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Based on an elaboration of the resource potential and annual production of tight sandstone gas and shale gas in the United States and China, this paper reviews the researches on the distribution of tight sandstone gas and shale gas reservoirs, and analyzes the distribution characteristics and genetic types of tight sandstone gas reservoirs. In the United States, the proportion of tight sandstone gas in the total gas production declined from 20%-35% in 2008 to about 8% in 2023, and the shale gas production was 8 310×108 m3 in 2023, about 80% of the total gas production, in contrast to the range of 5%-17% during 2000-2008. In China, the proportion of tight sandstone gas in the total gas production increased from 16% in 2010 to 28% or higher in 2023. China began to produce shale gas in 2012, with the production reaching 250×108 m3 in 2023, about 11% of the total gas production of the country. The distribution of shale gas reservoirs is continuous. According to the fault presence, fault displacement and gas layer thickness, the continuous shale gas reservoirs can be divided into two types: continuity and intermittency. Most previous studies believed that both tight sandstone gas reservoirs and shale gas reservoirs are continuous, but this paper holds that the distribution of tight sandstone gas reservoirs is not continuous. According to the trap types, tight sandstone gas reservoirs can be divided into lithologic, anticlinal, and synclinal reservoirs. The tight sandstone gas is coal-derived in typical basins in China and Egypt, but oil-type gas in typical basins in the United States and Oman.
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This paper expounds the basic principles and structures of the whole petroleum system to reveal the pattern of conventional oil/gas - tight oil/gas - shale oil/gas sequential accumulation and the hydrocarbon accumulation models and mechanisms of the whole petroleum system. It delineates the geological model, flow model, and production mechanism of shale and tight reservoirs, and proposes future research orientations. The main structure of the whole petroleum system includes three fluid dynamic fields, three types of oil and gas reservoirs/resources, and two types of reservoir-forming processes. Conventional oil/gas, tight oil/gas, and shale oil/gas are orderly in generation time and spatial distribution, and sequentially rational in genetic mechanism, showing the pattern of sequential accumulation. The whole petroleum system involves two categories of hydrocarbon accumulation models: hydrocarbon accumulation in the detrital basin and hydrocarbon accumulation in the carbonate basin/formation. The accumulation of unconventional oil/gas is self-containment, which is microscopically driven by the intermolecular force (van der Waals force). The unconventional oil/gas production has proved that the geological model, flow model, and production mechanism of shale and tight reservoirs represent a new and complex field that needs further study. Shale oil/gas must be the most important resource replacement for oil and gas resources of China. Future research efforts include: (1) the characteristics of the whole petroleum system in carbonate basins and the source-reservoir coupling patterns in the evolution of composite basins; (2) flow mechanisms in migration, accumulation, and production of shale oil/gas and tight oil/gas; (3) geological characteristics and enrichment of deep and ultra-deep shale oil/gas, tight oil/gas and coalbed methane; (4) resource evaluation and new generation of basin simulation technology of the whole petroleum system; (5) research on earth system - earth organic rock and fossil fuel system - whole petroleum system.
