Analysis of subsurface structural trend and stratigraphic architecture using 2D seismic data: a case study from Bannu Basin, Pakistan

It is curious that the typical feature of high-velocity layer (HVL) underneath the crust for the magma-rich margin was found in the magma-poor margin of the South China Sea. In order to better understand the nature and age of the HVL in the South China Sea, here we provide seismic imaging on the Cenozoic structure and sedimentation using a regional seismic reflection profile combined with existing drilling data and seismic refraction lines in the northeastern South China Sea. An important finding is that the extent of erosion since Neogene is only on the Dongsha Rise and is much smaller than that of the HVL observed across the northern margin of the South China Sea, which suggests the occurrence of the HVL has no influence on the erosion on Dongsha Rise through Neogene. On the regional seismic profiles, the different structures between the deepwater rifted margins and the continental shelf were also observed. The faults in the Zhuyi Sub-basins on the continental shelf are imaged to be high-angle and bound a series of grabens and horsts. In contrast, the deepwater region is characterized by tilted fault blocks and an array of listric normal faults, which extremely thinned the crust to be ~ 5–10 km. After middle Miocene, active magmatism occurred in the deepwater region at the time of post-spreading of oceanic crust. These listric faults on the hyper-extended crust is interpreted to be conduits for magma migration to the shallower levels. This typical structure in the deepwater region changed the geophysical nature of the HVL underneath the extreme thinned crust, which should be formed before the event of hyper-extension and is likely to be associated with the subduction of the paleo-Pacific toward the Asia in the late Cretaceous. Our study will answer the question why the South China Sea with the HVL underneath the crust is a magma-poor passive margin.

Relevance of the work. The paper considers challenging problems related with outlining of intervals with oil and gas presence in the mature Khylly field by use of latest 3D seismic survey techniques in order to gain larger crude resources base. The purpose of this research is to discover the most promising intervals of target horizons with relatively high reservoir properties outlined by 3D seismic data. The subjects of research are 3D seismic survey data, downhole seismic survey – Vertical Seismic Profiling (VSP) and well logging diagrams. The object of research is the Khylly deposit. The paper describes in brief geological and geophysical characteristics, stratigraphic and lithological features of rocks making the section. It is noted that despite repeated surveys by use of various geological and geophysical techniques, the field setting is not thoroughly studied and it has been covered by 3D seismic survey in 2012. Research results. 3D seismic survey applied across Khylly area is resulted in drawing of 4 structural maps for III and I horizons of Productive Series (PS), Akchagyl and Lower Absheron suites. Taking into account the relevance of structural planes of various stratigraphic levels and III horizon of PS being one of the major reference horizons the paper gives description of structural map drawn for this horizon. The detailed velocity model is designed based on VSP data with wide use of velocity analysis data. It has been made clear that Khylly area has block structure and each block has been described in detail. Based on acquired data it has been recommended to drill exploratory well R-1. Conclusion. Processing and interpretation of seismic data are aimed at solving some geological problems; the main task was to obtain results that ensure the study of the geological structure in the seismic survey area, including tracing of seismic horizons, faults and outlining the areas and section intervals which may be of interest due to possible oil and gas presence. VSP data acquired in well 2012 and velocity analysis made it possible to design velocity model of the section under the study, with the use of which the temporary 3D cube was transformed into a depth cube. The quality of seismic data is good and made it possible to solve the tasks set for this research.

Structural delineation and Stratigraphic evaluation of proven geological basins are of prime importance for hydrocarbon exploration and exploitation. The current study aims to map the subsurface geology in a part of Lower Indus basin of Pakistan in terms of structure and stratigraphy using seismic data with some borehole information. In this paper, conventional integrated geophysical technique has been used to analyze the seismic data to characterize reservoir formations. To pursue the interpretation, 2D seismic data in SEG-Y format was used along with velocity and well logs information. Visual interpretation of seismic profiles is transformed into 2D and 3D (Time and Depth domain) contour maps, which is the representation of true subsurface geology. Three promising closures at shallow time have been identified on structural contour maps which are indicative of possible prospects. A closure, covering approximately 1 Sq. Km area over Eocene aged Sui Main Limestone and further two over Cretaceous aged Lower Goru formation covering areas of 500 and 400 Sq. km along shot point 260 and 380-390, respectively. Conjugate normal fault system among the stratigraphic layers existing in the study area can smoothly provide the hydrocarbon trapping mechanism. In order to further confirm the probable future prospects and support the study, modeling of P and S wave Acoustic Impedance have also been done. The advance integrated study of AVO modeling and numerical rock physics analysis may be helpful in providing further insights into current research.

