水平井多裂纹同步扩展的偏折分析
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摘要
水平井压裂技术是近几年油气工业发展起来的新技术,用于提高油气井的产量。然而在裂纹扩展的过程中,裂尖决定了裂纹的起裂与扩展方向,这会直接影响储层的压裂效果,所以人们对于这项技术还需要更进一步的认识。根据裂尖的应力场特性建立了裂尖权函数,能较准确地描述裂尖的应力状态,判断裂纹的扩展方向。在利用网格重剖分方法并结合最大主应力准则对水平井多裂纹扩展进行分析的基础上,通过裂尖权函数方法分析了水压裂纹在应力差、裂纹数目和裂纹间距等条件下产生偏折的原因。最终结果表明,裂纹在开裂时裂尖处x与y方向的等效应力变化不明显,裂纹的偏折主要与裂尖xy方向的等效应力有关。
Horizontal well fracturing,a popular new technology developed in oil and gas industry,is utilized to enhance the production of wells. However,crack tips determine the crack initiation and propagation direction in the process of fracture growth and have a significant effect on the fracturing results. In this sense,in-depth understanding is required for this technology. In this paper,weight function at the crack tip is built according to the characteristics of stress field at the tip. The function can accurately describe the stress state at the crack tip and determine the growth direction. Based on the analysis of multi-crack propagation in the horizontal well,which is simulated by mesh regeneration method together with maximum principal stress principle,weight function at the crack tip is used to explain the reason of crack deflection under the conditions of stress contrast,crack number and distance among cracks. The final results indicate that the equivalent stresses in x and y direction at the crack tip have no distinct change and the deflections are mainly related to the equivalent stresses in xy direction.
Horizontal well fracturing,a popular new technology developed in oil and gas industry,is utilized to enhance the production of wells. However,crack tips determine the crack initiation and propagation direction in the process of fracture growth and have a significant effect on the fracturing results. In this sense,in-depth understanding is required for this technology. In this paper,weight function at the crack tip is built according to the characteristics of stress field at the tip. The function can accurately describe the stress state at the crack tip and determine the growth direction. Based on the analysis of multi-crack propagation in the horizontal well,which is simulated by mesh regeneration method together with maximum principal stress principle,weight function at the crack tip is used to explain the reason of crack deflection under the conditions of stress contrast,crack number and distance among cracks. The final results indicate that the equivalent stresses in x and y direction at the crack tip have no distinct change and the deflections are mainly related to the equivalent stresses in xy direction.
引文
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[2]WANG X L,LIU C,WANG H,et al.Comparison of consecutive and alternate hydraulic fracturing in horizontal wells using XFEM-based cohesive zone method[J].Journal of Petroleum Science&Engineering,2016,143:14-25.
[3]ZENG X,WEI Y.Crack deflection in brittle media with heterogeneous interfaces and its application in shale fracking[J].Journal of the Mechanics and Physics of Solids,2017,101:235-249.
[4]GALE J F W,LAUBACH S E,OLSON J E,et al.Natural fractures in shale:A review and new observations[J].AAPG Bulletin,2014,98(11):2165-2216.
[5]GALE J F W,REED R M,HOLDER J.Natural fractures in the Barnett shale and their importance for hydraulic fracture treatments[J].AAPG Bulletin,2007,91(4):603-622.
[6]LEE H P,OLSON J E,HOLDER J,et al.The interaction of propagating opening mode fractures with preexisting discontinuities in shale[J].Journal of Geophysical Research Solid Earth,2015,120(1):169-181.
[7]曾青冬,姚军.水平井多裂缝同步扩展数值模拟[J].石油学报,2015,36(12):1571-1579.ZENG Q D,YAO J.Numerical simulation of multiple fractures simultaneous propagation in horizontal well[J].Acta Petrolei Sinica,2015,36(12):1571-1579(in Chinese).
[8]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 Y T,YANG C H,JIA C G,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).
[9]衡帅,杨春和,郭印同,等.层理对页岩水力裂缝扩展的影响研究[J].岩石力学与工程学报,2015,34(2):228-237.HENG S,YANG C H,GUO Y T,et al.Influence of bedding planes on hydraulic fracture propagation in shale formations[J].Chinese Journal of Rock Mechanics and Engineering,2015,34(2):228-237(in Chinese).
[10]陈勉.页岩气储层水力裂缝转向扩展机制[J].中国石油大学学报(自然科学版),2013,37(5):88-94.CHEN M.Re-orientation and propagation of hydraulic fractures in shale gas reservoir[J].Journal of China University of Petroleum(Edition of Natural Sciences),2013,37(5):88-94(in Chinese).
[11]CHUPRAKOV D A,ZHUBAYEV A S.A variational approach to analyze a natural fault with hydraulic fracture based on the strain energy density criterion[J].Theoretical&Applied Fracture Mechanics,2010,53(3):221-232.
[12]HUANG J,GRIFFITHS D V,WONG S W.Initiation pressure,location and orientation of hydraulic fracture[J].International Journal of Rock Mechanics&Mining Sciences,2012,49(1):59-67.
[13]DOLBOW J,BELYTSCHKO T.A finite element method for crack growth without remeshing[J].International Journal for Numerical Methods in Engineering,1999,46(1):131-150.
[14]范天佑.断裂理论基础[M].北京:科学出版社,2003:74-75.FAN T Y.Foundation of fracture theory[M].Beijing:Science Press,2003:74-75(in Chinese).
[15]VENTURA G,GRACIE R,BELYTSCHKO T.Fast integration and weight function blending in the extended finite element method[J].International Journal for Numerical Methods in Engineering,2010,77(1):1-29.
[16]CASTONGUAY S T,MEAR M E,DEAN R H,et al.Predictions of the growth of multiple interacting hydraulic fractures in three dimensions[C]∥SPE Annual Technical Conference and Exhibition.Richardson:Society of Petroleum Engineers,2013:1-12.
[17]师访.岩石破裂过程的扩展有限元法研究[D].北京:中国矿业大学,2015.SHI F.Study on the cracking process of rock using the extended finite element method[D].Beijing:China University of Mining and Technology,2015(in Chinese).
[18]李根生,刘丽,黄中伟,等.水力射孔对地层破裂压力的影响研究[J].中国石油大学学报(自然科学版),2006,30(5):42-45.LI G S,LIU L,HUANG Z W,et al.Study of effect of hydraulic perforating on formation fracturing pressure[J].Journal of China University of Petroleum(Edition of Natural Sciences),2006,30(5):42-45(in Chinese).
[19]彪仿俊,刘合,张劲,等.螺旋射孔条件下地层破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 F J,LIU H,ZHANG J,et al.A numerical study of fracture initiation pressure under helical perforation conditions[J].Jouranl of University of Science and Technology of China,2011,41(3):219-226(in Chinese).
[20]BRINER A,CHAVEZ J C,NADEZHDIN S,et al.Impact of perforation tunnel orientation and length in horizontal wellbores on fracture initiation pressure in maximum tensile stress criterion model for tight gas fields in the sultanate of oman[C]∥SPEMiddle East Oil&Gas Show and Conference.Richardson:Society of Petroleum Engineers,2015:63-75.
[21]彪仿俊,刘合,张士诚,等.水力压裂水平裂缝影响参数的数值模拟研究[J].工程力学,2011,28(10):228-235.BIAO F J,LIU H,ZHANG S C,et al.A numerical study of parameter influences on horizontal hydraulic fracture[J].Engineering Mechanics,2011,28(10):228-235(in Chinese).