基于压汞和核磁共振对致密油储层渗透率的评价:以鄂尔多斯盆地陇东地区延长组长7油层组为例

摘要

To elucidate the relationship between permeability and pore throat size and T2 relaxation time of the 7i member sandstone reservoir of the Upper Triassic Yanchang Formation in the Ordos Basin (termed Chang 7),we establish the permeability estimation equations using linear regression analysis based on the mercury injection capillary pressure (MICP) and nuclear magnetic resonance (NMR) data in combination with present estimation methods of conventional reservoir permeability.Results show that unlike conventional reservoirs and other unconventional reservoirs (e.g.,tight gas and shale gas),the pore throat radii corresponding to the mercury saturation of 5％ (r5) of the Chang 7 tight oil sandstone yield the best correlation with permeability.This was mainly controlled by the pore throat sizes ranging from 0.1 μm to 1 μm,i.e.,micmpores and mesopores.Permeability evaluation parameters,i.e.,T2 cutoff value (T2cutoff) and T2 spectrum peak value (T2peak),which derived from NMR experiment,are no longer applicable to the Chang 7 tight oil reservoirs.Geometric mean of NMR T2 (T2gm),as a crucial parameter for estimating the permeability of the Chang 7 tight sandstones,manifests a perfect correlation with porosity and permeability.The established evaluation method using NMR T2gm shows that the predicted permeability is very close to the measured permeability,with a high degree of anastomosis (R2 =0.9599).Therefore,the method of permeability evaluation established by pore throat size (r5) and NMR T2gm is of guiding significance for the prediction of the quality of tight oil reservoirs in the Ordos Basin in the future.%为探讨鄂尔多斯盆地致密油储层渗透率与孔喉半径、T2弛豫时间的相关性,在分析目前对常规储层渗透率评价方法的基础上,基于压汞和核磁共振实验数据,利用线性回归分析建立了适应于长7致密油储层渗透率评价的方法.研究结果表明:不同于常规储层和其他类型的致密砂岩储层,长7致密油砂岩累积进汞饱和度5％所对应的孔喉半径(r5)与渗透率产生了良好的相关性,是渗透率预测的最佳孔喉半径,且在这个孔喉范围内孔喉大小主要介于0.1 ～lμm,由微孔和中孔构成;核磁共振渗透率评价参数T2截止值(T2cutoff)和T2谱峰(T2peak)对长7致密砂岩储层不再适用,而T2几何平均值(T2gm,)是长7致密砂岩渗透率评价的重要参数,其与渗透率、孔隙度产生良好的关联性,建立的评价方法结果显示预测渗透率与实测渗透率非常接近,吻合度较高(R2=0.9599).利用孔喉半径和T2弛豫时间建立的渗透率评价方法匹配使用,对今后鄂尔多斯盆地致密油储层质量预测具有指导意义.