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Based on the new data of drilling, seismic, logging, test and experiments, the key scientific problems in reservoir formation, hydrocarbon accumulation and efficient oil and gas development methods of deep and ultra-deep marine carbonate strata in the central and western superimposed basin in China have been continuously studied. (1) The fault-controlled carbonate reservoir and the ancient dolomite reservoir are two important types of reservoirs in the deep and ultra-deep marine carbonates. According to the formation origin, the large-scale fault-controlled reservoir can be further divided into three types: fracture-cavity reservoir formed by tectonic rupture, fault and fluid-controlled reservoir, and shoal and mound reservoir modified by fault and fluid. The Sinian microbial dolomites are developed in the aragonite-dolomite sea. The predominant mound-shoal facies, early dolomitization and dissolution, acidic fluid environment, anhydrite capping and overpressure are the key factors for the formation and preservation of high-quality dolomite reservoirs. (2) The organic-rich shale of the marine carbonate strata in the superimposed basins of central and western China are mainly developed in the sedimentary environments of deep-water shelf of passive continental margin and carbonate ramp. The tectonic-thermal system is the important factor controlling the hydrocarbon phase in deep and ultra-deep reservoirs, and the reformed dynamic field controls oil and gas accumulation and distribution in deep and ultra-deep marine carbonates. (3) During the development of high-sulfur gas fields such as Puguang, sulfur precipitation blocks the wellbore. The application of sulfur solvent combined with coiled tubing has a significant effect on removing sulfur blockage. The integrated technology of dual-medium modeling and numerical simulation based on sedimentary simulation can accurately characterize the spatial distribution and changes of the water invasion front. Afterward, water control strategies for the entire life cycle of gas wells are proposed, including flow rate management, water drainage and plugging. (4) In the development of ultra-deep fault-controlled fractured-cavity reservoirs, well production declines rapidly due to the permeability reduction, which is a consequence of reservoir stress-sensitivity. The rapid phase change in condensate gas reservoir and pressure decline significantly affect the recovery of condensate oil. Innovative development methods such as gravity drive through water and natural gas injection, and natural gas drive through top injection and bottom production for ultra-deep fault-controlled condensate gas reservoirs are proposed. By adopting the hierarchical geological modeling and the fluid-solid-thermal coupled numerical simulation, the accuracy of producing performance prediction in oil and gas reservoirs has been effectively improved.
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A new pore type, nano-scale organo-clay complex pore-fracture was first discovered based on argon ion polishing-field emission scanning electron microscopy, energy dispersive spectroscopy and three-dimensional reconstruction by focused ion-scanning electron in combination with analysis of TOC, Ro values, X-ray diffraction etc. in the Cretaceous Qingshankou Formation shale in the Songliao Basin, NE China. Such pore characteristics and evolution study show that: (1) Organo-clay complex pore-fractures are developed in the shale matrix and in the form of spongy and reticular aggregates. Different from circular or oval organic pores discovered in other shales, a single organo-clay complex pore is square, rectangular, rhombic or slaty, with the pore diameter generally less than 200 nm. (2) With thermal maturity increasing, the elements (C, Si, Al, O, Mg, Fe, etc.) in organo-clay complex change accordingly, showing that organic matter shrinkage due to hydrocarbon generation and clay mineral transformation both affect organo-clay complex pore-fracture formation. (3) At high thermal maturity, the Qingshankou Formation shale is dominated by nano-scale organo-clay complex pore-fractures with the percentage reaching more than 70% of total pore space. The spatial connectivity of organo-clay complex pore-fractures is significantly better than that of organic pores. It is suggested that organo-complex pore-fractures are the main pore space of laminar shale at high thermal maturity and are the main oil and gas accumulation space in the core area of continental shale oil. The discovery of nano-scale organo-clay complex pore-fractures changes the conventional view that inorganic pores are the main reservoir space and has scientific significance for the study of shale oil formation and accumulation laws.
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Based on the production curves, changes in hydrocarbon composition and quantities over time, and production systems from key trial production wells in lacustrine shale oil areas in China, fine fraction cutting experiments and molecular dynamics numerical simulations were conducted to investigate the effects of changes in shale oil composition on macroscopic fluidity. The concept of “component flow” for shale oil was proposed, and the formation mechanism and conditions of component flow were discussed. The research reveals findings in four aspects. First, a miscible state of light, medium and heavy hydrocarbons form within micropores/nanopores of underground shale according to similarity and intermiscibility principles, which make components with poor fluidity suspended as molecular aggregates in light and medium hydrocarbon solvents, such as heavy hydrocarbons, thereby decreasing shale oil viscosity and enhancing fluidity and outflows. Second, small-molecule aromatic hydrocarbons act as carriers for component flow, and the higher the content of gaseous and light hydrocarbons, the more conducive it is to inhibit the formation of larger aggregates of heavy components such as resin and asphalt, thus increasing their plastic deformation ability and bringing about better component flow efficiency. Third, higher formation temperatures reduce the viscosity of heavy hydrocarbon components, such as wax, thereby improving their fluidity. Fourth, preservation conditions, formation energy, and production system play important roles in controlling the content of light hydrocarbon components, outflow rate, and forming stable “component flow”, which are crucial factors for the optimal compatibility and maximum flow rate of multi-component hydrocarbons in shale oil. The component flow of underground shale oil is significant for improving single-well production and the cumulative ultimate recovery of shale oil.
