Characteristics of pore structure and fluid mobility differences under constraints of continental shale laminar and interbedded reservoirs: A case study of the Lucaogou Formation shale reservoir in the Jimusar Depression

China is rich in shale oil resources. By the end of 2022, the predicted reserves of continental shale oil in China have reached 3 billion tonnes, but only recoverable shale oil has economic value under such reserves. The shale oil reservoirs of the Lucaogou Formation in the Jimusar Sag can be divided into three types: interlayer type, lamina type and block type according to mineral composition and source-reservoir ratio. However, due to the large difference in pore structure characteristics and fluid occurrence state of the three types of reservoirs, the productivity difference is high using the same fracturing method. In order to clarify the pore structure characteristics of the Lucaogou interlayer and laminated reservoirs in the Jimusar sag and the difference of fluid mobility under their constraints, this paper studies the pore structure characteristics by means of XRD, casting thin sections, scanning electron microscopy and nitrogen adsorption. Nuclear magnetic resonance centrifugation technology was used to quantitatively evaluate the mobility of shale oil in laminated and laminated reservoir samples. The T₁-T₂ spectrum method was used to clarify the occurrence state of shale oil in different reservoir types. Finally, the main controlling factors of fluid mobility in shale oil reservoirs were analyzed by combining characteristic pore structure parameters. The results show that the carbonate content of laminated reservoirs is high, and the reservoir space is dominated by carbonate intergranular pores, clay mineral interlayer fractures and organic matter pores. The fluid component is dominated by kerogen, and the free oil component content is extremely low. The average value of movable fluid saturation is only 7.97%. The felsic content of the interlayer type is higher, the reservoir space is mainly composed of intercrystalline pores and dissolved pores in feldspar grains, the fluid composition is mainly movable oil, followed by bound oil and kerogen, and there is no movable water. The average saturation of movable fluid is 29.3%. The pore throat radius in the characteristic pore structure parameters is the main factor controlling the movable fluid saturation of shale oil reservoirs. The two are exponentially correlated, and the correlation coefficient can reach 0.95. Through the study, the main reservoir space types of the intergranular pores and intra - granular pores in the Lucaogou Formation and the laminar shale oil reservoirs in the Jimsal Depression are determined. The mobile fluid saturation decreases gradually from unimodal interlayer reservoirs to bimodal laminated reservoirs, but increases exponentially with the increase of the maximum pore throat radius. The results show that the maximum pore throat radius has a great influence on the mobile fluid saturation of shale oil reservoir.