CHARACTERISTICS OF THE SHALE OIL RESERVOIR IN ZHANHUA SAG AND ITS CONTROLLING FACTORS

A series of analyses and tests, including cores, thin sections, SEM, XRD, physical property, total organic carbon (TOC), rock pyrolysis, are made in order to reveal the characteristics and controlling factors for the shale reservoir in the Lower 3rd Member of Shahejie Formation, the Paleocene in the Zhanhua Sag. According to its mineral composition and micro-sedimentary structures, the lacustrine shale in the study area can be subdivided into 6 types of lithofacies. Reservoir spaces are made of fissures and pores. There are mainly 4 types of fissures, among which structural and abnormal pressure fissures are clearly visible on the cores, while shrinkage fissures and interlayer microcracks are both on a micron level. There are 3 types of pores: recrystallised pores, organic evolution pores and dissolution pores, ranging from nanometer to micron level. The four main factors, which control the development of shale reservoir space, include shale mineral composition and micro-sedimentary structures, organic matter content and occurrence, diagenesis and tectonic action. Based on the controlling factors mentioned above, therefore, six key parameters, i.e. calcite content, lamellar structure, TOC, R_o, porosity and total rate of fissures may be selected as the criteria to classify the shale reservoir in the Zhanhua Sag into 3 types: high quality reservoir, favorable reservoir and unfavorable reservoir.