应力卸载-水化协同作用下页岩井壁稳定性模型  

Wellbore stability model in shale formation under the synergistic effect of stress unloading-hydration

作　　者：丁乙[1] 刘向君[1] 梁利喜[1] 熊健[1,2] 李玮 魏晓琛 段茜[3] 侯连浪 DING Yi;LIU Xiangjun;LIANG Lixi;XIONG Jian;LI Wei;WEI Xiaochen;DUAN Xi;HOU Lianlang(State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University,Chengdu 610500,China;School of Geoscience and Technology,Southwest Petroleum University,Chengdu 610500,China;School of Science,Southwest Petroleum University,Chengdu 610500,China)

机构地区：[1]西南石油大学油气藏地质及开发工程国家重点实验室,成都610500 [2]西南石油大学地球科学与技术学院,成都610500 [3]西南石油大学理学院,成都610500

出　　处：《石油勘探与开发》2023年第6期1289-1297,共9页Petroleum Exploration and Development

基　　金：国家自然科学基金青年项目(42202194);中国石油-西南石油大学创新联合体科技合作项目(2020CX040102)。

摘　　要：采用三轴实验与剪切实验,以横观各向同性理论与弱面准则为依据,融合钻井应力卸载与水化作用下的力学损伤,建立了应力卸载-水化协同作用下的页岩井壁稳定模型,开展了页岩地层井壁稳定性影响因素分析。研究表明:页岩钻开后发生应力卸载,围压、轴向应力越大,应力卸载造成的页岩强度弱化越显著,应力卸载幅度与页岩力学强度弱化程度正相关。页岩层理越发育,越易沿层理破坏,应力卸载时,弱结构面与应力卸载协同作用,页岩强度弱化程度越高,力学稳定性越差,井壁失稳风险越大。外部流体易沿层理侵入,促进页岩水化,水化作用同样使页岩力学稳定性变差,降低井壁稳定性。应力卸载对页岩地层坍塌压力的影响主要发生在钻井前期,水化损伤对井壁失稳的影响主要发生在钻井后期。层理、应力卸载、水化作用共同影响页岩井壁稳定性,应力卸载-水化协同作用下页岩井壁稳定性模型综合考虑了三者的影响,经现场应用检验,预测结果符合钻井实际,可靠性较好。According to the transversely isotropic theory and weak plane criterion,and considering the mechanical damages due to stress unloading and hydration during drilling,a shale wellbore stability model with the influence of stress unloading and hydration was established using triaxial test and shear test.Then,factors influencing the wellbore stability in shale were analyzed.The results indicate that stress unloading occurs during drilling in shale.The larger the confining pressure and axial stress,the more remarkable weakening of shale strength caused by stress unloading.The stress unloading range is positively correlated with the weakening degree of shale strength.Shale with a higher development degree of bedding is more prone to damage along bedding.In this case,during stress unloading,the synergistic effect of weak structural plane and stress unloading happens,leading to a higher weakening degree of shale strength and poorer mechanical stability,which brings a higher risk of wellbore instability.Fluid tends to invade shale through bedding,promoting the shale hydration.Hydration also can weaken shale mechanical stability,causing the decline of wellbore stability.Influence of stress unloading on collapse pressure of shale mainly occurs at the early stage of drilling,while the influence of hydration on wellbore stability mainly happens at the late stage of drilling.Bedding,stress unloading and hydration jointly affect the wellbore stability in shale.The presented shale wellbore stability model with the influence of stress unloading and hydration considers the influences of the three factors.Field application demonstrates that the prediction results of the model agree with the actual drilling results,verifying the reliability of the model.

关 键 词：页岩 钻井 层理 应力卸载 水化作用 页岩强度 井壁稳定性 

分 类 号：TE122[石油与天然气工程—油气勘探]