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Considering the Neo-Tethyan tectonic process and the resulting environmental changes, a geodynamic model of “one-way train loading” is proposed to analyze the formation and evolution mechanism of the Persian Gulf Superbasin with the most abundant hydrocarbons in the world. The Persian Gulf Superbasin has long been in a passive continental margin setting since the Late Paleozoic in the process of unidirectional subduction, forming a superior regional space of hydrocarbon accumulation. During the Jurassic-Cretaceous, the Persian Gulf Superbasin drifted slowly at low latitudes, and developed multiple superimposed source-reservoir-caprock assemblages as a combined result of several global geological events such as the Hadley Cell, the Equatorial Upwelling Current, and the Jurassic True Polar Wander. The collision during the evolution of the foreland basin since the Cenozoic led to weak destruction, which was conducive to the preservation of oil and gas. Accordingly, it is believed that the slow drifting and long retention in favorable climate zone of the landmass are the critical factors for hydrocarbon enrichment. Moreover, the prospects of hydrocarbon potential in other landmasses in the Neo-Tethyan were proposed.
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The major enrichment type of shale oil in the Chang 73 shale of Upper Triassic Yanchang Formation in the Ordos Basin is unknown. This paper analyzes the organic matter transformation ratio, hydrocarbon expulsion efficiency and roof/floor sealing conditions of the Chang 73 shale, and evaluates the major enrichment type of shale oil in this interval. The average organic matter transformation ratio of the Chang 73 shale is about 45%; in other words, more than 50% of the organic matters have not transformed to hydrocarbons, and the lower the maturity, the greater the proportion of untransformed organic matters. The cumulative hydrocarbon expulsion efficiency of the transformed hydrocarbon is 27.5% on average, and the total proportion of untransformed organic matters plus retained hydrocarbons is greater than 70%. The relative hydrocarbon expulsion efficiency of the Chang 73 shale is 60% on average, that is, about 40% of hydrocarbons retain in the shale. The Chang 73 shale corresponds to Chang 71+2 and Chang 8 sandstones as the roof and floor, respectively, and is further overlaid by Chang 6 shale, where extensive low porosity and low permeability-tight oil reservoirs have formed in the parts with relatively good porosity and permeability. Moreover, the Chang 73 shale is tested to be in a negative pressure system (the pressure coefficient of 0.80-0.85). Therefore, the roof/floor sealing conditions of the Chang 73 shale are poor. The retained hydrocarbons appear mostly in absorbed status, with low mobility. It is concluded that the medium-high mature shale oil is not the major enrichment type of shale oil in the Chang 73 shale, but there may be enrichment opportunity for shale oil with good mobility in the areas where the sealing conditions are good without faults and fractures and oil reservoirs are formed off Chang 71+2, Chang 6 and Chang 8. Furthermore, low-medium mature shale oil is believed to have great potential and is the major enrichment type of shale oil in the Chang 73 shale. It is recommended to prepare relevant in-situ conversion technologies by pilot test and figure out the resource availability and distribution.
