Search Results (58)

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

The Wufeng–Longmaxi formations in the Sichuan Basin have emerged as China’s principal shale gas exploration target, with drilling results confirming substantial resource potential. Although the Neijiang–Rongchang Block demonstrates promising production, significant performance variations among lithofacies and reservoir types highlight the need for enhanced understanding of reservoir evolution. This study integrates petrological analyses, SEM imaging, XRD characterization, seismic interpretation, and production data from multiple wells targeting the Wufeng–Long 1-1 Sub-member. Key insights reveal the following: (1) reservoir lithology consists predominantly of siliceous shale (68% occurrence), characterized by high quartz content (48% avg), low carbonates (<15%), and low clay (<30%); (2) organic-rich intervals contain Type I kerogen derived from planktonic algae, with thermal maturity indicating post-mature evolution; (3) premium reservoirs develop multi-scale pore networks combining organic-hosted pores, interparticle pores, and micro-fractures. Despite high brittle mineral content, mechanical competence decreases stratigraphically from the Wufeng Formation (78%) to Long 1-1⁷ (63%); (4) depositional redox conditions facilitated exceptional organic preservation. Core analyses reveal low porosity (5.5% avg) and ultra-low permeability (0.27 × 10⁻³ μm² avg), classifying reservoirs as multiple tight unconventional systems in the study area. The proposed lithofacies-controlled pore evolution model elucidates reservoir heterogeneity mechanisms, providing critical geological criteria for optimized shale gas development. Full article

Low-permeability sandstone reservoirs have low permeability, but due to their high porosity and difficulty in development, the development difficulty is relatively high. They can fully tap into the high potential of oil and gas resources in low-permeability sandstone reservoirs and occupy an important position in the global energy supply The study area belongs to low-permeability dense sandstone reservoir, and the destination layer has complex lithology, strong physical inhomogeneity, and complicated pore–permeability relationship, so the conventional core pore–permeability regression method and NMR SDR method do not satisfy the requirements of fine evaluation in terms of the accuracy of permeability calculation. According to the principle of resistivity measurement by electromagnetic waves with Logging While Drilling (LWD), this paper analyzes the reasons for the magnitude of resistivity divergence with Logging While Drilling at different exploration depths. There is a “low invasion phenomenon” during the drilling process of the drill bit. The higher the permeability of the formation, the more severe the “low invasion phenomenon”, and the greater the magnitude of resistivity divergence. In this paper, through the conventional log curve response characteristics and correlation analysis, the P40H/P16H parameter were selected to characterize the magnitude of resistivity divergence, and a fine evaluation model of the reservoir based on the P40H/P16H parameter was established in the study area by relying on the theory of the flow unit, and was applied to the prediction of permeability of new wells. The application results show that the calculated permeability is in good agreement with the results of core analysis, which provides a theoretical basis for the fine evaluation of low-permeability tight reservoirs. Full article

Recent breakthrough exploration wells in the Huagang Formation in the Y-area of the central anticlinal zone of the Xihu Sag have confirmed the significant exploration potential of structure–lithology complex hydrocarbon reservoirs. However, limited understanding of the provenance system, sedimentary facies, and microfacies has hindered further progress in complex hydrocarbon exploration. Analysis of high-precision stratigraphic sequences and seismic facies data, mudstone core color, grain-size probability cumulative curves, core facies, well logging facies, lithic type, the heavy-mineral ZTR index, and conglomerate combinations in drilling sands reveals characteristics of the source sink system and provenance direction. The Huagang Formation in the Y-area represents an overall continental fluvial delta sedimentary system that evolved from a braided river delta front deposit into a meandering river channel large-scale river deposit. The results indicate that the primary provenance of the Huagang Formation in the Y-area of the Xihu Sag is the long-axis provenance of the Hupi Reef bulge in the northeast, with supplementary input from the short-axis provenance of the western reef bulge. Geochemical analysis of wells F1, F3, and G in the study area suggests that the prevailing sedimentary environment during the period under investigation was characterized by anoxic conditions in nearshore shallow waters. This confirms previous research indicating strong tectonic reversal in the northeast and a small thickness of the central sand body unrelated to the flank slope provenance system. The aforementioned findings deviate from conventional understanding and will serve as a valuable point of reference for future breakthroughs in exploration. Full article

