Search Results (24)

As a strategic replacement area for hydrocarbon exploration in the Tarim Basin, the Kuqa Depression has been the subject of relatively limited research on the sedimentary characteristics of the Triassic strata within its western Wushi Sag, which constrains exploration deployment in this region. This study focuses on the Wushi Sag, systematically analyzing the sedimentary facies types, the evolution of sedimentary systems, and the distribution patterns of the Triassic Kelamayi and Huangshanjie formations. This analysis integrates field outcrops, drilling cores, wireline logs, and 2D seismic data, employing methodologies grounded in foreland basin theory and clastic sedimentary petrology. The paleo-geomorphology preceding sedimentation was reconstructed through balanced section restoration to investigate the controlling influence of foreland tectonic movements on the distribution of sedimentary systems. By interpreting key seismic profiles and analyzing vertical facies successions, the study classifies and evaluates the petroleum accumulation elements and favorable source–reservoir-seal assemblages, culminating in the prediction of prospective exploration areas. The research shows that: (1) The Triassic in the Wushi Sag mainly develops fan-delta, braided-river-delta, and lacustrine–shallow lacustrine sedimentary systems, with strong planar distribution regularity. The exposed strata in the northern part are predominantly fan-delta and lacustrine systems, while the southern part is dominated by braided-river-delta and lacustrine systems. (2) The spatial distribution of sedimentary systems was demonstrably influenced by tectonic activity. Paleogeomorphological reconstructions indicate that fan-delta and braided-river-delta sedimentary bodies preferentially developed within zones encompassing fault-superposition belts, fault-transfer zones, and paleovalleys. Furthermore, Triassic foreland tectonic movements during its deposition significantly altered basin configuration, thereby driving lacustrine expansion. (3) The Wushi Sag exhibits favorable hydrocarbon accumulation configurations, featuring two principal source–reservoir assemblages: self-sourced structural-lithologic gas reservoirs with vertical migration pathways, and lower-source-upper-reservoir structural-lithologic gas reservoirs with lateral migration. This demonstrates substantial petroleum exploration potential. The results provide insights for identifying favorable exploration targets within the Triassic sequences of the Wushi Sag and western Kuqa Depression. Full article

As an important target for deep marine shale gas exploration, shale reservoirs near denudation areas have enormous resource potential. Based on the impression method, the sedimentary paleogeomorphology near the denudation area is identified as three units: the first terrace, the second terrace, and the third terrace. At the second terrace where Well Z212 is located, the thickness of the Longmaxi Formation first section is only 0.8 m, and the continuous thickness of the target interval is only 4.3 m, making it a typical thin shale reservoir. By integrating petrology, mineralogy and the seismic method, the thin shale reservoir is characterized. Compared to shale reservoirs far away from the denudation area, the Well Z212 (near denudation area) production interval (Wufeng Formation first section) has high porosity (6%–10%), moderate TOC (3%–4%), a high carbonate mineral content (10%–35%), and a high gas content (>7 m³/t). The correlation between the total porosity of shale and the density of high-frequency laminations is the strongest, indicating that the silt laminations have a positive effect on pore preservation. There is a significant positive correlation between carbonate content and the volume of mesopores and macropores, as well as the porosity of inorganic pores. It is suggested that carbonate minerals are the main carrier of inorganic pores in Well Z212, and the pores are mainly composed of mesopores and macropores. Under the condition of being far away from the fault zone, even near the denudation area, it has good shale gas preservation characteristics. The key development technologies consist of integrated geo-steering technology, acidification, and volume fracking technology. Based on geological characteristics, the fracturing process optimization of Well Z212 has achieved shale reservoir stimulation. Full article

The analysis of sand distribution in a marine–continental rift basin is of practical value for hydrocarbon prediction. The primary objective of this study is to investigate the correlation between Paleoproterozoic sand development and paleomorphology in the Nanpu sag, and to focus on identifying the key factors controlling sand deposition in the marine–continental rift basin. Correspondence between the development of the Paleoproterozoic sand in the Nanpu sag and the paleogeomorphology shows that the gully limited the deposition of the sand into the lake. The differentiation and aggregation of the sand in the lake basin were influenced by two kinds of slope break zones (the syn-sedimentary fracture tectonic slope break zone and the paleo-topographic flexural depositional slope break zone). Due to tectonic movements in the marine–continental rift basin, as well as provenance supply and weather during chasmic stages, the impact of valley and syndeposit slope break zone on sand development varies. In areas where allocation is better as valley–syndeposit slope break zone, basal slope and its vicinity usually are favorable for delta (braided channel) and fan delta sand development, which extend basinward through hydraulic transport. Meanwhile, under the influence of syntectonic and gravitational disequilibrium, gravity flow sand can be seen sporadically distributed in the deep end of fan fronts. This study is of great significance for oil and gas exploration in the Bohai Bay Basin region and contributes to a better understanding of depositional processes in similar marine–continental rift basins around the globe. Full article