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Unconventional gas in the Sichuan Basin mainly includes shale gas and tight gas. The development of shale gas is mainly concentrated in the Ordovician Wufeng Formation-Silurian Longmaxi Formation, but has not made any significant breakthrough in the Cambrian Qiongzhusi Formation marine shale regardless of exploration efforts for years. The commercial development of tight sandstone gas is mainly concentrated in the Jurassic Shaximiao Formation, but has not been realized in the widespread and thick Triassic Xujiahe Formation. Depending on the geological characteristics of the Qiongzhusi Formation and Xujiahe Formation, the feedback of old wells was analyzed. Then, combining with the accumulation mechanisms of conventional gas and shale gas, as well as the oil/gas shows during drilling, changes in production and pressure during development, and other characteristics, it was proposed to change the exploration and development strategy from source and reservoir exploration to carrier beds exploration. With the combination of effective source rock, effective carrier beds and effective sandstone or shale as the exploration target, a model of unconventional gas accumulation and enrichment in carrier beds was built. Under the guidance of this study, two significant results have been achieved in practice. First, great breakthrough was made in exploration of the silty shale with low organic matter abundance in the Qiongzhusi Formation, which breaks the traditional approach to prospect shale gas only in organic-rich black shales and realizes a breakthrough in new areas, new layers and new types of shale gas and a transformation of exploration and development of shale gas from single-layer system, Longmaxi Formation, to multi-layer system in the Sichuan Basin. Second, exploration breakthrough and high-efficient development were realized for difficult-to-produce tight sandstone gas reserves in the Xujiahe Formation, which helps address the challenges of low production and unstable production of fracture zones in the Xujiahe Formation, promote the transformation of tight sandstone gas from reserves without production to effective production, and enhance the exploration and development potential of tight sandstone gas.
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The origin of authigenic dolomites in the dolomitic reservoir of the Permian Fengcheng Formation in the Mahu Sag, the Junggar Basin, is unclear. The occurrence and genetic evolution of such authigenic dolomites in the dolomitic rock reservoir of the Fengcheng Formation in Mahu Sag were analyzed by polarized and fluorescence thin sections, scanning electron microscope (SEM) analysis, electron microprobe (EMP) analysis, C, O and Sr isotopes analysis, and other techniques. (1) Dolomites were mainly precipitated in three stages: penecontemporaneous-shallow burial stage (early stage of Middle Permian), middle burial stage (middle stage of Middle Permian), and middle-deep burial stage, with the former two stages in dominance. (2) The dolomitization fluid was high-salinity brine in the alkaline-lake sedimentary setting. In the penecontemporaneous-shallow burial stage, Mg2+ was mainly supplied by alkaline-lake fluid and devitrification of volcanic glass. In the middle burial stage, Mg2+ mainly came from the transformation of clay minerals, devitrification of volcanic glass and dissolution of aluminosilicates such as feldspar. (3) The regular changes of Mg, Mn, Fe, Sr, Si and other elements during the growth of dolomite were mainly related to the alkaline-lake fluid, and the different influences of devitrification and diagenetic alteration of volcanic materials in the Fengcheng Formation during the burial. (4) Induced by alkaline-lake microorganisms, in the penecontemporaneous stage, the micritic-microcrystalline dolomites were formed by primary precipitation, replacement of aragonite and high-Mg calcite, and other processes; in the shallow burial stage, the silt-sized dolomite was formed by the continuous growth of micritic-microcrystalline dolomite and replacement of calcite, tuffs and other substances; in the middle burial stage, the dolomite, mainly silt- and fine-sized, was formed by the replacement of volcanic materials by dolomitization fluid. The research results are referential for investigating the formation mechanism and distribution patterns of tight dolomitic reservoirs in the Mahu Sag and other similar oil and gas bearing areas.
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For black shales, laminae and bedding are hard to identify, grain size is difficult to measure, and trace fossils do not exist. Taking the Ordovician Wufeng - Silurian Longmaxi shale in southern Sichuan Basin, China, as an example, the types, characteristics and models of microfacies in epicontinental shale are analyzed by means of full-scale observation of large thin sections, argon-ion polishing field emission-scanning electron microscopy (FE-SEM), and kerogen microscopy. The epicontinental sea develops delta, tidal flat and shelf facies, with black shale found in microfacies such as the underwater distributary channel and interdistributary bay under delta front facies, the calcareous and clayey flats under intertidal flat facies, the calcareous and clayey shelfs under shallow shelf facies, the deep slope, deep plain and deep depression under deep shelf facies, and the overflow under gravity flow facies. Basinward, silty lamina decreases and clayey lamina increases, the grain size changes from coarse silt to fine mud, the silica content increases from about 20% to above 55%, the carbonate and clay minerals content decreases from above 40% to around 10%, and the kerogen type changes from type Ⅱ2 to type Ⅱ1 and type Ⅰ. Provenance and topography dominate the types and distribution of shale microfacies. The underwater distributary channel, interdistributary bay, clayey flat, clayey shelf, and overflow microfacies are developed in areas with sufficient sediment supply. The calcareous flat and calcareous shelf are developed in areas with insufficient sediment supply. The deep shelf shale area is divided into deep slope, deep plain, and deep depression microfacies as a result of three breaks. The formation of epicontinental shale with different microfacies is closely related to the tectonic setting, paleoclimate, and sea level rise. The relatively active tectonic setting increases the supply of terrigenous clasts, forming muddy water fine-grained sediment. The warm and humid paleoclimate is conducive to the enrichment of organic matter. The rapid sea level rise is helpful to the widespread black shale.