The lithofacies of a reservoir contain key information such as rock lithology, sedimentary structures, and mineral composition. Accurate prediction of shale reservoir lithofacies is crucial for identifying sweet spots for oil and gas development. However, obtaining shale lithofacies through core sampling during drilling is challenging, and the accuracy of traditional logging curve intersection methods is insufficient. To efficiently and accurately predict shale lithofacies, this study proposes a hybrid model called Stacking, which combines four classifiers: Random Forest, HistGradient Boosting, Extreme Gradient Boosting, and Categorical Boosting. The model employs the Grid Search Method to automatically search for optimal hyperparameters, using the four classifiers as base learners. The predictions from these base learners are then used as new features, and a Logistic Regression model serves as the final meta-classifier for prediction. A total of 3323 data points were collected from six wells to train and test the model, with the final performance evaluated on two blind wells that were not involved in the training process. The results indicate that the stacking model accurately predicts shale lithofacies, achieving an Accuracy, Recall, Precision, and F1 Score of 0.9587, 0.959, 0.9587, and 0.9587, respectively, on the training set. This achievement provides technical support for reservoir evaluation and sweet spot prediction in oil and gas exploration. Full article

Strategic breakthroughs have been made in the exploration and evaluation of Gulong shale oil in the Songliao Basin. However, the Heiyupao Depression, located near the Gulong Depression, hosts a thick section of the Qingshankou Formation shale that has not been extensively studied. This paper presents novel insights into the lithofacies characteristics, depositional environment, and reservoir features of the Qingshankou Formation shale in the Heiyupao Depression, with a specific focus on the origin and maturation of organic-rich shale. Four core wells were drilled, and 152 core samples were analyzed through a variety of techniques, including rock type classification, mineral composition, TOC content, rare earth elements, rock pyrolysis, organic matter type determination, and CT scanning. Results indicate that the Qingshankou shale is dominated by felsic compositions and Type I kerogen, with organic maturity varying across the section. Based on lithology, sedimentary structures, mineralogy, and organic matter abundance, five distinct lithofacies are identified: high-organic mud-rich felsic shale, high-organic sand-rich felsic shale, medium-organic sand-rich felsic shale, medium-organic massive shale, and low-organic sand-rich felsic shale. Notably, the Type A lithofacies (high-organic mud-rich felsic shale) is identified as a primary source rock due to its intergranular and organic matter pores, albeit with low porosity and poor connectivity. In contrast, the Type E lithofacies (low-organic sand-rich felsic shale) have high porosity, well-developed micro- and nano-scale pores, and strong connectivity, marking them as the primary reservoirs. The characteristics of this region differ significantly from those of Gulong shale oil, requiring different extraction strategies. The mineral composition of such shale is predominantly felsic rather than mixed. The findings not only provide theoretical support for the exploration of complex lacustrine shale in the Songliao Basin but also offer valuable insights for the resource development of similar non-marine shale systems worldwide. Full article

Reservoir space characteristics are the key to reservoir evaluation and the evaluation of reservoir capacity. The reservoir space of fracture-vuggy carbonate reservoirs is complex and diverse, and it develops from micro to macro. There is a lack of systematic study on the reservoir space of the Ordovician fracture-vuggy carbonate reservoir. Therefore, taking the Ordovician Yijianfang Formation in Yueman Block of Fuman Oilfield in Tarim Basin as an example, the microscopic reservoir space characteristics of the study area were characterized by rock thin section identification, X-ray diffraction, scanning electron microscopy, high-pressure mercury injection, and low-temperature nitrogen adsorption experiments, and the macroscopic reservoir space characteristics of the study area were characterized by core observation, drilling and logging data, and imaging logging data. The results showed that (1) the lithology of the Ordovician Yijianfang Formation in the Yueman area of Fuman Oilfield is mainly micrite and sparry grain limestone. The mineral composition is mainly calcite, accounting for 97.35%, containing a small amount of quartz and dolomite, accounting for 1.1% and 1.55%, respectively. (2) At the micro level, the reservoir space of Yijianfang Formation in Yueman Block is not developed in primary pores, mainly having developed dissolution pores, structural fractures, and pressure solution fractures, and the pore size is distributed from the nanometer to micron scale. (3) The dissolution caves in the study area are developed at the macro level, mainly including pore-type, cave-type, fracture-pore-type, and fracture-type reservoirs. The research results provide technical support for the accurate evaluation of fractured-vuggy carbonate reservoirs and the improvement of exploration and development effects. Full article

