Search Results (33)

The Dengying Formation gas reservoir in the Penglai gas field, located in the central Sichuan Basin, exhibits substantial resource potential and promising development prospects. This reservoir is characterized by well-developed fractures and dissolution cavities, strong heterogeneity, complex gas–water relationships, and widespread edge–bottom water. During production, edge–bottom water is prone to channeling and intrusion through high-permeability pathways, which severely constrains well productivity and overall gas recovery. To address these challenges, this study takes a fractured-vuggy carbonate edge–bottom water gas reservoir as an example. By integrating large-scale physical simulation with cross-scale numerical simulation, a rational production allocation method suitable for strongly heterogeneous gas reservoirs has been developed. The research results indicate that: (1) Large-scale physical simulation experiments demonstrate that for fractured-vuggy bottom water gas reservoirs, implementing rate reduction and pressure control after water breakthrough can effectively suppress water invasion and coning, extend the stable production period, and increase the recovery factor by approximately 16%; (2) Based on the dynamic characteristics of water invasion, key similarity criteria including the Bond number, capillary number, gravity–viscous force ratio, and geometric–temporal similarity ratio were selected to establish a scientific parameter design method for cross-scale numerical simulation; (3) By considering factors such as reservoir type and aquifer energy, single-well mechanistic models were used to determine appropriate production rates for individual wells, enabling rapid optimization of production allocation plans. This provides crucial guidance for efficient gas well development and surface facility planning. Full article

Located in the north of Yunnan Province, China, the Wuding geothermal area is a typical medium- and low-temperature geothermal system with strong hydrothermal activity and development potential as a clean and renewable energy resource. This study systematically investigates the main controlling factors of the Wuding geothermal field through field investigation, hydrochemical analysis, and stable isotope analysis, and puts forward a genetic model of the geothermal field. The results show that the Wuding geothermal field is a medium- to low-temperature, conduction-dominated geothermal system, and its geothermal water is predominantly of the Ca–HCO₃ (calcium bicarbonate) type. The recharge area lies at an altitude above 2250 m, which is speculated to be within the mountainous area in the southwest of the study area. The underground hot water in the area is immature water. The source water circulates to the deep heat storage zone along faults, rises to the surface through heat convection, and is exposed as hot springs. Upon discharge, the geothermal water mixes with shallow cold water, with cold-water dilution accounting for up to 85% of the total volume. Using the silica thermometer, cation thermometer, and silicon enthalpy model, the maximum temperature of heat storage is estimated to be 91 °C, with the depth of geothermal water circulation reaching 2200 m. The thermal reservoir is composed of dolomites of the Upper Cambrian Erdaoshui Formation (∈3e) and Sinian Dengying Formation (Zbd). Its heat source is heat flow from the upper mantle and the decay of radioactive elements. Continuous heat flow to the thermal reservoir is maintained through the fold fracture zone and faults in the core of the Hongshanwan anticline. The proposed genetic model of the Wuding geothermal field provides a scientific basis for the sustainable redevelopment and utilization of this geothermal resource and is of significance for regional low-carbon energy use and socio-economic sustainable development. Full article

The Sinian (Ediacaran) Dengying Formation in the northeastern Sichuan Basin exhibits a significant exploration potential. Nevertheless, the great burial depth of carbonates in the Dengying Formation and the scarcity of drilling data have imposed constraints on in-depth investigations into the evolution of lithofacies paleogeography as well as the primary controlling mechanisms. Through integrated analysis of field outcrops, core and well logging data, the evolution of the lithofacies and paleogeography of the Dengying Formation in the northeastern Sichuan Basin was reconstructed by using 3D stratigraphic forward modeling. The study area is predominantly characterized by platform margin facies and restricted platform facies, comprising four subfacies including microbial (algal) mound, grain shoal, intershoal sea, and intraplatform depression. The microbial (algal) mound and grain shoal subfacies are primarily developed along the western and eastern platform margins, exhibiting a near north–south trend. Scattered mound–shoal complexes and intershoal sea occur within the platform, with localized intraplatform depression zone. During the depositional stage of the Dengying Formation, three primary paleogeomorphic units were developed including the platform margin topographic high zone, intraplatform gentle slope zone, and intraplatform depression zone. During the Deng-1 and Deng-3 periods, sea level rise increased accommodation space, leading to a gradual decline in carbonate productivity and limited development of the mound–shoal complexes. In contrast, during the Deng-2 and Deng-4 periods, sea level decreased, water depth decreased, and carbonate productivity was enhanced, resulting in extensive development of the mound–shoal complexes. The simulation results indicate that carbonate-producing ecosystems thrive when wind blows from 270° W (80% frequency) or 15° N (60% frequency); with an effective water depth of 10–20 m, the elevated carbonate productivity is conducive to the growth of biogenic calcification. Comprehensive analysis suggests that paleogeomorphology, eustatic fluctuations, and paleowind fields collectively control the distribution and evolution of the lithofacies in the Dengying Formation in the northeastern Sichuan Basin. Paleogeomorphology governs the types and distribution of sedimentary facies belts as well as the spatial arrangement of lithofacies. Eustasy determines the magnitude of mound–shoals and their lateral migration. Three-dimensional stratigraphic forward modeling offers a novel approach for reconstructing paleogeographic evolution of carbonate platforms and analyzing key controlling factors, while also enhancing our ability to predict the distribution patterns of mound–shoal complexes. Full article

