Shale formation environment and comprehensive evaluation of shale oil potential of the Lower First Member of Shahejie Formation in Qikou Sag

Abstract

Bohai Bay Basin is one of the main exploitation areas of continental shale oil resources in China.Qikou Sag, located in the hinterland of the basin, is one of the typical oil and gas rich depressions in Bohai Bay Basin.This paper selects the organic rich shale in the Lower First Member of Shahejie Formation in Qikou Sag as the research object, and comprehensively uses geochemical logging technology and hydrocarbon generation and expulsion simulation technology to describe the shale sedimentary characteristics and comprehensive evaluation of shale oil potential in the Lower First Member of Shahejie Formation in Qikou Sag.The results show that the Lower First Member of Shahejie Formation in Qikou Sag was deposited in the reduction strong reduction environment with high water salinity, rich nutrients, hot and humid climate, suitable for biological mass reproduction and high productivity.Combined with the hydrocarbon generation and expulsion simulation experiment results, the Lower First Member of Shahejie Formation shale in the study area has strong hydrocarbon generation capacity, high hydrocarbon generation efficiency and low oil discharge rate.Most of the generated crude oil is still left in the shale, which has good exploration potential.The Lower First Member of Shahejie Formation shale in the study area contains an appropriate amount of carbonate minerals, which improves the reservoir conditions during diagenesis and provides a good reservoir site for shale oil.The occurrence of transgression in the southwest margin of Qikou Sag affects the enrichment of organic matter in the Lower First Member of Shahejie Formation from the aspects of sedimentary environment, paleoproductivity and its impact on diagenesis.The enrichment of organic matter, high hydrocarbon generation intensity and good reservoir conditions control the large-area distribution of shale oil in the Lower First Member of Shahejie Formation.Shale oil reservoirs in the Lower First Member of Shahejie Formation in the study area can be divided into carbonate rocks and mixed sedimentary rocks.After synthesizing the oil-bearing characteristics of the two reservoirs, it is found that the mineral content and brittleness index of carbonate rocks have a great impact on shale oil-bearing properties.In the process of further exploration, oil reservoirs can be found in the wide and gentle slope area conducive to the formation of structural fractures and the area with high degree of dolomitization in the study area.The favorable exploration intervals are dolomite, dolomitic shale and calcareous shale with developed pores and micro fractures.The research results provide guidance for the exploration and development of shale oil in Qikou Sag.

Keywords

• qikou sag
• lower first member of shahejie formation
• shale
• sedimentary environment
• shale oil
• potential assessment