After 20 years of shale gas exploration and development, China has become the third country that achieves commercial shale gas production, following the United States and Canada. However, earlier exploration and development of the layer were limited to the Silurian Longmaxi Formation. With improved theoretical understanding of shale gas exploration, China has made exploration breakthroughs in Permian and Cambrian shales in recent years, demonstrating the great potential of shale gas in Sichuan Basin. Based on a review of the exploration history of shale gas in the two major marine phases—Silurian Longmaxi Formation and Cambrian Qiongzhusi Formation, this study summarizes the three phases of shale gas exploration: research and exploration (2000-2011), discovery and production (2011-2022), and multi-layer breakthroughs (2022-present). This study thoroughly analyzes the process of two theoretical innovations and paradigm shifts in the exploration and research of marine shale gas in Sichuan Basin. (1) After comparing the formation conditions and exploration and development characteristics of shale gas between China and the United States, Chinese researchers abandoned the simple replication of North American experience, and highlighted the critical role of preservation conditions based on the evolution characteristics of China’s multi-phase tectonics. This completed the first paradigm shift and achieved major exploration breakthroughs in the Silurian Longmaxi Formation. (2) Research on the characteristics of low-organic matter and inorganic pores was enhanced. Traditional theories of enrichment and reservoir formation were developed and improved, and a “migration+in situ” reservoir formation mode was established. This completed the second paradigm shift and led to exploration breakthroughs in Cambrian Qiongzhusi Formation. Recent research breakthroughs in low-organic shale, inorganic pores, and other aspects have expanded both the scope and depth of shale gas exploration, leading to a multi-layer exploration pattern of marine shale gas. It demonstrates broad exploration prospects and strategic value for national energy security. Based on a review of the exploration history and paradigm shifts from the Silurian to the Cambrian periods, as well as an analysis of the implications from major breakthroughs, this study reveals an exploration path of shale gas with Chinese characteristics, providing important references for future exploration and development of multi-layer and multi-field shale gas.

In line with the strategy of “finding oil layers beneath oil layers”, exploration and development in the Jiangsu Oilfield have progressively extended into deeper formations. Deep, tight, and ultra-low permeability reservoirs in northern Jiangsu have become key targets for reserve enhancement and production expansion. However, due to complex structural settings, sedimentary conditions, and natural fractures, the effective utilization of these reservoirs remains highly challenging. This study conducted research on the effective utilization of deep tight reserves in northern Jiangsu. For “sweet spot” characterization, an integrated geological-seismic approach was developed by synthesizing multidisciplinary data from geology, geophysics, reservoir engineering, engineering, and economics. A multi-parameter comprehensive characterization and evaluation methodology was established for tight sandstone reservoirs, accurate delineation of tight reservoirs and effectively guiding reservoir classification and “sweet spot” selection. For volume fracturing, engineering techniques were implemented such as increasing fracture-controlled volume, using temporary plugging and diversion to enhance fracture complexity, and employing combined proppant injection to increase fracture filling volume. These techniques were further optimized based on the characteristics of specific reservoir blocks, resulting in a preliminary volume fracturing technology tailored to the deep tight reservoirs of Jiangsu. To optimize development strategies, well types, production methods, fracturing parameters, and well pattern designs were systematically refined to ensure stable production. For more efficient and cost-effective drilling, improvements in drilling techniques and well placement schemes were introduced, achieving accelerated drilling speed and cost reductions. The study provided effective guidance for field implementation. A total of 7 conventional wells and 1 horizontal well were drilled in block X17, block F125, and block Y48. The average daily oil production per conventional well exceeded 6 tonnes, while the horizontal well maintained a stable daily output of over 10 tonnes. The results demonstrate the effective utilization of deep tight reserves in northern Jiangsu. The research methodology and field practices can provide technical references for the development of other tight oil resources.