The dolomite of the fourth member of Dengying Formation in Gaoshiti-Moxi area of central Sichuan Basin is rich in hydrocarbon resources. It has experienced superimposition-reformation of multistage karstification, and is the key target for studying deep ancient carbonate reservoirs. Exploration and development practices show that there are great differences in the development of karst reservoirs of the fourth member of Dengying Formation between the platform margin and intraplatform in Gaoshiti-Moxi area. However, the differences in the genetic mechanism of karst reservoirs between these two zones are unclear. Therefore, based on an integrated analysis of core, thin section, drilling, logging, and geochemical test data, this study clarifies the differences in karstification between the platform margin and intraplatform and conducts a comparative analysis of the controlling factors for the differences in karst reservoirs. Results show that the fourth member of Dengying Formation experienced superimposition-reformation of four types of paleokarstification, including eogenetic meteoric water karst, supergene karst, coastal mixed water karst, and burial karst. Large-scale dissolved fractures and caves are mainly controlled by meteoric water karstification, primarily developing three types of reservoir space: vug type, fracture-vug type, and cave type. Dolomite and quartz fillings are mainly formed in the medium-deep burial period. Four types of paleokarstification are developed in the platform margin, while the coastal mixed water karst is not developed in the intraplatform. Eogenetic meteoric water karst and supergene karst in the platform margin are stronger than those in the intraplatform, while burial karst shows no notable difference between the two zones. The thickness of soluble rock (mound-shoal complex), karst paleogeomorphology, and different types of paleokarstification are the main controlling factors for the difference in karst reservoirs between the platform margin and the intraplatform. Full article

Analysis of pyrobitumen in reservoirs can yield key information about hydrocarbon evolution, which may provide vital insights for deep- to ultra-deep hydrocarbon exploration in high- to over-mature petroliferous deep basins. The Ediacaran Dengying Formation in the Penglai area of the Sichuan Basin contains large-scale gas reservoirs, where pyrobitumen is extensively present. To understand the hydrocarbon accumulation and alteration processes in these reservoirs, in this study, we systematically investigated the characteristics of the reservoir pyrobitumen using detailed petrographic analysis and laser Raman spectroscopy. The results indicated that four types of reservoir pyrobitumen are present: pyrobitumen with isotropic (type I), mosaic (type II), fibrous (type III), and honeycomb (type IV) textures. Pyrobitumen in the dolomite reservoirs of the Deng 2 and Deng 4 members of the Dengying Formation often co-occurs with hydrothermal minerals, including saddle dolomite, quartz, and fluorite. The equivalent vitrinite reflectance (Rmc Ro%) calculated indicated that the pyrobitumen is over-mature, with Rmc Ro% values ranging from 3.46% to 3.89%. In addition, significant differences were observed in the Raman parameters between the four types of pyrobitumen: type IV shows the greatest degree of structural ordering, while type II exhibits the highest level of disordering, with types I and III exhibiting intermediate structural ordering. Finally, the spatial distribution of the four types of pyrobitumen indicated that hydrothermal pulses driven by the Emeishan Large Igneous Province toward the end of the Permian Period may be primarily responsible for the extensive cracking of paleo-oil pools, causing the development of types II–IV pyrobitumen and gas generation. Full article

Siliceous dolomite is developed at the top of the fourth member of Dengying Formation in Penglai gas field, Sichuan Province, and can be used as a good cap rock to seal oil and gas. In this study, based on post-stack seismic data mining and optimization, sensitive logging curve analysis is found to be the optimal prediction method, subdividing small layers to finely characterize thin-layer siliceous dolomite. It is found that the navigation-pyramid two-stage classification seismic data and the waveform indication simulation method based on RXO parameters have a good recognition effect on the characterization of thin-layer siliceous dolomite. Studies have shown that faults can provide ascending channels for deep silicon-rich hydrothermal fluids, resulting in the development of siliceous dolomite mostly near the fault zone. The siliceous dolomite in the upper sub-member of the fourth member of Dengying Formation in Penglai area mainly develops two sets of siliceous dolomite in the vertical direction, and the lower siliceous rock develops on a larger scale. In the lateral direction, it is mainly distributed in the JT1-PS7-P8-PS9 well area in the north, in a continuous sheet shape. In the south, the development scale of siliceous dolomite is small and distributed in the shape of a strip. Full article

