Diagenesis and reservoir classification criteria for Jurassic continental sandstone oil reservoir in the western Ordos Basin, China

Abstract

The marginal area of a sedimentary basin is closer to the provenance, so the sand body is generally more developed. For the Western Margin Thrust Belt of the Ordos Basin, the quality of the Jurassic sandstone reservoirs is still less studied. Diagenesis and reservoir evaluation are important research contents and hotspots in sedimentary geology. Therefore, in this paper, the diagenesis and reservoir properties of the Jurassic Yan 6 to Yan 10 members (Yan'an Formation) have been systematically studied based on the latest 3D seismic, well logging, cast thin section, scanning electron microscope and petrophysical property tests in this area. Furthermore, the vertical heterogeneity of petrophysical properties of the Jurassic reservoir has been discussed in detail, and the diagenetic evolution sequence and classification criteria of Jurassic sandstone reservoir have been proposed. The research results show that the lithologies of the Yan 6 to Yan 10 members are mainly lithic quartz sandstone, lithic feldspar sandstone and feldspar lithic sandstone. The pore types of sandstone are mainly intergranular pores, followed by dissolution pores, intercrystalline pores and a few microfractures. There are two high-value porosity zones in the buried depths of 1,950-2,050 m and 2,150-2,250 m, which are the coupling results of dissolution and palaeo-overpressure. Based on the comprehensive study of petrology, petrophysical properties and diagenesis, the diagenetic evolution sequence of the Jurassic sandstone was restored and a comprehensive classification standard for the Jurassic sandstone reservoirs is proposed. The Jurassic reservoir in the study area is a structurallithological reservoir, which has a unified oil-water interface, the Type I and Type II reservoir areas in the structural high positions are conducive to the large-scale accumulation of hydrocarbons.

Factors That Control the Reservoir Quality of the Carboniferous–Permian Tight Sandstones in the Shilounan Block, Ordos Basin

“…Advances in research methods and technologies have allowed for substantial progress in studying the characteristics and controlling factors in the development of tight sandstone reservoirs. Advanced technologies that have been used in reservoir characterization include high-precision and high-resolution microscopic observation, fluid inclusion testing, mineralogical composition identification, genetic analysis, and pore system characterization [12][13][14]. These technologies and research methods provide a reliable foundation for analyzing pore genesis, diagenesis types, and diagenetic evolution, and shift the study of tight sandstone reservoir characteristics and their controlling factors from a qualitative description to a quantitative study.…”