四川盆地西部地区超深井大尺寸井眼井壁失稳机理及防治对策  

Mechanism and control measures of wellbore instability of large-sized boreholes in ultra-deep wells in western Sichuan Basin

作　　者：范宇 黄维安[2] 王月纯 郭建华 FAN Yu;HUANG Wei'an;WANG Yuechun;GUO Jianhua(Engineering Technology Research Institute,PetroChina Southwest Oil&Gasfield Company,Chengdu,Sichuan 610017,China;School of Petroleum Engineering,China University of Petroleum-East China,Qingdao,Shandong 266580,China)

机构地区：[1]中国石油西南油气田公司工程技术研究院,四川省成都市610017 [2]中国石油大学(华东)石油工程学院,山东省青岛市266580

出　　处：《天然气工业》2024年第12期116-127,共12页Natural Gas Industry

基　　金：国家自然科学基金项目“引入可靠性理论研究层理性页岩力—化—渗—热耦合井壁稳定化学调控方法与机理”(编号:52374026);“具有温度开关效应的环保型钻井液封堵剂研制及其作用机理”(编号:51974351)。

摘　　要：四川盆地纵向发育多套地层且地质结构复杂,深井超深井钻探过程中上部地层裂缝发育,井眼尺寸大,导致井壁坍塌复杂事故风险较高。为明确超深井大尺寸井眼失稳机理,针对四川盆地西部(以下简称川西)地区双鱼石区块超深井上部沙溪庙组地层开展了岩块XRD衍射、扫描电镜、直接剪切实验等,分析了岩样矿物组成和层理结构特征,测试了不同含水量与弱面强度之间的关系;并基于钻井液裂缝滤失、裂缝内压力分布以及井周应力分布,建立了考虑井眼尺寸效应的裂缝性地层坍塌压力计算模型;最后分析了沙溪庙组地层井壁失稳机理,提出了预防井壁失稳的技术对策。研究结果表明:①沙溪庙组地层为层理性泥页岩,微裂隙发育,Ø444.5 mm大尺寸井眼对地层坍塌压力具有显著影响,尺寸效应不可忽略;②由于裂缝的存在,盲目增加钻井液密度稳定井壁的方式可能造成更严重的坍塌后果;③原始地层压力、裂缝倾角对坍塌压力有不同程度的影响,增加钻井液黏度虽有利于降低坍塌压力,但实际应用意义不大;④提高泥饼质量、降低钻井液滤失量是保证裂缝性地层井壁稳定的重要且合理的方法。结论认为,该机理认识揭示了多场耦合作用下裂缝性地层大尺寸井眼井壁失稳机制,为四川盆地深井超深井钻井过程中大尺寸井眼井壁失稳预防和控制提供了理论参考。In the Sichuan Basin,there are multiple formations developed vertically,and the geological structures are complex.When deep to ultra-deep wells are drilled through the formations in the upper part,fractures are encountered and the hole size is large,imposing the operations to high risks of complexities such as wellbore collapse.In order to clarify the instability mechanism of ultra-deep largesized boreholes,core samples from the Shaximiao Formation in the upper interval of ultra-deep well in the Shuangyushi Block of western Sichuan Basin are conducted with XRD diffraction,scanning electron microscopy and direct shear test to analyze the mineral composition and bedding structure characteristics and test the relationship between water content and weak plane strength.Then,a calculation model of collapse pressure of fractured formation with consideration of hole size is established based on drilling fluid filtration towards fractures,pressure distribution within fractures,and stress distribution around the wellbore.Finally,the mechanism of wellbore instability in the Shaximiao Formation is analyzed,and the solutions to prevent wellbore instability are proposed.The following results are obtained.First,the Shaximiao Formation is bedding mud shale with developed microfractures,andØ444.5 mm large-sized borehole has a significant impact on the formation collapse pressure,so the size effect shall not be ignored.Second,due to the presence of fractures,blindly increasing the density of drilling fluid to stabilize the wellbore may cause more serious collapse.Third,initial formation pressure and fracture dip have varying degrees of influence on the collapse pressure.Increasing the viscosity of drilling fluid is favorable for the decrease of collapse pressure,but it is not significant in practical application.Fourth,improving the quality of mud cake and reducing the filtration rate of drilling fluid are important and reasonable methods to ensure the wellbore stability in fractured formations.In conclusion,the understanding on

关 键 词：四川盆地 川西地区 泥页岩 超深井 裂缝性地层 坍塌压力 井壁稳定 尺寸效应 

分 类 号：TE243.1[石油与天然气工程—油气井工程]