The gas reservoir of the Sinian Dengying Formation (Member 4) in Sichuan Basin exhibits extensive development of inter-clast dissolution pores and vugs within its carbonate reservoirs, characterized by low porosity (average 3.21%) and low permeability (average 2.19 mD). With the progressive development of the Moxi (MX)structure, the existing stimulation techniques require further optimization based on the specific geological characteristics of these reservoirs. Through large-scale true tri-axial physical simulation experiments, this study systematically evaluated the performance of three principal acid systems in reservoir stimulation: (1) Self-generating acid systems, which enhance etching through the thermal decomposition of ester precursors to provide sustained reactive capabilities. (2) Gelled acid systems, characterized by high viscosity and effectiveness in reducing breakdown pressure (18~35% lower than conventional systems), are ideal for generating complex fracture networks. (3) Diverting acid systems, designed to improve fracture branching density by managing fluid flow heterogeneity. This study emphasizes hybrid acid combinations, particularly self-generating acid prepad coupled with gelled acid systems, to leverage their synergistic advantages. Field trials implementing these optimized systems revealed that conventional guar-based fracturing fluids demonstrated 40% higher breakdown pressures compared to acid systems, rendering hydraulic fracturing unsuitable for MX reservoirs. Comparative analysis confirmed gelled acid’s superiority over diverting acid in tensile strength reduction and fracture network complexity. Field implementations using reservoir-quality-adaptive strategies—gelled acid fracturing for main reservoir sections and integrated self-generating acid prepad + gelled acid systems for marginal zones—demonstrated the technical superiority of the hybrid system under MX reservoir conditions. This optimized protocol enhanced fracture length by 28% and stimulated reservoir volume by 36%, achieving a 36% single-well production increase. The technical framework provides an engineered solution for productivity enhancement in deep carbonate gas reservoirs within the G-M structural domain, with particular efficacy for reservoirs featuring dual low-porosity and low-permeability characteristics. Full article

Tubular fossils are a unique metazoan group emerging in the late Ediacaran Period and demonstrating early skeletogenesis and an increase in the diversity of early biocommunities. Among the known records, Sinotubulites is widely distributed and distinct in morphology and ultrastructure, holding important evolutionary and stratigraphic significance comparable to the well-known Cloudina. However, its biological affinity remains unclear until now. Among various reasons, taphonomic bias is one of the major factors responsible for this, as it not only altered the primary morphology but also modified the ultrastructure and composition of the fossil. Thus, a further study on its taphonomic process would help to decode the biological affinity of Sinotubulites. For this purpose, we conducted a taphonomic study on Sinotubulites from the top of the Shibantan Member of the Dengying Formation at the Zhongling section in the Yangtze Gorges area (Hubei Province, China). We applied electron backscatter diffraction (EBSD) and cathodoluminescence (CL) to reveal its mineralogical features. EBSD and CL analyses demonstrate that both the fossils and matrix are composed of unoriented calcite, and the matrix shows slight dolomitization with sporadic dolomite grains. The calcite crystals within the Sinotubulites tubes are significantly larger than those in the matrix, indicating that the tubular structure provided sufficient space for crystal growth. The absence of lamellar structures in the tubular walls further suggests that the original biogenic material may have been dissolved during diagenetic calcification. The absence of dolomitization in the fossils indicates that this process may have been inhibited by either their large calcite crystals or the enclosed space confined by the outer shell. The identical non-luminescent features of the matrix and fossils suggest that their calcification likely occurred during the same stage. This study demonstrates that taphonomic biases must be accounted for when analyzing the original structure and composition. Additionally, this research documents the occurrence of Sinotubulites in the Shibantan Member, representing its lowest stratigraphic horizon in the Yangtze Block. Full article

