复杂储层连通孔隙度评价与渗透率定量计算方法

Method of connected porosity evaluation and quantitative permeability calculation for complex reservoirs

复杂储层中普遍存在孔隙度相近而渗透率差异较大的现象。为了揭示其原因,采用铸体薄片、核磁共振、CT扫描成像等实验评价孔隙的连通性。连通孔隙度是渗透率的一个主要贡献参数。因此,从岩石孔隙空间的导电机理出发,以导电孔隙度为桥梁,建立连通孔隙度的计算模型,并分析十二种不同类型岩石中连通孔隙度与总孔隙度的函数关系;基于连通孔隙度的计算模型,建立普适性的核磁共振T_(2)模型;以石灰岩储层为例,在相近孔隙度条件下,从不同类型岩石渗透率之间的差异出发,推导、建立孔隙度指数模型,得到孔隙度指数的分布范围。基于普适性的核磁共振T_(2)模型,可将石灰岩储层渗透率预测的平均绝对误差从20.41mD降至0.83mD。该方法具有一定的理论价值和实际意义。

Complex reservoirs of similar porosity generally have largely different permeability.To reveal the reason for this phenomenon,we conduct experiments such as those with casting thin sections,nuclear magnetic resonance(NMR),and computed tomography(CT)scan imaging to evaluate the connectivity of pores.Connected porosity is a main contributing parameter to permeability.For this reason,approaching from the conductive mechanism of rock pore spaces,we build a calculation model for connected porosity with conductive porosity as a bridge.Then,the functional relationship between connected porosity and total porosity is analyzed for 12types of rocks.A universal NMR T_(2)model is built on the basis of the calculation model for connected porosity.With limestone reservoirs as an example,aporosity index model is derived and developed from the perspective of the permeability difference among different types of rocks under the condition of similar porosity.The distribution range of the porosity index is thereby determined.With the universal NMR T_(2)model,the average absolute error in permeability prediction for limestone reservoirs is reduced from 20.41mD to 0.83mD.The proposed method holds great theoretical and practical significance.