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Based on the results of drilling, tests and simulation experiments, the shales of the Cretaceous Qingshankou Formation in the Gulong Sag of the Songliao Basin are discussed with respect to hydrocarbon generation evolution, shale oil occurrence, and pore/fracture evolution mechanism. In conjunction with a substantial amount of oil testing and production data, the Gulong shale oil enrichment layers are evaluated and the production behaviors and decline law are analyzed. The results are drawn in four aspects. First, the Gulong shales are in the stage of extensive hydrocarbon expulsion when Ro is 1.0%-1.2%, with the peak hydrocarbon expulsion efficiency of 49.5% approximately. In the low-medium maturity stage, shale oil migrates from kerogen to rocks and organic pores/fractures. In the medium-high maturity stage, shale oil transforms from adsorbed state to free state. Second, the clay mineral intergranular pores/fractures, dissolution pores, and organic pores make up the majority of the pore structure. During the transformation, clay minerals undergo significant intergranular pore/fracture development between the minerals such as illite and illite/smectite mixed layer. A network of pores/fractures is formed by organic matter cracking. Third, free hydrocarbon content, effective porosity, total porosity, and brittle mineral content are the core indicators for the evaluation of shale oil enrichment layers. Class-I layers are defined as free hydrocarbon content equal or greater than 6.0 mg/g, effective porosity equal or greater than 3.5%, total porosity equal or greater than 8.0%, and brittle mineral content equal or greater than 50%. It is believed that the favourable oil layers are Q2-Q3 and Q8-Q9. Fourth, the horizontal wells in the core area of the light oil zone exhibit a high cumulative production in the first year, and present a hyperbolic production decline pattern, with the decline index of 0.85-0.95, the first-year decline rate of 14.5%-26.5%, and the single-well estimated ultimate recovery (EUR) greater than 2.0×104 t. In practical exploration and production, more efforts will be devoted to the clarification of hydrocarbon generation and expulsion mechanisms, accurate testing of porosity and hydrocarbon content/phase of shale under formation conditions, precise delineation of the boundary of enrichment area, relationship between mechanical properties and stimulated reservoir volume, and enhanced oil recovery, in order to improve the EUR and achieve a large-scale, efficient development of shale oil.
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The geological characteristics and production practices of the major middle- and high-maturity shale oil exploration areas in China are analyzed. Combined with laboratory results, it is clear that three essential conditions, i.e. economic initial production, commercial cumulative oil production of single well, and large-scale recoverable reserves confirmed by the testing production, determine whether the continental shale oil can be put into large-scale commercial development. The quantity and quality of movable hydrocarbons are confirmed to be crucial to economic development of shale oil, and focuses in evaluation of shale oil enrichment area/interval. The evaluation indexes of movable hydrocarbon enrichment include: (1) the material basis for forming retained hydrocarbon, including TOC>2% (preferentially 3%-4%), and type I-II1 kerogens; (2) the mobility of retained hydrocarbon, which is closely related to the hydrocarbon composition and flow behaviors of light/heavy components, and can be evaluated from the perspectives of thermal maturity (Ro), gas-oil ratio (GOR), crude oil density, quality of hydrocarbon components, preservation conditions; and (3) the reservoir characteristics associated with the engineering reconstruction, including the main pore throat distribution zone, reservoir physical properties (including fractures), lamellation feature and diagenetic stage, etc. Accordingly, 13 evaluation indexes in three categories and their reference values are established. The evaluation indicates that the light shale oil zones in the Gulong Sag of Songliao Basin have the most favorable enrichment conditions of movable hydrocarbons, followed by light oil and black oil zones, containing 20.8×108 t light oil resources in reservoirs with Ro>1.2%, pressure coefficient greater than 1.4, effective porosity greater than 6%, crude oil density less than 0.82 g/cm3, and GOR>100 m3/m3. The shale oil in the Gulong Sag can be explored and developed separately by the categories (resource sweet spot, engineering sweet spot, and tight oil sweet spot) depending on shale oil flowability. The Gulong Sag is the most promising area to achieve large-scale breakthrough and production of continental shale oil in China.
