Formation Mechanisms of Paleogene Igneous Rock Plays in Huimin Sag, Eastern China

Abstract

In order to understand the impact of volcanism and intrusion on the source rocks, how the pores and fissures formed and how the hydrocarbon was trapped, this study focuses on the formation mechanisms of the igneous rock plays in the Huimin Sag based on geochemical and lithological analyses and typical anatomy. The results indicate that volcanism enhanced the formation of Es3 source rocks with high TOC (3.41–5.12%) in the distribution areas of igneous rocks. Volcanism caused an abnormal heat field and accelerated the maturation of hydrocarbon source rocks, leading to a higher heat gradient (3.4–4.4 °C /100 m), increase of HC and chloroform bitumen “A” contents, earlier hydrocarbon generation threshold and higher biomarker maturity closer to the igneous rocks. The primary fractures, vesicular structures, inter-breccia pores, intergranular pores, intercrystal and intracrystal pores are primarily-formed. The structural fractures and corrosion space are secondarily formed. Rising fluid pressure associated with volcanism accelerated the hydrocarbons expulsion. Igneous body can act as a migration pathway or a seal constrained by its physical property. Volcanism in the Huimin Sag produces diaper arch trap, overlap trap in volcano slope and drape anticline trap on the volcanic cone. Five models for igneous rocks plays in the Huimin Sag, such as volcaniclastic play with outside source rocks, diabase plays with interior and exterior source rocks, basalt plays with exterior and mixed source rocks are proposed.