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Based on drilling geological, geochemical, geophysical and production test data, the characteristics of source rocks, reservoir rocks and caprocks, as well as the process of hydrocarbon generation, trap evolution and oil accumulation of the oil-bearing assemblage composed of the Cretaceous Yingcheng Formation (K1yc) and Denglouku Formation (K1d) in the Shuangcheng area, northern Songliao Basin, were analyzed by using the research methods for petroleum systems. The source rocks mainly exist in K1yc, with the organic matters mainly originated from lower aquatic organisms and algae, and reaching the grade of high-quality source rock in terms of organic abundance. The crude oil, which is characterized by low density, high freezing point and high wax content, is believed to have generated by the K1yc source rocks. The reservoir rocks include K1d sandstones and K1yc glutenites. The mudstone in the fourth member of K1d serves as the direct caprock of the oil reservoir. The oil was generated during the period between Yaojia Formation and Nenjiang Formation, and then accumulated during the periods of Nenjiang Formation and Paleogene-Neogene. The traps evolved in three stages: the late Yingcheng Formation, the late Quantou Formation and the late Nenjiang Formation, forming structural and structural-lithologic reservoirs. It is concluded that good source-reservoir-caprock assemblage, late hydrocarbon charging, short migration distance and stable tectonic setting are favorable factors for the formation of oil reservoirs.
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To investigate the porosity, permeability and rock mechanics of deep shale under temperature-pressure coupling, we selected the core samples of deep shale from the Longmaxi Formation in the Weirong and Yongchuan areas of the Sichuan Basin for porosity and permeability experiments and a triaxial compression and sound wave integration experiment at the maximum temperature and pressure of 120 ℃ and 70 MPa. The results show that the microscopic porosity and permeability change and the macroscopic rock deformation are mutually constrained, both showing the trend of steep and then gentle variation. At the maximum temperature and pressure, the porosity reduces by 34%-71%, and the permeability decreases by 85%-97%. With the rising temperature and pressure, deep shale undergoes plastic deformation in which organic pores and clay mineral pores are compressed and microfractures are closed, and elastic deformation in which brittle mineral pores and rock skeleton particles are compacted. Compared with previous experiments under high confining pressure and normal temperature, the experiment under high temperature and high pressure coupling reveals the effect of high temperature on stress sensitivity of porosity and permeability. High temperature can increase the plasticity of the rock, intensify the compression of pores due to high confining pressure, and induce thermal stress between the rock skeleton particles, allowing the reopening of shale bedding or the creation of new fractures along weak planes such as bedding, which inhibits the decrease of permeability with the increase of temperature and confining pressure. Compared with the triaxial mechanical experiment at normal temperature, the triaxial compression experiment at high temperature and high pressure demonstrates that the compressive strength and peak strain of deep shale increase significantly due to the coupling of temperature and pressure. The compressive strength is up to 435 MPa and the peak strain exceeds 2%, indicating that high temperature is not conducive to fracture initiation and expansion by increasing rock plasticity. Lithofacies and mineral composition have great impacts on the porosity, permeability and rock mechanics of deep shale. Shales with different lithologies are different in the difficulty and extent of brittle failure. The stress-strain characteristics of rocks under actual geological conditions are key support to the optimization of reservoir stimulation program.
