提高地层承压能力的钻井液堵漏作用机理
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摘要
应用线弹性岩石力学和岩石断裂力学基本理论,揭示了钻井液堵漏阻止诱导裂缝延伸并提高裂缝重启压力从而提高地层承压能力的作用机理。通过分析承压堵漏后缝内压力分布,建立了封堵诱导裂缝的断裂力学模型,并给出承压堵漏阻止诱导裂缝延伸的必要条件;基于井周围岩裂缝诱导应力场的数学模型,提出了堵漏提高诱导裂缝重启压力的力学实质。理论研究表明,堵漏材料在裂缝入口后一定距离封堵为封堵诱导裂缝的最佳位置形式;裂缝尖端部分流体压力必须低于水平最小主应力,且该压力越低,越有利于裂缝的阻裂;诱导裂缝重启压力的提高依赖于周向诱导应力,堵漏材料必须支撑裂缝以维持周向诱导应力;承压堵漏作用机理包含密封和支撑裂缝两方面,堵漏材料应同时具有封堵性能和机械强度。
According to basic theories of the linear elastic lithomechanics and rock fracture mechanics,the present paper dealt with the plugging mechanism of drilling liquid by preventing induced fractures from extension and enhancing wellbore pressure through the increase of fracture reopening pressure.A fracture mechanics model was developed by means of analyzing the pressure distribution in factures after plugging,requirements for preventing induced fractures from extension by plugging were presented,and mechanic behaviors of the induced fracture reopening pressure enhanced by sealing were dealt with based on a mathematical model for the induced stress field of fractures in neighboring rocks of wellbore.Theoretical studies demonstrated that the best way of plugging induced fractures was to apply the lost circulation materials(LCM) at a certain distance near fracture mouth,the hydrodynamic pressure at the pointed end of fractures must be lower than the minimum horizontal major stress and the lower the pressure,the better the sealing effect.The increase of the fracture reopening pressure depended on the induced hoop stress,the lost circulation materials(LCM) must prop fracture walls to maintain the induced hoop stress.As the plugging mechanism of drilling fluid by enhancing wellbore pressure contained both sealing and propping fractures,the LCM should have a sealing property and certain mechanical strength.
According to basic theories of the linear elastic lithomechanics and rock fracture mechanics,the present paper dealt with the plugging mechanism of drilling liquid by preventing induced fractures from extension and enhancing wellbore pressure through the increase of fracture reopening pressure.A fracture mechanics model was developed by means of analyzing the pressure distribution in factures after plugging,requirements for preventing induced fractures from extension by plugging were presented,and mechanic behaviors of the induced fracture reopening pressure enhanced by sealing were dealt with based on a mathematical model for the induced stress field of fractures in neighboring rocks of wellbore.Theoretical studies demonstrated that the best way of plugging induced fractures was to apply the lost circulation materials(LCM) at a certain distance near fracture mouth,the hydrodynamic pressure at the pointed end of fractures must be lower than the minimum horizontal major stress and the lower the pressure,the better the sealing effect.The increase of the fracture reopening pressure depended on the induced hoop stress,the lost circulation materials(LCM) must prop fracture walls to maintain the induced hoop stress.As the plugging mechanism of drilling fluid by enhancing wellbore pressure contained both sealing and propping fractures,the LCM should have a sealing property and certain mechanical strength.
引文
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[12]Wang H,Soliman M Y,Towler B F.Investigation of factors forstrengthening a wellbore by propping fractures[R].SPE112629,2008.
[2]Soroush H,Sampaio J H B.Investigation into strengtheningmethods for stabilizing wellbores in fractured formations[R].SPE101802,2006.
[3]吕开河,邱正松,魏慧明,等.自适应防漏堵漏钻井液技术研究[J].石油学报,2008,29(5):757-760,765.LüKaihe,Qiu Zhengsong,Wei Huiming,et al.Study on tech-niques of auto-adapting lost circulation resistance and control fordrilling fluid[J].Acta Petrolei Sinica,2008,29(5):757-760,765.
[4]Aston M S,Alberty M W,Mclean M R,et al.Drilling fluids forwellbore strengthening[R].SPE87130,2004.
[5]Alberty M W,Mclean M R.A physical model for stress cages[R].SPE90493,2004.
[6]阿特金森B K.岩石断裂力学[M].尹祥础,修济刚,译.北京:地震出版社,1992:231-254.Atkinson B K.Fracture mechanics of rock[M].Translated byYin Xiangchu,Xiu Jigang.Beijing:Seismological Press,1992:231-254.
[7]陈勉,金衍,张广清.石油工程岩石力学[M].北京:科学出版社,2008:274-276.Chen Mian,Jin Yan,Zhang Guangqing.Rock mechanics of petro-leum engineering[M].Bejing:Science Press,2008:274-276.
[8]Sneddon I N.The distribution of stress in the neighbourhood of acrack in an elastic solid[J].Proceedings the Royal of Society A:Mathematical,Physical&Engineering Sciences,1946,187(1009):229-260.
[9]刘洪,胡永全,赵金洲,等.重复压裂气井诱导应力场模拟研究[J].岩石力学与工程学报,2004,23(23):4022-4027.Liu Hong,Hu Yongquan,Zhao Jinzhou,et al.Simulation study ofinduced stress field in refracturing gas well[J].Chinese Journalof Rock Mechanics and Engineering,2004,23(23):4022-4027.
[10]姚飞,翁定为,李阳,等.重复压裂前地应力场预测软件研究及现场应用[J].石油学报,2007,28(4):130-133.Yao Fei,Weng Dingwei,Li Yang,et al.Study and application ofstress field prediction software for refractured oil wells[J].ActaPetrolei Sinica,2007,28(4):130-133.
[11]Dupriest F E.Fracture closure stresses(FCS)and lost returnspractices[R].SPE92192,2005.
[12]Wang H,Soliman M Y,Towler B F.Investigation of factors forstrengthening a wellbore by propping fractures[R].SPE112629,2008.
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