With the continuous and further development in Sinopec shale oil exploitation, a series of characteristic technologies such as drilling, logging cementing and fracturing have been preliminarily formed. By the summary and analysis of the progress and achievements made by Sinopec in shale oil engineering technology during the "14th Five-Year Plan" period, the problems and challenges currently existing in shale oil development engineering technology are reviewed, and the technical countermeasures and development suggestions in the aspects of geological and drilling engineering integration, speed-up of drilling and completion, three-dimensional well development, and ultra-long horizontal wells are pointed out. Therefore, it promotes the development of shale oil engineering technology in China, realizes the low-cost, large-scale and cost-effective development of shale oil resources, and provides useful reference.

Generally there exist a large number of ineffective perforation clusters in multistage hydraulic fracturing of horizontal wells of shale gas reservoirs. So improving the effectiveness of perforation and maintaining the long-term conductivity of fractures are the main challenges to increase production and reduce costs for shale gas horizontal wells. Based on previous research results, the main reasons for low production of perforation clusters include: ① Fracture does not initiate or propagate effectively due to mechanical heterogeneity of shale reservoir, stress shadow between fractures, or difference of perforation erosion rate; ② The distribution of proppant is non-uniform between clusters and in fractures due to the difference of perforation displacement distribution within the stage, weak sand suspension ability of low viscosity fracturing fluid, and fracture bending, inclination and roughness; ③ The fracture conductivity is lost due to the breakage and embedding of proppant, diagenesis, formation and migration of formation particles. In order to solve the above problems, the optimization and technical solutions to facilitate the balanced initiation of fractures, the uniform distribution of proppants, and the improvement of fracture conductivity are proposed. They include new-type limited entry fracturing technique, degradable temporary plugging diversion, optimization of perforation parameters and sand-adding sequence, high-speed channel fracturing, high viscosity friction reducers and new-type proppants, etc., which are expected to provide benchmark for improving the effectiveness of perforation cluster fracturing of horizontal wells.

At present, China has encountered many problems and challenges in the exploration and development of continental shale oil. The mobility of shale oil is greatly affected by complex pore structure and poor seepage capacity, and restricts the efficient development of continental shale oil. Therefore, In order to solve such prominent problem, the present situation, existing problems and future development trend of the research methods and technical means of shale oil reservoir pore structure and shale oil seepage law are briefly introduced. The results show that the characterization withe multi-scale, fine and continuous is the key to characterize the pore structure of continental shale oil reservoir. The establishment of the uniform pore structure characterization technology and the classification evaluation criteria is the geological basis for the effective development of continental shale oil. The combination of multi-physical model and experimental method is the basis of the seepage characterization of continental shale oil. Strengthening the combination of numerical simulation, physical simulation and laboratory experiments is the main direction of the study on the seepage mechanism of continental shale oil. It provides an important guideline for breaking the bottleneck of continental shale oil development and is of great significance to realize the efficient development of continental shale oil reservoirs.

The availability of shale oil directly affects the degree of effective exploration and development, and the mobility of shale oil is closely related to its occurrence state. Therefore, studying the occurrence state of shale oil plays an important role in its development. The pore model is established by graphene and quartz, and the occurrence state of n-octane and its mixture in nanopores is studied by molecular simulation method. The effects of pore size, temperature, pressure, shale oil composition, wall wettability and wall composition on the occurrence state are analyzed. The results show that: ①shale oil is multi-layer adsorbed in the pores and symmetrical about the pore center, and the thickness of the adsorption layer is 0.4~0.5 nm; ②The larger the pore size of the reservoir, the higher the temperature, the lower the pressure, the lighter the molecular component, the weaker the polarity, and the higher the wall wettability are, the more unfavorable the adsorption of oil molecules on the wall is;③ In the combined wall, due to the influence of graphene wall, the adsorption amount of shale oil molecules increases with the increase of quartz wall wetting humidity. In addition, the adsorption transfer phenomenon of n-hexanoic acid and cyclohexane also occurs.