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According to the theory of sequence stratigraphy based on continental transgressive-regressive (T-R) cycles, a 500 m continuous core taken from the second member of Kongdian Formation (Kong 2 Member) of Paleogene in Well G108-8 in the Cangdong Sag, Bohai Bay Basin, was tested and analyzed to clarify the high-frequency cycles of deep-water fine-grained sedimentary rocks in lacustrine basins. A logging vectorgraph in red pattern was plotted, and then a sequence stratigraphic framework with five-order high-frequency cycles was formed for the fine-grained sedimentary rocks in the Kong 2 Member. The high-frequency cycles of fine-grained sedimentary rocks were characterized by using different methods and at different scales. It is found that the fifth-order T cycles record a high content of terrigenous clastic minerals, a low paleosalinity, a relatively humid paleoclimate and a high density of laminae, while the fifth-order R cycles display a high content of carbonate minerals, a high paleosalinity, a dry paleoclimate and a low density of laminae. The changes in high-frequency cycles controlled the abundance and type of organic matter. The T cycles exhibit relatively high TOC and abundant endogenous organic matters in water in addition to terrigenous organic matters, implying a high primary productivity of lake for the generation and enrichment of shale oil.
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Based on the typical dissection of various onshore tight oil fields in China, the tight oil migration and accumulation mechanism and enrichment-controlling factors in continental lake basins are analyzed through nuclear magnetic resonance (NMR) displacement physical simulation and Lattice Boltzmann numerical simulation by using the samples of source rock, reservoir rock and crude oil. In continental lake basins, the dynamic forces driving hydrocarbon generation and expulsion of high-quality source rocks are the foundational power that determines the charging efficiency and accumulation effect of tight oil, the oil migration resistance is a key element that influences the charging efficiency and accumulation effect of tight oil, and the coupling of charging force with pore-throat resistance in tight reservoir controls the tight oil accumulation and sweet spot enrichment. The degree of tight oil enrichment in continental lake basins is controlled by four factors: source rock, reservoir pore-throat size, anisotropy of reservoir structure, and fractures. The high-quality source rocks control the near-source distribution of tight oil, reservoir physical properties and pore-throat size are positively correlated with the degree of tight oil enrichment, the anisotropy of reservoir structure reveals that the parallel migration rate is the highest, and intralayer fractures can improve the migration and accumulation efficiency and the oil saturation.
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According to the latest drilling and the analysis of the burial history, source rock evolution history and hydrocarbon accumulation history, the sub-source hydrocarbon accumulation characteristics of the Permian reservoirs in the Jinan Sag, eastern Junggar Basin, are clarified, and the hydrocarbon accumulation model of these reservoirs is established. The results are obtained in four aspects. First, the main body of the thick salified lake basin source rocks in the Lucaogou Formation has reached the mature stage with abundant resource base. Large-scale reservoirs are developed in the Jingjingzigou, Wutonggou and Lucaogou formations. Vertically, there are multiple sets of good regional seals, the source-reservoir-caprock assemblage is good, and there are three reservoir-forming assemblages: sub-source, intra-source and above-source. Second, dissolution, hydrocarbon charging and pore-preserving effect, and presence of chlorite film effectively increase the sub-source pore space. Oil charging is earlier than the time when the reservoir becomes densified, which improves the efficiency of hydrocarbon accumulation. Third, buoyancy and source-reservoir pressure difference together constitute the driving force of oil charging, and the micro-faults within the formation give the advantage of “source-reservoir lateral docking” under the source rock. Microfractures can be critical channels for efficient seepage and continuous charging of oil in different periods. Fourth, the Jingjingzigou Formation experienced three periods of oil accumulation in the Middle-Late Permian, Middle-Late Jurassic and Late Neogene, with the characteristics of long-distance migration and accumulation in early stage, mixed charging and accumulation in middle stage and short-distance migration and high-position accumulation in late stage. The discovery and theoretical understanding of the Permian reservoirs in the Jinan Sag reveal that the thrust belt has good conditions for forming large reservoirs, and it is promising for exploration. The study results are of guidance and reference significance for oil and gas exploration in the Jinan Sag and other geologically similar areas.