The Emeishan Large Igneous Province (ELIP) is one of the largest igneous provinces, containing some of the world’s richest mineral resources. It mainly comprises magmatic Fe-Ti-V deposits and Cu-Ni sulfide deposits, with minor subvolcanic-type Fe deposits related to mafic–ultramafic rocks. The evaporite layer is involved in the metallogenic system, yet its contribution has not been examined in detail. In this study, an integrated geological study, single-mineral S and O isotopic analysis, and in situ S isotope analysis were carried out on pyrite and magnetite from the Kuangshanliangzi (KSLZ) subvolcanic-type Fe deposit to examine the role of evaporite layers in Fe mineralization. The O isotopic values of magnetite and the S isotopic values of pyrite were abnormally high in the KSLZ deposit. This indicates that the ore-forming system of the KSLZ deposit is contaminated by ¹⁸O- and ³⁴S-enriched evaporite layers, inferred from the Dengying Formation, which significantly increase the oxygen fugacity, sulfur fugacity, and water content of the metallogenic system via the basic–ultrabasic magma-upwelling process, thus promoting the formation of Fe ores. When the SO₄²⁻ (from evaporite layers) oxidizes Fe²⁺ to Fe³⁺, the SO₄²⁻ is reduced to S²⁻, and the ore-forming system can be changed from unsaturated sulfide to supersaturated sulfide, which also benefits the Cu-Ni sulfide deposit formation. Full article

The dispersed elements Ga, Ge, and In are crucial strategic mineral resources often enriched in Pb-Zn deposits. The Chipu Pb-Zn deposit, located on the western edge of the Yangtze Block, lies to the north of the Sichuan-Yunnan-Guizhou (SYG) Pb-Zn metallogenic province with large amounts of Emeishan basalt. Based on trace element and in situ sulfur isotope analyses by (LA)-ICP-MS, sphalerite is the main carrier mineral for Ga (17~420 ppm), Ge (3.87~444 ppm), and In (31~720 ppm). Ga or Ge correlate significantly with Cu, while In substitutes for Zn in sphalerite alongside Fe. Key substitution reactions include Ga³⁺ + Cu⁺ ↔ 2Zn²⁺, Ge⁴⁺ + 2Cu⁺ ↔ 3Zn²⁺, and 2In³⁺ + Fe²⁺ ↔ 4Zn²⁺. Sphalerite crystallized at medium to low temperatures (114–195 °C). Sulfide δ³⁴S values (+3.48 to +24.74‰) suggest sulfur mainly originated from Dengying Formation marine sulfates via thermochemical sulfate reduction (TSR). Metal-bearing fluid release at 30 Ma post-Emeishan mantle plume activity (261–257 Ma) coincides with the Chipu deposit’s mineralization period (230–200 Ma), suggesting the Chipu deposit is associated with Emeishan plume activity. The magmatic activity drove basinal brine circulation, extracting In from intermediate-felsic igneous rocks and metamorphic basement. Elevated temperatures promoted the coupling of Fe and In into sphalerite, causing anomalous In enrichment. 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 development of cracks and solution cavities in carbonate reservoirs can notably reduce the rock’s mechanical properties, leading to a severe wellbore collapse problem during drilling operations. To clarify the influence of the characteristics of cracks and solution cavities on the wellbore stability in the Dengying Formation carbonate reservoir in the Gaoshiti–Moxi area of Sichuan, the mechanical properties of carbonate rock were analyzed. Then, the influences of the attitude and width of cracks, the size and quantity of solution cavities, and their connectivity on wellbore stability were studied using FLAC3D 6.00 numerical simulation software. Our results show the following: (1) The cracks and solution cavities in the Dengying Formation carbonate rock cause significant differences in the rock’s mechanical properties. (2) The equivalent drilling fluid density of collapse pressure (ρ_c) considering the effects of cracks and solution cavities is 6.4% higher than without these effects, which is in good accordance with engineering practice. Additionally, cracks play a more significant role than solution cavities in affecting the wellbore stability. (3) When the orientation of a crack is closer to the direction of maximum horizontal stress, and the dip angle and width of the crack increase, the stress and deformation at the intersection of the crack and wellbore gradually increase, and correspondingly, ρ_c also increases. (4) The stress and displacement of various points around the solution cavities gradually increase with the increases in diameter and quantity of solution cavities, and ρ_c also increases. (5) Compared with the situation where cracks and solution cavities are not interconnected, the stress disturbance area around the wellbore is larger, and ρ_c is greater when cracks and solution cavities are interconnected. Full article

