库车坳陷东部侏罗系砂岩构造裂缝定量预测

摘要

The Jurassic low-porosity and low-permeability sandstone is an important reservoir of Yinan-Tuzi area in Kuche Depression. Well-developed tectonic fractures serve as important migration pathways and accumulation spaces, and their nature and distribution are the key to guiding further exploitation. Most fractures without filling veins are supposed to develop after the Miocene, on the base of the analysis of fossil stress field evolution and the nature of filling. On the basis of previous acoustic emission studies and rock mechanical tests, a 3-D finite elemental simulation on the tectonic stress field of Kuche depression was made to predict the distribution of tectonic fractures in Yinan-Tuzi area, considering several factors such as geologic setting, geometry of strata, and faults etc. With the constraints of 14 segments of wells, the modeling result showed that the distribution of tectonic fractures is controlled by several aspects such as different rock fracture mechanics for each layers, the shape of fault, and the curvatures of strata. Among all layers, the formation of Lower Jurassic has the highest density of fractures, within which the density in the southwest area towards Well Yinan 2 reaches more than 1.5 m-1on average and decreases gradually eastward.%塔里木盆地库车坳陷依南-吐孜地区侏罗系低孔低渗砂岩是该区主要的油气储集层，构造裂缝作为油气运移通道和储集空间，其发育特征和分布规律是制约油气勘探开发的关键。通过对区域构造应力场演化以及裂缝充填特征的分析，认为依南-吐孜地区侏罗系砂岩裂缝主要形成于新近纪之后。在声发射古应力测量和岩石力学参数测试的基础上，考虑研究区地质背景、地层形态、断层分布等诸多因素，利用三维有限元法对库车坳陷新近纪以来的构造应力场进行数值模拟，并在该地区14个井段裂缝面密度的约束下，预测出依南-吐孜地区侏罗系砂岩构造裂缝发育程度与分布规律。结果表明，裂缝分布受到岩性、地层形态与断层的共同影响，下侏罗统阿合组构造裂缝最为发育，平面上依南2井西南区域的裂缝面密度较大，达到1.5 m-1以上，而向东裂缝面密度逐渐减小。