过断层井段井壁稳定性分析
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摘要
考虑断层周围地层非均质性和各向异性,根据弱面强度准则,分析了地层各向异性对地应力的影响,探讨了井壁坍塌压力随断层走向及倾角的变化规律,建立了过断层的坍塌压力计算模型,开展了不同性质断层构造坍塌压力分析,结果表明:随着Eh/Ev、vv/vh值的增大,水平最大应力、水平最小应力增加,过断层应考虑地层各向异性对地应力的影响;不同的断层类型、断层走向及倾角所对应的坍塌压力存在差异性,且不存在单调递增或递减的井斜方位,安全区域和危险区域交替出现;井眼轨迹设计应考虑断层类型及弱面结构,选择合理的钻入角钻穿断层。将本文预测模型用于渤海油田A井取得了良好工程效果,井眼扩大率基本小于10%。本文研究结果对过断层时钻井安全具有指导意义,可为井眼轨迹设计提供理论参考。
Taking into account formation heterogeneity and anisotropy around a fault,and based on the weak surface strength criterion,the influence of the formation anisotropy on in-situ stresses was analyzed,and the changing pattern of the borehole collapse pressure with the fault strike and dipping angle was discussed. Furthermore a model for calculating the collapsing pressure through faults was established and the collapsing pressure analyzed. The results show that maximum and minimum horizontal stresses increase with the increasing values of Eh/Evand vv/ vh,so the influence of formation anisotropy on in-situ stresses should be considered when the hole section cuts through a fault. Collapse pressures corresponding to different fault types,fault strikes or dip angles are different,and there is no inclination azimuth where collapse probability is monotonically increasing or decreasing;safe area and dangerous area occur alternately. Fault types and the weak surface structure should be considered in well trajectory designs,with the fault being drilled through at the reasonable angle. The prediction model developed here was applied to Well A in Bohai oilfield,achieving sound engineering effects,with the hole enlargement being generally less than 10%. The results of this paper have a guiding significance for drilling safety through faults,which can provide theoretical reference for designing wellbore trajectories.
Taking into account formation heterogeneity and anisotropy around a fault,and based on the weak surface strength criterion,the influence of the formation anisotropy on in-situ stresses was analyzed,and the changing pattern of the borehole collapse pressure with the fault strike and dipping angle was discussed. Furthermore a model for calculating the collapsing pressure through faults was established and the collapsing pressure analyzed. The results show that maximum and minimum horizontal stresses increase with the increasing values of Eh/Evand vv/ vh,so the influence of formation anisotropy on in-situ stresses should be considered when the hole section cuts through a fault. Collapse pressures corresponding to different fault types,fault strikes or dip angles are different,and there is no inclination azimuth where collapse probability is monotonically increasing or decreasing;safe area and dangerous area occur alternately. Fault types and the weak surface structure should be considered in well trajectory designs,with the fault being drilled through at the reasonable angle. The prediction model developed here was applied to Well A in Bohai oilfield,achieving sound engineering effects,with the hole enlargement being generally less than 10%. The results of this paper have a guiding significance for drilling safety through faults,which can provide theoretical reference for designing wellbore trajectories.
引文
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[11]王珂,戴俊生.地应力与断层封闭性之间的定量关系[J].石油学报,2012,33(1):74-81.WANG Ke,DAI Junsheng.A quantitative relationship between the crustal stress and fault sealing ability[J].Acta Petrolei Sinica,2012,33(1):74-81.
[2]许浚远,杨东胜,陈国童.渤海湾盆地铲形正断层及其次级断层组合成因[J].石油勘探与开发,1996,23(5):37-39.XU Junyuan,YANG Dongsheng,CHEN Guotong.Genesis of a variety of listric faults and their reversed branch faults in Bohai Gulf basin,east China[J].Petroleum Exploration and Development,1996,23(5):37-39.
[3]宋国奇,刘克奇.断层两盘裂缝发育特征及其石油地质意义[J].油气地质与采收率,2009,16(4):1-3.SONG Guoqi,LIU Keqi.Fracture characteristics around faults and their significance in petroleum accumulation[J].Petroleum Geology and Recovery Efficiency,2009,16(4):1-3.
[4]程远方,沈海超,赵益忠,等.复杂断块构造的地应力场研究——以海拉尔盆地贝尔凹陷希3断块为例[J].西安石油大学学报(自然科学版),2008,23(5):15-20.CHENG Yuanfang,SHEN Haichao,ZHAO Yizhong,et al.Study on the earth stress field in complex fault block—taking Xi-3 fault block in Beier Sag,Hailaer Basin as an example[J].Journal of Xi’an Shiyou University(Natural Science Edition),2008,23(5):15-20.
[5]阮彦晟.断层附近应力分布的异常和对地下工程围岩稳定的影响[D].济南:山东大学,2008.RUAN Yansheng.Abnormal stress distribution near the fault and influence on the stability of surrounding rock of underground engineering[D].Jinan:Shandong Univeristy,2005.
[6]邓金根,程远方,陈勉,等.井壁稳定预测技术[M].北京:石油工业出版社,2008.
[7]THIERCELIN M J,PLUMB R A.A core-based prediction of lithologic stress contrasts in East Texas formations[J].SPE Formation Evaluation,1994,9(4):251-258.
[8]AADNOY B S.Continuum mechanics analysis of the stability of boreholes in anisotropic rock formations[D].Norway:Norwegian Institute of Technology University of Trondheim,1987.
[9]温航,陈勉,金衍,等.硬脆性泥页岩斜井段井壁稳定性耦合研究[J].石油勘探与开发,2014,41(6):748-754.WEN Hang,CHEN Mian,JIN Yan,et al.A chemo-mechanical coupling model of deviated borehole stability in hard brittle shale[J].Petroleum Exploration and Development,2014,41(6):748-754.
[10]闫传梁,邓金根,蔚宝华,等.页岩气储层井壁坍塌压力研究[J].岩石力学与工程学报,2013,32(8):1595-1602.YAN Chuanliang,DENG Jingen,YU Baohua,et al.Research on collapsing pressure of gas shale[J].Chinese Journal of Rock Mechanics and Engineering,2013,32(8):1595-1602.
[11]王珂,戴俊生.地应力与断层封闭性之间的定量关系[J].石油学报,2012,33(1):74-81.WANG Ke,DAI Junsheng.A quantitative relationship between the crustal stress and fault sealing ability[J].Acta Petrolei Sinica,2012,33(1):74-81.