Formation mechanisms of good-quality clastic reservoirs in deep formations in rifted basins: A case study of Raoyang sag in Bohai Bay Basin, East China

Abstract

In order to reveal the development mechanism of high-quality clastic rock reservoir, the basic characteristics of Sha-3 Member of the Shahejie Formation in the Raoyang sag, Bohai Bay Basin, are analyzed based on cores observation, thin-sections and SEM images, and petrophysical properties measurements as well. It is found that high-mature composition and texture, early oil charging, and dissolution are the main factors controlling the formation and preservation of pores in deep reservoirs. Compaction is the major factor destructing pores, whereas formation overpressure is conducive to the preservation of original pores, high compositional and medium textural maturity can enhance the resistance capacity to compaction and protect primary pores. Early oil charging could lead to temporary cessation of diagenesis and thus inhibit the cementation. When organic acids entered reservoir formations, considerable amounts of secondary pores were formed, leading to the local improvement of petrophysical properties. When predicting good quality belt in exploration of deep basin, it is recommended that the superimposing effects of the multiple factors (overpressure, early oil charging, compositional and textural maturity, diagenesis) be taken into consideration. Key words: Bohai Bay Basin, Raoyang sag, rifted basin, Shahejie Formation, diagenesis, high porosity zone, dissolution