低渗透储层构造裂缝长度表征及应用——以四川盆地磨溪—高石梯地区寒武系龙王庙组为例

为明确低渗透储层构造裂缝长度定量表征方法，以四川盆地磨溪—高石梯地区寒武系龙王庙组为例，综合采用岩心裂缝统计及岩石力学实验方法，从构造应力场的角度推导低渗透储层构造裂缝长度的关系式。该方法将裂缝长度与裂缝体密度、应变能密度及岩体应力状态联系起来，建立了裂缝长度与裂缝体密度之间的定量计算关系。结果表明:裂缝长度与裂缝数量呈负指数幂关系；裂缝体密度与应变能密度呈正比线性关系；裂缝长度与裂缝体密度呈负指数幂关系。将推导的裂缝长度公式应用于磨溪—高石梯地区龙王庙组，数值模拟结果显示:裂缝体密度值普遍介于1~5 m2/m3，最高为9 m2/m3，高值区主要分布于断层及周边地区；裂缝长度主要介于1~20 m，断层及周边区域裂缝密而短，长度普遍小于3 m。 

Characterization of the length of structural fractures in low permeability reservoirs and its application:a case study of Longwangmiao Formation in MoxiGaoshiti areas,Sichuan Basin

In order to classify the quantitative characterization method of structural fracture length in low-permeability reservoirs, the Cambrian Longwangmiao Formation of Moxi-Gaoshiti areas in the Sichuan Basin is taken an example in this study. The relationship between structural fracture lengths of low-permeability reservoirs was derived from the perspective of structural stress field by the means of core fracture statistics and rock mechanical experiment. Quantitative relationships between fracture length and fracture volume density, strain energy density and rock mass stress state were established. Results showed a negative exponential power relationship between fracture length and number, a proportional linear relationship between fracture volume density and strain energy density, and a negative exponential power relationship between fracture length and volume density. The derived fracture length formula was applied to the Longwangmiao Formation in Moxi-Gaoshiti areas. Numerical simulation results showed that fracture density generally ranges from 1-5 m2/m3, and the highest value is 9 m2/m3, mainly distributed in fault and its surrounding areas. Fracture length is mainly between 1-20 m. The fractures in fault and surrounding areas are dense and short, usually less than 3 m.