多套复合盐层的地应力确定方法

A method for determining the in-situ stresses in multi-compound salt formation

在库车坳陷古近系多套复合盐层的钻井工程设计当中,通常以上覆岩层压力作为最大水平地应力。现场资料调查表明,以此为依据所设计的套管,常常不能满足该地层套管的抗外挤强度要求。为了解决套管抗外挤强度问题,通过实验测试得到该研究区块多套复合盐层上、下泥岩地层的地应力值及中间每一层复合盐层的岩石力学参数,并以此作为边界条件,建立了多套复合盐层及上、下泥岩层地应力计算的有限元分析模型,运用数值模拟方法,反演得到每一层复合盐层的地应力场。采用该方法对库车坳陷某地区多套复合盐层的地应力场进行分析,结果表明,中间盐层的水平地应力最高,其上、下的膏盐岩含泥岩层、泥岩含膏盐岩层、泥岩层的水平地应力依次降低。所建立的分析模型,为该地区井壁稳定及套管安全设计工作奠定了基础。

During the process of drilling engineering design for multi-compound salt formation of piedmont structure in the Kuqa depression,it is usually assumed that overburden pressure equals to the maximum horizontal stress. Field data indicates that the casing designed by the above means can not satisfy collapse resistance frequently. In-situ stresses of mudstone strata and rock mechanics parameters of each layer in multi-compound salt formation are calculated in this study area based on laboratory tests. Taking the above parameters as boundary condition for in-situ stresses analysis,a finite element model is presented to invert in-situ stresses field of each layer in multi-compound salt formation. By analysis of the in-situ stresses field of multi-compound salt-rock in the Block X of the Kuqa depression,it is indicated that the horizontal stress of salt formation in the middle layer is the highest,while that of overlapping or underlying strata such as salt gypsum rock containing mudstone,mudstone containing salt gypsum rock and mudstone is decreasing in order. The built-up analytical model provides sound foundation for designs of borehole stability and casing safety in this area.