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Acoustic reflection imaging logging technology can detect and evaluate the development of reflection anomalies, such as fractures, caves and faults, within a range of tens of meters from the wellbore, greatly expanding the application scope of well logging technology. This article reviews the development history of the technology and focuses on introducing key methods, software, and on-site applications of acoustic reflection imaging logging technology. Based on the analyses of major challenges faced by existing technologies, and in conjunction with the practical production requirements of oilfields, the further development directions of acoustic reflection imaging logging are proposed. Following the current approach that utilizes the reflection coefficients, derived from the computation of acoustic slowness and density, to perform seismic inversion constrained by well logging, the next frontier is to directly establish the forward and inverse relationships between the downhole measured reflection waves and the surface seismic reflection waves. It is essential to advance research in imaging of fractures within shale reservoirs, the assessment of hydraulic fracturing effectiveness, the study of geosteering while drilling, and the innovation in instruments of acoustic reflection imaging logging technology.
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Based on the situation and progress of marine oil/gas exploration in the Sichuan Basin, SW China, the whole petroleum system is divided for marine carbonate rocks of the basin according to the combinations of hydrocarbon accumulation elements, especially the source rock. The hydrocarbon accumulation characteristics of each whole petroleum system are analyzed, the patterns of integrated conventional and unconventional hydrocarbon accumulation are summarized, and the favorable exploration targets are proposed. Under the control of multiple extensional-convergent tectonic cycles, the marine carbonate rocks of the Sichuan Basin contain three sets of regional source rocks and three sets of regional cap rocks, and can be divided into the Cambrian, Silurian and Permian whole petroleum systems. These whole petroleum systems present mainly independent hydrocarbon accumulation, containing natural gas of affinity individually. Locally, large fault zones run through multiple whole petroleum systems, forming a fault-controlled complex whole petroleum system. The hydrocarbon accumulation sequence of continental shelf facies shale gas accumulation, marginal platform facies-controlled gas reservoirs, and intra-platform fault- and facies-controlled gas reservoirs is common in the whole petroleum system, with a stereoscopic accumulation and orderly distribution pattern. High-quality source rock is fundamental to the formation of large gas fields, and natural gas in a whole petroleum system is generally enriched near and within the source rocks. The development and maintenance of large-scale reservoirs are essential for natural gas enrichment, multiple sources, oil and gas transformation, and dynamic adjustment are the characteristics of marine petroleum accumulation, and good preservation conditions are critical to natural gas accumulation. Large-scale marginal-platform reef-bank facies zones, deep shale gas, and large-scale lithological complexes related to source-connected faults are future marine hydrocarbon exploration targets in the Sichuan Basin.
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Taking the Paleozoic of the Sichuan and Tarim basins in China as example, the controlling effects of the Earth system evolution and multi-spherical interactions on the formation and enrichment of marine ultra-deep petroleum in China have been elaborated. By discussing the development of “source-reservoir-seal” controlled by the breakup and assembly of supercontinents and regional tectonic movements, and the mechanisms of petroleum generation and accumulation controlled by temperature-pressure system and fault conduit system, Both the South China and Tarim blocks passed through the intertropical convergence zone (ITCZ) of the low-latitude Hadley Cell twice during their drifts, and formed hydrocarbon source rocks with high quality. It is proposed that deep tectonic activities and surface climate evolution jointly controlled the types and stratigraphic positions of ultra-deep hydrocarbon source rocks, reservoirs, and seals in the Sichuan and Tarim basins, forming multiple petroleum systems in the Ediacaran-Cambrian, Cambrian-Ordovician, Cambrian-Permian and Permian-Triassic strata. The matching degree of source-reservoir-seal, the type of organic matter in source rocks, the deep thermal regime of basin, and the burial-uplift process across tectonic periods collectively control the entire process from the generation to the accumulation of oil and gas. Three types of oil and gas enrichment models are formed, including near-source accumulation in platform marginal zones, distant-source accumulation in high-energy beaches through faults, and three-dimensional accumulation in strike-slip fault zones, which ultimately result in the multi-layered natural gas enrichment in ultra-deep layers of the Sichuan Basin and co-enrichment of oil and gas in the ultra-deep layers of the Tarim Basin.
