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Accurately characterizing the cross-scale structure of pores and fractures in shale reservoirs is the theoretical basis for efficient exploration and development of shale oil and gas. In this paper, (a) Based on the research background of different shale maturity and sedimentary characteristics, a three-dimensional model of cross-scale pore-fracture structure is established; (b) Based on a large number of CT characterization data of core pore-fracture structure, the characteristics of pore-fracture development under different geometric dimensions (25 mm and 2 mm) are statistically analyzed; (c) Pore and fracture structures of mixed shale, felsic shale and laminated felsic shale is comparatively studied, and the pore structure and bedding fracture characteristics of shale oil reservoir is revealed. Results show that: (a) for the bedding fracture porosity, felsic shale in Group I is 0.36 %–0.89%; mixed shale in Group I is 0.34 %–0.47%; mixed shale in Group III is 0.12 %–0.86%; mixed shale gravelly dolomite in Group III is 0.13 %–0.15%. (b) Compared with block 1, the laminated felsic shale bedding in block 2 is more developed. (c) CT imaging is based on density difference. Different components of shale samples are distinguished by gray scale. • Considering shale maturity and sedimentary characteristics, a 3D model of cross-scale pore-fracture structure is established. • The characteristics of pore-fracture development under different geometric dimensions are statistically analyzed. • Pore and fracture structures of mixed shale, felsic shale and laminated felsic shale is comparatively studied. [ABSTRACT FROM AUTHOR]

With the global assistance of oil fields entering the stage of improving oil recovery, diversified composite flooding technology has become one of the key research targets. This article takes composite flooding to improve oil recovery as the research object, explores the differential mechanism of crude oil displacement efficiency under water flooding and composite flooding conditions, and elucidates the dynamic evolution characteristics of pore structure before and after composite flooding. Results show that: (a) The permeability and porosity of Daqing oilfield cores have a good correlation. The porosity of cores after water driving and ternary composite driving mainly ranged from 23.6 % to 27.4 % and 22.8 %–26.8 %. The water-driving permeability mainly ranged from 168 × 10−3 μm2 to 2162 × 10−3 μm2. Ternary composite driving permeability mainly ranges from 302 × 10−3 μm2 to 2307 × 10−3 μm2. (b) Compared with water driving, quartz and clay minerals are corroded by alkali during ternary composite driving. (c) Under the condition of similar permeability, the average pore size of the core after ternary composite driving is smaller than the average pore size after water driving. • The differential mechanism of oil displacement efficiency under water flooding and ASC flooding conditions is explored. • The dynamic evolution characteristics of pore structure before and after composite flooding is elucidated. • The increase of permeability after water injection leads to a slight increase of water distribution in pore space. [ABSTRACT FROM AUTHOR]

The distribution pattern of oil and water in different stages of low permeability reservoirs is one of the main research topics in oilfield development. This paper takes low-permeability and tight oil reservoirs as the research object, systematically carries out experimental research on water flooding efficiency, and carries out theoretical comparative analysis. The innovations of this paper mainly include three aspect: (a) the experimental study of water drive efficiency under the conditions of different water drive stages is carried out, and the dynamic evolution characteristics of remaining oil distribution is analyzed. (b) The comparative analysis of water drive efficiency under different combination conditions of "permeability and crude oil physical properties" is studied. (c) The dynamic evolution mechanism of the coupling of "bound water - semi-bound water - free water" is explored by using the frozen core method. Results show that: (a) At the original oil bearing stage of the core in F Oilfield, the free microscale residual oil is the majority, followed by the bound and semi-bound residual oil. (b) Water flooding mainly develops the free residual oil. The remaining oil in clusters decreased from 22.35% to 2.21%. The residual oil in the form of inter-particle adsorption decreased from 28.56% to 2.53%. (c) It is difficult to develop bound and semi-bound residual oil in water drive. As the cluster like remaining oil is developed, the facial mask like remaining oil on the pore surface increases from 1.13% to 4.04%. • The dynamic evolution characteristics of remaining oil distribution is analyzed. • The comparative analysis of water drive efficiency under different "permeability - oil properties" combination is studied. • The dynamic evolution mechanism of "bound water - semi-bound water - free water" is explored. [ABSTRACT FROM AUTHOR]