柴达木盆地英西地区下干柴沟组上段构造裂缝的分布预测

Distribution prediction of tectonic fractures in the upper member of Xiaganchaigou Formation in Yingxi area,Qaidam Basin

柴达木盆地英西地区下干柴沟组上段碳酸盐岩储层普遍发育裂缝,裂缝是控制其油气高产的关键,但对区内构造裂缝的分布规律认识不清.以声发射测试获得的古构造应力大小和前人研究获得的古构造应力方向为约束条件,利用有限元分析软件ANSYS,数值模拟恢复了研究区目的层在喜马拉雅晚期构造挤压背景下的构造应力大小的分布;依据岩石破裂准则计算了岩石破裂值,从而定量预测了研究区目的层构造裂缝的分布,并总结了其分布规律.结果表明,英西地区下干柴沟组上段水平最大主压应力主要分布于110~180 MPa,其展布由北东至南西方向呈逐渐增大的趋势;研究区内盐下层的水平最大主压应力值整体比盐间层高;差应力大小决定着构造裂缝的发育,在差应力为高值的断层附近裂缝发育程度高;构造裂缝的分布主要受断层展布和岩性的控制,邻近盐间层底部的盐下储层和构造上处于北带、中带区域的构造裂缝发育程度较高,是英西地区深层油气的有利勘探区.该研究成果可对柴达木盆地英西地区深层勘探区的预测提供依据.

Fractures are generally developed in carbonate reservoirs in the upper member of Xiaganchaigou Formation in Yingxi area of Qaidam Basin,which are the key to control production of oil and gas,but the distribution regularity of tectonic fractures is not clear in the area.Taking the magnitude of paleotectonic stress obtained by acoustic emission test and the direction of paleotectonic stress obtained by previous studies as constraints,the distribution of tectonic stress of the target reservoir in the study area under tectonic compression in the late Himalayan was simulated numerically by using finite element analysis software ANSYS.According to rock failure criterion,the rock rupture incidence was calculated,accordingly the distribution of tectonic fractures of the target reservoir in the study area was quantitatively predicted and their distribution characteristics were evaluated synthetically.The results indicate that the maximum horizontal principal compressive stress mainly ranges from 110 to 180 MPa in the upper member of Xiaganchaigou Formation in Yingxi area,and gradually increases from north-east to south-west direction.The maximum horizontal principal compressive stress of the sub-salt strata is generally higher than that of the inter-salt strata in the study area.The differential stress determines the development of tectonic fractures,the areas with well-developed fractures are mainly located around faults with the high differential stress.The distribution of tectonic fractures is mainly controlled by fault distribution and lithology,and the development level of tectonic fractures is comparatively high in the sub-salt reservoir near the bottom of the inter-salt strata and in the northern and middle tectonic zones,these areas are favorable for oil and gas exploration in the deep strata of Yingxi area.The research results include distribution of tectonic stress and tectonic fractures,which can provide a basis for predicting exploration areas in the deep strata in Yingxi area of Qaidam Basin.