance of structural stages and heritance of tectonic movements. Mud volcano and diapiric folding and their sizes are the major distinguishing features of the area.

Fault Identification of U-Net Based on Enhanced Feature Fusion and Attention Mechanism

Accurate fault identification is essential for geological interpretation and reservoir exploitation. However, the unclear and noisy composition of seismic data makes it difficult to identify the complete fault structure using conventional methods. Thus, we have developed an attentional U-shaped network (EAResU-net) based on enhanced feature fusion for automated end-to-end fault interpretation of 3D seismic data. EAResU-net uses an enhanced feature fusion mechanism to reduce the semantic gap between the encoder and decoder and improve the representation of fault features in combination with residual structures. In addition, EAResU-net introduces an attention mechanism, which effectively suppresses seismic data noise and improves model accuracy. The experimental results on synthetic and field data demonstrate that, compared with traditional deep learning methods for fault detection, our EAResU-net can achieve more accurate and continuous fault recognition results.

Determination of effective seismic wave velocities using time gradients obtained from response and CDP reflection hodographs

Seismic wave velocities, including effective velocities, play a critical role in the kinematic processing and interpretation of 2D and 3D seismic data. Along with other parameters of elastic waves, the geological efficiency of seismic exploration also depends on the level of knowledge of the velocity model of the medium, on the accuracy of information about velocities. The article briefly lists the main methods for determining the effective velocities according to the seismic wave field, developed and applied in the practice of seismic research. The methods used to determine the effective velocities of reflected waves can be divided into two groups: methods for determining the effective velocities based on automatic or visual tracking of the in-phase axes (i.e. hodographs) of reflected waves on seismic records, then their approximation by hyperbolas constitute the first group, and the second the group consists of methods based on the application of the analysis of the seismic wave field in controlled directions on the seismograms of a common depth point (CDP). Each proposed method for determining effective speeds has advantages and disadvantages. The article focuses on the industrial method, widely used at present, based on the analysis of the wave field in controlled directions, which do not provide sufficient information to solve the main problems of kinematic interpretation. The main disadvantages of the existing methods are indicated. The article describes a new method for determining the effective velocity, which is fundamentally different from the methods that are still used in the practice of seismic exploration. The fact is that in this method, seismic survey data of single and multiple profiling are not used separately, as it was in the methods used in seismic survey practice so far, but together. Formulas have been derived for determining the effective velocity based on the time gradients of the travel time curves of the CSP and CDP of reflected waves, which makes it possible to determine the speeds even from incomplete travel time curves. A technique for determining the effective speed has been developed and a sequence of procedures has been determined for solving the problem. The results of research are given on a specific example by solving the direct and inverse problems for the Sazhdag area between the Kura and Gabyrra rivers. The influence of errors in the values of the parameters included in the formula for calculating the effective speed on the final results is studied. At the end of the article, the main advantages of the proposed method are indicated.

Ключевые моменты интерпретации сейсмических данных внутри зон аномального разреза баженовской свиты на примерах Поточной, Спорышевской, Выинтойской и Ватинской зон.

The Bazhenovo horizon of Western Siberia has traditionally been one of the objects most studied by geologists and geophysicists in recent decades in Russia. However, along with the more familiar "classical" structure, there are areas where gray-colored inclusions of sandy-silty-clayey deposits are present between the carbonate-clayey-siliceous rocks of the Bazhenovo Black Shales Formation. Such sections geologists call "anomalous". The paper describes the application of the spectral decomposition method for detailing the structure of anomalous sections zones of the Bazhenovo Formation or in another words Giant Sand injection Complex (GSIC) of the Ob river region. Combining the results of dynamic interpretation of 3D seismic data with well logging data for a vast fund of exploration and production wells made it possible to build a seismogeological model of the of the Ob river region GSIC in the Potochnaya area. The clue approach was tested on the Sporyshevskaya and Vyyntoyskaya, Vatinskaya areas, which were much less explored by drilling. The listed zones were formed at different geological times, belong to different regional clinoforms, but have common patterns of structure, which is reflected in the seismogeological model of the Ob river region GSIC. The model describes the distal and proximal parts of the intrusion, which were formed in the Neocomian time, when gravity-driven flows of sandy-silty material injected and spread inside high-bituminous Jurasic Bazhenovo formation Black Shales. Within the proximal part gravity-driven flows were accompanied by slumps of more clayey rocks. The dimensions of these flows and slumps, their location over the area are shown, their mapping in the 3D seismic data is discussed. In this work, we managed to get closer to solving the problem of predicting the development of sandy downward intrusions. There are oil reservoirs in the Ob river region GSIC, but they are insufficiently studied.