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The conventional linear time-frequency analysis method cannot achieve high resolution and energy focusing in the time and frequency dimensions at the same time, especially in the low frequency region. In order to improve the resolution of the linear time-frequency analysis method in the low-frequency region, we have proposed a W transform method, in which the instantaneous frequency is introduced as a parameter into the linear transformation, and the analysis time window is constructed which matches the instantaneous frequency of the seismic data. In this paper, the W transform method is compared with the Wigner-Ville distribution (WVD), a typical nonlinear time-frequency analysis method. The WVD method that shows the energy distribution in the time-frequency domain clearly indicates the gravitational center of time and the gravitational center of frequency of a wavelet, while the time-frequency spectrum of the W transform also has a clear gravitational center of energy focusing, because the instantaneous frequency corresponding to any time position is introduced as the transformation parameter. Therefore, the W transform can be benchmarked directly by the WVD method. We summarize the development of the W transform and three improved methods in recent years, and elaborate on the evolution of the standard W transform, the chirp-modulated W transform, the fractional-order W transform, and the linear canonical W transform. Through three application examples of W transform in fluvial sand body identification and reservoir prediction, it is verified that W transform can improve the resolution and energy focusing of time-frequency spectra.
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In recent years, great breakthroughs have been made in the exploration and development of natural gas in deep coal-rock reservoirs in Junggar, Ordos and other basins in China. In view of the inconsistency between the industrial and academic circles on this new type of unconventional natural gas, this paper defines the concept of "coal-rock gas" on the basis of previous studies, and systematically analyzes its characteristics of occurrence state, transport and storage form, differential accumulation, and development law. Coal-rock gas, geologically unlike coalbed methane in the traditional sense, occurs in both free and adsorbed states, with free state in abundance. It is generated and stored in the same set of rocks through short distance migration, occasionally with the accumulation from other sources. Moreover, coal rock develops cleat fractures, and the free gas accumulates differentially. The coal-rock gas reservoirs deeper than 2000 m are high in pressure, temperature, gas content, gas saturation, and free-gas content. In terms of development, similar to shale gas and tight gas, coal-rock gas can be exploited by natural formation energy after the reservoirs connectivity is improved artificially, that is, the adsorbed gas is desorbed due to pressure drop after the high-potential free gas is recovered, so that the free gas and adsorbed gas are produced in succession for a long term without water drainage for pressure drop. According to buried depth, coal rank, pressure coefficient, reserves scale, reserves abundance and gas well production, the classification criteria and reserves/resources estimation method of coal-rock gas are presented. It is preliminarily estimated that the coal-rock gas in place deeper than 2 000 m in China exceeds 30×1012 m3, indicating an important strategic resource for the country. The Ordos, Sichuan, Junggar and Bohai Bay basins are favorable areas for large-scale enrichment of coal-rock gas. The paper summarizes the technical and management challenges and points out the research directions, laying a foundation for the management, exploration, and development of coal-rock gas in China.
