Formation porosity thermocompression simulations of hydrocarbon generation and expulsion of lamellar shales and their geological implications for shale oil exploration in the 2nd member of Kongdian Formation， Cangdong Sag， Bohai Bay Basin

This study aims to systematically compare the hydrocarbon generation and expulsion characteristics of various types of lamellar lacustrine shales. Using semi-closed formation porosity thermocompression simulation experiments on hydrocarbon generation and expulsion， as well as associated geochemical analyses and tests， we conduct a systematic comparative study on the hydrocarbon generation， expulsion， and retention processes of three types of lamellar shales in the 2nd member of the Kongdian Formation （also referred to as the Kong 2 Member） in the Cangdong Sag. Accordingly， we explore the mechanisms underlying the differential evolution of hydrocarbon generation， expulsion， and retention of these lamellar shales. The results indicate that the threshold for retained oil enrichment in lamellar shales corresponds to vitrinite reflectance （Ro） values of 0.4% ~ 1.4%， with the oil retention efficiency （ORE） varying across different types of lamellar shales. In contrast， the “golden window” for retained oil enrichment corresponds to Ro values of 0.8% ~ 1.3%. Compared to the lamellar mixed shales and lamellar carbonate shales， the lamellar feldspathic shales exhibit higher total hydrocarbon yield， total oil yield， and total gas yield. The laminar carbonate shales reach the threshold for the retained oil enrichment earlier （Ro = 0.4%）， exhibiting the characteristics of early generation and early expulsion. The three types of lamellar shales show varying retained hydrocarbon compositions and diverse gas/oil ratios （GORs） across different thermal evolution stages. Notably， the lamellar feldspathic shales show the highest GOR during the highly mature stage. The differences in the paleolake environment govern the organic matter composition and hydrocarbon-generation activation capacity of the three types of lamellar shales， further affecting the differences in their ORE and hydrocarbon generation， expulsion， and retention processes.