页岩储层射孔水平井水力裂缝起裂数值模拟研究
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摘要
为明确页岩储层射孔水平井水力裂缝起裂机制,利用Abaqus有限元计算软件,建立三维单级三簇射孔和单射孔段(包含天然裂缝)的压裂裂缝起裂计算模型,研究地应力、井筒方位、射孔参数以及天然裂缝等对裂缝起裂压力和位置的影响。结果表明:裸眼射孔的起裂压力远低于套管射孔;起裂压力随最小水平地应力的增加而增大,但影响程度受垂向地应力与最小水平地应力的比值控制;最大水平地应力和垂向地应力的变化对起裂压力影响不显著;起裂压力大致随井筒方位角的增加而减小,当存在天然裂缝时,起裂压力没有任何线性规律,天然裂缝在剪应力区易发生剪切滑移起裂;起裂压力随射孔方位角的增加先减小后增大,射孔方位角的变化严重影响裂缝的起裂形态;起裂位置与最小和最大水平地应力、井筒方位角和天然裂缝的胶结强度、方位密切相关;由于内部射孔受到两侧射孔产生的沿井筒方向的附加应力干扰,闭合应力增加,因而更难起裂,导致起裂次序从端部射孔开始向中部射孔发展,当应力差较高(>7 MPa)时,附加应力干扰明显,要实现多射孔的多裂缝起裂扩展,需提高注入压力;起裂位置在射孔孔道中的变化是射孔根部应力集中强度与远端受射孔附加应力干扰程度相互竞争的结果;由于射孔簇间距较大,射孔簇间的应力干扰对裂缝起裂影响微弱,各射孔簇压力分布相似。
To understand hydraulic fracture initiation mechanism of perforated horizontal well in shale play,the fracture initiation models of a 3D single-stage three clusters perforation and a single cluster perforation(containing natural fracture) were established by using Abaqus finite element calculation software. The effects of crustal stress,wellbore orientation,perforation parameters and natural fracture on fracture initiation pressure and location was studied. The results show that the initiation pressure of open hole perforation is far below that of the casing perforation. The fracture initiation pressure increases with the increasing of the minimum horizontal stress,but the influence degree is controlled by the ratio of vertical stress to the minimum stress. The effects of the maximum horizontal stress and vertical stress on the initiation pressure is very weak. The initiation pressure decreases roughly with the wellbore azimuth increases,when the natural fracture is presented,the initiation pressure does not show any linear law. The shear slip for natural fracture easily appears in the shear stress zone. Initiation pressure firstly decreases and then increases with the perforation azimuth increases. The change of perforation azimuth can seriously affect the fracture initiation morphology. The fracture initiation location is closely related to the minimum and maximum horizontal stress,wellbore azimuth and the cementing strength and azimuth of natural fractures. The internal perforations bear the additional stress along the wellbore direction generated by both sides of the perforations,the closure stress is increased,thus these perforations initiate more difficult,resulting in that fracture initiation sequence is from the endmost perforations to the middle perforations. When the stress difference is higher(>7 MPa),the additional stress interference becomes significant. To achieve a multi-fractures initiation from multi-perforations,the injection pressure needs to be improved. The change of initiation location in perforation tunnel is a competitive result between the strength of stress concentration on perforation root and the interference degree of additional stress on the distal end of perforation. Due to the great perforation cluster spacing,the effect of stress interference between perforation clusters on fracture initiation is very weak,the pressure distributions of every perforation cluster are almost identical.
To understand hydraulic fracture initiation mechanism of perforated horizontal well in shale play,the fracture initiation models of a 3D single-stage three clusters perforation and a single cluster perforation(containing natural fracture) were established by using Abaqus finite element calculation software. The effects of crustal stress,wellbore orientation,perforation parameters and natural fracture on fracture initiation pressure and location was studied. The results show that the initiation pressure of open hole perforation is far below that of the casing perforation. The fracture initiation pressure increases with the increasing of the minimum horizontal stress,but the influence degree is controlled by the ratio of vertical stress to the minimum stress. The effects of the maximum horizontal stress and vertical stress on the initiation pressure is very weak. The initiation pressure decreases roughly with the wellbore azimuth increases,when the natural fracture is presented,the initiation pressure does not show any linear law. The shear slip for natural fracture easily appears in the shear stress zone. Initiation pressure firstly decreases and then increases with the perforation azimuth increases. The change of perforation azimuth can seriously affect the fracture initiation morphology. The fracture initiation location is closely related to the minimum and maximum horizontal stress,wellbore azimuth and the cementing strength and azimuth of natural fractures. The internal perforations bear the additional stress along the wellbore direction generated by both sides of the perforations,the closure stress is increased,thus these perforations initiate more difficult,resulting in that fracture initiation sequence is from the endmost perforations to the middle perforations. When the stress difference is higher(>7 MPa),the additional stress interference becomes significant. To achieve a multi-fractures initiation from multi-perforations,the injection pressure needs to be improved. The change of initiation location in perforation tunnel is a competitive result between the strength of stress concentration on perforation root and the interference degree of additional stress on the distal end of perforation. Due to the great perforation cluster spacing,the effect of stress interference between perforation clusters on fracture initiation is very weak,the pressure distributions of every perforation cluster are almost identical.
