高压气层气体钻井井壁稳定性分析  

Analysis of wellbore stability during gas drilling through high-pressure gas formations

作　　者：刘厚彬[1] 孟英峰[1] 万尚贤[2] 李皋[1] 蒋祖军[3] 吕滨 

机构地区：[1]"油气藏地质及开发工程"国家重点实验室.西南石油大学 [2]川庆钻探工程有限公司 [3]中国石化西南油气分公司 [4]中国石油辽河油田公司勘探开发研究院储量室

出　　处：《天然气工业》2010年第11期59-62,共4页Natural Gas Industry

基　　金：国家高技术发展研究计划(863计划)"气体钻井技术与装备"项目(编号:2006AA06A103);"油气藏地质及开发工程"国家重点实验室开放课题(PLN0909)的研究成果

摘　　要：在利用气体钻井技术揭开高压气层的初期,由于低密度气体在井底产生的压力很小,远远低于气层的孔隙压力,高压气层的气体在压力势差作用下由地层向井眼高速流动,导致高压产气层段井壁稳定性下降,易引起井下复杂事故。通过分析高压气层高速产气影响气体钻井井壁稳定性的作用机理,建立了一套高压产气层气体钻井井壁稳定性的评价方法。结果发现:高压气层高速产气过程中,一方面导致产气层近井壁地带的孔隙压力降低,形成一个压降漏斗,作用在井壁表面岩石上的有效应力增加,有利于气层的井壁稳定;另一方面由于产层孔道迂回曲折,高压气体在快速流出地层时,在近井壁地带会产生一个附加径向应力,降低了井底气体对井壁岩石的有效支撑作用,不利于气层的井壁稳定。综合分析正、反两方面的影响因素后发现:高压产气层被气体钻井揭开瞬间,气层井壁表面岩石稳定性最差;随后,井壁表面岩石孔隙压力降低,井壁稳定性变好;随着产气层暴露时间的增加,气层深部位置点高压气体开始流动,井壁稳定性先变差后变好。When gas drilling starts to get through high-pressure gas formation,the bottomhole pressure is very low,far less than the pore pressure,so under the differential pressure,high-pressure gas flows instantly from the formation into the hole,which threatens the wellbore stability and will lead to downhole problems.Through an in-depth study on how the high-speed gas escaping from high-pressure formations has influence on the wellbore stability of gas drilling,a set of evaluation method is thus established.The results show that the produced high-pressure gas will lead to both positive and negative changes.The positive one is that the pore pressure of near-wellbore gas-formation is reduced,and the effective stresses on rock surface increased,which is conductive to the wellbore stability.The negative one is that the high-pressure gas flowing out of the tortuous pore canals will generate an additional radial stress on the near wellbore rocks while the formation,which will reduce the effective support on the wellbore and is not conductive to the wellbore stability.Through a comprehensive analysis of these two contrary impacts,it can be seen that the stability of surface rocks is the worst at the moment when the high-pressure gas formation just starts to be penetrated,subsequently the pore pressure of surface rocks is reduced,and the wellbore stability becomes better.With the exposure time of gas reservoir being prolonged,the deep high-pressure gas begins to flow,the wellbore stability becomes worse first and then becomes better afterwards.

关 键 词：气体钻井 高压气层 井壁稳定性 评价方法 孔隙压力 拖曳力 

分 类 号：TE21[石油与天然气工程—油气井工程]