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Based on outcrop, seismic and drilling data, the main regional unconformities in the Sichuan Basin and their controls on hydrocarbon accumulation were systematically studied. Three findings are obtained. First, six regional stratigraphic unconformities are mainly developed in the Sichuan Basin, from the bottom up, which are between pre-Sinian and Sinian, between Sinian and Cambrian, between pre-Permian and Permian, between middle and upper Permian, between middle and upper Triassic, and between Triassic and Jurassic. Especially, 16 of 21 conventional (and tight) gas fields discovered are believed to have formed in relation to regional unconformities. Second, regional unconformity mainly controls hydrocarbon accumulation from five aspects: (1) The porosity and permeability of reservoirs under the unconformity are improved through weathering crust karstification to form large-scale karst reservoirs; (2) Good source-reservoir-caprock assemblage can form near the unconformity, which provides a basis for forming large gas field; (3) Regional unconformity may lead to stratigraphic pinch-out and rugged ancient landform, giving rise to a large area of stratigraphic and lithologic trap groups; (4) Regional unconformity provides a dominant channel for lateral migration of oil and gas; and (5) Regional unconformity is conducive to large-scale accumulation of oil and gas. Third, the areas related to regional unconformities are the exploration focus of large gas fields in the Sichuan Basin. The pre-Sinian is found with source rocks, reservoir rocks and other favorable conditions for the formation of large gas fields, and presents a large exploration potential. Thus, it is expected to be an important strategic replacement.
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Through core observation, thin section identification, and logging and testing data analysis, the types and characteristics of event deposits in the ninth member of Yanchang Formation of Triassic (Chang 9 Member) in southwestern Ordos Basin, China, are examined. There are 4 types and 9 subtypes of event deposits, i.e. earthquake, gravity flow, volcanic and anoxic deposits, in the Chang 9 Member in the study area. Based on the analysis of the characteristics and distribution of such events deposits, it is proposed that the event deposits are generally symbiotic or associated, with intrinsic genetic relations and distribution laws. Five kinds of sedimentary microfacies with relatively developed event deposits are identified, and the genetic model of event deposits is discussed. Seismites are mainly developed in the lake transgression stage when the basin expands episodically, and commonly affected by liquefaction flow, gravity action and brittle shear deformation. Gravity flow, mainly distributed in the high water level period, sandwiched in the fine-grained sediments of prodelta or semi-deep lake, or creates banded or lobate slump turbidite fan. It is relatively developed above the seismites strata. The volcanic event deposits are only seen in the lower part of the Chang 9 Member, showing abrupt contact at the top and bottom, which reflects the volcanic activity at the same time. Anoxic deposits are mostly formed in the late stage of lake transgression to the highstand stage. Very thick organic-rich shales are developed in the highstand stage of Chang 9 Member, and the event deposits in the depositional period of these shales are conducive to potential reservoirs.
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In the second member of the Upper Triassic Xujiahe Formation (T3x2) in the Xinchang area, western Sichuan Basin, only a low percent of reserves has been recovered, and the geological model of gas reservoir sweet spot remains unclear. Based on a large number of core, field outcrop, test and logging-seismic data, the T3x2 gas reservoir in the Xinchang area is examined. The concept of fault-fold-fracture body (FFFB) is proposed, and its types are recognized. The main factors controlling fracture development are identified, and the geological models of FFFB are established. FFFB refers to faults, folds and associated fractures reservoirs. According to the characteristics and genesis, FFFBs can be divided into three types: fault-fracture body, fold-fracture body, and fault-fold body. In the hanging wall of the fault, the closer to the fault, the more developed the effective fractures; the greater the fold amplitude and the closer to the fold hinge plane, the more developed the effective fractures. Two types of geological models of FFFB are established: fault-fold fracture, and matrix storage and permeability. The former can be divided into two subtypes: network fracture, and single structural fracture, and the later can be divided into three subtypes: bedding fracture, low permeability pore, and extremely low permeability pore. The process for evaluating favorable FFFB zones was formed to define favorable development targets and support the well deployment for purpose of high production. The study results provide a reference for the exploration and development of deep tight sandstone oil and gas reservoirs in China.