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Based on well horizon calibration, the typical seismic profiles in southwestern Tarim Basin were interpreted systematically, regional geological sections were established, and the regional denudation thickness of each tectonic period was restored. On this basis, the plane morphology maps of ancient structures of the Cambrian pre-salt dolomites in different periods were compiled, and the spatial distribution, development, evolution and migration of paleo-uplift in the late Early Paleozoic were analyzed. In the late Early Paleozoic, there existed a unified regional paleo-uplift widely distributed in southwestern Tarim Basin, which is called the southwestern Tarim plaeo-uplift. The “Tarim SW paleo-uplift” and “Hotan paleo-uplift” proposed in previous literatures are not independent, but the result of the spatio-temporal migration and evolution of the southwestern Tarim paleo-uplift identified in this paper. The southwestern Tarim paleo-uplift emerged at the end of Middle Ordovician, and took its initial shape with increased amplitude in the Late Ordovician. During the Silurian, the southwestern Tarim paleo-uplift rose steadily and expanded rapidly to the east, incorporating Pishan-Hotan and other areas, with the structural high locating in the Pishan-Hotan area. During the Devonian, the southwestern Tarim paleo-uplift began to shrink gradually, to a limited range in the Pishan-Hotan area in the southern part of the basin. During the Carboniferous, the southwestern Tarim paleo-uplift became an underwater uplift, that is, the paleo-uplift gradually died out. The southwestern Tarim paleo-uplift belongs to the forebulge of the southwestern Tarim foreland basin in the late Early Paleozoic, and its formation and evolution are related to the early Paleozoic orogeny of the West Kunlun orogenic belt in the south of the Tarim Basin. The migration of the southwestern Tarim paleo-uplift from the northwestern part of the southwestern Tarim Basin to the Pishan-Hotan area indicates the early Paleozoic orogenic process of the West Kunlun orogenic belt, which started in the western section at the end of Middle Ordovician and extended from west to east in a “scissor” style. The migration and evolution of the southwestern Tarim paleo-uplift controlled the development of unconformities at the end of Middle Ordovician, the end of Late Ordovician, and the end of Middle Devonian, and the spatial distribution of dissolved fracture-cave reservoirs in weathered crust below the unconformities in the southwest of Tarim Basin. The migration of the structural high of the southwestern Tarim paleo-uplift also played an important role in controlling the development of dissolved fracture-cave reservoirs in weathered crust.
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The element geochemical characteristics and diagenetic alteration products of tuffaceous components in sandstone reservoirs of Paleogene Wenchang Formation in typical low-lying zones of the Huizhou-Lufeng area of the Zhu I Depression, Pearl River Mouth Basin, were identified through microscopic analysis and quantitative analysis of main and trace elements. The impacts of dissolution of different tuffaceous components on physical properties of reservoirs were discussed through quantitative characterization of reservoir physical properties. The results show that there are mainly four types of tuffaceous components in the study area, which are acidic, intermediate, basic and alkaline tuffaceous components. The acidic tuffaceous components evolved in a process of strong alteration and weak dissolution of alteration products, with a large amount of kaolinite precipitated during alteration to disenable the improvement of porosity and permeability. The intermediate and alkaline tuffaceous components evolved in a process of strong dissolution of tuffaceous components and strong alteration of residual tuffaceous components; the dissolution of tuffaceous components created intergranular pores, but the alteration products such as autogenic quartz, apatite and illite deteriorated the pore structure; ultimately, the dissolution of tuffaceous components resulted in the increase of porosity but no increase of permeability of the reservoir. The basic tuffaceous components dominantly evolved in a process of dissolution of tuffaceous components to strong dissolution of alteration products; both tuffaceous components between particles and laumontite generated from alteration can be strongly dissolved to create pores; thus, the dissolution of tuffaceous components can significantly increase the physical properties of the reservoir.