In order to realize the efficient development of lacustrine organic-rich shale oil reservoir in the lower sub-member of the third member of the Eocene Shahejie Formation and the upper sub-member of the fourth member of the Eocene Shahejie Formation in the Boxing Sag, Dongying depression, the geological data, such as thin sections, X-ray diffraction and the content of major and trace elements are analyzed. After the data analysis, the types of lithofacies and the evolution stage of sedimentary paleoenvironment are determined, and eight lithofacies assemblages are also divided based on the relationship between lithofacies and sedimentary environments. Then, the favorable lithofacies for shale oil exploration and development are determined based on the comparison of geological and engineering “sweet spot” parameters of different lithofacies assemblages. The results indicate that: ① Six lithofacies types of organic-rich laminated argillaceous limestone and limestone mudstone, organic-rich layered argillaceous limestone and limestone mudstone, organic-poor massive argillaceous limestone and calcareous mudstone are mainly developed in the study area; ② The sedimentary paleoenvironment with the characteristics of paleoclimate from arid to humid, little change in paleoredox, paleosalinity from high to low, and paleo-provenance from less to more exhibited eight evolutionary stages, corresponding to eight lithofacies assemblage types; ③ Lithofacies assemblage D and F, with high shale oil productivity, are the favorable in the Es^3L and Es^4U, respectively, and are in good agreement with the production practices. On the plane, the former is mainly distributed in the F159-F156-F160 well areas, and the latter is mainly distributed in FYP1-F116-F119 and F156-F159-F161 well area, which is a shale oil enrichment and high yield area in Boxing sag.

Gas bearing shale is widely developed in continental faulted basins in China. In the past, it was mainly studied as the gas source rock, and there was little research on its reservoir and influencing factors. It is urgent to carry out corresponding researches to clarify the main controlling factors of shale reservoir development in continental faulted basins. For the researches, the shale of Shahezi Formation in Xujiaweizi fault depression of Songliao Basin and Longmaxi Formation in Sichuan Basin are selected, and the difference of reservoir characteristics between high over mature continental fault depression basin and marine gas shale is compared and studied by the experiments such as organic geochemistry, whole rock analysis, scanning electron microscope, low-temperature nitrogen adsorption and nuclear magnetic resonance. The research shows that the shale formation environment of Shahezi Formation is diverse, the organic matter type is mainly type Ⅲ, the clay mineral content is high, the cemented quartz is developed, the clay related pores and quartz intergranular pores are the main pore types, the specific surface area is small but the pore diameter is large, and the reservoir development is controlled by compaction, clay mineral transformation and coal seam development; Longmaxi Formation shale was formed in shelf environment. The type of organic matter is mainly type Ⅰ, with high abundance of organic matter and high content of biogenic quartz. Organic pores and clay related pores are the main pore types, and the type and maturity of organic matter mainly control the development of pores. On the whole, the shale reservoir development conditions of Shahezi Formation are slightly worse than those of Longmaxi Formation, but the plain swamp microfacies shale is developed close to the coal seam, the authigenic cemented quartz is developed, the proportion of Yimeng mixed layer is high, the reservoir has high organic matter abundance, good compressibility, large pore volume and specific surface area and good porosity development, which can be used as a potential favorable target for further evaluation and research.

Shale gas reservoirs, which develope micro-nano pore throats and fractures, have high clay mineral content, and strong heterogeneity of porosity. Therefore, large-scale hydraulic fracturing is usually needed to realize the effective exploitation. In the process of hydraulic fracturing, the spontaneous imbibition of the water phase will trigger a series of physical and chemical effects on the shale gas reservoir, changing the pore structures, physical and chemical properties of shale gas reservoirs, thereby affecting the production of shale gas. In order to further clarify the influence mechanism of water phase imbibition in shale gas reservoirs, multiple repetitive imbibition experiments were carried out. Based on the changes in rock sample quality caused by mineral dissolution, the visual characteristics of samples from scanning electron microscope, the observation of nuclear magnetic resonance pore structures, and the change of physical properties, the impact of imbibition on the microscopic pore structure, permeability and porosity of shale are revealed. The results show that: ① Water imbibition causes fractures in shale, thus changing the pore structure; ② The proportion of macropores increases in shale samples with significantly improved porosity, which indicates that water imbibition will increase the pore space in shale; ③ The imbibition capacity is positively correlated with the porosity and permeability of shale, and the physical properties of shale are significantly improved after imbibition. In addition, the time index is found to be able to quantitatively characterize the influence of imbibition on the pore-throat connectivity of shale.