During the two legs of cruise MSM34 of R/V MARIA S. MERIAN regional 2D seismic surveying, high resolution 2D and 3D seismic imaging, geo-chemical sampling, heatflow measurements and long-term piezometer installations were undertaken. A grid of 28 2D seismic profiles was collected across the palaeo Danube delta. A number of inactive and partly buried channel systems could be mapped. Most of them were underlain by one or more bottom simulation reflectors (BSR). Based on the seismic brute stack images and the limits of the MeBo drilling device a prospective channel system with indications for possible gas hydrate formation at shallow depth (BSR, inverted strong amplitudes) could be identified in about 1500 m water depth. High resolution 2D seismic and 3D P-Cable seismic were used together with OBS deployments in order to allow structural mapping and physical description of the channel infill. Heatflow measurements and geochemical analyses of gravity and multi corer samples accompany these investigations. Neither the multibeam water column images nor Parasound records show any evidence of flares (gas bubbles in the water column) in this working area suggesting a well sealed hydrate reservoir. Active gas expulsion from the seafloor was observed at about 200 m water depth circling around a slump area. The base plane of the failed sediment volume builds the current seafloor at about 600 m to 700 m water depth. On regional 2D seismic profiles a BSR has been mapped underneath the slope failure with unexpectedly strong upward bending. High resolution 2D and 3D P-Cable seismic investigations with complementary OBS deployment will allow imaging the BSR outline. Moreover velocity analyses, heatflow measurements and geo-chemical samples will be available for a detailed description of hydrate distribution and sediment parameters. In a third working area high resolution 2D seismic reflection profiles were acquired across a fully buried channel system. Together with the regional seismic lines slope failure of the channel fill material can be studied across the slope extension of the system.

The Sipoholon Geothermal Field and adjacent geothermal systems along the North-Central Sumatra Fault Belt, Indonesia: Reviews on geochemistry, tectonics, and natural heat loss

Coalbed methane (CBM) is the only unconventional gas in Poland with estimated recoverable resources. The prospects for developing deep CBM have been explored in recent years by drilling deep exploration wells within the depocenter of the Upper Silesian Coal Basin. The purpose of this study is to analyze the occurrence and potential for CBM extraction in this area of the basin, which can be considered prospective due to the confirmed presence of significant amounts of gas and thick coal seams at depths > 1500 m. The study examined the vertical and horizontal variability of the gas content in the studied area, the coal rank in the seams, thermal conditions, and coal reservoir parameters. The gas content in the seams, reaching more than 18 m3/t coaldaf at a depth of 2840 m, and indicative estimated gas resources of 9 billion m3 were found. The high gas content is accompanied by positive thermal and coal rank anomalies. The permeability and methane saturation of the coal seams are low, and therefore, potential methane production may prove problematic. However, the development of CBM extraction technologies involving directional drilling with artificial fracturing may encourage gas production testing in the study area.

Distribution prediction of the glutenite in Member 3 of Triassic Xujiahe Formation in Yuanba area, northern Sichuan Basin

The available geological data on the Meso-and Neoproterozoic rocks in the north of the East European Platform are considered, involving the results of a comprehensive study along regional seismic profile I-I that extends for 460 km and crosses the main structural units of the Mezen Syneclise from SW to NE. Many previously unknown structural features of aulacogens filled with thick (up to 4–8 km) sequences of the Meso-and Neoproterozoic sedimentary rocks that make up the preplate complex are demonstrated in this profile. The Riphean rocks are subdivided into three seismostratigraphic sequences: the lower part of the Lower Riphean, the Lower-Middle Riphean, and the Upper Riphean. The geodynamic events in the north of the East European Platform are correlated with those that occurred in its central part and the adjacent foldbelts.

This study presents a comprehensive workflow to detect low seismic amplitude gas fields in hydrocarbon exploration projects, focusing on the West Delta Deep Marine (WDDM) concession, offshore Egypt. The workflow integrates seismic spectral decomposition and machine learning algorithms to identify subtle anomalies, including low seismic amplitude gas sand and background amplitude water sand. Spectral decomposition helps delineate the fairway boundaries and structural features, while Amplitude Versus Offset (AVO) analysis is used to validate gas sand anomalies. The entire seismic volume is classified into facies domains using machine learning, which isolates target features from seismic background data. The study area, covering 1850 km2, includes major structures such as the Rosetta fault and Nile Delta offshore anticline, with reservoirs consisting of layered sandstones and mudstones. Over 90 wells, including exploration and development wells, have been drilled in the area. Seismic amplitude data, including full and partial offset stacked, were analyzed to classify gas, water, and shale zones. The workflow’s performance is demonstrated through the successful identification of the low-amplitude Swan-E Messinian anomaly, characterized as a high-risk gas prospect. Machine learning techniques, specifically neural network models, were trained to differentiate seismic features such as low-amplitude gas sand from background-amplitude water sand and shale. By iterating over multiple attributes and validating the models on blind test sets and on a blind section, which excluded a known shallow gas field, the workflow significantly improved the ability to detect potential hydrocarbon reservoirs characterized by low seismic amplitude. The results show that this integrated approach reduces exploration risk, quantifies the chance of success, and enhances decision-making in well placement and hydrocarbon exploration. This method is particularly useful for identifying low seismic amplitude anomalies, which are often challenging to detect with conventional seismic analysis. (1) This study developed a workflow to detect low seismic amplitude gas fields in near-field exploration. (2) It uses a machine learning algorithm to classify and explore low-seismic-amplitude gas sand reservoirs. (3) This approach helps estimate the likelihood of success and reduces the risk associated with hydrocarbon exploration wells.