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Based on analysis of pore features and pore skeleton composition of shale, a “rigid elastic chimeric” pore model of shale gas reservoir was built. Pore deformation mechanisms leading to increase of shale porosity due to the pore skeleton deformation under overpressure were sorted out through analysis of stress on the shale pore and skeleton. After reviewing the difficulties and defects of existent porosity measurement methods, a dynamic deformed porosity measurement method was worked out and used to measure the porosity of overpressure Silurian Longmaxi Formation shale under real formation conditions in southern Sichuan Basin. The results show: (1) The shale reservoir is a mixture of inorganic rock particles and organic matter, which contains inorganic pores supported by rigid skeleton particles and organic pores supported by elastic-plastic particles, and thus has a special “rigid elastic chimeric” pore structure. (2) Under the action of formation overpressure, the inorganic pores have tiny changes that can be assumed that they don’t change in porosity, while the organic pores may have large deformation due to skeleton compression, leading to the increase of radius, connectivity and ultimately porosity of these pores. (3) The “dynamic” deformation porosity measurement method combining high injection pressure helium porosity measurement and kerosene porosity measurement method under ultra-high variable pressure can accurately measure porosity of unconnected micro-pores under normal pressure conditions, and also the porosity increment caused by plastic skeleton compression deformation. (4) The pore deformation mechanism of shale may result in the "abnormal" phenomenon that the shale under formation conditions has higher porosity than that under normal pressure, so the overpressure shale reservoir is not necessarily “ultra-low in porosity”, and can have porosity over 10%. Application of this method in Well L210 in southern Sichuan has confirmed its practicality and reliability.
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The fluvial-deltaic reservoirs of the Oligocene Huagang Formation in the Xihu sag of the East China Sea shelf basin reflect rapid lateral change in sedimentary facies and poor morphology of conventional slice attributes, which bring difficulties to the reservoir prediction for subsequent exploration and development of lithologic reservoirs. The traditional seismic sedimentology technology is optimized by applying the characteristic technologies such as frequency-boosting interpretation, inversion-conventional- -90° phase shift joint construction of seismic lithologic bodies, nonlinear slices, paleogeomorphology restoration, and multi-attribute fusion, to obtain typical slice attributes, which are conducive to geological form description and sedimentary interpretation. The Huagang Formation developed three types of sedimentary bodies: braided river, meandering river and shallow water delta, and the vertical sedimentary evolution was controlled by the mid-term base-level cycle and paleogeomorphology. In the early-middle stage of the mid-term base-level ascending cycle, braided channel deposits were dominant, and vertical superimposed sand bodies were developed. In the late stage of the ascending half-cycle and the early stage of the descending half-cycle, meandering river deposits were dominant, and isolated sand bodies were developed. In the middle-late stage of the descending half-cycle, shallow-water delta deposits were dominant, and migratory medium-thick sand bodies were developed. Restricted paleogeomorphology controlled the sand body distribution, while non-restricted paleogeomorphology had little effect on the sand body distribution. Based on reservoir characterization, the fault sealing type and reservoir updip pinch-out type structural lithological traps are proposed as the main directions for future exploration and development in the Xihu sag.
