Petrophysics and Geochemical Evaluation of the Lacustrine Chang 7 Member’s Shale Oil Reservoir in Ordos Basin, China

Using well Logs, organic geochemical data, core and rock cutting samples, X-ray diffraction and QEMSCAN analysis, this study is an attempt to comprehensively evaluate the geological and geochemical characteristics of lacustrine shale oil reservoir in Chang 7 Member of the Triassic Yanchang Formation, with emphasis on hydrocarbon generation conditions and hydrocarbon retention characteristics, reservoir conditions, hydrocarbon-bearing properties, lithofacies characteristics, and mineralogical association. The organic geochemical characteristics show that the Chang 7 oil shale is characterized by a good hydrocarbon generation potential which is reflected in the abundance of organic matter (an average total organic carbon of 13.14%), of type I–II1, moderately mature kerogen, which is mostly at the beginning of oil window (Vitrinite reflectance = 0.9% to 1.03%). The pyrolysis parameters S1 and chloroform asphalt (A), and the measured oil saturation collectively elucidate that the Chang 7 shale has a good hydrocarbons retention characteristic. The mineral compositions of Chang 7 oil shale in the study area contains a high content of brittle minerals represented in quartz and feldspars. The main mineral constituent of the shale by average is (42.5%) clay minerals, (26%) quartz, (22%) feldspars, and (9.5%) iron oxides and siderite collectively. Carbonate minerals are virtually absent. Based on the organic matter content and the mineral association of the shale, Chang 7 oil shale can be classified as argillite rock with high- moderate content of organic matter. The porosity of the Chang 7 Member shale oil reservoir emphatically associates with TOC, which indicates the reservoiring space is mainly the porosity within the organic matter (Intra organic matter pores). According to the shale oil reservoir evaluation criteria adopted in this study, the Chang 7 Member shale oil reservoir is promising for the exploration and exploitation of shale oil resources.