引文
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[8]金衍,陈勉,张旭东.天然裂缝地层斜井水力裂缝起裂压力模型研究[J].石油学报,2006,9(5):124–126.(JIN Yan,CHEN Mian,ZHANG Dongxu.Hydraulic fracturing initiation pressure models for directional wells in naturally fractured formation[J].Acta Petrolei Sinica,2006,9(5):124–126.(in Chinese))
[9]黄中伟,李根生.水力射孔参数对起裂压力影响的实验研究[J].中国石油大学学报:自然科学版,2007,31(6):48–54.(HUANG Zhongwei,LI Gensheng.Experimental study on effects of hydrauperforation parameters on initial fracturing pressure[J].Journal of China University of Petroleum:Natural Science,2007,31(6):48–54.(in Chinese))
[10]CHERNY S G,LAPIN V N,CHIRKOV D V,et al.2D Modeling of Hydraulic Fracture Initiating at a Wellbore with or without Microannulus[C]//SPE Hydraulic Fracturing Technology Conference and Exhibition.[S.l.]:Society of Petroleum Engineers Inc.,2009:SPE119352.
[11]YUAN Y,ABOUSLEIMAN Y,WENG X,et al.Three-dimensional elastic analysis on fracture initiation from a perforated borehole[C]//SPE Annual Technical Conference and Exhibition.[S.l.]:Society of Petroleum Engineers Inc.,1995:SPE 29601.
[12]PAPANASTASIOU P,ZERVPS A.Three-dimensional stress analysis of a wellbore with perforations and a fracture[C]//SPE/ISRM Rock Mechanics in Petroleum Engineering.[S.l.]:Society of Petroleum Engineers Inc.,1998:SPE 47378.
[13]张广清,陈勉.定向射孔水力压裂复杂裂缝形态[J].石油勘探与开发,2009,36(1):103–107.(ZHANG Guangqing,CHEN Mian.Complex fracture shapes in hydraulic fracturing with orientated perforations[J].Petroleum Exploration and Development,2009,36(1):103–107.(in Chinese))
[14]彪仿俊,刘合,张劲,等.螺旋射孔条件下地层起裂压力的数值模拟研究[J].中国科学技术大学学报,2011,41(3):219–226.(BIAO Fangjun,LIU He,ZHANG Jin,et al.A numerical study of fracture initiation pressure under helical perforation conditions[J].Journal of University of Science and Technology of China,2011,41(3):219–226.(in Chinese))
[15]李庆辉,陈勉,金衍,等.含气页岩破坏模式及力学特性的试验研究[J].岩石力学与工程学报,2012,31(增2):3 763–3 771.(LI Qinghui,CHEN Mian,JIN Yan,et al.Experimental research on failure modes and mechanical behaviors of gas-bearing shale[J].Chinese Journal of Rock Mechanics and Engineering,2012,31(Supp.2):3 763–3 771.(in Chinese))
[16]盛茂,李根生,黄中伟,等.页岩气藏流固耦合渗流模型及有限元求解[J].岩石力学与工程学报,2013,32(9):1 894–1 900.(SHENG Mao,LI Gensheng,HUANG Zhongwei,et al.Hydromechanical coupling model of shale gas reservoir and its finite element analysis[J].Chinese Journal of Rock Mechanics and Engineering,2013,32(9):1 894–1 900.(in Chinese))
[17]殷有泉,李志明,张广清,等.蠕变地层套管载荷分析研究[J].岩石力学与工程学报,2004,23(14):2 381–2 384.(YIN Youquan,LI Zhiming,ZHANG Guangqing,et al.Study on casing loads in creep formations[J].Chinese Journal of Rock Mechianics and Engineering,2004,23(14):2 381–2 384.(in Chinese))
[2]郭印同,杨春和,贾长贵,等.页岩水力压裂物理模拟与裂缝表征方法研究[J].岩石力学与工程学报,2014,33(1):52–59.(GUO Yintong,YANG Chunhe,JIA Changgui,et al.Research on hydraulic fracturing physical simulation of shale and fracture characterization methods[J].Chinese Journal of Rock Mechanics and Engineering,2014,33(1):52–59.(in Chinese))
[3]WENG X,KRESSE O,COHEN C,et al.Modeling of hydraulic fracture network propagation in a naturally fractured formation[C]//SPE Hydraulic Fracturing Technology Conference and Exhibition.[S.l.]:Society of Petroleum Engineers Inc.,2011:SPE 140253.