The physical properties of shale oil reservoir are extremely poor, so it is necessary to form a network fracture system through volume fracturing to realize economic and effective development. However, there are lower permeability interlayers both in the top and bottom of shale oil reservoirs, so to master the fracture propagation law of reservoir with interlayers is the key for the successful fracturing of shale oil. With the help of the numerical simulation software, RFPA, of the rock fracture damage analysis system, the influencing factors of fracture propagation in the reservoir interlayers are studied. On the premise of considering the heterogeneity of strata, and by the comprehensively consideration of the elastic modulus, Poisson's ratio, uniaxial compressive strength, tensile strength, horizontal stress difference and interlayer stress difference of the reservoir, the fracability of shale oil reservoir is evaluated by the analytic hierarchy process. The results show that the elastic modulus of the reservoir interlayer, the difference of horizontal in-situ stress and the uniaxial compressive strength of the reservoir are negatively correlated with the degree of crack propagation. As these parameters increase, the cracks are more difficult to expand. However, there is a positive correlation between the ratio of tension and compression of reservoir and the stress difference between layers of reservoir and the degree of fracture propagation, that is, the increase of tensile strength and interlayer stress difference will help to increase the scale of fracture propagation, and the larger interlayer stress difference will make the fractures pass through the interlayers and continue to develop in the interlayer. Meanwhile, the mathematical model of the fracability is established by the analytic hierarchy process in fuzzy mathematics, and applied to the fractured wells in the work area. The predicted results are consistent with the experimental microseismic monitoring results, and the research results can provide reference for shale oil fracturing reform.

The shale oil development in Sinopec Jiangsu Oilfield is facing the problems of high investment and low production. After 45 years of development, there are a lot of abandoned old wells. Developing shale oil by old borehole side drilling can reduce drilling costs. In 2022, the sidetracking slimhole horizontal drilling in old wells is carried out in Huangzhuang. The slimhole drilling tools have the problems of large flexibility, difficult track control, slow drilling speed, small clearance, large air pressure consumption, poor cementing quality and high well control risk. In order to solve these problems, a system of efficient sidetracking slimhole horizontal drilling technology system is formed by the applications of large casing windowing, well track optimizations, high-efficiency drill bit+screw+LWD geosteering drilling, foam cementing, oil-based drilling fluid plugging, narrow gap well controlling, small hole coring, etc. A test application in H2CHF well shows that the actual drilling speed is up to 5.0 m/h, which is equivalent to the conventional drilling speed in adjacent wells, and the total drilling cost is reduced by 50 %, saved by 15 million. The new development and test would provide important ideas and reference for future development of shale oil in Jiangsu Oilfield.

The complex fracture networks are often formed after large-scale hydraulic fracturing in shale gas reservoirs, and the shale gas production rates decrease quickly due to the stress sensitivity. Therefore, it is necessary to study the influence of the stress sensitivity and production schedule under the controlled pressure for shale gas wells to determine the reasonable pressure drop and optimize the production schedule. Firstly, the natural and hydraulic fractures in shale gas reservoir are accurately characterized based on the embedded discrete fracture model（EDFM）, and the numerical simulation models of the shale gas wells based on the complex fracture networks are established. Then, the gas production performance of shale gas wells under different stress sensitivity conditions of fractures and matrix are analyzed. Finally, the numerical simulation on the production schedule optimization under the controlled pressure is performed. Forty groups of different production pressure schemes are designed to clarify the relationship between production pressure and performance of shale gas wells. The relationship curves of the accumulative gas and production pressure are established for Block A of W shale gas reservoir, and the optimal production pressure drop under controlled pressure is determined to be 14 MPa. The results show that the production under the controlled pressure is important for enhancing the production of shale gas wells and can reduce the influence of stress sensitivity on gas production. The optimization method and results of the production schedule under the controlled pressure can provide guidance for the production optimization of the shale gas wells.

