Pore Structure Characteristics and Influencing Factors of Tight Reservoirs Controlled by Different Provenance Systems: A Case Study of the Chang 7 Members in Heshui and Xin’anbian of the Ordos Basin

Abstract

The evaluation of pore structure is critical in understanding reservoir characteristics. This study aims to analyze the microscopic pore structure characteristics of tight reservoirs from various provenances through physical property analysis, casting thin sections, scanning electron microscopy (SEM), and constant−rate mercury injection. The pore throat parameters of the Chang 7 reservoir were analyzed and compared to those of the Xin’anbian and the Heshui areas. The results show that intergranular pores dominate the pore type of the Chang 7 reservoir in the Xin’anbian area, followed by feldspathic dissolution pores, with high-necked and tubular throat content caused by weak compaction and dissolution, respectively. On the other hand, feldspar dissolution pores dominate the pore type of the Chang 7 reservoir in the Heshui area, followed by intergranular pores, with a high content of tube−bundle throats caused by dissolution and flake−bent flake throats caused by compaction. The difference in pore parameters between the two blocks is minimal, but the difference in throat parameters is significant. Under the same permeability conditions, the throat radius distribution range of the Chang 7 reservoir samples in the Heshui area is narrower than that in the Xin’anbian area, with tiny throats contributing significantly to reservoir permeability. Sedimentary hydrodynamic conditions and diagenesis are the primary reasons for the differences in the pores, throats, and pore structure parameters of the Chang 7 tight reservoirs.