The Changling Depression, located in the southern part of the central depression zone of the Songliao Basin, is characterized by complex structures and has been shaped by multiple phases of tectonic activity. The strata in this region have undergone significant uplift and denudation, resulting in an incomplete understanding of the prototype basin and hindering progress in oil and gas exploration. To better understand the geological characteristics and exploration potential of the Changling Depression, this study begins with the reconstruction of denudation amounts. Using the stratigraphic trend extrapolation method, the denudation of strata during the faulting period of the Changling Depression is quantified. By combining the denudation thickness with the remaining strata thickness, the original strata thickness is restored. Employing MOVE 2018version and Petrel 2021version software, the paleogeomorphology of different geological periods is reconstructed. Through an analysis of the prototype basin’s structure, its evolution history, sedimentary filling patterns, and paleogeomorphological features, it is determined that the maximum depositional thickness and rate during the Huoshiling period occurred in the Shenzijing, Heidimiao, and Fulongquan areas, with strong central deposition that weakened toward the north and south. During the Shahezi period, depositional thickness and rates exhibited a pattern of weaker deposition in the south and stronger in the north. In the Yingcheng Formation–Denglouku Formation period, the basin entered a subsidence phase, with an expanded range of strata subsidence. During the Denglouku period, the Qianbei area experienced strong deposition, while the Heidimiao area saw even more pronounced deposition; in contrast, the Shenzijing area displayed very weak depositional activity. The study reveals a south-to-north migration of lateral subsidence centers over time, influenced by left-lateral tectonic forces, reflecting a shift in the dominant influence pattern. These findings clarify the morphology of the prototype basin and the distribution and migration of subsidence centers across different periods, providing valuable insights that will facilitate deeper oil and gas exploration efforts in the Changling Depression. Full article

The development pattern of the high-quality reservoir in the Changxing Formation in the Wolonghe-Yangduxi area of southeastern Sichuan is complex. To clarify its evolution, genetic mechanisms, and distribution patterns, this study integrates data from profiles, cores, thin sections, and well logs. It reveals the distribution mechanisms of the bio-reef and shoal reservoirs in the Changxing Formation and discusses the controlling effects of tectonic, sedimentary, and diagenetic processes on reservoir development. The results show the following: (1) The Changxing Formation mainly develops open platform facies, platform margin facies, and slope-basin facies, which can be further subdivided into subfacies of platforms, intra-platform depressions, intra-platform depressions marginal reefs, and intra-platform depressions marginal shoals. The intra-platform margin reefs and the reefs at the edge of the platforms are favorable microfacies for reservoir development. (2) The high-quality reservoirs of the Changxing Formation are dominated by medium-thick-layered biogenic reef limestone and bioclastic limestone, with secondary porosity as the main reservoir space. (3) Sedimentary conditions, sea level fluctuations, and diagenesis are crucial factors for reservoir development. Paleogeomorphological conditions provide the foundation for reservoir development, while sea level fluctuations control the internal structure of the reef–shoal and the cyclical variations in the reservoir. Full article

Based on the special geological background of the east and north slopes of the Baiyun Depression, the development conditions of Paleogene structure–lithology traps, the development conditions of high-quality reservoirs and the difficulty in characterizing the distribution characteristics are studied in this paper. It is concluded that the eastern Baiyun is located on the Baiyun–Liwan continental–oceanic large-scale intershell separation system, with a complex tectonic background and a tectono-sedimentary pattern of “fault and uplift interlocking and uplift and depression interphase”. The palaeo source sink system of the low bulge in the east of Yundong is restored, the favorable position of reservoir collective development and the favorable characteristics of reservoir–cap assemblage are clarified, and the paleo-geomorphology and sedimentary filling evolution law are clarified. Guided by the drive of oil and gas accumulation, three types of large and medium-sized structure–stratigraphic traps have been implemented in the eastern Baiyun system, including the convex inclined end, the restricted fault gully and the magmatic floor intrusion, and the corresponding oil and gas accumulation models have been perfected. By studying the structure, source and sink system and trap characterization of the eastern Baiyun basin, the development conditions and exploration direction of the large and medium-sized Palaeogene traps are systematically summarized. Full article