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Granular calcite is an authigenic mineral in fine-grained sedimentary rocks. Core observation, thin section observation, cathodoluminescence analysis, fluid inclusion analysis, scanning electron microscope (SEM), and isotopic composition analysis were combined to clarify the genesis of granular calcite in the lacustrine fine-grained sedimentary rocks of the Permian Lucaogou Formation in the Jimusar Sag, Junggar Basin. It is found that the granular calcite is distributed with laminated characteristics in fine-grained sedimentary rocks in tuffite zones (or the transitional zone between tuffite and micritic dolomite). Granular calcite has obvious cathodoluminesence band, and it can be divided into three stages. Stage-I calcite, with non-luminesence, high content of Sr element, inclusions containing COS, and homogenization temperature higher than 170 °C, was directly formed from the volcanic-hydrothermal deposition. Stage-II calcite, with bright yellow luminescence, high contents of Fe, Mn and Mg, enrichment of light rare earth elements (LREEs), and high homogenization temperature, was formed by recrystallization of calcareous edges from exhalative hydrothermal deposition. Stage-III calcite, with dark orange luminescence band, high contents of Mg, P, V and other elements, no obvious fractionation among LREEs, and low homogenization temperature, was originated from diagenetic transformation during burial. The granular calcite appears regularly in the vertical direction and its formation temperature decreases from the center to the margin of particles, providing direct evidences for volcanic-hydrothermal events during the deposition of the Lucaogou Formation. The volcanic-hydrothermal event was conducive to the enrichment of organic matters in fine-grained sedimentary rocks of the Lucaogrou Formation, and positive to the development of high-quality source rocks. The volcanic-hydrothermal sediments might generate intergranular pores/fractures during the evolution, creating conditions for the self-generation and self-storage of shale oil.
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According to the capillary theory, an equivalent capillary model of micro-resistivity imaging logging was built. On this basis, the theoretical models of porosity spectrum (?i), permeability spectrum (Ki) and equivalent capillary pressure curve (pci) were established to reflect the reservoir heterogeneity. To promote the application of the theoretical models, the Archie's equation was introduced to establish a general model for quantitatively characterizing ?i, Ki, and pci. Compared with the existing models, it is shown that: (1) the existing porosity spectrum model is the same as the general equation of ?i; (2) the Ki model can display the permeability spectrum as compared with Purcell's permeability model; (3) the pci model is constructed on a theoretical basis and avoids the limitations of existing models that are built only based on the component of porosity spectrum, as compared with the empirical model of capillary pressure curve. The application in the Permian Maokou Formation of Well TSX in the Central Sichuan paleo-uplift shows that the ?i, Ki, and pci models can be effectively applied to the identification of reservoir types, calculation of reservoir properties and pore structure parameters, and evaluation of reservoir heterogeneity.
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Aiming at the four issues of underground storage state, exploitation mechanism, crude oil flow and efficient recovery, the key theoretical and technical issues and countermeasures for effective development of Gulong shale oil are put forward. Through key exploration and research on fluid occurrence, fluid phase change, exploitation mechanism, oil start-up mechanism, flow regime/pattern, exploitation mode and enhanced oil recovery (EOR) of shale reservoirs with different storage spaces, multi-scale occurrence states of shale oil and phase behavior of fluid in nano confined space were provided, the multi-phase, multi-scale flow mode and production mechanism with hydraulic fracture-shale bedding fracture-matrix infiltration as the core was clarified, and a multi-scale flow mathematical model and recoverable reserves evaluation method were preliminarily established. The feasibility of development mode with early energy replenishment and recovery factor of 30% was discussed. Based on these, the researches of key theories and technologies for effective development of Gulong shale oil are proposed to focus on: (1) in-situ sampling and non-destructive testing of core and fluid; (2) high-temperature, high-pressure, nano-scale laboratory simulation experiment; (3) fusion of multi-scale multi-flow regime numerical simulation technology and large-scale application software; (4) waterless (CO2) fracturing technique and the fracturing technique for increasing the vertical fracture height; (5) early energy replenishment to enhance oil recovery; (6) lifecycle technical and economic evaluation. Moreover, a series of exploitation tests should be performed on site as soon as possible to verify the theoretical understanding, optimize the exploitation mode, form supporting technologies, and provide a generalizable development model, thereby supporting and guiding the effective development and production of Gulong shale oil.
