Main controlling factors for the enrichment of shale oil and significant discovery in second member of Paleogene Funing Formation, Qintong Sag, Subei Basin

Abstract

Based on the study of hydrocarbon generation features, oil bearing property and reservoir property of shale in the second member of Paleogene Funing Formation in the Qintong Sag of the Subei Basin, the main controlling factors of shale oil enrichment were analyzed. Shale of the second member of Funing Formation in the Qintong Sag was featured by large-scale thickness and medium TOC content, which provided a material basis for shale oil enrichment. The vitrinite reflectance (%Ro) of shale in the second member of Funing Formation in the deep sag distributed between 0.9%-1.0%, indicating a moderate thermal evolution degree. Shale oil has the characteristics of light hydrocarbon, high gas-measured total hydrocarbon value and good fluidity. Few faults were developed, resulting in good preservation conditions and high formation pressure, which were conducive to hydrocarbon enrichment. High content of brittle minerals and well-developed lamella and natural fractures made formation fracturing easier. The continuous and large-area distribution of high-quality shale is the basis for oil and gas abundance. Preservation condition is the key factor to reservoir formation. The degree of evolution is a decisive factor of oil-bearing. High pressure, lamina development and high brittle mineral content are important factors for high yield. The shale oil in second member of Funing Formation in Shaduo area has the characteristics of low TOC content (1%), low gas oil ratio (40-80 m3/t) and high pressure (1.25 MPa). The success of this well has reduced the shale oil evaluation standard and threshold, and expanded the development space of shale oil.