Shiyou shiyan dizhi (Mar 2021)
Constant velocity mercury injection and nuclear magnetic resonance in evaluation of tight sandstone reservoirs in western Sichuan Basin
Abstract
The reservoir porosity, pore structure type, pore-throat characteristics, pore-throat ratio and their correlations with porosity and permeability of the fourth member of Upper Triassic Xujiahe Formation in the Xinchang area of the western Sichuan Basin were discussed based on constant velocity mercury injection and nuclear magnetic resonance. The effects of pores and throats on capillary curves were studied, and the influence of pore throat characteristics on movable fluid parameters was discussed. The reservoir of the fourth member of Xujiahe Formation in the study area has low porosity and low to ultra-low permeability. Its porosity ranges from 1.6% to 10.9%, with an average of 5.9%, and the permeability ranges from 0.01×10-3 μm2 to 2.81×10-3 μm2, with an average of 0.37×10-3 μm2. There are four types of pore structures: coarse throat and macro pore, coarse throat and small pore, fine throat and macro pore, and fine throat and small pore. The pore radius is 8-180 μm, with an average of 112 μm, mainly micropores and small pores. The throat radius ranges from 0.100 to 1.008 μm, with an average of 0.484 μm, mainly microthroats. Pore radius has little influence on the physical properties of low to ultra-low permeability reservoirs. Pore throat radius has a good correlation with permeability, which determines the variation characteristics of capillary curves and controls the physical properties of low permeability reservoirs, and is the key factor to determine the development effect of gas reservoirs. The experimental parameters, such as pore radius, throat radius and final mercury saturation, which have great influence on movable fluid parameters, were optimized. A pore structure index was put forward based on the three parameters mentioned above, and the reservoir evaluation of the whole well section was carried out, which was applied to the evaluation of tight sand reservoirs in the western Sichuan Basin.
Keywords