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In the Jiaoshiba block of the Fuling shale gas field, the employed reserves and recovery factor by primary well pattern are low, no obvious barrier is found in the development layer series, and layered development is difficult. Based on the understanding of the main factors controlling shale gas enrichment and high production, the theory and technology of shale gas three-dimensional development, such as fine description and modeling of shale gas reservoir, optimization of three-dimensional development strategy, highly efficient drilling with dense well pattern, precision fracturing and real-time control, are discussed. Three-dimensional development refers to the application of optimal and fast drilling and volume fracturing technologies, depending upon the sedimentary characteristics, reservoir characteristics and sweet spot distribution of shale gas, to form “artificial gas reservoir” in a multidimensional space, so as to maximize the employed reserves, recovery factor and yield rate of shale gas development. In the research on shale gas three-dimensional development, the geological + engineering sweet spot description is fundamental, the collaborative optimization of natural fractures and artificial fractures is critical, and the improvement of speed and efficiency in drilling and fracturing engineering is the guarantee. Through the implementation of three-dimensional development, the overall recovery factor in the Jiaoshiba block has increased from 12.6% to 23.3%, providing an important support for the continuous and stable production of the Fuling shale gas field.
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To improve the design and management of an integrated production system (IPS), a set of mathematical models and workflows are developed for evaluating the capacity of an IPS at steady-state conditions. Combining the conservation laws with applicable multiphase fluid and choke models, these mathematical models are solved to characterize the hydraulics of an integrated system of reservoir, wells, chokes, flowlines, and separator at steady state. The controllable variables such as well count, choke size and separator pressure are adjusted to optimize the performance of the IPS at a specific time. It is found that increasing the well count can increase the bulk flow rate of the production network, but too many wells may increase the manifold pressure, leading to decline of single-well production. Increasing the choke size can improve the capacity of the IPS. The production of the IPS is negatively correlated with the separator pressure. With increasing separator pressure and decreasing choke size, the increment of total fluid production (the capacity of IPS) induced by increasing well count decreases. Validation tests with field examples show a maximum absolute deviation is 1.5%, demonstrating the robustness and validity of the proposed mathematical models and workflows.
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This study used the diethylene triamine pentaacetic acid (DTPA)-seawater (SW) system to modify the sandstone rock wettability and enhance oil recovery. The investigation involved conducting wettability measurement, Zeta potential measurement, and spontaneous imbibition experiment. The introduction of 5% DTPA-SW solution resulted in a significant decrease in the rock-oil contact angle from 143° to 23°, along with a reduction in the Zeta potential from ?2.29 mV to ?13.06 mV, thereby altering the rock surface charge and shifting its wettability from an oil-wet state to a strongly water-wet state. The presence or absence of potential determining ions (Ca2+, Mg2+, SO42?) in the solution did not impact the effectiveness of DTPA in changing the rock wettability. However, by tripling the concentration of these ions in the solution, the performance of 5% DTPA-SW solution in changing wettability was impaired. Additionally, spontaneous imbibition tests demonstrated that the 5% DTPA-SW solution led to an increase in oil recovery up to 39.6%. Thus, the optimum mass fraction of DTPA for changing sandstone wettability was determined to be 5%.