In order to study the influence of mineral interface action on the initiation and propagation of shale hydraulic fracturing fractures, a shale microstructure model was established. In the model, the zero-thickness cohesive element was embedded in the solid element. A numerical simulation of the effect of mineral boundary interface stiffness on hydraulic fracture propagation was carried out to reveal the law of shale hydraulic fracturing crack propagation under the influence of mineral interface action. The results show that the tensile destruction is the main form of fracture failure of shale hydraulic fracturing. The crack propagation path consists of two ways, one is to extend along the mineral boundary, and the other is to cross the mineral boundary and enter the mineral to expand. With the increase of the mineral boundary interface stiffness, the crack initiation pressure and pore pressure gradually increase, the length, number and area of the cracks gradually decrease, and the width of the cracks gradually increases, so that it is easy to form short and wide cracks. When carrying out shale hydraulic fracturing operations, the location where the stiffness of the mineral boundary interface is lower should be selected first. The research results help to reveal the action mechanism of the mineral interface action on the expansion of the shale hydraulic fracture, and provide a theoretical basis for the reasonable selection of the hydraulic fracturing layer position of the shale gas reservoir.

Real-time monitoring and evaluation of fractures is one of the core issues in the multi-stage fracturing process of horizontal wells, and has long been a focus of many scholars. During the fracturing construction, the pressure during pump shutdown includes water hammer pressure and seepage pressure. By installing a high-frequency pressure device at the wellhead, not only the pump shutdown pressure drop curve but also the water hammer waveform curve can be completely collected. In this paper, the simulated pressure data are obtained by numerically solving the governing equation of wellbore water hammer. The cepstrum analysis of the simulated water hammer pressure verifies that the pressure generated by the water hammer has convolution characteristics. According to the related theory of wave impedance and cepstrum analysis, the water hammer wave can be used to determine the number of fracture clusters and the depth in multi-cluster fracturing of horizontal wells. The field application in Sichuan shale gas well shows that this method can find five liquid inlet points, of which the inversion results of four liquid inlet points are close to four perforation positions, and the remaining four clusters of holes in the design correspond to the liquid inlet points It was not detected in the cepstrum analysis.

In order to reduce the damage of adsorption and retention of traditional gelled acid in carbonate porous media, and reduce the damage to permeability of dense carbonate rock after stimulation. It is proposed that the quaternary ammonium cationic surfactant can be adsorbed on the rock surface for modification and then show retarding performance. Taking the carbonate rock in Majiagou Formation of Ordos Basin as the research object, based on the basic property tests, the adsorption capacity of cationic surfactant with different carbon chain length is determined, and the retarding mechanism of cationic surfactant is proposed by using molecular simulation technology combined with atomic force microscope and wetting angle observation. Then, the retarding performance and formation damage degree of cationic surfactant are studied by dynamic/static retarding performance test and damage evaluation experiment. The research results show that: ① Carbon chain length affects the interfacial adsorption effect by changing the adsorption form of surfactant molecules. C₁₄TAC can form a vertical dense adsorption layer on the rock surface with the best wetting modification effect. ② The surface of rock is covered by cationic surfactant with interface adsorption, which can increase its hydrophobicity, prevent H⁺ from contacting the rock surface, control the surface reaction rate, and achieve the purpose of retardation. ③ Compared with conventional acids, cation surfactants have good actionic and static slow performance, the kinetic parameters are reduced by 50 %~60 %, reducing the damage to the carbonate orifice throat. It is concluded that the quaternary ammonium salt cationic surfactant has the advantages of low molecular weight and strong interfacial adsorption ability, while maintaining the retarding ability, and effectively reducing the damage of thickened acid to the formation. This study is helpful to understand the rapid performance of the surfactant, improve the slow acid system, and improve the effect of carbonate reservoir reformation. They are all of positive significance.

The connected media of fault-karst reservoir are fractures, caves and pores, the decrease of pressure will lead to the decrease of permeability and conductivity, which will have an irreversible impact on oil well production. According to the stress-sensitive characteristics of fault-karst reservoir, 72 groups of physical simulation experiments on conductivity are designed and carried out to analyze the stress-sensitive characteristics of different connected media and influencing factors. Based on the results of physical simulation experiment and the theory of porous flow, a numerical inversion model of flow in fractured solution reservoir is established, and the stress sensitivity effect caused by reservoir pressure drop on oil well production is studied. The results show that the pressure drop has great influence on the conductivity, productivity and recovery ability of different connected media. The pressure inflection points of fracture type, karst cave type and pore type are 5.3 %, 20.4 % and 35.1 %, respectively, and the conductivity loss of the first two are 99.7 % and 45.0 %. The conductivity loss of pore type decreases linearly in the test range. The research on the characteristics of pressure drop inflection point provides the basis for reasonable production control and the determination of energy replenishment time, and has important guiding significance for stable production of oil wells.