核磁共振T_2谱构建页岩储层孔隙结构研究——以张家界柑子坪地区下寒武统牛蹄塘组的页岩为例

针对页岩储层低孔低渗、非均质性较强的特点,通过联合应用压汞法与气体吸附法,分段构建实验条件下页岩的孔隙分布,其中宏孔部分由高压压汞实验计算,微介孔部分通过N2气体吸附实验再由BJH方程换算。借助于低磁场核磁共振岩样分析仪,从页岩核磁共振T_2谱响应特征出发,将研究区页岩样品T_2谱分为3种类型,构建了T_2谱与压汞-气体吸附联合法建立的页岩孔隙分布的幂函数关系。通过岩样样品的核磁共振T_2谱与实验测得孔隙分布的幂函数拟合,发现各样品T_2谱拟合的孔隙分布与实验测得孔隙分布相关系数均较高,各岩块样品对应参数数值均较为接近,适合研究区应用,由此建立了研究区牛蹄塘组的页岩核磁共振T_2谱与孔隙半径对应关系。

Pore structure of shale reservoir built by NMR T2 spectrum:taking Niutitang shale of lower Cambrian in Zhangjiajie Ganziping area as an example

In view of the low porosity and low permeability and strong heterogeneity of shale reservoirs,combined by mercury injection method and gas adsorption method,the pore of shale under the experimental conditions was constructed, in which the macro-pores was calculated by the high pressure mercury injection test,and the micro-mesopores was got by the N2 gas adsorption experiment and then converted by the BJH equation.With low magnetic field nuclear magnetic resonance rock analyzer,from the point of NMR T2 spectrum response characteristic,the T2 spectrum of the shale samples was divided into three types ,and then the power function of the T2 spectrum and pore distribution got from pressure mercu-ry -gas adsorption was constructed,which shows a high correlation between the pore distribution of T2 spectrum and the experimental result,and the corresponding parameters of rock samples are close,which is suitable for the application in the study area.Thus,the corresponding relationship of nuclear magnetic resonance T2 spectrum and pore radius of shale of Niutitang Formation was established.