A three-dimensional numerical model to simulate Iranian NW Sabalan geothermal system

The Chattian Lower Freshwater Molasse (USM) of the Thun area comprises a thick series of continental sediments which occur in three imbricate thrust sheets (Steffisburg, Zulg-Hombach, Blueme) of the Subalpine Molasse and over wide areas of the autochthonous Plateau Molasse. Facies analysis of outcrops, complemented by conglomerate clast counts, sandstone petrography, heavy mineral analysis and data from two deep exploration wells and seismics permit structural restoration of the thrust sheets, correlation of subalpine and autochthonous USM and consequently the reconstruction of the geometry and facies evolution of the alluvial fan systems. The most complete succession measuring more than 4500 m is preserved in the structurally highest Blueme thrust sheet

Extended abstract for SPE 30353 Offshore Europe conference In recent years in the U.K.C.S, small fields have been successfully exploited both as satellites to existing infrastructure and as standalone projects using floating production techniques. Amerada Hess Limited has pioneered this approach, particularly in two areas in the Central North Sea: Quadrant 15 around the Ivanhoe/Rob Roy and Scott fields and the Fife area in Quadrants 31/39. The former area is close to existing infrastructure and pipelines whilst the latter is over 30 Kms from the nearest facility. The search for these small fields in the North Sea has been heralded by the widespread use of 3D seismic which has allowed the identification of much smaller prospective structures and more efficient targeting of exploration wells which may be suspended for use as development wells or later sidetracked for optimum reservoir development. The use of 3D seismic for exploration drilling became more common through the late 1980’s and early 1990’s. Such data-sets have helped to more accurately image small, often low relief structures and to optimise the location of exploration and appraisal wells which are often few in number in order to sustain viable economic margins. In parallel with geophysical developments, advances in offshore engineering technology have helped to achieve lower capital expenditure so necessitating much smaller reserve sizes to make tie-backs economic.

Machine-learning algorithms have been used by geoscientists to infer geologic and physical properties from hydrocarbon exploration and development wells for more than 40 years. These techniques historically utilize digital well-log information, which, like any remotely sensed measurement, have resolution limitations. Core is the only subsurface data that is true to geologic scale and heterogeneity. However, core description and analysis are time-intensive, and therefore most core data are not utilized to their full potential. Quadrant 204 on the United Kingdom Continental Shelf has publicly available open-source core and well log data. This study utilizes this dataset and machine-learning models to predict lithology and facies at the centimeter scale. We selected 12 wells from the Q204 region with well-log and core data from the Schiehallion, Foinaven, Loyal, and Alligin hydrocarbon fields. We interpreted training data from 659 m of core at the sub-centimeter scale, utilizing a lithology-based labeling scheme (five classes) and a depositional-process-based facies labeling scheme (six classes). Utilizing a “color-channel-log” (CCL) that summarizes the core image at each depth interval, our best performing trained model predicts the correct lithology with 69% accuracy (i.e., the predicted lithology output from the model is the same as the interpreted lithology) and predicts individual lithology classes of sandstone and mudstone with over 80% accuracy. The CCL data require less compute power than core image data and generate more accurate results. While the process-based facies labels better characterize turbidites and hybrid-event-bed stratigraphy, the machine-learning based predictions were not as accurate as compared to lithology. In all cases, the standard well-log data cannot accurately predict lithology or facies at the centimeter level. The machine-learning workflow developed for this study can unlock warehouses full of high-resolution data in a multitude of geological settings. The workflow can be applied to other geographic areas and deposit types where large quantities of photographed core material are available. This research establishes an open-source, python-based machine-learning workflow to analyze open-source core image data in a scalable, reproducible way. We anticipate that this study will serve as a baseline for future research and analysis of borehole and core data.

