沿河湾探区低渗透储层构造裂缝特征及分布规律定量预测

鄂尔多斯盆地沿河湾探区主力油层上三叠统延长组长6¹油层组属于特低渗透储层,其裂缝发育和分布状况成为制约油气勘探和有效开发的瓶颈。根据露头地层、钻井岩心及岩石薄片等实物资料,利用古地磁岩心定向方法,对沿河湾探区上三叠统延长组长6¹储层构造裂缝的基本特征、裂缝力学性质和裂缝有效性进行了定性-定量化观测统计。结果表明,沿河湾探区长6¹储层主要发育有区域性NEE向和近SN向高角度的共轭构造裂缝系统;储层段岩心构造裂缝密度为0.12~3.56条/m,以偏张性裂缝为主,充填较为严重,多为无效裂缝。依据长6¹岩心构造裂缝观测值,以有限元数值模拟方法为基础,岩石破裂法和能量法相结合,建立了长6¹储层构造裂缝分布定量预测数学模型。利用该模型预测了目的层裂缝相对发育区、次发育区和不发育区,并预测了张剪裂缝走向,为建立沿河湾探区长6¹储层裂缝分布网络模型和今后油气勘探、开发提供了地质依据。

Characteristics and quantitative prediction of distribution laws of tectonic fractures of low-permeability reservoirs in Yanhewan area

The Chang 6¹ layer is a low-permeability reservoir of Yanchang Formation in the Upper Triassic System and is also the main oil layer in Yanhewan area of Ordos Basin. The distribution and development degree of tectonic fractures restrict the petroleum exploration and valid development. The observation of outcrop and drilled core, thin-section analysis and paleo-magnetis core orientation were applied to the quantitative statistics of tectonic fractures, including the basic characteristics,mechanics and valitidy of tectonic fractures of Chang 6¹ low-permeability reservoir in the Yanhewan area. Chang 6¹ reservoir developed the regional conjugate high-angle tectonic fracture system with NEE and NS directions. The density of tectonic fractures is from 0.12 to 3.56 ribbons per meter. The most tectonic fractures are tensional and filled seriously,which belong to the invalid tectonic fractures in Chang 6¹ reservoirs of Yanhewan area. According to the density of tectonic fractures in cores obtained from different drilling wells in Yanhewan area, a mathematical model for quantitatively predicting and evaluating the distribution and development degree of tectonic fractures was developed by using the finite element simulation method,the rock burst method and the strain energy method. The model was used to predict the areas of developed, sub-developed and un-developed fractures and to determine the strikes of tensile-shear fractures. These results can provide the important geological references for establishment of fracture network model and further petroleum exploration in Yanhewan area.