This study focuses on the PS8 well in the Penglai Gas Field (Sichuan Basin), a newly identified key exploration area, where high-yield gas testing has been achieved from the Ediacaran Fourth Member of the Dengying Formation. Comprehensive analyses of drilling cores, cuttings, thin sections, analytical data, well logging, and production testing data were conducted to investigate the main characteristics of the gas reservoir and the factors controlling the formation model of the reservoir. The results reveal that the reservoir rocks in the Fourth Member of the Dengying Formation are primarily algal-clotted dolomite, algal-laminated dolomite, and arenaceous dolomite. The reservoir porosity is dominated by secondary pores, such as algal-bonded framework pores, intergranular dissolved pores, and intercrystalline dissolved pores, which contribute to the overall low porosity and extremely low permeability. The gas reservoir is classified as a unified structural–lithological reservoir, with the upper sub-member of the Fourth Member serving as a completely gas-bearing unit. This unit is characterized as an ultra-deep, dry gas reservoir with medium sulfur and medium CO₂ contents. The development of this gas reservoir follows a “laterally generated and laterally stored, upper generation and lower storage” reservoir formation model. Regional unconformities and fracture systems developed during the Tongwan II Episode tectonic movement provide efficient pathways for hydrocarbon migration and accumulation. The high-quality source rocks in the lower Cambrian Qiongzhusi Formation serve as both the direct cap rock and lateral seal of the gas reservoir, creating an optimal source–reservoir spatial configuration. This study provides valuable insights into the giant gas reservoir of the Dengying Formation, which can aid in optimizing exploration activities in the Sichuan Basin. Full article

The light oil wells within the Neogene Shawan Formation have been extensively drilled in the Chepaizi Uplift, reflecting an increase that provides new targets for unconventional resources in the Junggar Basin of northwestern China. However, the original sources of light oil remain controversial, as several source rocks could potentially generate the oil. For this study, we collected light oils and sandstone cores for biomarker detection using gas chromatography–mass spectrometry (GC-MS). Additionally, fluid inclusions were observed and described, and the homogenization temperatures of saltwater inclusions were measured to confirm the oil charging history in conjunction with well burial and thermal history analysis. Based on these geochemical characteristics and carbon isotopic analysis, the results indicate that light oil in the Chepaizi Uplift zone primarily originates from Jurassic hydrocarbon source rocks in the Sikeshu depression, with some contribution from Cretaceous hydrocarbon source rocks. Jurassic hydrocarbon source rocks reached a peak of hydrocarbon generation in the middle to late Neogene. The resulting crude oil predominantly migrated along unconformities or faults to accumulate at the bottom of the Cretaceous or Tertiary Shawan Formation, forming anticlinal or lithologic oil reservoirs. Some oil reservoirs contain mixtures of Cretaceous immature crude oil. During the Neogene light oil accumulation process, the burial rate of reservoirs was high, and the efficiency of charging and hydrocarbon supply was relatively high as well. Minimal loss occurred during the migration of light oil, which significantly contributed to its rapid accumulation. Full article

The medium development characteristics and controlling factors of the karst peak forest plain water system constitute the core of analyzing the complex and variable hydrogeological environment, especially in revealing the controlling factors between the hydrological system and karst development characteristics, which is crucial for a deeper understanding of karst hydrogeological environments. This study takes Zengpiyan in Guilin as an example and conducts a dynamic clustering analysis on the advantageous occurrence of fracture development in three sampling areas. A total of 3472 karst channels and fractures were identified and measured. Our research reveals the following: (1) The high degree of development of fissures on surface rock outcrops is mainly formed by the expansion of shear joints through dissolution and erosion. The dip angles of fissures are mainly characterized by low angles, with fissures with dip angles between 18° and 80° accounting for 65.44% of the total observed fissures. The linear density of fissures is 3.64 per meter. (2) There are significant differences in the line density of cracks and fissures in different areas of the research area. For example, the line density in Sampling Area 1 is 0.99 lines per meter, while the line density in Sampling Area 3 reaches 5.02 lines per meter. In addition, the extension length of cracks is generally long, with joints with extension lengths exceeding 1.5 m accounting for 77.46% of the total observed joints and through cracks with extension lengths exceeding 5 m accounting for 23.33%. (3) The development characteristics of underground karst reveal that underground karst caves are mainly distributed at elevations of 120 to 160 m, with a drilling encounter rate of about 43.3%. It is also noted that geological structures control the horizontal distribution of karst, and geological lithology, hydrodynamic conditions, and water carbon dioxide concentrations are key factors affecting the vertical zoning of karst. This study provides an important scientific basis for understanding the development characteristics and controlling factors of karst water system media in peak forest plains and has important guiding significance for water resource management in karst areas and disaster prevention during tunnel excavation. 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

