新疆A井区深部辉绿岩地层井壁垮塌严重,多次引发井下复杂,阻碍了该地区深部油气资源的勘探开发进程.通过开展辉绿岩微观组构、水理化性能及力学特性实验研究,揭示了辉绿岩地层井壁岩石垮塌失稳机理及主要控制因素.实验结果表明,辉绿岩岩体微细观裂缝十分发育,裂缝间主要为长石充填,含有少量黏土,部分裂缝为无充填缝,且裂缝纵横交错,连通性好;发育有裂缝的辉绿岩岩体力学强度远低于均质无裂缝岩体,仅为后者的10％～20％;水化效应对辉绿岩岩体力学强度影响不明显,影响幅度为2％～7％.理论计算结果表明,裂缝的力学弱面效应对辉绿岩地层坍塌压力影响最大,影响幅度为21％;裂缝间的渗流效应影响次之,影响幅度为11％,水化效应影响不明显,仅为2％.因此,考虑辉绿岩地层裂缝的力学弱面效应影响,准确设计钻井液密度是稳定辉绿岩地层的关键.其次,结合辉绿岩微裂缝缝宽尺寸大小,优化设计钻井液防塌封堵材料尺寸,增强的钻井液防塌封堵性能可有效改善辉绿岩地层井壁稳定性.现场应用实例表明,合理设计钻井液密度和增强钻井液防塌封堵性可有效提高辉绿岩地层井壁稳定性,井下垮塌遇阻复杂情况大幅好转.%The wellbore collapse of diabase formation is serious in A area of Xinjiang,and which repeatedly causes down-hole accidents and hinders the exploration and development process of deep oil and gas resources.By conducting experimental researches on microscopic structure,physical and chemical properties and mechanical characteristics,the wellbore collapse mechanism and main controlling factors were revealed.The experimental results showed that,diabase developed large number of micro-fractures,and fractures were mainly filled with feldspar and small amount of clay.Parts of those fractures were no-filling fractures,and those fractures were intercross and owned good connectivity.The mechanical strengths of fractured diabase rocks were much lower than that of homogeneous rocks,and the former was only 10％～20％of the latter.The hydration effect of water-based drilling fluids on mechanical strengths of diabase rocks was not obvious,and the influencing amplitude was only 2％～7％.Theoretical calculations indicated that,the weak mechanical strength effect of fractures on the collapse pressure of diabase formations was largest,influencing amplitude 21％,the seepage effect of drilling fluids in fractures was middle,influencing amplitude 11％,and the hydration effect of drilling fluid was the least,only 2％.Therefore,accurately designing the drilling fluid density with considering the weak mechanical strengths effect of fractures was the key for safe drilling in diabase formations.Simultaneously the optimal design of plugging material size for drilling fluid and enhancing the sealing capacity can effectively improve the wellbore stability of diabase formations.The field applications showed that,reasonable design of drilling fluid density and enhancing sealing properties of drilling fluid can effectively improve the wellbore stability of diabase formations,and that can prevent the down-hole complex.
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