断背斜应变中和面张性段储层主控因素及预测方法——以克拉苏冲断带为例

摘要

塔里木盆地库车坳陷克拉苏冲断带白垩系巴什基奇克组储集层垂向上一直被认为主要受沉积相带控制.在钻井过程中, 相同应力背景、同一相带储集层垂向上物性、裂缝特征、地应力、钻遇复杂程度均存在差异.本文以克拉苏冲断带克深井区为例, 从实际地质资料出发, 根据实钻过程中的岩心、FMI成像测井、常规测井、地应力等特征, 提出断背斜目的层垂向上基于应力差异分为张性段、过渡段、压扭段.三段中, 以张性段储集层储层品质最好, 储层物性高、挤压应力相对较弱、裂缝溶蚀强度高、钻井事故少, 天然气量占天然气地质储量的60%以上, 为勘探的首选区.结合有限元数值模拟技术, 提出控制张性段的主要因素为构造最大主曲率、南翼边界断层倾角、断控幅度角、构造枢纽与高点之间夹角.根据四个控制因素的相关性及实际应用性提出了利用构造最大主曲率及断控幅度角预测张性段厚度的方法, 两者误差均低于20%.构造最大主曲率法适用于井控程度高的井区, 如评价–开发阶段; 断控幅度角法基于过目标靶点的地震资料, 对井控无要求, 适用于圈闭预探?评价?开发阶段.%The reservoir of the Cretaceous Bashijiqike Formation in the Kelasu anticline zone of the Kuqa Depression in Tarim Basin has long been considered to be controlled by sedimentary facies in vertical direction. The drilling practice showed that the physical properties, fracture characteristics, geostress and drilling complexity of the reservoir are vertically different in the same facies belt with similar geostress background. In this paper, with the Keshen block of the Kelasu fold-thrust belt as an example, combing features of cores, FMI imaging logging, conventional logging, geostress and other drilling data, we divided the reservoir of faulted fold into three zones in the vertical direction, tensional zone, transitional zone and transpressional zone. In these three zones, the tensional zone has the best reservoir quality, with high physical property, relatively weak compression stress, strong fracture dissolution and low drilling incident. The tensional zone accounts for more than 60% of the total gas reserve, and is the best choice for exploration in the Keshen block. Using finite element numerical simulation, we discussed the main controlling factors of the tensional zone reservoir, including the maximum structural curvature, dip of southern boundary fault, angle controlled by fault, angle between pivotal zone and structural high. Two methods were proposed to predict the thickness of tensional zone, using the maximum structural curvature and angle controlled by fault respectively. The errors of both prediction methods are better than 20%. The method of maximum structural curvature is applicable to the well area with high well controlling extent such as evaluation-development stage. The method of angle controlled by fault is based on the seismic data crossing the target. As no controlling well is needed, it is applicable to the trap-preliminary-prospect and evaluation-development stage.