Study on pore structure and permeability sensitivity of tight oil reservoirs

Abstract

The tight oil reservoir is rich in microscale pores, which has a significant impact on oil and water distribution and seepage. In this paper, first, the microscale pore-throat structure characteristics of tight oil reservoir is analyzed, and the injection medium sensitivity characteristics of the pore-throat structure is explored. Second, considering the dynamic evolution characteristics of permeability, the injection medium influence mode of permeability in tight reservoirs is elucidate. Results show that: (a). The average porosity ratio of microscale pores and small pores (64.35 %) is higher than that of mesoscale pores and large pores (35.65 %), indicating that there are more microscale pores and small pores developed in the reservoir. (b). The mineral content of reservoir rock is 23.93 % quartz, 8.48 % potassium feldspar, 27.28 % plagioclase, 17.63 % calcite, 5.65 % dolomite and 17.03 % clay mineral. (c). Acidic fluids have a weak improvement effect on the porosity of tight sandstone. The average total porosity change rate after interaction with 3 % HF is 8.06 %. (d). Acidic fluids have weak improvement on reservoir pore structure and strong improvement on reservoir permeability. Alkaline fluids have a strong improvement effect on reservoir fluids, but have a moderate to weak improvement effect on reservoir permeability.