低渗油气储层孔喉的分形结构与物性评价新参数

通过常规压汞手段，获得了松辽盆地南部长岭凹陷大情字井地区下白垩统泉四上亚段低渗碎屑储集岩的孔喉空间分布数据。储集砂岩孔喉分布的自相似结构宽广而连续，在整个孔喉测度区间0.02～104 μm的宽广孔喉尺寸范围内，泉四上亚段低渗透砂岩均具分形特征。孔喉的分布在整个可测区间均具有两个无标度区的多重分形性质，不同尺度（无标度区）上的分维值不同，无标度区1的分维值平均为2.995，无标度区2的分维值平均为2.512。无标度区2的下限、上限以及其分维数与储集物性（特别是渗透率）关系密切。据此提出了评价储集层的“喉道分形综合指数”--ITF。ITF与渗透率的正相关系数的平方可达0.91，与孔隙度的正相关系数的平方，为0.65。该参数综合反映了低渗储集层的储集和渗滤性能，充分揭示了油气储集岩的孔喉结构特征对其储渗性能（特别是渗流能力）的影响。

THE FRACTAL STRUCTURES OF PORE AND THROAT AND NEW PHYSICAL EVALUATION PARAMETER OF THE OIL-GAS RESERVOIR WITH LOW PERMEABILITY

By means of routine mercury penetration test, the distribution data of throat and pore space of the low permeability clastic reservoir of K1 q4 in Daqingzijing area of Changling sag in south part of Songliao Basin are obtained. The pore and throat distribution self similarity of reservoir sandstone is wide and continuous. All of the K1 q4 low permeability sandstones are of fractal characteristics within the limits of 0.02—104 μm pore and throat measuring. The pore and throat distributions within all of measuring limits are of multi fractal property of two zones without graduation. The fractal dimension values are different in different scale (in different zones without graduation). The fractal dimension average value in the zone Ⅰ without graduation is 2.995; but the fractal dimension average value in the zone Ⅱ without graduation is 2.512. The upper limit, the lower limit and fractal dimension of the zone Ⅱ without graduation have close relationship with the reservoir physical property, especially the permeability, so the new comprehensive index of pore throat fractal (ITF) used to evaluate the reservoir bed is put forward. The square of ITF and permeability positive correlation coefficient can come up to 0.91 and that of ITF and property positive correlation coefficient is a little slower, i.e. 0.65. The new parameter ITF can comprehensively reflect the reservoir and percolation property of low permeability reservoir, fully reveal the pore throat fractal structure characteristics of oil gas reservoir rock, especially the influence on infiltration ability.