恒速压汞及核磁共振技术在四川盆地西部致密砂岩储层评价中的应用

Constant velocity mercury injection and nuclear magnetic resonance in evaluation of tight sandstone reservoirs in western Sichuan Basin

在深入分析恒速压汞法和核磁共振实验原理的基础上,结合岩心实验结果,分析川西新场地区上三叠统须家河组四段储集空间类型、孔隙结构类型、孔喉特征、孔喉比特征及其与孔、渗相关关系,研究孔隙和喉道对毛细管曲线的影响,探讨孔喉特征对可动流体参数的影响。川西须四段为低孔、低—超低渗致密储层,孔隙度介于1.6%~10.9%,平均5.9%,渗透率介于(0.01~2.81)×10^(-3)μm^(2),平均0.37×10^(-3)μm^(2)。发育粗喉大孔、粗喉小孔、细喉大孔和细喉小孔4类孔隙结构类型,孔隙半径介于8~180μm,平均112μm,以微孔—小孔为主;喉道半径介于0.100~1.008μm,平均0.484μm,以微喉为主。孔隙半径对低—超低渗储层的物性影响较小,喉道半径与渗透率相关性较好,其影响了毛细管曲线的变化,控制了低渗透储层的物性特征,是决定气藏开发效果的关键性因素。孔隙半径、喉道半径和最终进汞饱和度对可动流体参数影响较大,基于此三项参数提出孔隙结构指数,结合测井曲线开展了川西致密砂岩储层评价,评价结果与实际效果吻合较好。

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)μm^(2) to 2.81×10^(-3)μm^(2),with an average of 0.37×10^(-3)μm^(2).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 8-180μm,with an average of 112μm,mainly micropores and small pores.The throat radius ranges from 0.100 to 1.008μm,with an average of 0.484μm,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.