Heterogeneity and influencing factors of marine gravity flow tight sandstone under abnormally high pressure: A case study from the Miocene Huangliu Formation reservoirs in LD10 area, Yinggehai Basin, South China Sea

Abstract

The characteristics of reservoir heterogeneity of the marine gravity flow tight sandstone from the Miocene Huangliu Formation under abnormally high pressure setting at LD10 area in Yinggehai Basin are studied, and the influencing factors on reservoir heterogeneity are discussed, based on modular formation dynamics test, thin sections, XRD analysis of clay minerals, scanning electron microscopy, measurement of pore throat image, porosity and permeability, and high pressure Hg injection, as well as the stimulation of burial thermal history. The aim is to elucidate characteristics of the heterogeneity and the evolution process of heterogeneity of the reservoir, and predict the favorable reservoirs distribution. (1) The heterogeneity of the reservoir is mainly controlled by the cement heterogeneity, pore throat heterogeneity, quality of the reservoir heterogeneity, and the diagenesis under an abnormally high pressure setting. (2) The differences in pore-throat structure caused by diagenetic evolution affected the intergranular material heterogeneity and the pore throat heterogeneity, and finally controlled the heterogeneity of reservoir quality. (3) Compared with the reservoir under normal pressure, abnormally high pressure restrains strength of the compaction and cementation and enhances the dissolution of the reservoir to some extent, and abnormally high pressure thus weakening the heterogeneity of the reservoir to a certain degree. The favorable reservoirs are mainly distributed in the gravity flow sand body under the strong overpressure zone in the middle and lower part of Huangliu Formation.