基于核磁共振测井的致密砂岩储层孔喉空间有效性定量评价

Quantitative evaluation of the effectiveness of pore-throat space in tight sandstone reservoirs based on nuclear magnetic resonance log

油气储层孔隙可分为毫米级孔隙、微米级孔隙和纳米级孔隙3种类型,常规储层的孔喉直径一般大于1 μm,致密含气砂岩储层的孔喉直径为0.03～1 μm,纳米级孔隙是致密砂岩储层连通储集空间的主体,因此对其储层有效性评价的难度较大.核磁共振T2谱与压汞曲线均能很好地反映储层的孔隙结构,利用核磁共振T2谱与压汞实验的相关性,将核磁共振T2谱转化为孔喉分布图谱.在此基础上对岩心核磁共振T2谱和压汞实验数据进行深入处理分析,并结合前人研究成果,确定SLG油田致密砂岩储层孔喉空间的有效性划分标准为：孔喉半径小于0.04 μm孔喉体系为粘土束缚水体积,孔喉半径为0.04～0.1 μm孔喉体系为非泥质微孔隙地层水体积,孔喉半径为0.1～0.2μm的孔喉体系为毛细管束缚水体积,孔喉半径大于0.2 μm的孔喉体系为可采出流体体积.实践证实,该方法可以对孔喉空间进行快速地定量计算,明确孔隙中的含水特征与赋存状态,实现了对致密砂岩储层孔喉空间的有效性定量评价.

The pores in reservoirs bearing hydrocarbon have been divided into three types:millimeterpore,micropore and nanopore. The diameter of pore throat in conventional reservoir is generally larger than1 μm. The diameter of pore-throat in tight gas reservoirs ranges from 0.03 to 1 μm. The nanopore is the main body of the connected reservoir space in tight sand,so it is difficult to evaluate the effectiveness of tight reservoirs. Both NMR T2 spectrum and capillary pressure curves can well reflect the pore throat structure of rocks. The NMR T2 spectrum was translated into pore throat distributions using the correlation between NMR T2 experiment and mercury injection. On the basis of previous research results,the core NMR T2 spectrum and capillary pressure data were processed and analyzed deeply to determine effectiveness criteria of the tight sand pore throat in SLG oilfield:the pore-throat system with pore radius less than 0.04 μm is associated with clay bound water volume;the pore-throat system with a pore radius between 0.04 and 0.1 μm is associated with non-shale micro-po-rosity formation water volume;the pore-throat system with pore radius between 0.1 and 0.2 μm is associated with capillary bound water volume;the pore-throat system with pore radius more than 0.2 μm is associated with the volume in which the fluid can be taken out. The practice proves that the method can be used to quickly calculate pore-throat space quantitatively and to determine the pore water features and its occurrence,which can evaluate the space effectiveness of tight sand reservoirs effectively.