In post-rift basins, the thickness center, fine-grained deposit center, and subsidence center rarely converge. Clearing the three centers with the thickest center is difficult. In the Huangyan district of Xihu Sag, the East China Sea Shelf Basin, an Oligocene post-rift basin beneath major potential igneous provinces, has inconsistent thickness and composition. Analysis of core samples, drilling, and 3D seismic data corroborated this finding. This means that the formation thickness center does not match the lithology center, which indicates water depth. Gravity and magnetic measurements in the studied region show that significant magmatic activity is responsible for the difference between the center of thickness and the fine-grained deposit. Thermal sinking must be restored to fix this. Therefore, we propose (1) recreating the early Oligocene residual geomorphology in Huangyan using 3D seismic data. (2) Software computing quantitative subsidence. (3) Paleogeomorphology is verified by normal and trace element paleowater depths. (4) Reconstruct the paleogeomorphology and analyze how volcanic activity affected them and the three centers in the basin formed after tectonic plates separated. A shallow water delta and thermal subsidence show that magmatic activity is persistent in the north. With less thermal subsidence and deeper water, the southern area features a shallow lake sedimentary system. The thickness and fine-grained deposition centers were in the north and south, respectively. Geophysical and geological methods were used to reproduce the post-rift paleogeomorphology shaped by magmatic processes. Full article

The Qiulitage fold and thrust belt (QFTB) is situated in the Kuqa Depression, exhibiting spectacular salt structures with well-defined geometric and kinematic characteristics and thereby playing a significant role in advancing the study of salt structures worldwide. This research, based on regional geology, well logging, and newly acquired three-dimensional seismic data, applies principles of salt-related fault structures to interpret seismic data and restore structural equilibrium in the Qiulitage fold and thrust belt within the Kuqa Depression by conducting quantitative studies on structural geometry and kinematics. Results indicate clear differences in salt structures between the eastern and western segments of it, vertically divided into upper salt, salt layer, and lower salt and horizontally into four parts. The Dina segment features a single-row basement-involved thrust fault, the East QFTB segment displays detachment thrust faults involving cover layers, the Central QFTB segment exhibits detachment thrust faults involving multiple rows of cover layers, the leading edge forms structural wedges, and the West QFTB segment develops blind-thrust faults. During the deposition of the Kangcun formation, the eastern profile experiences an 18% shortening rate, 14% in the central part, and 9% in the western part. For the Kuqa formation, the eastern profile experiences a 10% shortening rate, 9% in the central part, and 3% in the western part, indicating more significant deformation in the east than in the west. Quantitative statistical analysis reveals that different types of detachments, paleogeomorphology, and northeast-directed compressive stress exert control over the Qiulitage fold-thrust belt. Full article

The 2012 satellite ASTER geoscience maps of Australia were designed to provide public, web-accessible, and spatially comprehensive surface mineralogy for improved mapping and solutions to geoscience challenges. However, a number of the 2012 products were clearly compromised by variable green and/or dry vegetation cover. Here, we show a strategy to first estimate and then unmix the contributions of both these vegetation components to leave, as residual, the target surface mineralogy. The success of this unmixing process is validated by (i) visual suppression/removal of the regional climate and/or local fire-scar vegetation patterns; and (ii) pixel values more closely matching field sample data. In this process, we also found that the 2012 spectral indices used to gauge the AlOH content, AlOH composition, and water content can be improved. The updated (new indices and vegetation unmixed) maps reveal new geoscience information, including: (i) regional “wet” and “dry” zones that appear to express “deep” geological characters often expressed through thick regolith cover, with one zone over the Yilgarn Craton spatially anti-correlated with Archaean gold deposits; (ii) a ~1000 km wide circular feature over the Lake Eyre region defined by a rim of abundant “muscovite” that appears to coincide with opal deposits; (iii) a N–S zonation across the western half of the continent defined by abundant muscovite in the south and kaolinite in the north, which appears to reflect opposing E ↔ W aeolian sediment transport directions across the high-pressure belt; (iv) various paleo-drainage networks, including those over aeolian sand covered the “lowlands” of the Canning Basin, which are characterized by low AlOH content, as well as those over eroding “uplands”, such as the Yilgarn Craton, which have complicated compositional patterns; and (v) a chronological history of Miocene barrier shorelines, back-beach lagoons, and alluvial fans across the Eucla Basin, which, to date, had proved elusive to map using other techniques, with potential implications for heavy mineral sand exploration. Here, we explore the latter three issues. Full article

