Analysis of the factors influencing movable fluid in shale oil reservoirs: a case study of Chang 7 in the Ordos Basin, China

Shale oil in the Ordos Basin is one of the most important areas for further exploration. In this paper, the relationships between the organic geochemistry, physical properties, micropore structure and mobile fluid composition of the Chang7 shale were studied via field emission scanning electron microscopy field emission scanning electron microscopy, nuclear magnetic resonance and computed tomography. The results indicate that the shales are mainly composed of quartz, clay and feldspar. The micro/nanopores are composed of mineral intergranular pores, dissolution pores and intercrystalline pores. The pore size of the mobile fluid ranges from 10 to 30 nm and from 0.1 to 10 mu m, and a higher temperature is associated with a better fluidity of 10-30 nm. Based on the fractal turning point method, the shale reservoirs are classified as moderate or high heterogeneity. The mobile liquid was mainly controlled by the brittleness index, permeability, permeability, radius of the throat, radius of the pore throat, and volume ratio of the pore throat. The second factor was the heterogeneity strength and burial depth, but the relationship with TOC content and maturity was not obvious. 1. It is found that the occurrence law of movable fluid in Yanchang exploration area is found within the investigation scope. The pore size of the movable fluid was mainly distributed in the range of 10-30 nm and 0.1-10 mu m, and a higher temperature correlated to better fluidity of the 10-30 nm reservoir pores.2. A new fractal dimension method with parameters greater than T2 cutoff value is proposed. The fractal turning point method divided the shale reservoirs in the study area into two categories: moderate heterogeneity and strong heterogeneity.New understanding of movable fluid of shale oil in Ordos Basin is reorganized. The movable fluid was predominantly controlled by the brittleness index, permeability, permeability pore ratio, throat radius, pore throat radius ratio and pore throat volume ratio, followed by the heterogeneity strength and burial depth; however, no significant correlation was observed with the organic carbon content and maturity.