运用高压压汞及扫描电镜多尺度表征致密砂岩储层微纳米级孔喉特征——以渤海湾盆地沾化凹陷义176区块沙四段致密砂岩储层为例

摘要

选取渤海湾盆地沾化凹陷义176区块沙河街组四段32块致密砂岩样品进行高压压汞、覆压孔渗等实验,结合环境扫描电镜的镜下特征,探讨致密砂岩储层的微观孔喉结构特征及其渗透性,特别是流体在纳米级及微米级喉道的渗流特征.实验表明:研究区的排替压力分布范围大,结合孔喉的分布情况和渗透率的相对大小,将该区的储层分成4大类6亚类;dv/d(logd)能够准确形象地反映各级孔喉分布情况,结合环境扫描电镜对孔喉相对大小的识别结果,将研究区的孔喉体系分为纳米级、微纳米级、纳微米级及微米级等4类,将喉道分为纳米级喉道和微米级喉道;通过相关性分析,发现纳米级喉道控制着渗透率,而微米级喉道更多贡献于孔隙度;高压压汞在研究致密储层的孔喉特征时,不仅能够表征常规孔喉的结构特征,同时也能反映微纳米级孔喉的大小及流体在其中的渗流特征,对进一步精细评价储层具有良好效果.%Thirty-two samples of tight sandstone from the fourth member of Shahejie Formation in Yi176 block, Zhanhua Sag,Bohai Bay Basin were selected for high pressure mercury injection and overpressure pore infiltration experiments.The microscopic pore throat structure and permeability of tight sandstone reservoirs,especially the flow characteristics of fluid in nano-and micro-scale throats,were discussed along with their microscopic features observed with environmental scanning electron microscopy(SEM).Experiments showed that the discharge pressure in the study area has a wide distribution. According to the distribution of pore throats and relative permeability,the reservoirs in this area were divided into 4 major types and 6 sub-categories. dv/d(logd)reflects the distribution of pore throats at all levels. Combined with the identification of the relative sizes of pore throats by environmental SEM, the pore throat system in the study area was divided into 4 categories:nano scale,micro-nano scale,nano-micro scale and micro scale,while throat was classified into nano and micro types.According to the correlation analysis,it was found that the nano-scale throats controlled permeability,while the micro throats contributed more to porosity. High pressure mercury injection not only characterizes the structural characteristics of conventional pore throats, but also reflects the size of the micro- and nano-pore throats and the fluid flow characteristics in them, which allows further detailed evaluation of reservoirs.