Shale oil reservoir characteristics and exploration implication in Da'anzhai Member of Jurassic Ziliujing Formation in central Sichuan Basin

Abstract

To further guide the exploration and development of shale oil in the Da'anzhai Member of the Jurassic Ziliujing Formation in the Sichuan Basin, it is urgent to clarify the favorable lithofacies of shale oil. In this study, core observation, thin section authentication, high pressure mercury injection, NMR, rock pyrolysis analysis and other experiments were used to analyze the reservoir space types, pore structure characteristics and oil-bearing properties of different lithofacies of shale series in the Da'anzhai Member. The results show that mainly six types of lithofacies are developed in the Da'anzhai Member: massive (argillaceous) shell limestone, layered argillaceous shell limestone, layered shell shale, laminar shell-bearing shale, massive shell-bearing clay shale and foliated siltstone-bearing clay shale. The physical properties of shale in the Da'anzhai Member are much better than those of shell limestone, and with the increase of calcareous content, the pore size of the shale gradually increases, but the total pore volume and total connected volume gradually decrease. The average free oil value (S1) of the shale series in the Da'anzhai Member is 1.31 mg/g, with moderate oil-bearing property. The S1 values of the foliated siltstone-bearing clay shale and the laminar shell-bearing shale are relatively higher, which are 2.37 mg/g and 1.82 mg/g, respectively. In summary, it is believed that the foliated siltstone-bearing clay shale and the laminar shell-bearing shale have good reservoir properties and high oil-bearing properties. The lithofacies combination of the two can be a key exploration target for shale oil in the Da'anzhai Member.

Keywords

• reservoir space
• oil-bearing property
• shale oil
• reservoir characteristics
• da'anzhai member
• jurassic
• sichuan basin