Influence of clay minerals and cementation on pore throat of tight sandstone gas reservoir in the eastern Ordos Basin, China

Abstract

The distribution characteristics of pore throat play a vital role in the exploration and development of tight sandstone reservoirs. Based on the thin sections and scanning electron microscopy, this paper studied the petrological characteristics of tight sandstone reservoirs the Permian Shihezi Formation and the Shanxi Formation in the Ordos Basin. The micro-scale and nano-scale pore throat parameters of the target samples were quantitatively analyzed by high-pressure mercury injection experiments. At the same time, the content of clay minerals and various cement in the samples was extracted and obtained by X-ray diffraction to explore the effects of the clay minerals and cementation on the pore-throat. The results showed that the micro-scale pore space of the tight sandstone in the study area was mainly composed of residual intergranular pores and dissolution pores. The nano-scale pore throat consisted with the intercrystalline pore of clay minerals, dissolution pores of fake matrix, micro-crack and the intergranular pore of quartz overgrowth, the intergranular pore of quartz grains, which correspond to four types of mercury injection curves. According to XRD data and mercury injection results, the evolution of the tight sandstone pore-throat is mainly controlled by kaolinite, illite, and the companion product: siliceous cement. Chlorite and calcareous cement have little effect on reservoir porosity, average pore throat radius and permeability. Two evolution models of the pore-throat of tight sandstones in which clay minerals and cement as the dominant factors were established.