The Middle Permian Maokou Formation in the Sichuan Basin has huge resources and is an important target for natural gas exploration. In recent years, significant exploration breakthroughs have been made in the dolomite field of member Mao-2 in central Sichuan, and the gas production of several wells has exceeded 1 × 10⁶ m³/d, indicating promising prospects for exploration. However, the origin of the dolomite reservoir in member Mao-2 remains ambiguous, which restricts the accurate prediction of favorable reservoirs. This study focuses on drilling in the Hechuan area as its research object, by using a detailed description of the cores from member Mao-2 of seven wells; samples were selected for tests of the degree of dolomite cation ordering, stable carbon and oxygen isotopic compositions, strontium isotopic composition, rare earth elements, LA-ICP-MS element mapping and U-Pb dating. It is clarified that: (1) The crystalline dolomite of member Mao-2 in the Hechuan area is the main reservoir rock, and the heterogeneous vugs and fractures are the main reservoir space. The dolomite in member Mao-2 has been characterized by a low degree of cation ordering value (avg. 0.59), with values of δ¹³C (avg. 3.87‰), δ¹⁸O (avg. −7.15‰) and ⁸⁷Sr/⁸⁶Sr (avg. 0.707474) having similar geochemical characteristics to Middle Permian seawater; the REEs normalized distribution patterns have similar characteristics to limestone; and the U-Pb age (261.0~262.0 Ma) corresponds to the age in the Capitanian stage of the Permian Guadalupian Series. (2) Petrological studies show that member Mao-2 has vertical karstification zonation characteristics; syngenetic karstification controls the formation of a large-scale fracture-cave system in the phreatic zone; the dolomitization of sediment in the fracture-cave system occurred during the penecontemporaneous period with locally restricted seawater. (3) The main controlling factors of the reservoir were syngenetic karstification, early dolomitization and hydrothermal dissolution related to Emei taphrogenesis. The research results are of great significance for dolomite reservoir prediction; the highlands of paleogeomorphology with syndepositional faults are favorable areas for dolomite reservoirs. Full article

The Benxi Formation is one of the most important gas-producing layers in the Ganquan–Fuxian area, but the complex gas–water distribution and lack of sandstone have severely constrained natural gas exploration and development in this area. This study analyzed the structure, paleogeomorphology, sedimentary facies, reservoir closures, and gas–water distribution of the Benxi Formation in the study area through drilling, coring, logging, seismic surveying, and experimental testing. The results show that the gas reservoirs in the Benxi Formation are mainly lithologic traps distributed along NW-trending barrier sandstones, with a small portion of updip pinchout closures. The water layers are mainly composed of thin sandstones with a single-layer thickness of less than 2 m, which are tidal-channel or barrier-margin microfacies sandstones. The water saturation in some thick sandstones is related to the activity and destruction of large individual faults. The dry layers are tight sandstones with porosity of less than 3.2%, mainly associated with high amounts of volcaniclastic matrix and lithic fragments, as well as compaction. The charging of the underlying high-quality Ordovician limestone reservoirs by carboniferous source rocks in the Benxi Formation reduces the probability of gas accumulation in Benxi sandstone. Based on the control of sedimentary facies and physical properties on gas accumulation, favorable reservoir distributions were predicted using seismic attributes and gas detection methods, providing the basis for the next phase of natural gas exploration and development in this area. Full article