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Through modifying the viscoelastic-plastic damage constitutive equation for the nonlinear tensile-shear pattern of hydraulic fractures in shale, and considering the competitive fluid diversion in perforation clusters and the dynamic erosion effect of fracturing fluid on perforations, a fracture propagation numerical algorithm for temporary plugging based on discrete fracture network combined with finite element method (DFN-FEM) was developed, and it was verified with monitoring data acquired during field fracturing operations. Based on the characteristics of deep shale in the Sichuan Basin, SW China, a multi-cluster complex fracture propagation numerical model was built. With this model, the multi-cluster fracture competitive propagation morphology and drainage area for horizontal wells were investigated, the competitive interference and intersecting propagation patterns of complex fractures before and after temporary plugging fracturing were analyzed, and the plugging timing was optimized depending upon the orientation, density and clustering mode of natural fractures. The research results show that fractures in the middle cluster are restricted by the fractures in two-side clusters, so temporary plugging of fractures in two-side clusters is conducive to the uniform propagation of fractures in all clusters. The higher the density or the lower the orientation of natural fractures, the latter the optimal plugging time. In Weiyuan, considering the distribution of natural fractures in shale, it is recommended to take 2/3 of total fluid injection time as the optimal plugging time under different clustering modes.
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In order to evaluate the stress sensitivity of carbonate reservoirs, a series of rock stress sensitivity tests were carried out under in-situ formation temperature and stress condition. Based on the calibration of capillary pressure curve, the variable fractal dimension was introduced to establish the conversion formula between relaxation time and pore size. By using the nuclear magnetic resonance (NMR) method, the pore volume loss caused by stress sensitivity within different scales of pore throat was quantitatively analyzed, and the microscopic mechanism of stress sensitivity of carbonate gas reservoirs was clarified. The results show that fractures can significantly affect the stress sensitivity of carbonate reservoirs. With the increase of initial permeability, the stress sensitivity coefficient decreases and then increases for porous reservoirs, but increases monotonously for fractured-porous reservoirs. The pore volume loss caused by stress sensitivity mainly occurs for mesopores (0.02-0.50 μm), contributing more than 50% of the total volume loss. Single high-angle fracture contributes 9.6% of the stress sensitivity and 15.7% of the irreversible damage. The microscopic mechanism of the stress sensitivity of carbonate gas reservoirs can be concluded as fracture closure, elastic contraction of pores and plastic deformation of rock skeleton.
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The oil-water two-phase flow pressure-transient analysis model for polymer flooding fractured well is established by considering the comprehensive effects of polymer shear thinning, shear thickening, convection, diffusion, adsorption retention, inaccessible pore volume and effective permeability reduction. The finite volume difference and Newton iteration methods are applied to solve the model, and the effects of fracture conductivity coefficient, injected polymer mass concentration, initial polymer mass concentration and water saturation on the well-test type curves of polymer flooding fractured wells are discussed. The results show that with the increase of fracture conductivity coefficient, the pressure conduction becomes faster and the pressure drop becomes smaller, so the pressure curve of transitional flow goes downward, the duration of bilinear flow becomes shorter, and the linear flow appears earlier and lasts longer. As the injected polymer mass concentration increases, the effective water phase viscosity increases, and the pressure loss increases, so the pressure and pressure derivative curves go upward, and the bilinear flow segment becomes shorter. As the initial polymer mass concentration increases, the effective water phase viscosity increases, so the pressure curve after the wellbore storage segment moves upward as a whole. As the water saturation increases, the relative permeability of water increases, the relative permeability of oil decreases, the total oil-water two-phase mobility becomes larger, and the pressure loss is reduced, so the pressure curve after the wellbore storage segment moves downward as a whole. The reliability and practicability of this new model are verified by the comparison of the results from simplified model and commercial well test software, and the actual well test data.
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To solve the problems of convolutional neural network-principal component analysis (CNN-PCA) in fine description and generalization of complex reservoir geological features, a 3D attention U-Net network was proposed not using a trained C3D video motion analysis model to extract the style of a 3D model, and applied to complement the details of geologic model lost in the dimension reduction of PCA method in this study. The 3D attention U-Net network was applied to a complex river channel sandstone reservoir to test its effects. The results show that compared with CNN-PCA method, the 3D attention U-Net network could better complement the details of geological model lost in the PCA dimension reduction, better reflect the fluid flow features in the original geologic model, and improve history matching results.