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This paper reviews the multiple rounds of upgrades of the hydraulic fracturing technology used in the Gulong shale oil reservoirs and gives suggestions about stimulation technology development in relation to the production performance of Gulong shale oil wells. Under the control of high-density bedding fractures, fracturing in the Gulong shale results in a complex fracture morphology, yet with highly suppressed fracture height and length. Hydraulic fracturing fails to generate artificial fractures with sufficient lengths and heights, which is a main restraint on the effective stimulation in the Gulong shale oil reservoirs. In this regard, the fracturing design shall follow the strategy of “controlling near-wellbore complex fractures and maximizing the extension of main fractures”. Increasing the proportions of guar gum fracturing fluids, reducing perforation clusters within one fracturing stage, raising pump rates and appropriately exploiting stress interference are conducive to fracture propagation and lead to a considerably expanded stimulated reservoir volume (SRV). The upgraded main hydraulic fracturing technology is much more applicable to the Gulong shale oil reservoirs. It accelerates the oil production with a low flowback rate and lifts oil cut during the initial production of well groups, which both help to improve well production. It is suggested to optimize the hydraulic fracturing technology in six aspects, namely, suppressing propagation of near-wellbore microfractures, improving the pumping scheme of CO2, managing the perforating density, enhancing multi-proppant combination, reviewing well pattern/spacing, and discreetly applying fiber-assisted injection, so as to improve the SRV, the distal fracture complexity and the long-term fracture conductivity.
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A fracture propagation model of radial well fracturing is established based on the finite element-meshless method. The model considers the coupling effect of fracturing fluid flow and rock matrix deformation. The fracture geometries of radial well fracturing are simulated, the induction effect of radial well on the fracture is quantitatively characterized, and the influences of azimuth, horizontal principle stress difference, and reservoir matrix permeability on the fracture geometries are revealed. The radial wells can induce the fractures to extend parallel to their axes when two radial wells in the same layer are fractured. When the radial wells are symmetrically distributed along the direction of the minimum horizontal principle stress with the azimuth greater than 15°, the extrusion effect reduces the fracture length of radial wells. When the radial wells are symmetrically distributed along the direction of the maximum horizontal principal stress, the extrusion increases the fracture length of the radial wells. The fracture geometries are controlled by the rectification of radial borehole, the extrusion between radial wells in the same layer, and the deflection of the maximum horizontal principal stress. When the radial wells are distributed along the minimum horizontal principal stress symmetrically, the fracture length induced by the radial well decreases with the increase of azimuth; in contrast, when the radial wells are distributed along the maximum horizontal principal stress symmetrically, the fracture length induced by the radial well first decreases and then increases with the increase of azimuth. The fracture length induced by the radial well decreases with the increase of horizontal principal stress difference. The increase of rock matrix permeability and pore pressure of the matrix around radial wells makes the inducing effect of the radial well on fractures increase.
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A method to generate fractures with rough surfaces was proposed according to the fractal interpolation theory. Considering the particle-particle, particle-wall and particle-fluid interactions, a proppant-fracturing fluid two-phase flow model based on computational fluid dynamics (CFD)-discrete element method (DEM) coupling was established. The simulation results were verified with relevant experimental data. It was proved that the model can match transport and accumulation of proppants in rough fractures well. Several cases of numerical simulations were carried out. Compared with proppant transport in smooth flat fractures, bulge on the rough fracture wall affects transport and settlement of proppants significantly in proppant transportation in rough fractures. The higher the roughness of fracture, the faster the settlement of proppant particles near the fracture inlet, the shorter the horizontal transport distance, and the more likely to accumulate near the fracture inlet to form a sand plugging in a short time. Fracture wall roughness could control the migration path of fracturing fluid to a certain degree and change the path of proppant filling in the fracture. On the one hand, the rough wall bulge raises the proppant transport path and the proppants flow out of the fracture, reducing the proppant sweep area. On the other hand, the sand-carrying fluid is prone to change flow direction near the contact point of bulge, thus expanding the proppant sweep area.
