页岩气水平井井筒完整性失效机理与控制方法研究

Breakthrough progress has been made in shale gas development of China. However, there are serious problems of wellbore integrity in the process of multi-stage fracturing for horizontal wells, even the failure ratio up to 40% in some blocks. The failure mechanism is unclear. The main control factor is unknown. There are short of effective control methods. Based on the characteristics of shale reservoirs in China, such as strong anisotropy, heterogeneity, fault and natural fracture development and dynamic changes of wellbore geologic mechanics during fracturing, this project will research on the casing stress and its control method during fracturing process. This study mainly focuses on: ①Original mechanical characteristics of casing-cement -formation assemblage in anisotropic shale reservoir. The evaluation method can be formed for casing original stress in complex geological conditions. ②Failure mechanics behaviors of wellbore integrity during multi-stage fracturing in horizontal shale gas wells. A new method can be established to calculate casing stress in multi-factor coupling conditions based on four-dimensional geo-mechanical. ③Failure mechanism experiments of wellbore integrity in horizontal shale gas wells. Based on full-size casing deformation test, combined with the numerical simulations, the failure mechanism can be obtained. ④Control method for wellbore integrity in horizontal shale gas wells. Based on multi-objective optimization, such as the wellbore trajectory design, the casing optimization, the cementing quality, the non-uniform segmented clusters and fracturing parameters, a new control method about drilling-to-fracturing integration can be developed covering the full life cycle wellbore integrity.

我国页岩气开发已取得突破性进展，然而在水平井分段压裂过程中遇到了严重的井筒完整性失效问题，部分区块失效比例高达40%，其失效机理不清，主控因素不明，缺乏有效控制方法。本项目基于我国页岩储层各向异性强、非均质性突出、断层及天然裂缝发育、压裂过程中井筒地质力学条件动态变化的特点，对压裂前、压裂中的套管应力变化及其控制方法展开攻关：①各向异性页岩储层套管-水泥环-地层组合体原始力学特征分析，形成复杂地质条件下套管原始应力评估方法；②页岩气水平井分段压裂过程中井筒完整性失效力学行为研究，建立基于四维地质力学的多因素耦合作用下套管应力计算新方法；③页岩气水平井井筒完整性失效机理试验研究，基于全尺寸套管变形试验，结合数值模拟，明确井筒完整性失效机理；④页岩气水平井井筒完整性控制方法研究，基于井眼轨道设计、套管优选、固井质量、非均匀分段分簇、压裂参数等多目标优化，形成井筒完整性钻井压裂一体化控制新方法。

我国页岩气开发已取得突破性进展，然而在水平井分段压裂过程中遇到了严重的井筒完整性失效问题，部分区块失效比例高达40%，其失效机理不清，主控因素不明，缺乏有效控制方法。. 本项目基于我国页岩储层各向异性强、非均质性突出、断层及天然裂缝发育、压裂过程中井筒地质力学条件动态变化的特点，对压裂前、压裂中的套管应力变化及其控制方法进行了攻关，首先建立了各向异性页岩储层套管-水泥环-地层组合体原始力学特征分析模型，明确了复杂地质条件下套管/水泥环的原始应力状态。其次研究了页岩气水平井分段压裂过程中地应力动态变化特征，建立了多因素耦合作用下套管载荷谱。进一步建立了国内首套全尺寸水泥环完整性测试试验装置和非常规油气井套管柱模拟试验系统，进行了全尺寸套管变形试验和水泥环密封失效实验，明确了井筒完整性失效机理。最后集成所有研究成果确定了页岩气水平井井筒完整性控制方法，形成了适合我国页岩气储层特征的钻井压裂一体化井筒完整性控制新方法。