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The Santos Basin in Brazil has witnessed significant oil and gas discoveries in deepwater pre-salt since the 21st century. Currently, the waters in eastern Brazil stand out as a hot area of deepwater exploration and production worldwide. Based on a review of the petroleum exploration and production history in Brazil, the challenges, researches and practices, strategic transformation, significant breakthroughs, and key theories and technologies for exploration from onshore to offshore and from shallow waters to deep-ultra-deep waters and then to pre-salt strata are systematically elaborated. Within 15 years since its establishment in 1953, Petrobras explored onshore Paleozoic cratonic and marginal rift basins, and obtained some small to medium petroleum discoveries in fault-block traps. In the 1970s, Petrobras developed seismic exploration technologies and several hydrocarbon accumulation models, for example, turbidite sandstones, allowing important discoveries in shallow waters, e.g. the Namorado Field and Enchova fields. Guided by these models/technologies, significant discoveries, e.g. the Marlim and Roncador fields, were made in deepwater post-salt in the Campos Basin. In the early 21st century, the advancements in theories and technologies for pre-salt petroleum system, carbonate reservoirs, hydrocarbon accumulation and nuclear magnetic resonance (NMR) logging stimulated a succession of valuable discoveries in the Lower Cretaceous lacustrine carbonates in the Santos Basin, including the world-class ultra-deepwater super giant fields such as Tupi (Lula), Mero and Buzios. Petroleum development in complex deep water environments is extremely challenging. By establishing the Technological Capacitation Program in Deep Waters (PROCAP), Petrobras developed and implemented key technologies including managed pressure drilling (MPD) with narrow pressure window, pressurized mud cap drilling (PMCD), multi-stage intelligent completion, development with Floating Production Storage and Offloading units (FPSO), and flow assurance, which remarkably improved the drilling, completion, field development and transportation efficiency and safety. Additionally, under the limited FPSO capacity, Petrobras promoted the world-largest CCUS-EOR project, which contributed effectively to the reduction of greenhouse gas emissions and the enhancement of oil recovery. Development and application of these technologies provide valuable reference for deep and ultra-deepwater petroleum exploration and production worldwide. The petroleum exploration in Brazil will consistently focus on ultra-deep water pre-salt carbonates and post-salt turbidites, and seek new opportunities in Paleozoic gas. Technical innovation and strategic cooperation will be held to promote the sustainable development of Brazil's oil and gas industry.
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We present a systematic summary of the geological characteristics, exploration and development history and current state of shale oil and gas in the United States. The hydrocarbon-rich shales in the major shale basins of the United States are mainly developed in six geological periods: Middle Ordovician, Middle-Late Devonian, Early Carboniferous (Middle-Late Mississippi), Early Permian, Late Jurassic, and Late Cretaceous (Cenomanian-Turonian). Depositional environments for these shales include intra-cratonic basins, foreland basins, and passive continental margins. Paleozoic hydrocarbon-rich shales are mainly developed in six basins, including the Appalachian Basin (Utica and Marcellus shales), Anadarko Basin (Woodford Shale), Williston Basin (Bakken Shale), Arkoma Basin (Fayetteville Shale), Fort Worth Basin (Barnett Shale), and the Wolfcamp and Leonardian Spraberry/Bone Springs shale plays of the Permian Basin. The Mesozoic hydrocarbon-rich shales are mainly developed on the margins of the Gulf of Mexico Basin (Haynesville and Eagle Ford) or in various Rocky Mountain basins (Niobrara Formation, mainly in the Denver and Powder River basins). The detailed analysis of shale plays reveals that the shales are different in facies and mineral components, and "shale reservoirs" are often not shale at all. The United States is abundant in shale oil and gas, with the in-place resources exceeding 0.246×1012 t and 290×1012 m3, respectively. Before the emergence of horizontal well hydraulic fracturing technology to kick off the "shale revolution", the United States had experienced two decades of exploration and production practices, as well as theory and technology development. In 2007-2023, shale oil and gas production in the United States increased from approximately 11.2×104 tons of oil equivalent per day (toe/d) to over 300.0×104 toe/d. In 2017, the shale oil and gas production exceeded the conventional oil and gas production in the country. In 2023, the contribution from shale plays to the total U.S. oil and gas production remained above 60%. The development of shale oil and gas has largely been driven by improvements in drilling and completion technologies, with much of the recent effort focused on “cube development” or “co-development”. Other efforts to improve productivity and efficiency include refracturing, enhanced oil recovery, and drilling of “U-shaped” wells. Given the significant resources base and continued technological improvements, shale oil and gas production will continue to contribute significant volumes to total U.S. hydrocarbon production.