[4]李士斌,李磊,张立刚.清水压裂多场耦合下裂缝扩展规律数值模拟分析[J].石油化工高等学校学报,2014,27(1):42–47.(LI Shibin,LI Lei,ZHANG Ligang.The numerical simulation analysis of crack propagation law under riverfrac treatment multi-field coupling[J].Journal of Petrochemical Universities,2014,27(1):42–47.(in Chinese))
[5]赵金洲,李勇明,王松,等.天然裂缝影响下的复杂压裂裂缝网络模拟[J].天然气工业,2014,34(1):68–73.(ZHAO Jinzhou,LI Yongming,WANG Song,et al.Simulation of a complex fracture network influenced by natural fractures[J].Natural Gas Industry,2014,34(1):68–73.(in Chinese))
[6]孙可明,王松,张树翠.页岩气储层水力压裂裂纹扩展数值模拟[J].辽宁工程技术大学学报:自然科学版,2014,33(1):5–10.(SUN Keming,WANG Song,ZHANG Shucui.A numerical simulation on rules of crack extension during hydraulic fracturing in shale gas reservoir[J].Journal of Liaoning Technical University:Natural Science,2014,33(1):5–10.(in Chinese))
[7]HOSSAIN M M,RAHMAN M K,RAHMAN S S.A comprehensive monograph for hydraulic fracture initiation from deviated wellbores under arbitrary regimes[C]//SPE Asia Pacific Oil and Gas Conference and Exhibition.[S.l.]:Society of Petroleum Engineers Inc.,1999:SPE54360.
[8]金衍,陈勉,张旭东.天然裂缝地层斜井水力裂缝起裂压力模型研究[J].石油学报,2006,9(5):124–126.(JIN Yan,CHEN Mian,ZHANG Dongxu.Hydraulic fracturing initiation pressure models for directional wells in naturally fractured formation[J].Acta Petrolei Sinica,2006,9(5):124–126.(in Chinese))
[9]黄中伟,李根生.水力射孔参数对起裂压力影响的实验研究[J].中国石油大学学报:自然科学版,2007,31(6):48–54.(HUANG Zhongwei,LI Gensheng.Experimental study on effects of hydrauperforation parameters on initial fracturing pressure[J].Journal of China University of Petroleum:Natural Science,2007,31(6):48–54.(in Chinese))
[10]CHERNY S G,LAPIN V N,CHIRKOV D V,et al.2D Modeling of Hydraulic Fracture Initiating at a Wellbore with or without Microannulus[C]//SPE Hydraulic Fracturing Technology Conference and Exhibition.[S.l.]:Society of Petroleum Engineers Inc.,2009:SPE119352.
[11]YUAN Y,ABOUSLEIMAN Y,WENG X,et al.Three-dimensional elastic analysis on fracture initiation from a perforated borehole[C]//SPE Annual Technical Conference and Exhibition.[S.l.]:Society of Petroleum Engineers Inc.,1995:SPE 29601.
[12]PAPANASTASIOU P,ZERVPS A.Three-dimensional stress analysis of a wellbore with perforations and a fracture[C]//SPE/ISRM Rock Mechanics in Petroleum Engineering.[S.l.]:Society of Petroleum Engineers Inc.,1998:SPE 47378.
[13]张广清,陈勉.定向射孔水力压裂复杂裂缝形态[J].石油勘探与开发,2009,36(1):103–107.(ZHANG Guangqing,CHEN Mian.Complex fracture shapes in hydraulic fracturing with orientated perforations[J].Petroleum Exploration and Development,2009,36(1):103–107.(in Chinese))
[14]彪仿俊,刘合,张劲,等.螺旋射孔条件下地层起裂压力的数值模拟研究[J].中国科学技术大学学报,2011,41(3):219–226.(BIAO Fangjun,LIU He,ZHANG Jin,et al.A numerical study of fracture initiation pressure under helical perforation conditions[J].Journal of University of Science and Technology of China,2011,41(3):219–226.(in Chinese))
[15]李庆辉,陈勉,金衍,等.含气页岩破坏模式及力学特性的试验研究[J].岩石力学与工程学报,2012,31(增2):3 763–3 771.(LI Qinghui,CHEN Mian,JIN Yan,et al.Experimental research on failure modes and mechanical behaviors of gas-bearing shale[J].Chinese Journal of Rock Mechanics and Engineering,2012,31(Supp.2):3 763–3 771.(in Chinese))
[16]盛茂,李根生,黄中伟,等.页岩气藏流固耦合渗流模型及有限元求解[J].岩石力学与工程学报,2013,32(9):1 894–1 900.(SHENG Mao,LI Gensheng,HUANG Zhongwei,et al.Hydromechanical coupling model of shale gas reservoir and its finite element analysis[J].Chinese Journal of Rock Mechanics and Engineering,2013,32(9):1 894–1 900.(in Chinese))
[17]殷有泉,李志明,张广清,等.蠕变地层套管载荷分析研究[J].岩石力学与工程学报,2004,23(14):2 381–2 384.(YIN Youquan,LI Zhiming,ZHANG Guangqing,et al.Study on casing loads in creep formations[J].Chinese Journal of Rock Mechianics and Engineering,2004,23(14):2 381–2 384.(in Chinese))