Deep and ultra-deep reservoirs are characterized by low porosity and permeability, pronounced heterogeneity, and complex pore structures, complicating permeability evaluations. Permeability, directly influencing the fluid production capacity of reservoirs, is a key parameter in comprehensive reservoir assessments. In the X Depression, low-porosity and low-permeability formations present highly discrete and variable core data points for porosity and permeability, rendering single-variable regression models ineffective. Consequently, accurately representing permeability in heterogeneous reservoirs proves challenging. In the following study, lithological and physical property data are integrated with mercury injection data to analyze pore structure types. The formation flow zone index (FZI) is utilized to differentiate reservoir types, and permeability is calculated based on core porosity–permeability relationships from logging data for each flow unit. Subsequently, the average permeability for each flow unit is computed according to reservoir classification, followed by a weighted average according to effective thickness. This approach transforms logging permeability into drill stem test permeability. Unlike traditional point-by-point averaging methods, this approach incorporates reservoir thickness and heterogeneity, making it more suitable for complex reservoir environments and resulting in more reasonable conversion outcomes. Full article

Analyzing rock and underground layers is known as drill core lithology. The extracted core sample helps not only in exploring the core properties but also reveals the lithology of the entire surrounding area. Automating rock identification from drill cuttings is a key element for efficient reservoir characterization, replacing the current subjective and time-consuming manual process. The recent advancements in computer hardware and deep learning technology have enabled the automatic classification of various applications, and lithology is not an exception. This work aims to design an automated method for rock image classification using deep learning technologies. A novel CNN (Convolution Neural Network) is proposed for lithology classification in addition to thorough comparison with benchmark CNN models. The proposed CNN model has the advantageous of having very low complexity while maintaining high accuracy. Experimental results on rock mages taken from the “digitalrocksportal” database demonstrate the ability of the proposed method to classify three classes, carbonate, sandstone and shale rocks, with high accuracy, and comparisons with related work demonstrated the efficiency of the proposed model, with more than 98% saving in parameters. Full article

The application of geophysical methods in saline environments is limited in their ability to discern shallow subsurface geology and tectonics due to the high subsurface conductivity, which can play havoc with the geophysical signal. Recent changes in the hypersaline Dead Sea provided the opportunity to demonstrate the effectiveness and adequacy of the terrestrial frequency domain electromagnetic (henceforth FDEM) method in such settings. Since the International Continental Drilling Program (ICDP) 5017-3-C borehole was cored in 2011 in a water depth of ~2.1 m, the lake level has dropped by almost 15 m, exposing some 320 m of a new, salt-encrusted shore. An FDEM survey was carried out on what is now land across the borehole. The results of the survey were compared to downhole gamma ray logging data. Three lithologies were found based on gamma-ray cutoff values, and they are in agreement with changes in apparent electric conductivity. The FDEM survey supplied additional spatial information on the subsurface geology, highlighting areas of fluid flow and fracturing, which were found to be aligned with the trend of small strike-slip faults and earthquake clusters from previous studies. The FDEM method is a reliable way of discerning shallow subsurface geology, even in harsh conditions where other geophysical methods are limited. Full article

The crucial parameters influencing drilling operations, reservoir production behavior, and well completion are lithology and reservoir rock. This study identified optimal reservoir rocks and facies in 280 core samples from a drilled well in the Asmari reservoir of the Mansouri field in SW Iran to determine the number of hydraulic flow units. Reservoir samples were prepared, and their porosity and permeability were determined by measuring devices. The flow zone index (FZI) was calculated for each sample using MATLAB software; then, a histogram analysis was performed on the logarithmic data of the FZI, and the number of hydraulic flow units was determined based on the obtained normal distributions. Electrical facies were determined based on artificial neural network (ANN) and multi-resolution graph-based clustering (MRGC) approaches. Five electrical facies with dissimilar reservoir conditions and lithological compositions were ultimately specified. Based on described lithofacies, shale and sandstone in zones three and five demonstrated elevated reservoir quality. This study aimed to determine the Asmari reservoir’s porous medium’s flowing fluid according to the C-mean fuzzy logic method. Furthermore, the third and fourth flow units in the Asmari Formation have the best flow units with high reservoir quality and permeability due to determining the siliceous–clastic facies of the rock units and log data. Outcomes could be corresponded to the flow unit determination in further nearby wellbores without cores. Full article