潜江凹陷盐间页岩油储层孔隙结构分形表征与评价

目前, 众多学者从地球化学特征、储层物性特征等方面对潜江凹陷潜江组页岩展开了较多研究, 并取得了一定的进展, 但对其孔隙的复杂性、形成孔喉的主要矿物及其影响因素的分析存在盲点。依据分形理论, 结合氮气吸附实验、高压压汞实验, 选取沉积位置不同的BX7井以及BYY2井, 分别对潜三段第四亚段(Eq₃4-10)页岩的比表面分形特征、孔隙结构分形特征以及孔喉分形特征进行了评价, 分析了其影响因素。结果表明, 该地区的孔隙表面较为平整, 比表面分形维数D1趋近于2, 孔隙表面的粗糙程度主要受黏土矿物本身特性影响。相较于沉积边缘的BX7井, 位于沉积中心的BYY2井储层孔隙结构分形特征更为简单。小孔径孔隙的孔体积所占比例越大, 孔隙结构分形特征越复杂。BX7井储层孔隙结构分形维数D2主要受黏土矿物以及石英的影响, 而BYY2井储层孔隙结构分形维数D2主要受白云石的影响。白云石为构成BX7井储层孔喉的主要矿物, 随白云石增加, 孔喉特征复杂, 连通性变差。BYY2井储层中石英形成的孔喉直径较小, 石英的增加会使孔隙连通性变差; 方解石形成的孔喉直径较大。页岩油的赋存会使孔隙的分形维数变小, 对孔喉分形特征的影响较小。盐类矿物的存在会阻塞孔隙, 使孔隙连通性变差。 

Characterization and evaluation of fractal dimension of intersalt shale oil reservoirs in Qianjiang Depression

At present, studies of the shales in Qianjiang Formation from the Qianjiang Depression has been widely documented and significant progress has been made in the aspects of geochemical characteristics and reservoir physical properties.However, the complexity of pores, the main minerals forming pore throats and their influencing factors is still poorly understood. In this work, based on fractal theory and combined with nitrogen adsorption and high-pressure mercury injection experiments, Wells BX7 and BYY2 at different deposition locations were selected to evaluate the specific surface fractal characteristics, pore structure fractal characteristics and pore throat fractal characteristics of the Eq₃4-10 rhythmic shale of the Qianjiang Formation and analyses the influencing factors.The results show that the pore surface of shale in study are a is relatively flat, with the fractal dimension D1 being close to 2, and the roughness of the pore surface is mainly affected by the characteristics of the clay minerals. Compared with Well BX7 at the sedimentary edge, Well BYY2 at the sedimentary center has simpler fractal characteristics of reservoir pore structure. The larger the proportion of pore volume with a small pore size is, the more complex the fractal characteristics of the pore structure are. The fractal dimension D2 of the reservoir pore structure in Well BX7 is mainly affected by clay minerals and quartz, while dolomiteis the dominant controlling factor for the fractal dimension D2 of the reservoir pore structure in Well BYY2. Dolomite is the main mineral that constitutes the pore throat of the Well BX7 reservoir. With the increase in dolomite, the pore throat features are complex, and the pore connectivity becomes poor. The pore throat diameter formed by quartz in the Well BYY2 reservoir is small.The increase in quartz will worsen the pore connectivity, and the pore throat diameter formed by calcite is large. The occurrence of shale oil will reduce the fractal dimension of pores and have little influence on the fractal characteristics of pore throats. The presence of salt minerals can block the pores and make the pore connectivity poor.