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In response to the problems of unclear distribution of deep-water pre-salt carbonate reservoirs and formation conditions of large oil fields in the Santos passive continental margin basin, based on comprehensive utilization of geological, seismic, and core data, and reconstruction of Early Cretaceous prototype basin and lithofacies paleogeography, it is proposed for the first time that the construction of pre-salt carbonate build-ups was controlled by two types of isolated platforms: inter-depression fault-uplift and intra-depression fault-high. The inter-depression fault-uplift isolated platforms are distributed on the present-day pre-salt uplifted zones between depressions, and are built on half- and fault-horst blocks that were inherited and developed in the early intra-continental and inter-continental rift stages. The late intra-continental rift coquinas of the ITP Formation and the early inter-continental rift microbial limestones of the BVE Formation are continuously constructed; intra-depression fault-high isolated platforms are distributed in the current pre-salt depression zones, built on the uplifted zones formed by volcanic rock build-ups in the early prototype stage of intra-continental rifts, and only the BVE microbial limestones are developed. Both types of limestones formed into mound-shoal bodies, that have the characteristics of large reservoir thickness and good physical properties. Based on the dissection of large pre-salt oil fields discovered in the Santos Basin, it has been found that both types of platforms could form large-scale combined structural-stratigraphic traps, surrounded by high-quality lacustrine and lagoon source rocks at the periphery, and efficiently sealed by thick high-quality evaporite rocks above, forming the optimal combination of source, reservoir and cap in the form of “lower generation, middle storage, and upper cap”, with a high degree of oil and gas enrichment. It has been found that the large oil fields are all bottom water massive oil fields with a unified pressure system, and they are all filled to the spill-point. The future exploration is recommended to focus on the inter-depression fault-uplift isolated platforms in the western uplift zone and the southern section of eastern uplift zones, as well as intra-depression fault-high isolated platforms in the central depression zone. The result not only provides an important basis for the advanced selection of potential play fairways, bidding of new blocks, and deployment of awarded exploration blocks in the Santos Basin, but also provides a reference for the global selection of deep-water exploration blocks in passive continental margin basins.
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This paper reviews the basic research means for oilfield development and also the researches and tests of enhanced oil recovery (EOR) methods for mature oilfields and continental shale oil development, analyzes the problems of EOR methods, and proposes the relevant research prospects. The basic research means for oilfield development include in-situ acquisition of formation rock/fluid samples and non-destructive testing. The EOR methods for conventional and shale oil development are classified as improved water flooding (e.g. nano-water flooding), chemical flooding (e.g. low-concentration middle-phase micro-emulsion flooding), gas flooding (e.g. micro/nano bubble flooding), thermal recovery (e.g. air injection thermal-aided miscible flooding), and multi-cluster uniform fracturing/water-free fracturing, which are discussed in this paper for their mechanisms, approaches, and key technique researches and field tests. These methods have been studied with remarkable progress, and some achieved ideal results in field tests. Nonetheless, some problems still exist, such as inadequate research on mechanisms, imperfect matching technologies, and incomplete industrial chains. It is proposed to further strengthen the basic researches and expand the field tests, thereby driving the formation, promotion and application of new technologies.
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Laboratory experiments, numerical simulations and fracturing technology were combined to address the problems in shale oil recovery by CO2 injection. The laboratory experiments were conducted to investigate the displacement mechanisms of shale oil extraction by CO2 injection, and the influences of CO2 pre-pad on shale mechanical properties. Numerical simulations were performed about influences of CO2 pre-pad fracturing and puff-n-huff for energy replenishment on the recovery efficiency. The findings obtained were applied to the field tests of CO2 pre-pad fracturing and single well puff-n-huff. The results show that the efficiency of CO2 puff-n-huff is affected by micro- and nano-scale effect, kerogen, adsorbed oil and so on, and a longer soaking time in a reasonable range leads to a higher exploitation degree of shale oil. In the "injection + soaking" stage, the exploitation degree of heavy hydrocarbons is enhanced by CO2 through its effects of solubility-diffusion and mass-transfer. In the "huff" stage, crude oil in large pores is displaced by CO2 to surrounding larger pores or bedding fractures and finally flows to the production well. The injection of CO2 pre-pad is conducive to keeping the rock brittle and reducing the fracture breakdown pressure, and the CO2 is liable to filter along the bedding surface, thereby creating a more complex fracture. Increasing the volume of CO2 pre-pad can improve the energizing effect, and enhance the replenishment of formation energy. Moreover, the oil recovery is more enhanced by CO2 huff-n-puff with the lower shale matrix permeability, the lower formation pressure, and the larger heavy hydrocarbon content. The field tests demonstrate a good performance with the pressure maintained well after CO2 pre-pad fracturing, the formation energy replenished effectively after CO2 huff-n-puff in a single well, and the well productivity improved.
