Distribution of oil bearing and shale oil-rich strata in the second member of Funing Formation in Qintong Sag

The objective of this study is to delve deeper into the hydrocarbon generation potential and oil-bearing characteristics of various source rocks within the second section of the Funing Formation in Qintong Sag, Subei Basin, and to assess the degree of shale oil enrichment. Through geochemical analysis and simulation experiment research, this investigation proposes a method for characterizing shale oil content that is adapted to the geological features of the second section of the Funing Formation. The study establishes the oil content, occurrence state, and distribution characteristics of shale oil within this section. Findings indicate that the mudstone and calcium mudstone of the fourth and fifth sub-members demonstrate higher total oil content, lower free hydrocarbon content, medium to high adsorbed hydrocarbon content, and limited mobility. Meanwhile, the calcium shale, calcareous shale, and laminated marlstone of the first to third sub-members exhibit higher total oil content and free hydrocarbon content, but lower adsorbed hydrocarbon content, which enhances their mobility. The calcium mudstone and calcareous mudstone of the first to third sub-members display a moderate level of total oil content and adsorbed hydrocarbon content but relatively low free hydrocarbon content. The marlstone from these sub-members shows comparatively low levels of total oil content as well as free and adsorbed hydrocarbon contents. The study also reveals the distribution of shale oil enrichment intervals. Class Ⅰ and Class Ⅱ shale oil enrichment intervals are primarily located in the middle and lower sections of the first and second sub-members in the deep depression zone. In contrast, the slope zone features limited development of shale oil enrichment strata but contains Class Ⅱ and Class Ⅲ shale oil.