疏松砂岩油藏压裂裂缝延伸规律数值模拟
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摘要
压裂充填防砂可实现增产与防砂双重目的,是疏松砂岩油藏的一种重要完井方式。疏松砂岩具有高孔、高渗特点,且强度低、塑性强,裂缝起裂与延伸机理较为复杂。为研究疏松砂岩储层压裂裂缝延伸机理,揭示压裂工艺参数对裂缝形态的影响,建立了考虑储层岩石弹塑性变形、裂缝起裂与延伸、压裂液流动与滤失以及储层孔隙流体渗流复杂耦合作用的流固耦合有限元数值模型,针对渤海油田绥中36-1区块典型疏松砂岩储层,开展了压裂裂缝延伸规律数值模拟计算,并重点分析了压裂液效率、排量对于裂缝延伸规律的影响。结果表明:低效率压裂液在疏松砂岩中仅形成极短而窄的裂缝,裂缝两侧伴随着一定范围的剪胀高渗带,难以容纳支撑剂,无法实现充填防砂目的;高效率压裂液可在疏松砂岩中形成压裂充填防砂工艺所需的短宽裂缝,裂缝壁面两侧存在轻微压实现象,对渗透率的影响较小;提高压裂液排量,裂缝长度减小,裂缝宽度增加。研究结果可为疏松砂岩压裂充填设计提供一定理论参考。
Frac-packing and sand control technology can realize the double targets of stimulation and sand control, and it is one important well completion method for unconsolidated sandstone oil reservoirs. Unconsolidated sandstone is characterized by high porosity, high permeability, low strength and strong plasticity, so its fracture initiation and propagation mechanisms are more complicated. In order to study the propagation mechanisms of hydraulic fractures in unconsolidated sandstone reservoirs and reveal the effects of fracturing technologies on fracture morphologies, a finite-element numerical model of fluid-solid coupling was established in this paper. In this numerical model, the elastic plastic deformation of rock, the initiation and propagation of fracture, the flowing and filtration of fracturing fluid and the complex coupling effect of fluid flow through porous medium are taken into consideration. Then, a case study was conducted on the typical unconsolidated sandstone reservoir in Suizhong 36-1 Block of Bohai Oilfield. Its propagation law of hydraulic fractures was numerically simulated and calculated. In addition, the effects of the efficiency and displacement of fracturing fluid on the fracture propagation law were mainly analyzed. It is indicated that the fractures initiated by low-efficiency fracturing fluid in unconsolidated sandstone are quite short and narrow, and they are accompanied with high-permeability dilation zones on both sides, so proppant can be hardly held and consequently sand control cannot be realized. The high-efficiency fracturing fluid can create the short and wide fractures in unconsolidated sandstone that are needed in frac-packing and sand control technology. There are phenomena of slight compaction on both sides of the fracture wall surface, and they have less effect on the permeability. As the displacement of fracturing fluid is increased, the fracture length is decreased and the fracture width is increased. The research results can be used as the theoretical reference for the design of unconsolidated sandstone frac-packing.
Frac-packing and sand control technology can realize the double targets of stimulation and sand control, and it is one important well completion method for unconsolidated sandstone oil reservoirs. Unconsolidated sandstone is characterized by high porosity, high permeability, low strength and strong plasticity, so its fracture initiation and propagation mechanisms are more complicated. In order to study the propagation mechanisms of hydraulic fractures in unconsolidated sandstone reservoirs and reveal the effects of fracturing technologies on fracture morphologies, a finite-element numerical model of fluid-solid coupling was established in this paper. In this numerical model, the elastic plastic deformation of rock, the initiation and propagation of fracture, the flowing and filtration of fracturing fluid and the complex coupling effect of fluid flow through porous medium are taken into consideration. Then, a case study was conducted on the typical unconsolidated sandstone reservoir in Suizhong 36-1 Block of Bohai Oilfield. Its propagation law of hydraulic fractures was numerically simulated and calculated. In addition, the effects of the efficiency and displacement of fracturing fluid on the fracture propagation law were mainly analyzed. It is indicated that the fractures initiated by low-efficiency fracturing fluid in unconsolidated sandstone are quite short and narrow, and they are accompanied with high-permeability dilation zones on both sides, so proppant can be hardly held and consequently sand control cannot be realized. The high-efficiency fracturing fluid can create the short and wide fractures in unconsolidated sandstone that are needed in frac-packing and sand control technology. There are phenomena of slight compaction on both sides of the fracture wall surface, and they have less effect on the permeability. As the displacement of fracturing fluid is increased, the fracture length is decreased and the fracture width is increased. The research results can be used as the theoretical reference for the design of unconsolidated sandstone frac-packing.
引文
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[9]XU B, WONG R C. A 3D finite element model for historymatchinghydraulicfracturinginunconsolidated sandsformation[J].JournalofCanadianPetroleum Technology, 2010, 49(4):58-66.
[10]ZHAI Z, SHARMA M M. A new approach to modeling hydraulic fractures in unconsolidated sands[R]. SPE96246, 2005.
