四川盆地HC地区须二段致密砂岩储层地应力评价及其在致密气开发中的应用

Evaluation of in-situ stress in dense sandstone reservoirs in the second member of Xujiahe Formation of the HC area of the Sichuan Basin and its application to dense sandstone gas development

【研究目的】四川盆地HC地区须二段勘探开发潜力巨大,但该地区为典型的低孔低渗致密气藏,需要进行地应力精细评价来为后期纵向上压裂选层和平面上工程甜点区优选提出建议进而提高产能。【研究方法】基于25组声发射和13组差应变等实验测试分析,结合水压致裂、常规和特殊测井资料,进行地应力的精细评价,以期分析在致密砂岩储层中不同实验测试方法的适用性,查明有利于工程改造的层位和甜点区。【研究结果】实验测试结果表明HC地区须二段最大水平主应力值为50.77~75.65 MPa,均值为59.71 MPa;最小水平主应力值为45.37~54.31 MPa,均值为49.31 MPa;垂向主应力为48.11~65.62 MPa,均值为56.53 MPa。模拟结果表明储层内部应力隔层厚度和两向应力差异系数越小,越有利于压裂改造。通过对比小层间的三向应力关系,表明须二段处于走滑应力状态。HC地区须二段致密砂岩均质性较强,声发射测试结果误差较大,差应变测试结果与其他地应力大小解释结果具有更高一致性,故该测试方法更加适用于均质性较强的砂岩地层。【结论】结合地应力大小,纵向上建议选择隔层组合更有利的须二2亚段中上部为压裂目的层;且为了达到较好的体积缝网压裂改造效果,平面上建议避开两向应力差异系数较大的断层附近区域,应选择优质储层发育且水平应力差异系数相对较小的HC地区中部HC102-HC111井区。

This paper is the result of oil and gas exploration engineering.[Objective]The second member of Xujiahe formation of the HC area in the Sichuan Basin has great potential for exploration and development,but it is a typical low-porosity and low-permeability tight gas reservoir,which requires in-situ stress refined evaluation to recommend the optimal selection of engineering sweet spots for later vertical fracturing and plane fracturing to increase production.[Methods]Based on experimental test analysis such as 25 groups of acoustic emission and 13 groups of differential strain,combined with hydraulic fracturing,conventional and special logging data,we analyze the applicability of different experimental test methods in tight sandstone reservoirs by performing a fine-scale evaluation of in-situ stress and identified layers and sweet spots conducive to engineering modifications.[Results]The results of the experimental tests of the second member of Xujiahe formation in the HC area showed that the maximum horizontal principal stress values ranged from 50.77 to 75.65 MPa,with a mean value of 59.71 MPa;the minimum horizontal principal stress values ranged from 45.37 to 54.31 MPa,with a mean value of 49.31 MPa;and the vertical stress values ranged from 48.11 to 65.62 MPa,with a mean value of 56.53 MPa.The simulation results show that the smaller the thickness of the stress barrier within the reservoir and the differential coefficient of in-situ stress in both directions,the more favorable the fracture modification.The comparison of the three-dimensional stress relationships between the minor layers indicates that the second member of Xujiahe Formation is in a strike-slip stress state.The dense sandstone in the second member of the Xujiahe Formation is more homogeneous,the acoustic emission test results are more inaccurate.The results of the differential strain test are in better agreement with the results of the in-situ stress magnitude interpretation,making the test method more suitable for more homogeneous sandstone formations.[Conclusions]In combination with the magnitude of in-situ stress,it is recommended vertically that the more favorable combination of compartments,upper middle of the second subsection of Xu-II,be selected as the target layer for fracturing.To achieve a better volume fracturing network,it is recommended to avoid areas near faults with a large differential coefficient of two-dimensional stress.The area of HC102-HC111 well in the central part of the HC area,where high-quality reservoirs are developed and two-dimensional stress difference factor is relatively small,should be selected.