The deep oil and gas exploration area serves as a crucial position for resource development in Subei Basin. However, challenges including generally poor physical properties of deep reservoirs, insufficient understanding of oil and gas enrichment mechanisms, and ineffective reservoir prediction to meet exploration demands have constrained the expansion of deep oil and gas exploration. To understand the enrichment mechanisms of deep oil and gas, develop key exploration technologies, and indicate future research directions, this paper focuses on the deep layers of Gaoyou and Jinhu Sags, which are rich in oil and gas resources. Firstly, by analyzing the exploration development trends and oil and gas resource potential in oil and gas enrichment Sags such as Gaoyou and Jinhu, along with physical characteristics and main controlling factors of deep reservoirs, it was believed that the deep oil and gas reservoirs in Gaoyou and Jinhu Sags were mainly characterized by low to extra-low porosity and permeability. Secondary pore was the main pore type, while primary pore occurred locally. Overall, as burial depth increased, the proportion of primary pores gradually decreased. Subsequently, based on the relationship between pores and pore throats, deep reservoirs were classified into four types of pore-throat structures: large intergranular pores and wide lamellar throats; small intergranular pores and narrow lamellar throats; intragranular dissolution pores and narrow lamellar throats; and micropores and tubular throats. The physical properties of deep reservoirs were generally poor, with locally developed favorable reservoirs. The factors influencing the physical properties of deep reservoirs were complex. Analysis suggests that sedimentary factors, diagenesis, tectonic activity, oil and gas injection, and abnormal formation pressures all significantly affected the physical properties of deep reservoirs, although the controlling factors and their effects varied across different regions. Secondly, investigations were conducted on the occurrence conditions, main controlling factors, and accumulation models of deep oil and gas. The occurrence conditions of oil and gass suggested that oil and gas migration and accumulation were controlled by the pressure systems and physical properties between source rocks and reservoirs, as well as between different reservoirs. Oil and gas accumulation occurred when migration forces overcame migration resistance. Microscopically, pore-throat structure determined the fluid occurrence state and permeability. Larger throat radii, lower pore-throat radius ratios, and smaller tortuosities led to enhanced pore-throat connectivity and higher reservoir permeability. Macroscopically, pressure increase with oil and gas generation provided the driving force for oil and gas migration and accumulation. The magnitude and direction of source-reservoir pressure difference decided the favorable trends for oil and gas migration and accumulation, controlling their favorable areas. In terms of the main controlling factors for oil and gas enrichment, it was believed that oil and gas accumulation and enrichment in deep reservoirs were jointly controlled by source-reservoir configuration, pressure increase with oil and gas generation, fault-sandstone carrier system, and reservoir physical properties. Three accumulation models for deep oil and gas enrichment were established: stepped accumulation driven by combined abnormal overpressure and buoyancy, accumulation via fault-sandstone carrier system driven by abnormal overpressure, and accumulation of early-stage oil and gas injection followed by later-stage compaction. These models elucidated the enrichment mechanisms of deep oil and gass. Based on the above, to address exploration challenges such as unclear reservoir distribution, undefined enrichment zones, and low identification accuracy of effective reservoirs, three breakthrough technologies were developed: (1) A facies-controlled index method for deep reservoir classification was developed based on “facies-controlled index, porosity-permeability characteristics, pore structures, and diagenetic facies”. Reservoir classification criteria were formulated, categorizing reservoirs into four grades. Effective reservoirs in deep layers were mainly grades Ⅱ and Ⅲ. The distribution of effective reservoirs in the deep layers was evaluated across key stratigraphic intervals, revealing the graded distribution of reservoirs in deep zones of the first and third member of Funing Formation, the third submember in the first member of Dainan Formation in Gaoyou Sag, and the second member of Funing Formation in Jinhu Sag. The favorable areas of effective reservoirs in the deep layers of each stratigraphic system in each Sag were finally determined. (2) Through the analysis of deep oil and gas enrichment mechanisms, and according to the dynamic conditions of oil and gas injection, models for calculating reservoir potential energy, fluid potential, and source-reservoir pressure differences were established. Subsequently, a model for calculating the reservoir injection potential energy index were established based on the above models. Finally, the obtained reservoir injection potential energy index was used to assess the probability of oil and gas accumulation, providing technical support for the selection of favorable oil and gas accumulation zones in deep layers. (3) Subaqueous distributary channels and beach-bar sand bodies were effective reservoirs for deep oil and gass. To address the challenge of effective reservoir prediction in thin sandstone-mudstone interbeds within favorable oil and gas accumulation zones in selected deep layers, an integrated technical suite for effective reservoir prediction was developed. This technique, tailored to different sand body types such as channels and beach bars, integrated pre-stack and post-stack multi-attribute analysis. It leveraged geological, petrophysical, seismic, statistical, and other disciplinary theories to provide a comprehensive approach to reservoir prediction. Based on the distinction between sandstone and mudstone, this suite included six techniques for reservoir prediction: effective reservoir modeling based on petrophysical analysis, post-stack multi-parameter inversion constraint method, pre-stack and post-stack joint inversion method, seismic attribute threshold analysis method, seismic multi-attribute neural network prediction method, and SP curve reconstruction for acoustic curve. These techniques collectively improved the prediction accuracy of effective reservoirs in deep layers. These research findings provide theoretical guidance and technical support for the expansion of deep oil and gas exploration. Significant exploration progress has been made in deep layers such as slope zones, fault zones, and deep sag zones, enabling the expansion of deep oil and gas exploration. In the future, the research directions for addressing challenges in deep oil and gas exploration are clarified, which are continuing to consolidate and expand deep exploration to support the increase in oilfield reserves and production.