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The essence of energy system transition is the “energy revolution”. The development of the “resource-dominated” energy system with fossil energy as the mainstay has promoted human progress, but it has also triggered energy crisis and ecological environment crisis, which is not compatible with the new demands of the new round of scientific and technological revolution, industrial transformation, and sustainable human development. It is in urgent need to research and develop a new-type energy system in the context of carbon neutrality. In the framework of “technique-dominated” new green and intelligent energy system with “three new” of new energy, new power and new energy storage as the mainstay, the “super energy basin” concepts with the Ordos Basin, NW China as a representative will reshape the concept and model of future energy exploration and development. In view of the “six inequalities” in global energy and the resource conditions of “abundant coal, insufficient oil and gas and infinite new energy” in China, it is suggested to deeply boost “China energy revolution”, sticking to the six principles of independent energy production, green energy supply, secure energy reserve, efficient energy consumption, intelligent energy management, economical energy cost; enhance “energy scientific and technological innovation” by implementing technique-dominated “four major science and technology innovation projects”, namely, clean coal project, oil production stabilization and gas production increasing project, new energy acceleration project, and green-intelligent energy project; implement “energy transition” by accelerating the green-dominated “four-modernization development”, namely, fossil energy cleaning, large-scale new energy, coordinated centralized energy distribution, intelligent multi-energy management, so as to promote the exchange of “two 80%s” in China's energy structure and construct the new green and intelligent energy system.
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A smart response fluid was designed and developed to overcome the challenges of gas channeling during CO2 flooding in low-permeability, tight oil reservoirs. The fluid is based on Gemini surfactant with self-assembly capabilities, and the tertiary amine group serves as the response component. The responsive characteristics and corresponding mechanism of the smart fluid during the interaction with CO2/oil were studied, followed by the shear characteristics of the thickened aggregates obtained by the smart fluid responding to CO2. The temperature and salt resistance of the smart fluid and the aggregates were evaluated, and their feasibility and effectiveness in sweep-controlling during the CO2 flooding were confirmed. This research reveals: (1) Thickened aggregates could be assembled since the smart fluid interacted with CO2. When the mass fraction of the smart fluid ranged from 0.05% to 2.50%, the thickening ratio changed from 9 to 246, with viscosity reaching 13 to 3100 mPa?s. As a result, the sweep efficiency in low-permeability core models could be increased in our experiments. (2) When the smart fluid (0.5% to 1.0%) was exposed to simulated oil, the oil/fluid interfacial tension decreased to the level of 1×10?2 mN/m. Furthermore, the vesicle-like micelles in the smart fluid completely transformed into spherical micelles when the fluid was exposed to simulated oil with the saturation greater than 10%. As a result, the smart fluid could maintain low oil/fluid interfacial tension, and would not be thickened after oil exposure. (3) When the smart fluid interacted with CO2, the aggregates showed self-healing properties in terms of shear-thinning, static-thickening, and structural integrity after several shear-static cycles. Therefore, this fluid is safe to be placed in deep reservoirs. (4) The long-term temperature and salt resistance of the smart fluid and thickened aggregates have been confirmed.
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In response to the lack of global quantitative research on the potential and scale prediction of CO2 capture, utilization and storage (CCUS) in China under the background of carbon peak and carbon neutrality goals, this study predicts the future economic costs of different links of CCUS technologies and the carbon capture needs of different industries in the scenario of fossil energy continuation. Based on the CO2 utilization and storage potential and spatial distribution in China, a cost-scale calculation model for different regions in China in 2060 is constructed to predict the whole-process economic cost and its corresponding scale potential of CCUS. The results show that a local + remote storage mode is preferred, together with a local utilization mode, to meet China's 27×108 t/a CO2 emission reduction demand under the scenario of fossil energy continuation. Specifically, about 5×108 t CO2 emission is reduced by capture utilization, and the whole-process cost is about ?1400-200 RMB/t; about 22×108 t CO2 emission is reduced by capture storage, and the whole-process cost is about 200-450 RMB/t. According to the model results, it is recommended to develop the chemical utilization industry based on P2X (Power to X, where X is raw material) technology, construct the CCUS industrial cluster, and explore a multi-party win-win cooperation mode. A scheme of national trunk pipeline network connecting areas connecting intensive emission reduction demand areas and target storage areas is suggested. The emission reduction cost of thermal power based on CCUS is calculated to be 0.16 RMB/(kW·h).
