页岩气井分段压裂套损影响因素分析

Analysis of casing damage for staged fracturing in shale gas well

 李军¹ 李玉梅² 张德龙³ 杨宏伟¹ 孙世斌⁴

中国石油大学（北京）石油工程学院，北京 102249 北京信息科技大学高动态导航技术北京市重点实验室，北京 100101 北京探矿工程研究所，北京 100083 中国海洋石油工程股份有限公司，天津 300461）

 四川盆地长宁—威远页岩气示范区分段压裂过程中出现的套管变形、挤毁问题已经严重影响到页岩气井的井筒完整性以及勘探开发效果。考虑非均匀地应力、套管偏心、页岩各向异性、地层岩性非均质性等多因素的逐级耦合作用，利用有限元数值方法建立了偏心套管￣水泥环￣地层耦合的全尺寸数值模型，对页岩气水平井分段压裂过程中套管损坏机理进行研究分析。研究发现：套管偏心不是套管先期损坏的主控因素；随着非均匀地应力比增大，套管内壁应力极值及周向应力不均匀程度明显增大；页岩各向异性比越大，偏心角径向位置对应的套管内壁应力越大，此处承载风险也越高；套管内壁应力最大值出现在岩性交替变化界面，非均质性差异对套管内壁应力极值有较大的影响。研究结果可为页岩气井分段压裂过程中套损预测提供理论依据。

 The issue of casing deformation and collapse during the process of staged fracturing in Changning-Weiyuan shale gas reservoir in Sichuan Basin has seriously affected the exploration and development and wellbore integrity in shale gas. Considering the effects of multi-factor coupling of the non?-uniform stress, casing eccentric, shale anisotropy, lithologic heterogeneity step by step, a finite element numerical model coupling of the eccentric casing-cement sheath?-formation was established to explore the mechanism of casing damage during the staged fracturing process of shale gas well. The analysis results show that the casing eccentricity is not the main factor for the casing damage in early stage; as the non-uniform in-situ stress ratio increases, the stress extreme value of the casing wall and non-uniformity of circumferential stress increases significantly; the greater the anisotropy ratio, the greater the casing stress of the inner wall corresponding to the radial position of the eccentric angle, and the higher the risk here; the casing stress maximum of the inner wall appears in the interfaces of the lithology variations, and the heterogeneity differences have influences in different degree on the casing stress maximum of the inner wall. The study results will provide the theoretical basis for the casing damage prediction during the staged fracturing process of shale gas well.

10.6056/dkyqt201703020