3D Evolution of Detachment Fault Systems in Necking Domains: Insights From the Klakk Fault Complex and the Frøya High, Mid‐Norwegian Rifted Margin

AbstractDetachment fault systems typically record displacements in the order of 10s of kilometers. The principles that control the growth of smaller magnitude normal faults are not fully applicable to the evolution of detachment fault systems. We use interpretation of 2D and 3D seismic reflection data from the mid‐Norwegian rifted margin to investigate how the structural evolution of a detachment fault interacted with the effects of isostatic footwall rollback to produce complex 3D geometries and control the configuration of associated supradetachment basins. We further investigate the effects of lateral interaction and linkage of extensional detachment faults on the necking domain configuration. In our study area, the domain‐bounding Klakk Fault Complex demonstrates how successive incision may induce a complex structural relief in response to faulting and fault plane folding. We interpret the previously proposed metamorphic core complex within its footwall as an extension‐parallel turtleback‐structure. The now eroded turtleback is flanked by a major supradetachment basin, connecting two main basin segments. We attribute footwall‐ and turtleback exhumation to Middle Jurassic‐Early Cretaceous rifting. The study area further demonstrates how detachment fault geometries can change during rifting and lead to the formation of younger, successively incising fault splays. Lateral linkage between the original detachment fault plane and these fault splays enables displacement along a detachment fault system consisting of fault segments generated at different stages in time. Implicitly, detachment faults are complex 3D systems that change configuration during their evolution, perpetually controlling associated basin formation, footwall configuration, subsidence and uplift patterns.

Evaluation of Hydrocarbon Reservoir in the “SIMA” Field of Niger Delta Nigeria from Interpretation of 3D Seismic and Petrophysical Log Data

3D seismic and petrophysical log data interpretation of reservoir sands in “SIMA” Field, onshore Niger Delta has been undertaken in this study to ascertain the reservoir characteristics in terms of favourable structural and petrophysical parameters suitable for hydrocarbon accumulation and entrapment in the field. Horizon and fault interpretation were carried out for subsurface structural delineation. In all, seven faults (five normal and two listric faults) were mapped in the seismic section. These faults were major structure building faults corresponding to the growth and antithetic faults in the area within the well control. The antithetic fault trending northwest-southeast and the normal fault trending northeast-southwest on the structural high in the section act as good trapping mechanisms for hydrocarbon accumulations in the reservoir. From the manual and auto-tracking methods applied, several horizons were identified and mapped. The section is characterized by high amplitude with moderate-to-good continuity reflections appearing parallel to sub-parallel, mostly disturbed by some truncations which are more fault related than lithologic heterogeneity. The southwestern part is, however, characterized by low-to-high or variable amplitude reflections with poor-to-low continuity. Normal faults linked to roll-over anticlines were identified. Some fault truncations were observed due to lithologic heterogeneity. The combination of these faults acts as good traps for hydrocarbon accumulations in the reservoir. Reservoir favourable petrophysical qualities, having average NTG, porosity, permeability and water saturation of 5 m, 0.20423, 1128.219 kD and 0.458 respectively.

Anisotropic 4D seismic response inferred from ultrasonic laboratory measurements: A direct comparison with the isotropic response

AbstractPore‐pressure depletion causes changes in the triaxial stress state. Pore‐pressure depletion in a flat reservoir, for example, can be reasonably approximated as uniaxial compaction, in which the horizontal effective stress change is smaller than the vertical effective stress. Furthermore, the stress sensitivity of velocities can be angle‐dependent. Therefore, time‐lapse changes in reservoir elastic anisotropy are expected as a consequence of production, which can complicate the interpretation of the 4D seismic response. The anisotropic 4D seismic response caused by pore‐pressure depletion was investigated using existing core velocity measurements. To make a direct comparison between the anisotropic 4D seismic response and the isotropic response based only on vertical velocities, pseudoisotropic elastic properties were utilized, and the two responses were compared in terms of a dynamic rock physics template. A comparison of the dynamic rock physics templates indicates that time‐lapse changes in reservoir elastic anisotropy have a noticeable impact on the interpretation of 4D seismic data. Changes in anisotropy as a result of pore‐pressure depletion cause a time‐lapse amplitude variation with offset response as if there is a reduction in VP/VS (i.e., pseudoisotropic VP/VS decreases), although the vertical VP/VS increases. The impact of time‐lapse changes in anisotropy on the amplitude variation with offset gradient was also investigated, and the time‐lapse anisotropy was found to enhance changes in the amplitude variation with offset gradient for a given case.