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By benchmarking with the iteration of drilling technology, fracturing technology and well placement mode for shale oil and gas development in the United States and considering the geological characteristics and development difficulties of shale oil in the Jiyang continental rift lake basin, East China, the development technology system suitable for the geological characteristics of shale oil in continental rift lake basins has been primarily formed through innovation and iteration of the development, drilling and fracturing technologies. The technology system supports the rapid growth of shale oil production and reduces the development investment cost. By comparing it with the shale oil development technology in the United States, the prospect of the shale oil development technology iteration in continental rift lake basins is proposed. It is suggested to continuously strengthen the overall three-dimensional development, improve the precision level of engineering technology, upgrade the engineering technical indicator system, accelerate the intelligent optimization of engineering equipment, explore the application of complex structure wells, form a whole-process integrated quality management system from design to implementation, and constantly innovate the concept and technology of shale oil development, so as to promote the realization of extensive, beneficial and high-quality development of shale oil in continental rift lake basins.
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Aiming at the problems of large load of rotation drive system, low efficiency of torque transmission and high cost for operation and maintenance of liner steering drilling system for the horizontal well, a new method of liner differential rotary drilling with double tubular strings in the horizontal well is proposed. The technical principle of this method is revealed, supporting tools such as the differential rotation transducer, composite rotary steering system and the hanger are designed, and technological process is optimized. A tool face control technique of steering drilling assembly is proposed and the calculation model of extension limit of liner differential rotary drilling with double tubular strings in horizontal well is established. These results show that the liner differential rotary drilling with double tubular strings is equipped with measurement while drilling (MWD) and positive displacement motor (PDM), and directional drilling of horizontal well is realized by adjusting rotary speed of drill pipe to control the tool face of PDM. Based on the engineering case of deep coalbed methane horizontal well in the eastern margin of Ordos Basin, the extension limit of horizontal drilling with double tubular strings is calculated. Compared with the conventional liner drilling method, the liner differential rotary drilling with double tubular strings increases the extension limit value of horizontal well significantly. The research findings provide useful reference for the integrated design and control of liner completion and drilling of horizontal wells.
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The research progress of deep and ultra-deep drilling fluid technology systematically reviewed, the key problems existing are analyzed, and the future development direction is proposed. In view of the high temperature, high pressure and high stress, fracture development, wellbore instability, drilling fluid lost circulation and other problems faced in the process of deep and ultra-deep complex oil and gas drilling, scholars have developed deep and ultra-deep high-temperature and high-salt resistant water-based drilling fluid technology, high-temperature resistant oil-based/synthetic drilling fluid technology, drilling fluid technology for reservoir protection and drilling fluid lost circulation control technology. However, there are still some key problems such as insufficient resistance to high temperature, high pressure and high stress, wellbore instability and serious lost circulation. Therefore, the development direction of deep and ultra-deep drilling fluid technology in the future is proposed: (1) The technology of high-temperature and high-salt resistant water-based drilling fluid should focus on improving high temperature stability, improving rheological properties, strengthening filtration control and improving compatibility with formation. (2) The technology of oil-based/synthetic drilling fluid resistant to high temperature should further study in the aspects of easily degradable environmental protection additives with low toxicity such as high temperature stabilizer, rheological regulator and related supporting technologies. (3) The drilling fluid technology for reservoir protection should be devoted to the development of new high-performance additives and materials, and further improve the real-time monitoring technology by introducing advanced sensor networks and artificial intelligence algorithms. (4) The lost circulation control of drilling fluid should pay more attention to the integration and application of intelligent technology, the research and application of high-performance plugging materials, the exploration of diversified plugging techniques and methods, and the improvement of environmental protection and production safety awareness.