With the increasing difficulty in oil and gas development and insufficient replacement of resources, traditional development of oil and gas reservoirs faces multiple challenges, requiring intelligent analysis solutions for enhanced development efficiency. This study focused on the demand and application scenarios for efficient development in conventional oil and gas reservoirs and shale gas reservoirs and proposed an innovative intelligent technology for oil and gas development based on multi-model approaches. It enabled decision-making of production and efficiency allocation, comprehensive abnormal situation awareness, and intelligent balanced injection-production optimization. This effectively promoted the intelligent exploitation of reservoir resources, providing technical support for balanced injection-production and efficient development in multilayered complex waterflood reservoirs. A pressure prediction and capacity factor analysis technology for shale gas reservoirs was developed, along with an abnormality warning mechanism to push alerts about abnormal factors and their root causes. This achieved a transition from post-event analysis to early warning and pre-emptive intervention, thereby supporting the efficient development of gas reservoirs. Breakthroughs were made in establishing a multi-modal self-diagnosis and evaluation technology for oil wells, achieving intelligent diagnosis of pumping well operating conditions, self-diagnosis and intelligent evaluation of electric pumping well conditions, and real-time calculation of dynamic fluid levels in oil wells. These supported measure formulation, enabled refined management of oil wells, and made injection-production adjustments more timely and accurate, effectively improving the production time ratio of oil wells. The integrated technology application supported developing a new operational model featuring “comprehensive awareness, integrated coordination, early warning, and analysis and optimization” for the dynamic management and control of oil and gas reservoirs. These research technologies have been widely promoted among upstream companies of Sinopec, with practical application focusing on multi-model oil and gas development technologies. This study offers new ideas and technical approaches to address key challenges in the efficient development of oil and gas reservoirs, driving the digital and intelligent transformation of the oil and gas sector and facilitating the efficient and high-quality development of oil and gas fields.

The Tarim Basin serves as the major area for deep and ultra-deep oil and gas exploration and development. A significant breakthrough has recently been achieved in the exploration of ancient buried hill-type oil and gas reservoirs within the Cambrian System of the Paleozoic strata in well Tuotan 1, Kuqa Depression, Tarim Basin. Due to the ancient geological age and complex reservoir geology, systematic studies on oil and gas accumulation process and fluid evolution in this area remain insufficient. In this study, methods including biomarker analysis, petrological analysis, in-situ micro-area trace element and strontium isotope analysis, and fluid inclusions were used to determine the fluid origins of vein formation and the timing of multiple-phase of oil and gas charging in the dolomite reservoirs of the Xiaqiulitage Formation. The results revealed that the dolomite reservoirs in Xiaqiulitage Formation, well Tuotan 1 primarily developed two phases of calcite veins that filled fractures and dissolution pores. The first phase of calcite originated from deep, strontium-rich fluids, while the second phase of calcite veins derived from seawater. Two phases of oil-bearing fluid inclusions were predominantly developed within the second-phase calcite veins, comprising secondary blue-white fluorescent oil inclusions and secondary green fluorescent oil inclusions. The integration of fluid inclusion thermometry with single-well burial history reconstruction revealed that the first-phase blue-white fluorescent inclusions recorded oil and gas accumulation during the deposition of the Neogene Jidike Formation (23-20 Ma), while the second-phase green oil inclusions recorded oil and gas accumulation during the deposition of the Neogene Kuqa Formation (5-3 Ma). Oil-source correlation analysis indicated that the two phases of crude oil in the reservoirs of Xiaqiulitage Formation were derived from mixed contributions of lacustrine source rocks in the Triassic Huangsanjie Formation and Jurassic Qakmak Formation. The new findings from well Tuotan 1 in Kuqa Depression demonstrate that ancient strata in the foreland region of the Tarim Basin still retain favorable conditions for large-scale oil and gas accumulation, making buried hill-type oil and gas reservoirs a promising frontier for increasing reserves and production in Kuqa Depression.

