鄂尔多斯盆地杭锦旗地区盒1段致密砂岩孔隙结构分形特征及其与储层物性的关系

基于物性、铸体薄片、电镜扫描和高压压汞等测试分析资料,利用汞饱和度法和含水饱和度法对杭锦旗地区盒1段致密储层孔隙结构分形维数进行了计算,并分析其与储层物性的关系。结果表明:盒1段储层平均孔隙度、渗透率分别为9.83%、1.03×10^-3μm^2,储集空间以粒间溶孔、粒内溶孔和残余粒间孔为主。汞饱和度法计算的整体分形维数分布在2.1384~2.8292,平均值为2.3965,含水饱和度法计算的整体分形维数分布在2.5294~2.8797,平均值为2.6791。相比于含水饱和度法,汞饱和度法计算的分形维数与孔隙度、渗透率及各孔隙结构参数之间具有更好的相关性,是因为含水饱和度法易对孔喉较小的样品产生偏差。基于汞饱和度法分形维数,将盒1段储层孔隙结构分为四类:Ⅰ类(D f≤2.31),Ⅱ类(2.31

Pore structure fractal characteristics and its relationship with reservoir properties of the first Member of Lower Shihezi Formation tight sandstone in Hangjinqi area,Ordos Basin

Based on physical property, casting thin section, scanning electron microscope, high-pressure mercury injection and other test analysis data, the fractal dimension of pore structure of tight sandstone reservoir was calculated by the method of mercury saturation and water saturation in the first Member of Lower Shihezi Formation in Hangjinqi area, and the relationship between fractal dimension and the physical properties of reservoir was analyzed.The results have shown that the average porosity and permeability of the Lower Shihezi Formation reservoir were 9.83% and 1.03×10-3 μm2, respectively.The reservoir space is mainly composed of intergranular dissolved pores, intragronular dissolved pores and residual intergranular pores.The overall fractal dimension calculated by the mercury saturation method is distributed in 2.138 4-2.829 2 with an average value of 2.396 5 while calculated by the water saturation method is distributed in 2.529 4-2.879 7 with an average value of 2.679 1.Compared with the water saturation method, the fractal dimension calculated by the mercury saturation method has a better correlation with the porosity, permeability and pore structure parameters, because the water saturation method tends to produce deviation on samples with smaller pore throat.The pore structure was divided into four types based on fractal dimension: Type Ⅰ(D_f≤2.31), Type Ⅱ(2.31 < D_f < 2.4), Type Ⅲ(2.4≤D_f < 2.52), Ⅳ(D_f≥2.52).Fractal dimension(D_f), averoged radius of pore throct(R_m) and porosity(φ) were selected to calculate permeability by multiple nonlinear regression.The calculated permeability by multiple nonlinear regression shows strong correlation with measured permeability, whose correlation coefficient squared is more than 0.9, which means the permeability estimation model is suitable for the study area.