Chapter 11 - The influence of diagenesis on low-porosity, low-permeability gas reservoirs in the Sulige Gas Field (Ordos Basin, China)

Abstract

The successive stages of compaction- and lithification-induced porosity reduction (densification) and hydrocarbon accumulation have been investigated in a tight sandstone reservoir in the Permian Sulige Gas Field in central China. Thin-section analysis, scanning electron microscopy, X-ray diffraction, cathodoluminescence, fluid-inclusion analysis, and confocal Raman spectrometer analysis were used to identify the authigenic minerals involved in the reservoir development: illite, kaolinite, dickite, chlorite, and smectite illitization, in combination with quartz and calcite cement. The types of pores are dominated by illite and kaolinite intercrystalline pores, pores originating from matrix dissolution, and primary intergranular pores. Particularly compaction and cementation resulted in porosity loss, but kaolinite and illite preserved intercrystalline pore spaces. Consequently, the secondary porosity contributes most to the reservoir quality. It is also inferred that the tight gas accumulation took place during the densification of the reservoirs. These findings may help understand the formation of other tight reservoirs.