Interpretation of 2D Seismic Data of Shurau and Sheikh Alas Formations in Ismail Area, Northern Iraq

The 2D seismic reflection data were used to study the structure of Shurau and Sheikh Alas formations (Oligocene) in the Ismail area, northern Iraq. The horizons of Shurau and Sheikh Alas reflectors were identified based on seismic data and well logs through a synthetic seismogram construction. The Two-Way Time, velocity and depth maps of two coinciding formations were obtained. A Great coincidence was noticed between two identical maps of the two formations. The Main closure (syncline) trending NE-SE was detected at the southwestern part of the study area, the syncline is associated with many anticlines in the same trend. The northern part of Bai Hassan structure was appeared at the southeast part of the study area, while some northeastern part of Qara chauq structure was detected in the southwestern part of the study area. The structure features of the two formations mostly trending NW-SE with some local variations may be due to transversal faults.

Causes of a premature thermal breakthrough of a hydrothermal project in Germany

Sustainable heat extraction is of utmost importance for the economic life of geothermal production systems. Especially in hydrothermal sedimentary basins, a temperature decrease at the production well prompts a financial loss. A premature thermal breakthrough occurred in one of the geothermal projects in the Greater Munich Area, a well-known region for deep, low enthalpy geothermal development in the Upper Jurassic carbonate reservoir (syn. Malm) beneath the North Alpine Foreland Basin. Accordingly, questions are raised regarding the geologic controls on the reservoir´s permeability, the occurring type of heat and mass transport mechanism, and the fitting reservoir model type. 3D seismic data interpretation delineates seismic scale structures potentially influencing the reservoir permeability. Geophysical borehole data characterize sub-seismic scale elements (fractures, karst, and lithofacies), where we correlate them with the inflow zones and the interpreted seismic scale structures. The integration of both scales delineates the reservoir heterogeneity controlled by a lateral change in the carbonate lithofacies overprinted by faults and fractures. A NNW-SSE oriented seismic scale structure matches the orientation of hydraulically active sub-seismic scale fractures, where they are aligned with the maximum horizontal stress orientation. This structure induces additional anisotropic permeability, providing a preferential hydraulic pathway between the wells of the project. This study recommends considering fractured reservoir models to simulate the mass and heat flow in the highly heterogeneous Malm carbonates instead of composite reservoir models of equivalent hydraulic properties. Finally, we present a hydrogeological model describing the reservoir's structural and matrix permeability distribution to act as a basic concept for future thermal-hydraulic numerical modeling. The applied methods in this study are applicable in similar geothermal systems with adequate seismic and geophysical borehole data for future geothermal reservoir characterization, modeling, and management.

Interaction between volcanic and non-volcanic systems and its implication for prospectivity in the Faroe–Shetland Basin, NE Atlantic continental margin

Exploration in the Faroe–Shetland Basin on the Faroese Continental Shelf has revealed thick and complex volcanic successions and discovery of inter-volcanic oil-bearing siliciclastic sandstone fan deposits in the central parts of the basin. The possibility for such play types at the fringe of the North Atlantic Igneous Province requires a better understanding of the interaction between competing sedimentary and volcanic depositional transport systems. We have re-examined volcanic units in cuttings from exploration wells in the greater Judd Sub-basin area for evaluation of facies and geochemical affinity. This allows for chemostratigraphical correlation of wells to the absolute radiometrically age-constrained Faroe Islands Basalt Group. The collective well data were subsequently tied to a regional interpretation of 2D seismic data which facilitated a detailed interpretation of temporal development of the volcanic successions in the Judd Sub-basin area in terms of geometry, volcanic facies, depositional environment, and interdigitation with non-volcanic sedimentary units.The Judd Sub-basin was influenced by major volcanic phases during pre-breakup and syn-breakup. The influence was both direct, in the form of volcanic deposits, and indirect, in the form of obstructing established sedimentary transport systems and creating new provenance areas. The volcanic transport systems reached different areas of the Judd Sub-basin at different times during pre-breakup volcanism. The earliest incursion in the west was during late Mid Paleocene (T-sequence T31/T32). With at least three stratigraphically discrete incursions of volcanic material into the Judd Sub-basin, possibilities arise for sub- and inter-volcanic stratigraphic and structural traps for each incursion.