In recent years, with the discovery of oil and gas in the Carboniferous bauxite reservoir in the Ordos basin, the formation and distribution of bauxite and bauxite reservoirs have attracted the attention of oil and gas explorers. Based on the slightly equidistant core testing of minerals and the porosity on the formation and calibration on the logging curves, we established a logging identification method for bauxite in the study area and fitted the formula for calculating the diaspore content and porosity using logging data. By applying this formula and a large amount of logging data, thickness and porosity maps of the Taiyuan formation of bauxite in the southeastern part of the basin were produced. Then, according to the thickness of the earliest deposited Taiyuan formation on the unconformity surface, we analyzed the paleogeomorphology of the bauxite deposition. Finally, a sedimentary facies map of the Taiyuan formation was developed based on the content of sandstone, coal seams, and carbonate rocks contained there. The results show that the diaspore content of bauxite is positively correlated with the natural gamma logging (GR) values. According to the diaspore contents and the GR values, the aluminiferous rocks in the Taiyuan formation can be divided into three categories: ① Bauxite for GR values > 450 API and diaspore content >70%; ② Argillaceous bauxite for GR values = 300–450 API and diaspore content = 25%–70%; and ③ Bauxitic mudstone for GR values = 220–300 API and diaspore content = 0%–25%. Bauxite mainly occurred in the middle and deep lagoon environments in the lower part of the Taiyuan formation. The lagoon is distributed along the paleokarst groove in the NW strike, with a width of approximately 30–40 km and a length of approximately 150–200 km, among which the thickness of pure bauxite is 9 m, argillaceous bauxite 26 m and alumina mudstone 6 m. Bauxite with a high porosity mainly existed in pure bauxite. The lagoon bauxite in the lower part of the Taiyuan formation gradually changes upward into a tidal flat swamp and carbonate platform environment. Full article

A new method incorporating geophysical analysis and geological analysis is proposed to define the sedimentary characteristics and distributions in basins with few drilling wells to promote the exploration of reservoirs. This method is applied to a study, through which its principles, closed-loop workflow and technologies are introduced in detail and the sedimentary characteristics and distributions of the study area are accurately defined. During the application process of the method, a compatible geological model is established, based on which the seismic data are interpreted and the results derived from the interpretation are further verified via seismic forward modeling. The study results exhibit a successive sand-rich deposition from the retrogradational gully-filling gravity flow deposition including near-shore fans, slope fans and basin-floor fans delimited by different slope break belts in transgressive sequences to the progradational delta deposition in a retrogressive sequence including braided river deltas with a long extension distance and fan deltas developed along a steep slope belt. And the potential reservoirs are located at the point-out sites of sand bodies with lower average P-wave velocities than those of muddy sediments. The proposition and application of this method are of great significance for oil and gas exploration. Full article

Based on core observation, rock thin sections, logging data, and testing data, taking the shale of the upper submember of the 4th Member to the lower submember of the 3rd Member of Paleogene Shahejie Formation in Jiyang Depression of Bohai Bay Basin as an example, we determine the lithofacies division scheme, divide the main lithofacies types, analyze the sedimentary origin and development location of different shale lithofacies, establish the continental lake basin sedimentary model, determine the types and enrichment areas of favorable lithofacies, and provide guidance for the exploration and development of Shale oil. The results show that: (1) According to the mineral composition, sedimentary structure, and organic matter abundance, the division scheme of shale lithofacies in the study area is proposed, and the shale lithofacies of the study area was mainly divided into 17 types. (2) Based on the lithologic changes, the lacustrine sedimentary shale area was divided into muddy water area, transition area, and clear water area. (3) Under the background of locally uplifted slope paleogeomorphology, considering the combined effects of climate, topography, hydrodynamic, mechanical, and chemical differentiation of sediments and biological habits, the sedimentary model of shale was established. (4) Organic-rich shale was mainly deposited between the clear water area and the end of the muddy water area, with the characteristics of water, brackish water, strong reduction, and water stratification, and was mainly enriched in the low-lying parts of paleotopography. Full article

Bauxite, in central Guizhou, is predominantly karst bauxite, but there is insufficient research on the effect of karst paleogeomorphology on bauxite development. Xiaoyuan bauxite is also a karst bauxite, and high- and low-iron bauxite deposits exist in the study area. This study conducts geological modeling of karst bauxite using controlled-source audio-frequency magnetotelluric (CSAMT) data and drill core data. The effects of karst paleogeomorphology on bauxite deposition and mineralization are evaluated by assessing karst paleogeomorphology, conducting a mineralogical analysis of drill cores at different locations, and determining the geochemical distribution characteristics of the elements in the horizontal and vertical directions. Combined with previous research results, we propose two metallogenic processes of high-iron and low-iron bauxite. The findings are significant for understanding the mechanism of bauxite formation. Full article