As an important target for deep to ultra-deep carbonate oil and gas exploration, Fractured-Vuggy dolomite reservoirs have strong heterogeneity. Accurate characterization of reservoir facies is crucial for their exploration and exploitation. Three methods, including the unsupervised intelligent clustering method of improved Fuzzy C-means clustering Algorithm Based on Density Sensitive Distance and Fuzzy Partrition (FCM-DSDFP), the fusion method of Principal Components Analysis (PCA) dimensionality reduction and noise reduction, and the principle of clustering feature analysis are applied to identify reservoir facies based on logging data. Based on the PCA method, the logging response characteristics of the reservoir facies are excavated, and the fusion characterization data of dimensionality reduction and noise reduction are extracted. The FCM-DSDFP unsupervised intelligent clustering method, a model that approximates the subsurface conditions is established, and the reliability of the model is tested according to the elbow rule and silhouette coefficient. Combining drilling core observation, Fractured-Vuggy type, partially cemented Fractured-Vuggy type, Pore-Vuggy type, Pore Type I, Pore Type II, Tight Type I, and Tight Type II are divided in the Dengying Formation 4th Member. Fractured-Vuggy type, partially cemented Fractured-Vuggy type, Pore-Vuggy Type I, Pore-Vuggy Type II, Pore Type I, Pore Type II, and Tight Type are divided in the Dengying Formation 2nd Member, respectively. Two methods were applied to verify the reservoir facies identification results based on intelligent algorithms. The first method is to compare the identification results with the reservoir facies types identified by core observations (Well PT103 and PS13). The second method is to verify the recognition results of intelligent algorithms by utilizing the relationship between reservoir facies types and bitumen. The test results show that the accuracy of the reservoir level identification is higher than 0.9, and the applicability is better than the commonly used algorithms such as FCM and K-means. Full article

The Rongchang–Dazu region in western Chongqing (eastern Sichuan Basin, China), known for its seismic activity, is a promising area for deep geothermal resource development; however, practical development is limited. Key geological understandings, such as heat flux, geothermal gradients, the nature of heat sources, thermal reservoir rock characteristics, and the classification of geothermal resources, remain in need of further study. In this work, the targeted area is surrounded by Sinian–Cambrian carbonate gas fields. An analysis of the deep geothermal prospects was conducted using exploration and development data from the Gaoshiti–Moxi gas fields within the Longwangmiao and Dengying Formations. The results indicate that the Rongchang–Dazu area has relatively high heat flow values and geothermal gradients within the Sichuan Basin, correlating with fault structure and seismic activity. Gas test data confirm that the Longwangmiao Formation in the study area reaches depths of 4000 to 4500 metres and exhibits anomalous pressures and temperatures exceeding 140 °C. Meanwhile, the Dengying Formation of the Sinian system lies at depths of 5000 to 5500 metres, with normal pressure, minimal water production, and temperatures exceeding 150 °C, characterising it as a dry-hot rock resource. Adjacent to western Chongqing, the Gaoshiti area within the Longwangmiao Formation, with an estimated flow rate of 100 kg/s, shows that the dynamic investment payback period is significantly shorter than the estimated 30-year life of a geothermal power plant, indicating strong economic viability. Deep geothermal resource development aids in conserving gas resources and enhancing the energy mix in western Chongqing. Future research should prioritise understanding the links between basement faults, seismic activity, and heat flow dynamics. Full article

Deep carbonate rocks are characterized by strong heterogeneity and fracture and cavity development, which have important influence on the storage and seepage capacity of reservoirs. To comprehensively characterize the developmental characteristics of the reservoir body in the intra–platform reservoir of the fourth member of the Dengying Formation in the Anyue gas field, this study employed a multiscale pore–throat structure characterization method that combines physical property analysis, core surface observation, cast thin section observation, a nuclear magnetic resonance (NMR) test, and CT scanning analysis. The results reveal that the primary storage spaces in the intra–platform reservoirs consist of inter–crystalline pores and small cavities (<2 mm), with thick throats and fractures serving as the primary flow channels. The rock density is lower in areas where solution fractures and cavities are developed, and the fractures and cavities are generally distributed in clusters. Notably, the intra–platform reservoir of the fourth member of the Dengying Formation is characterized by low asphaltene content. The presence of fractures in fracture–cavity type cores can reduce seepage resistance in the near–fracture area and enhance the drainage efficiency of small pores, as observed in the NMR test combined with centrifugation. In the centrifugal experiments, the increase in centrifugal force had the most significant impact on drainage efficiency, with the highest efficiency being 25.82% for cavity–type cores and the lowest being 6.39% for pore–type cores. Furthermore, by integrating the results of cast thin section and NMR test, the cavity–type reservoirs were further classified into two categories: dissolved cavity storage type and dissolved pore storage type. This study clarifies the storage and seepage characteristics of dissolved–pore storage reservoirs, which are challenging to develop but have high development potential. With reasonable surface operation measures, these reservoirs can provide important support for stable production in the middle and late stages of intra–platform reservoir development. Full article