BACKGROUNDThe development potential of tight gas reservoirs of the Shanxi Formation in the southeastern Ordos Basin is huge. High-pressure mercury injection has been one of the most important methods for analyzing the pore-throat structure, however, it has seldom been applied in this area. The high-pressure mercury injection experiment can effectively characterize the pore-throat structure at a lower cost.

OBJECTIVESTo apply high-pressure mercury injection to characterize pore-throat distribution of the tight gas reservoirs in the southeastern Ordos Basin.

METHODSTypical cores of tight gas reservoirs in the Shanxi Formation are selected for high-pressure mercury injection experiments. The research was carried out using the mercury withdrawal curve to represent the process of mercury withdrawal in the throat and the decimal capillary pressure interval division method, and then a completely separated double peak feature was shown according to the pore-throat radius distribution curves. The small and large pore-throat areas were defined, and their influence on physical property parameters was analyzed.

RESULTSThe experiment results showed that the main capillary pressure ranges of the total pore-throat and the single pore-throat were 0.1-1MPa and 1-10MPa, respectively. The throat determined the pore-throat ratio and mercury ejection efficiency. The average relative volume of small and large pore-throat areas were 91.59% and 8.41%, respectively. The small pore-throat area controlled the reservoir seepage capacity, while the large pore-throat zone controlled the reservoir capacity.

CONCLUSIONSBased on the experimental results, the application research of the high-pressure mercury injection method further revealed that the small pore-throat area determines the development of pores and throats, and the large pore-throat area determines the early productivity of gas wells. The research shows that the high-pressure mercury injection test has a good application prospect in the characterization of integral pore-throat distribution and early productivity evaluation of tight gas reservoirs, which can effectively enrich the knowledge about the distribution characteristics of tight gas reservoir pore-throat and provide ideas for scientific development in this area.