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This article outlines the development of downhole monitoring and data transmission technology for separated zone water injection in China. According to the development stages, the principles, operation processes, adaptability and application status of traditional downhole data acquisition method, cable communications and testing technology, cable-controlled downhole parameter real-time monitoring communication method and downhole wireless communication technology are introduced in detail. Problems and challenges of existing technologies in downhole monitoring and data transmission technology are pointed out. According to the production requirement, the future development direction of the downhole monitoring and data transmission technology for separated zone water injection are proposed. For the large number of wells adopting cable measuring and adjustment technology, the key is to realize the digitalization of downhole plug. For the key monitoring wells, cable-controlled communication technology needs to be improved, and downhole monitoring and data transmission technology based on composite coiled tubing needs to be developed to make the operation more convenient and reliable. For large-scale application in oil fields, downhole wireless communication technology should be developed to realize automation of measurement and adjustment. In line with ground mobile communication network, a digital communication network covering the control center, water distribution station and oil reservoir should be built quickly to provide technical support for the digitization of reservoir development.
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By summarizing the composition, classification, and performance characterization of functional adhesive materials, the adhesion mechanisms of functional adhesive materials, such as adsorption/surface reaction, diffusion, mechanical interlocking, and electrostatic adsorption, are expounded. The research status of these materials in oil and gas drilling and production engineering field such as lost circulation prevention/control, wellbore stabilization, hydraulic fracturing, and profile control and water plugging, and their application challenges and prospects in oil and gas drilling and production are introduced comprehensively. According to the applications of functional adhesive materials in the field of oil and gas drilling and production at this stage, the key research directions of functional adhesive materials in the area of oil and gas drilling and production are proposed: (1) blending and modifying thermoplastic resins or designing curable thermoplastic resins to improve the bonding performance and pressure bearing capacity of adhesive lost circulation materials; (2) introducing low-cost adhesive groups and positive charge structures into polymers to reduce the cost of wellbore strengthening agents and improve their adhesion performance on the wellbore; (3)introducing thermally reversible covalent bond into thermosetting resin to prevent backflow of proppant and improve the compressive strength of adhesive proppant; (4) introducing thermally reversible covalent bonds into thermoplastic polymers to improve the temperature resistance, salt-resistance and water shutoff performance of adhesive water shutoff agents.
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Carbon dioxide storage and utilization has become an inevitable trend and choice for sustainable development under the background of global climate change and carbon neutrality. Carbon industry which is dominated by CO2 capture, utilization and storage/ CO2 capture and storage (CCUS/CCS) is becoming a new strategic industry under the goal of carbon neutrality. The sustainable development of carbon industry needs to learn from the experiences of global oil and gas industry development. There are three types of “carbon” in the earth system. Black carbon is the CO2 that has not been sequestered or used and remains in the atmosphere for a long time; grey carbon is the CO2 that has been fixed or permanently sequestered in the geological body, and blue carbon is the CO2 that could be converted into products for human use through biological, physical, chemical and other ways. The carbon industry system covers carbon generation, carbon capture, carbon transportation, carbon utilization, carbon sequestration, carbon products, carbon finance, and other businesses. It is a revolutionary industrial field to completely eliminate “black carbon”. The development of carbon industry technical system takes carbon emission reduction, zero carbon, negative carbon and carbon economy as the connotation, and the construction of a low-cost and energy-efficient carbon industry system based on CCUS/CCS are strategic measures to achieve the goal of carbon neutrality and clean energy utilization globally. This will promote the “four 80%s” transformation of China's energy supply, namely, to 2060, the percentage of zero-carbon new energy in the energy consumption will be over 80% and the CO2 emission will be decreased by 80% to ensure the carbon emission reduction of total 80×108 t from the percentage of carbon-based fossil energy in the energy consumption of over 80%, and the percentage of CO2 emission from energy of over 80% in 2021. The carbon industry in China is facing three challenges, large CO2 emissions, high percentage of coal in energy consumption, and poor innovative system. Three strategic measures are proposed accordingly, including: (1) unswervingly develop carbon industrial system and ensure the achievement of carbon neutrality as scheduled by 2060; (2) vigorously develop new energy sources and promote a revolutionary transformation of China’s energy production and consumption structure; (3) accelerate the establishment of scientific and technological innovation system of the whole CO2 industry. It is of great significance for continuously optimization of ecological environment and construction of green earth and ecological earth to develop the carbon industry system, utilize clean energy, and achieve the strategic goal of global carbon neutrality.
