Hydrocarbon Accumulation Mechanism of WC Formation in the HZ Sag, Pearl River Mouth Basin

This study, based on the characteristic that a small number of hydrocarbon-rich sub-sags control the majority of oil and gas reservoirs discovered in the HZ sag, establishes a foothold on the HZ26 sub-sag—the most prolific hydrocarbon-generating sub-sag in the HZ sag, focuses on WC formation of its peripheral structures, and discusses the hydrocarbon accumulation mechanism of WC formation in the HZ sag. Hydrocarbon charging periods were determined through an integrated analysis of homogenization temperatures of brine inclusions coexisting with hydrocarbon inclusions, stratigraphic burial and thermal history, and hydrocarbon generation stages of source rocks. A multiphase fluid charging physical simulation experiment was conducted to establish a covariant relationship between reservoir permeability and hydrocarbon charging pressure difference. Based on the residual pressure history and reservoir property evolution, a coupling relationship was established between the hydrocarbon charging driving force and resistance during hydrocarbon charging periods. The covariant relationship between reservoir permeability and hydrocarbon charging pressure difference and the coupling relationship between hydrocarbon charging driving force and resistance during hydrocarbon charging periods were then integrated to reconstruct the hydrocarbon charging process. The results reveal a mechanism for large-scale hydrocarbon charging and differential accumulation under the influence of overpressure.