The Sichuan Basin has rich resources of tight sandstone gas. Currently, research on the pore evolution of ultra-deep, ultra-tight sandstone reservoirs in the eastern slope of the western Sichuan Depression is relatively scarce. Using core observation, cast thin section identification, scanning electron microscopy, carbon-oxygen isotope analysis, and homogenization temperature of fluid inclusion, combined with burial history and thermal history, the coupling characteristics of pore evolution and oil and gas charge in the ultra-deep, ultra-tight sandstone reservoirs in the second member of Xujiahe Formation (hereinafter referred to as Xu 2 member) on the eastern slope of the western Sichuan Depression were clarified. The Xu 2 member reservoir is mainly composed of lithic sandstone and lithic quartz sandstone, with authigenic quartz and carbonates as the primary cementing materials. The storage space is dominated by intragranular pores. The densification period of the reservoir varies among different submembers. The upper submember is less resistant to compaction due to the presence of higher plastic materials like mudstone clasts, and it became compacted during the Middle to Late Jurassic. Subsequently, under continuous deep burial and the dual destructive effects of pressure dissolution and quartz, the middle and lower submembers became compacted during the Late Jurassic. At the end of the Cretaceous, tectonic uplift led to the formation of fractures that promoted the dissolution of the middle and lower submembers, increasing the reservoir porosity to around 5%, with a more significant increase in permeability. There were two main periods of oil and gas charge. The upper submember had a poorer coupling relationship, with early densification that was unfavorable for oil and gas charge and natural gas accumulation. In contrast, the main oil and gas charge period for the middle and lower submembers occurred prior to the densification of the reservoir, which was favorable for natural gas accumulation and reservoir formation. The Xu 2 member on the eastern slope of the western Sichuan Depression exhibits three “sweet spot” reservoir development modes: ancient trap+source fracture superposition, ancient trap+internal source rock+late fracture superposition, and ancient trap+source fracture+late fracture superposition. The study provides examples and theoretical guidance for understanding the evolution-oil and gas charge coupling characteristics of deeply buried ultra-tight sandstone reservoirs.

The southeastern Sichuan region is characterized by complex tectonic structures. The shale gas reservoir from the first member of the upper Ordovician Wufeng Formation to the Lower Silurian Longmaxi Formation is buried at considerable depths, which significantly affects the rock mechanical properties. However, systematic studies remain limited. This study focuses on the deep shale gas reservoir in the Lintanchang area of southeastern Sichuan. A series of mechanical experiments, including triaxial compressive tests, acoustic wave velocity measurements, tensile strength tests, and fracture toughness tests, were carried out. Based on the results of these multi-mechanical experiments, the rock mechanical properties of shale samples were analyzed, and a vertical mechanical property profile for a single well was established. With increasing temperature and pressure, the residual stress after fracture, Young’s modulus, and Poisson’s ratio of the deep shale samples showed an upward trend. The post-peak stress-strain curves exhibited more pronounced fluctuations. Acoustic wave velocities at the plunging end of the Lintanchang anticline were lower than those at the flanks. Young’s modulus and Poisson’s ratio values, corrected using a dynamic-static linear transformation, exhibited improved accuracy. The maximum load borne by the deep shale samples was less than 10 kN. Type Ⅰ and Type Ⅱ fractures displayed notable differences in propagation characteristics, and the degree of fracture penetration was greatly affected by sampling direction. The vertical mechanical profile of well T4 revealed that the bottom section of the first member of the Wufeng-Longmaxi Formation has higher Young’s modulus, lower Poisson’s ratio, and stronger brittleness, while the compressive and tensile strengths, as well as the fracture toughness index, remain relatively low. These mechanical properties show a weak compressive-tensile state, providing favorable conditions for reservoir stimulation. Thus, this interval represents an optimal target for future exploration and development.