ABSTRACT: A comparative approach is applied in the north part of the Hoggar shield to highlight the subsurface architecture and determine the kinematics, the dip, and the geometry of the major fault sets that affect the Ahnet and the Mouydir basins by using a combination of seismic 2D profiles and the surface geological maps. The analysis of geological maps shows that a dense fracture network affects the Paleozoic series. The N-S fault network constitutes large and long fracture corridors that design the edges of the two basins. These faults are strike-slip faults trending dextral and sinistral. The NNE-SSW and NW-SE are also strike-slip faults trending sinistral. They are also strike-slip faults trending dextral and sinistral. On the other hand, the structural analysis of 2D seismic profiles reveals that the deep strike-slip faults that affect the Ahnet and Mouydir basin are not only pure strike-slip trending sinistral and dextral, but they have also vertical components trending as normal and reverse faults. The outcomes suggest that the Hercynian orogeny could be considered as a continuous deformation instead of separate tectonic events. 1. INTRODUCTION The Paleozoic analog overlays in the north part of the Hoggar shield and in the southern edges of Ahnet, Mouydir, and Illizi basins. It is mainly composed of the Cambro-Ordovician, Silurian, and Devonian formations. The Cambro-Ordovician formations are characterized by brittle tectonic style, linked with the major basement fractures inherited from the Pan-African orogeny (Arab et al, 2011 and Djezzar et al, 2020a). The latter were reactivated during the Hercynian orogeny, creating the actual basins’ architecture in horst and graben in a major part of the Saharan platform. The Mouydir basin is designed as horst and graben where two main horsts constitute the edges of the basin and are clearly visible through the 2D seismic data. In addition, other horsts in the center of the basin are highlighted and constitute positive structures where several wells were drilled. The structural analysis revealed that the Saharan platform has been marked by several tectonic phases where the Hercynian orogeny that occurred at the end of the Carboniferous is the most important event that structured the Saharan platform (Boualam et al. 2019). A comparative approach is used to highlight the subsurface architecture of the Mouydir basin and determine the kinematics, the dip, and the geometry of the major fault sets that affect the Ahnet and the Mouydir basins by using a combination of seismic 2D profiles and the surface geological maps. The analysis of surface geological maps shows that a dense fracture network affects the Paleozoic series. The fracture network is composed of 3 main fracture sets oriented N-S, NNE-SSW, and NW-SE, respectively. The N-S fault network constitutes large and long fracture corridors that structured the edges of the two basins namely Idjerane and Amguid spurs. These faults are strike-slip faults trending dextral and sinistral. The NNE-SSW and NW-SE are also strike-slip faults trending dextral and sinistral. On the other hand, the structural analysis of 2D seismic profiles reveals that the deep strike-slip faults that affect the Ahnet and Mouydir basins are not pure strike-slip trending sinistral and dextral, but they have also vertical components trending as normal and reverse faults (Djezzar et al, 2020b). They are mainly generated through transpressional and transtensional strain regimes that affected the area of study during the Hercynian orogeny. The 2D seismic profiles show clearly that the area of study was affected at least by two tectonic events oriented N040 and N120, expressed by compressive and distensive structures generating anticlines/reverse faults and synclines/normal faults. The results suggest that the Hercynian orogeny could be considered as a continuous deformation instead of separate tectonic events.

The sedimentary sequence of the Caspian Sea is generally well studied by geological and geophysical methods [1], particularly multichannel seismic profiling, which was mainly aimed at study of the deep structure of the sedimentary cover with perspectives for the discovery of hydrocarbon traps (see, e.g., [2]). However, data available for the upper part of the Pliocene‐ Quaternary sedimentary sequence are insufficiently detailed, because the majority of regional continuous seismic profiling (CSP) works were carried out in the 1970s‐1980s using low-resolution equipment [3]. New detailed data on the structure of these sediments in the Middle Caspian area near the Dagestan coast from the upper part of the western slope to the adjacent deep part of the Derbent basin were obtained by a team of scientists from the Institute of Oceanology and Moscow State University during Cruise 19 of the R/V Rift in autumn 2004‐winter 2005 (Fig. 1). The expedition was conducted in the framework of the Federal Targeted Program “The World Ocean” (Subprogram 8 “Complex Study of Processes, Characteristics, and Resources of the Caspian Sea”) simultaneously with engineeringgeological prospecting of the Yalama‐Samur structure for the Lukoil Company. A Geont-shelf high-resolution single-channel seismoacoustic profiler equipped with a spark transmitter (sparker with capacity of 600 J), which provided vertical resolution up to 2 m at a depth of 300‐400 mbsf, was used to study the fine structure of the upper sedimentary sequence. Geological works in the cruise included sampling of sediments with gravity piston corers and study of their physicochemical properties at the Yalama‐Samur test site (Figs. 1, 2). The study area is located in the steepest area of the western slope of the Derbent basin characterized by the highest dip angles and maximal relief differentiation in the entire Middle Caspian [4]. The CSP data show that the slope is composed of two distinct sedimentary complexes with different seismic record patterns. They are separated by a near-horizontal intense reflector (R-2), which extends in the eastern part at a depth of approximately 400 m and gently rises toward the coast (Fig. 2). Comparison with previous materials, including drilling