The tectonic transition from rifting to strike-slip in the Liaodong Bay Depression, offshore China

The Liaodong Bay Depression was shaped by the Bohai Bay rift basin (BBRB) and the Tan-Lu strike-slip fault system (TSFS) in the Cenozoic and has undergone a tectonic transition from rifting to strike-slip. Therefore, it is an ideal region to study the transition from rifting to strike-slip. Based on new 3D serial seismic data interpretation, we investigated the types and formation times of the main faults in the Liaodong Bay Depression and restored them within the palaeogeography of each evolution stage. Our results show that the Liaodong Bay Depression underwent a tectonic transition from rifting to strike-slip: (1) The mantle material upsurge caused by the Izanagi plate trapped in the mantle transition zone led to rifting of the Liaodong Bay Depression from the Palaeocene to the Eocene. (2) In the middle Eocene, the change in the subduction direction of the Pacific plate led to dextral strike-slip movement along the Tan-Lu fault zone. (3) The rifting and strike-slip in the Liaodong Bay depression are related, and the transition from rifting to strike-slip occurred from the middle Eocene to the early Oligocene. The strike-slip faults developed when rifting was weak in the Oligocene. The transition from rifting to strike-slip faulting formed oil-gas accumulation zones along the strike-slip fault zone and thus resulted in the good oil and gas exploration prospects of this area.

Distribution and gas exploration of the strike–slip faults in the central Sichuan Basin

The Sichuan Basin has abundant oil and gas resources and it has been generally acknowledged as a super petroliferous basin. In recent years, immense exploration and development potential of deep natural gas emerges in the Sichuan Basin. The identification of strike–slip faults and their reservoir controlling effects are of great significance to develop a new exploration domain of fault-controlled gas reservoirs. In order to clarify the distribution of strike–slip faults in the Sichuan Basin and their relationships with natural gas exploration, in view that the strike–slip faults in this basin are small and complex with poor seismic data and influenced more by the fold deformation of Triassic gypsum salt beds, this paper identifies strike–slip faults and analyzes their characteristics, distribution and genesis based on the interpretation of continuous 3D seismic data of the central Sichuan Basin. Then, the fault-controlled gas reservoir model of strike-slip fault is established by reviewing old wells and evaluating geological conditions of hydrocarbon accumulation. Finally, the exploration potential and exploration direction of fault-controlled gas reservoirs are discussed. And the following research results are obtained. First, intraplate weak strike–slip faults can be identified by combining the seismic profile marker of strike–slip fault with the plane marker. Second, eight large strike–slip fault zones with a total length of 1280 km are identified and confirmed in the central Sichuan Basin. Third, strike–slip faults are mainly distributed in the Sinian–Permian System, mainly composed of small-displacement oblique faults and echelon faults, and different in stratification, grading, classification and segmentation. Fourth, under the control of the oblique subduction of the Proto-Tethys Ocean and the different structures of the basement, the strike–slip faults in the central Sichuan Basin were formed in the Sinian and there are multiple stages of inherited Caledonian–Hercynian activities. Fifth, the strike–slip faults in the central Sichuan Basin play a role in source–reservoir connection, reservoir stimulation, and gas accumulation and high yield, and constitute the fault-controlled natural gas accumulation system of “three-element controlling reservoir and composite hydrocarbon accumulation” based on source rock, fault and reservoir. In conclusion, a large intraplate strike–slip fault system is developed in the Sichuan Basin, which has the geological conditions of hydrocarbon accumulation to form strike–slip fault-controlled large gas field, and the large source connecting strike-slip fault zones are the main breakthrough directions of natural gas exploration in fault-controlled carbonate rocks.