The deep Permian Maokou Formation in the Penglai area, central Sichuan, is located in the Sichuan Basin. It is a sedimentary formation primarily composed of carbonate rocks, with dolomite being the main lithology. With good reservoir properties, it represents an important oil and gas reservoir in the Sichuan Basin. However, due to characteristics such as deep burial, thin reservoirs, strong heterogeneity, minimal impedance contrast with surrounding rocks, and weak reflection signals, seismic prediction becomes challenging. Conventional frequency enhancement processing either fails to identify thin reservoirs or results in a large area of coherent seismic events, making seismic prediction of thin reservoirs in this region difficult. Therefore, the application of “high-fidelity and high-resolution” processing technology for identifying thin reservoirs in the Maokou Formation was investigated. In response to the adverse factors such as deep burial, weak signals, thin reservoirs, and small impedance contrast with surrounding rocks in the Maokou Formation, research on weak-signal processing techniques for deep carbonate formations was conducted. In addition, the “high-fidelity and high-resolution” processing technology involving the concept of “protecting low frequencies and enhancing high frequencies” throughout the processing workflow was proposed. Methods such as pre-stack fidelity denoising, high-frequency residual static correction, multiple-wave suppression, pre-stack time migration in the Offset Vector Tile (OVT) domain, anisotropic correction, and frequency enhancement based on compressed sensing were studied to highlight the weak reflection signals of the Permian dolomite reservoirs. The research results effectively identified favorable reservoirs in the Maokou Formation as discontinuous, medium-to-strong amplitude reflections, with a well-seismic calibration match rate of 100%, thereby achieving effective identification and precise characterization of heterogeneity of thin dolomite reservoirs in the Maokou Formation. Based on the new findings, the drilled well PY001-H1 successfully reached high-quality reservoirs. Therefore, the results demonstrate that the studied “high-fidelity and high-resolution” processing technology is beneficial for deep reservoir prediction by improving seismic data resolution, amplitude preservation, heterogeneity analysis, and weak signal recovery.

Key Technical Descriptions

1. Pre-stack Fidelity Denoising Technology

Fidelity processing aims to preserve both amplitude and phase integrity. The current approach primarily employs the “six-step method” for denoising in the F-X, F-K, and Tau-P domains, which involves classification and segmentation by time, frequency, domain, step, and region. The principle of fidelity ensures that the chosen modules protect effective signals while maintaining relative amplitude relationships, particularly preserving low-frequency signals and improving the signal-to-noise ratio of weak high-frequency signals.

The data in this area is primarily affected by impulsive noise, surface waves, and linear noise. While methods for suppressing impulsive and surface waves are well-established, this study used frequency-domain suppression and localized surface wave suppression to maintain the original data’s frequency range. Due to wide-azimuth acquisition, residual surface waves and linear noise often remain at non-vertical offsets. In these cases, cross-spread domain suppression was applied post-static correction. This method considers interference wave frequency, apparent velocity, and non-vertical offsets for effective suppression.

2. Multiple-Wave Suppression Technology

A combination of Radon transforms and curvelet transform achieved effective suppression of interlayer multiples. Specifically, high-precision Radon transform was used to obtain multiple models, enhancing signal identification during curvelet transform. The curvelet transform better differentiates energy by frequency, dip, and position. By controlling the strength of simulated multiples through thresholds and applying adaptive subtraction, this approach improves multiple-wave suppression and enhances data quality for low signal-to-noise ratio datasets.

3. Compressed Sensing Frequency-Expansion Technology

Compressed sensing is a novel signal sampling theory. The method used here employs a robust compressed sensing spectral inversion algorithm. It determines initial reflection coefficients using a thin-layer matching pursuit algorithm and then performs post-stack sparse inversion based on the L0-norm compressed sensing theory. The final reflection coefficient model is obtained by applying regularization. Subsequently, wavelet decomposition and high-frequency wavelet replacement are conducted to expand the high-frequency spectrum while maintaining amplitude and fidelity, significantly improving seismic data resolution.

Application Results

The test area spans 200 km², using an observation system with 24 lines, 7 sources, 270 receivers, and 180-fold coverage. The bin size is 20 × 20 meters, with a maximum offset of 6 332.46 meters and an aspect ratio of 0.62, representing typical high-density and wide-azimuth acquisition. The raw data exhibits high noise levels, low dominant frequencies in deep layers, and narrow frequency bandwidths. Interferences include surface waves, impulsive noise, interlayer multiples, and anisotropy effects. After applying “Double-High Processing,” multiple-wave interferences were eliminated, and the quality of gathers significantly improved. Well-to-seismic profiles achieved good alignment, yielding favorable results.

For example, well PY1, with a burial depth of 6 040 meters and a reservoir thickness of 7 meters, showed a weak reflective base on synthetic seismograms and seismic profiles, with consistent matching between synthetic records and seismic waveforms. Clear reservoir characteristics were identified. Following these advancements, a new development well was drilled to a depth of 6 103 meters. In the second member of the Maokou Formation, a dolomite reservoir was encountered with a slanted thickness of 23.1 meters, a vertical thickness of 8.5 meters, and an average porosity of 3.8%. This high-quality dolomite reservoir achieved excellent drilling results.