Effect of Microscopic Pore-Throat Heterogeneity on Gas-Phase Percolation Capacity of Tight Sandstone Reservoirs
Fan Zhang, Zhenxue Jiang, Wei Sun, Xi Zhang, Lin Zhu, Xiaohui Li, Wen Zhao
Abstract
This study delved into the pore-throat heterogeneity of the tight sandstone in the Ordos basin for NMR and Rate-Controlled Mercury Intrusion tests (RCMI). The aim of the present study was to qualitatively and quantitatively characterize microscopic heterogeneity of a pore throat based on the merits of NMR and RCMI. On this basis, the effect of pore-throat heterogeneity on gas-phase percolation capacity was studied by a gas-water relative permeability test. As revealed from the results, ① the difference in fractal characteristics of the same sample is caused by the different principles and range in measuring pore throats of two experiments. The pore heterogeneity was characterized by the NMR test, while the throat heterogeneity was characterized by the RCMI test. ② Dt1 ranges from 2.51 to 2.92, and Dt2 ranges from 2.93 to 2.99, whereas Dmax ranges from 2.66 to 2.95 based on RCMI tests, revealing that the Shihezi sandstones exhibited moderate to high complexity and heterogeneity of the pore structure. ③ With the increase of Dt2 and Dmax, the effective seepage space is narrowed for the gas phase, and the interference in gas-water two phases tends to increase. As a result, low gas-phase permeability, high bound water saturation, and a small common infiltration area are achieved. ④ The more robust the pore-throat heterogeneity, the slower the gas-phase permeability curve will rise with the increase in gas saturation, which reflect the higher producing water ratio of the reservoir, suggesting that microscopic heterogeneity of the pore throat restrains the migration of the two-phase fluid and sweep area of single-phase fluid. The stronger the pore-throat heterogeneity, the worse the exchange of gas and liquid will be. The research results have important guiding significance for tight gas development of the Shihezi reservoir.