[11]PAPANASTASIOU P. The influence of plasticity in hydraulicfracturing[J].InternationalJournalof Fracture, 1997, 84(1):61-79.
[12]SARRISN,PAPANASTASIOUP.Numerical investigationofahydraulicfracturedriveninweak poroplastic formation[C]. 48th US Rock Mechanics/Geomechanics Symposium, 2014, ARMA-2014-7763.
[13]LEE D, SHARMA M M. A fully-coupled, poro-elastoplastic,3-Dmodelforfrac-packtreatmentsinpoorly consolidated sands[R]. SPE 184847, 2017.
[14]ABOU-SAYED A,ZAKIK,WANGG,MENG F,MANOJS.Fracturepropagationandformation disturbance during injection and Frac-Pack operations in soft compacting rocks[R]. SPE 90656, 2004.
[15]郑颖人,沈珠江,龚晓楠.岩土塑性力学原理[M].北京:中国建筑工业出版社,2002.ZHENG Yingren,SHENZhujiang,GONGXiaonan.The principles of geotechnical plastic mechanics[M].Beijing:China Architecture and Building Press, 2012.
[16]COUSSY O. Poromechanics[M]. John Wiley&Sons,2004.
[17]YUAN S, HARRISON J. Development of a hydromechanical local degradation approach and its application to modelling fluid flow during progressive fracturing of heterogeneous rocks[J]. International Journal of Rock Mechanics and Mining Sciences, 2005, 42(7):961-984.
[2]郭建春,赵金洲,庞长渝,唐寒冰.高渗油层压裂充填裂缝模拟评价研究[J].钻采工艺,2002,25(1):52-54.GUO Jianchun, ZHAO Jinzhou, PANG Changyu, TANG Hanbing. Fracture simulation and evaluation of frac and packinhighpermeabilityreservoirs[J].Drilling&Production Technology, 2002, 25(1):52-54.
[3]谢桂学,李行船,杜宝坛.压裂防砂技术在胜利油田的研究和应用[J].石油勘探与开发,2002,29(3):99-102.XIE Guixue, LI Xingchuan, DU Baotan. The research and application of FracPac technique in Shengli oil field[J].Petroleum exploration and development, 2002, 29(3):99-102.
[4]张卫东,杨志成,魏亚蒙.疏松砂岩水力压裂裂缝形态研究综述[J].力学与实践,2014,36(4):396-402.ZHANGWeidong,YANGZhicheng,WEIYameng.Advances in research of hydraulic fractures in unconsolidated sands[J]. Mechanics in Engineering, 2014, 36(4):396-402.
[5]PATER D, DONG Y. Experimental study of hydraulic fracturing in sand as a function of stress and fluid rheology[R]. SPE 105620, 2007.
[6]BOHLOLI B, DE PATER C. Experimental study on hydraulicfracturingofsoftrocks:influenceoffluid rheology and confining stress[J]. Journal of Petroleum Science and Engineering, 2006, 53(1):1-12.
[7]KHODAVERDIAN M, MCELFRESH P. Hydraulic fracturingstimulationinpoorlyconsolidatedsand:mechanisms and consequences[R]. SPE 63233, 2000.
[8]GERMANOVICHLN,HURTRS, AYOUBJ A,SIEBIITSE,NORMAND,&ISPASI.Experimental study of hydraulic fracturing in unconsolidated materials[R]. SPE 151827, 2012.
[9]XU B, WONG R C. A 3D finite element model for historymatchinghydraulicfracturinginunconsolidated sandsformation[J].JournalofCanadianPetroleum Technology, 2010, 49(4):58-66.
[10]ZHAI Z, SHARMA M M. A new approach to modeling hydraulic fractures in unconsolidated sands[R]. SPE96246, 2005.
[11]PAPANASTASIOU P. The influence of plasticity in hydraulicfracturing[J].InternationalJournalof Fracture, 1997, 84(1):61-79.
[12]SARRISN,PAPANASTASIOUP.Numerical investigationofahydraulicfracturedriveninweak poroplastic formation[C]. 48th US Rock Mechanics/Geomechanics Symposium, 2014, ARMA-2014-7763.
[13]LEE D, SHARMA M M. A fully-coupled, poro-elastoplastic,3-Dmodelforfrac-packtreatmentsinpoorly consolidated sands[R]. SPE 184847, 2017.
[14]ABOU-SAYED A,ZAKIK,WANGG,MENG F,MANOJS.Fracturepropagationandformation disturbance during injection and Frac-Pack operations in soft compacting rocks[R]. SPE 90656, 2004.
[15]郑颖人,沈珠江,龚晓楠.岩土塑性力学原理[M].北京:中国建筑工业出版社,2002.ZHENG Yingren,SHENZhujiang,GONGXiaonan.The principles of geotechnical plastic mechanics[M].Beijing:China Architecture and Building Press, 2012.
[16]COUSSY O. Poromechanics[M]. John Wiley&Sons,2004.
[17]YUAN S, HARRISON J. Development of a hydromechanical local degradation approach and its application to modelling fluid flow during progressive fracturing of heterogeneous rocks[J]. International Journal of Rock Mechanics and Mining Sciences, 2005, 42(7):961-984.