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To address the key problems in the application of intelligent technology in geothermal development, smart application scenarios for geothermal development are constructed. The research status and existing challenges of intelligent technology in each scenario are analyzed, and the construction scheme of smart geothermal field system is proposed. The smart geothermal field is an organic integration of geothermal development engineering and advanced technologies such as the artificial intelligence. At present, the technology of smart geothermal field is still in the exploratory stage. It has been tested for application in scenarios such as intelligent characterization of geothermal reservoirs, dynamic intelligent simulation of geothermal reservoirs, intelligent optimization of development schemes and smart management of geothermal development. However, it still faces many problems, including the high computational cost, difficult real-time response, multiple solutions and strong model dependence, difficult real-time optimization of dynamic multi-constraints, and deep integration of multi-source data. The construction scheme of smart geothermal field system is proposed, which consists of modules including the full database, intelligent characterization, intelligent simulation and intelligent optimization control. The connection between modules is established through the data transmission and the model interaction. In the next stage, it is necessary to focus on the basic theories and key technologies in each module of the smart geothermal field system, to accelerate the lifecycle intelligent transformation of the geothermal development and utilization, and to promote the intelligent, stable, long-term, optimal and safe production of geothermal resources.
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This article elucidates the concept of large model technology, summarizes the research status of large model technology both domestically and internationally, provides an overview of the application status of large models in vertical industries, outlines the challenges and issues confronted in applying large models in the oil and gas sector, and offers prospects for the application of large models in the oil and gas industry. The existing large models can be briefly divided into three categories: large language models, visual large models, and multimodal large models. The application of large models in the oil and gas industry is still in its infancy. Based on open-source large language models, some oil and gas enterprises have released large language model products using methods like fine-tuning and retrieval augmented generation. Scholars have attempted to develop scenario-specific models for oil and gas operations by using visual/multimodal foundation models. A few researchers have constructed pre-trained foundation models for seismic data processing and interpretation, as well as core analysis. The application of large models in the oil and gas industry faces challenges such as current data quantity and quality being difficult to support the training of large models, high research and development costs, and poor algorithm autonomy and control. The application of large models should be guided by the needs of oil and gas business, taking the application of large models as an opportunity to improve data lifecycle management, enhance data governance capabilities, promote the construction of computing power, strengthen the construction of “artificial intelligence + energy” composite teams, and boost the autonomy and control of large model technology.
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Super oil and gas basins provide the energy foundation for social progress and human development. In the context of climate change and carbon peak and carbon neutrality goals, constructing an integrated energy and carbon neutrality system that balances energy production and carbon reduction becomes crucial for the transformation of such basins. Under the framework of a green and intelligent energy system primarily based on “four news”, new energy, new electricity, new energy storage, and new intelligence, integrating a “super energy system” composed of a huge amount of underground resources of coal, oil, gas and heat highly overlapping with abundant wind and solar energy resources above ground, and a regional intelligent energy consumption system with coordinated development and utilization of fossil energy and new energy, with a carbon neutrality system centered around carbon cycling is essential. This paper aims to select the traditional oil and gas basins as “super energy basins” with the conditions to build world-class energy production and demonstration bases for carbon neutrality. The Ordos Basin has unique regional advantages, including abundant fossil fuel and new energy resources, as well as matching CO2 sources and sinks, position it as a carbon neutrality “super energy basin” which explores the path of transformation of traditional oil and gas basins. Under the integrated development concept and mode of “coal + oil + gas + new energy + carbon capture, utilization and storage (CCUS)/carbon capture and storage (CCS)”, the carbon neutrality in super energy basin is basically achieved, which enhance energy supply and contribute to the carbon peak and carbon neutrality goals, establish a modern energy industry and promote regional green and sustainable development. The pioneering construction of the world-class carbon neutrality “super energy system” demonstration basin in China represented by the Ordos Basin will reshape the new concept and new mode of exploration and development of super energy basins, which is of great significance to the global energy revolution under carbon neutrality.