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The development history of carbon capture, utilization and storage for enhanced oil recovery (CCUS-EOR) in China is comprehensively reviewed, which consists of three stages: research and exploration, field test and industrial application. The breakthrough understanding of CO2 flooding mechanism and field practice in recent years and the corresponding supporting technical achievements of CCUS-EOR project are systematically described. The future development prospects are also pointed out. After nearly 60 years of exploration, the theory of CO2 flooding and storage suitable for continental sedimentary reservoirs in China has been innovatively developed. It is suggested that C7-C15 are also important components affecting miscibility of CO2 and crude oil. The mechanism of rapid recovery of formation energy by CO2 and significant improvement of block productivity and recovery factor has been verified in field tests. The CCUS-EOR reservoir engineering design technology for continental sedimentary reservoir is established. The technology of reservoir engineering parameter design and well spacing optimization has been developed, which focuses on maintaining miscibility to improve oil displacement efficiency and uniform displacement to improve sweep efficiency. The technology of CO2 capture, injection and production process, whole-system anticorrosion, storage monitoring and other whole-process supporting technologies have been initially formed. In order to realize the efficient utilization and permanent storage of CO2, it is necessary to take the oil reservoir in the oil-water transition zone into consideration, realize the large-scale CO2 flooding and storage in the area from single reservoir to the overall structural control system. The oil reservoir in the oil-water transition zone is developed by stable gravity flooding of injecting CO2 from structural highs. The research on the storage technology such as the conversion of residual oil and CO2 into methane need to be carried out.
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This paper systematically presents the established technologies and field applications with respect to research and engineering practice of CO2 capture, enhanced oil recovery (EOR), and storage technology in Jilin Oilfield, NE China, and depicts the available series of supporting technologies across the industry chain. Through simulation calculation + pilot test + field application, the adaptability of the technology for capturing CO2 with different concentrations in oilfields was confirmed. The low energy-consumption, activated N-methyl diethanolamine (MDEA) decarburization technology based on a new activator was developed, and the operation mode of CO2 gas-phase transportation through trunk pipeline network, supercritical injection at wellhead, and produced gas-liquid separated transportation was established. According to different gas source conditions, liquid, supercritical phase, high-pressure dense phase pressurization technologies and facilities were applied to form the downhole injection processes (e.g. gas-tight tubing and coiled tubing) and supporting anti-corrosion and anti-blocking techniques. In the practice of oil displacement, the oil recovery technologies (e.g. conical water-alternating-gas injection, CO2 foam flooding, and high gas-oil ratio CO2 flooding) and produced fluid processing technologies were developed. Through numerical simulation and field tests, three kinds of CO2 cyclic injection technologies (i.e. direct injection, injection after separation and purification, and hybrid injection) were formed, and a 10×104 m3/d cyclic injection station was constructed to achieve "zero emission" of associated gas. The CO2 storage safety monitoring technology of carbon flux, fluid composition and carbon isotopic composition was formed. The whole-process anti-corrosion technology with anticorrosive agents supplemented by anticorrosive materials was established. An integrated demonstration area of CO2 capture, flooding and storage with high efficiency and low energy-consumption has been built, with a cumulative oil increment of 32×104 t and a CO2 storage volume of 250×104 t.
