基于离散元数值法的页岩压裂复杂网络裂缝研究
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摘要
页岩气藏天然裂缝发育,非均质性强,连续介质模型不能准确表征页岩储层特征。基于离散裂缝网络模型(DFN)和渗流-应力耦合数值算法,建立了水力压裂裂缝与天然裂缝相互作用的数值计算模型,利用该模型开展了相邻多裂缝间距、力学特性参数等对缝网扩展及连通性影响规律研究。结果表明,无论天然裂缝网络如何分布或者水力裂缝长短,次生人造水力裂缝的形成可稳定先压水力裂缝顶端天然裂缝的剪切破坏区域。水力裂缝尖端处的天然裂缝开度较大,裂缝间距越大,剪切破坏面积越大,缝距在一定范围内可实现远井带网缝贯通的可行性;内摩擦角对天然网络裂缝连通面积影响较大,较小的内摩擦角,易于形成复杂网络裂缝;不同天然裂缝倾角组合条件下复杂网络裂缝连通面积不同。研究结果可为页岩气井复杂网络裂缝形成预测提供理论依据。
The shale gas reservoir has the characteristics of natural fracture development and strong heterogeneity,the continuum model can not be used to accurately characterize the shale reservoir. Based on the discrete fracture network( DFN)model and seepage-stress coupling numerical algorithm,a numerical model of the network fracture for modeling the complex interactions between created hydraulic fractures and natural fracture system is established,to analyze the effects of the hydraulic fracture spacing,mechanical properties parameters on the fracture network extension and connectivity. Results show that no matter how natural fracture networks distribution or artificial hydraulic fracture length,the formation of the secondary fractures can stabilize the shear failure zone of natural fractures at the top of the initial hydraulic fractures. The larger the aperture of the natural fractures at the tip of hydraulic fractures,the greater the fracture spacing,the greater the shear failure area,the possibility of fracture network connection far away from well is larger if fracture spacing within a certain range. The smaller the internal friction angle of the fracture,the greater the connected area of the natural network,the more easily the complex fracture network formed. The connected area of the complex network fractures is different under the condition of different natural fracture dip angle combination. Numerical simulation results can provide theoretical basis for the prediction of complex network fractures in shale gas wells.
The shale gas reservoir has the characteristics of natural fracture development and strong heterogeneity,the continuum model can not be used to accurately characterize the shale reservoir. Based on the discrete fracture network( DFN)model and seepage-stress coupling numerical algorithm,a numerical model of the network fracture for modeling the complex interactions between created hydraulic fractures and natural fracture system is established,to analyze the effects of the hydraulic fracture spacing,mechanical properties parameters on the fracture network extension and connectivity. Results show that no matter how natural fracture networks distribution or artificial hydraulic fracture length,the formation of the secondary fractures can stabilize the shear failure zone of natural fractures at the top of the initial hydraulic fractures. The larger the aperture of the natural fractures at the tip of hydraulic fractures,the greater the fracture spacing,the greater the shear failure area,the possibility of fracture network connection far away from well is larger if fracture spacing within a certain range. The smaller the internal friction angle of the fracture,the greater the connected area of the natural network,the more easily the complex fracture network formed. The connected area of the complex network fractures is different under the condition of different natural fracture dip angle combination. Numerical simulation results can provide theoretical basis for the prediction of complex network fractures in shale gas wells.
引文
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[2]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(1):68-73.
[3]Cottrell M,Hosseinpour H,&Dershowitz W.Rapid Discrete Fracture Analysis of Hydraulic Fracture Development in Naturally Fractured Reservoirs[C].SPE168843,2013.
[4]Gu H R,Siebrits Eduard.Effect of Formation Modulus Contrast on Hydraulic Fracture Height Containment[C].SPE 170176,May 2008.
[5]Chuprakov D A,Akulich A V,Siebrits E,Thiercelin M.Hydraulicfracture propagation in a naturally fractured reservoir[J].SPE Production&Operations,February 2011:88-97.
[6]Holt R,Fjaer E,Nes O M.A Shaly Look at Brittleness.ARMA 11366.2011.
[7]罗天雨,王嘉淮.天然裂缝对水力压裂的影响研究[J].石油天然气学报,2007(5):141-142.
[8]Nagel N B,Garcia X,Lee B.Hydraulic Fracturing Optimization for Unconventional Reservoirs The Critical Role of the Mechanical Properties of the Natural Fracture Network[C].SPE 161934,2012.
[9]朱焕春,Andrieux Patrick,钟辉亚,等.节理岩体数值计算方法及其应用(二):工程应用[J].岩石力学与工程学报,2005,24(1):89-96.
[10]Deisman N,et al.Empirical and numerical approaches for geomechanical characterization of coal seam reservoirs[J].International Journal of Coal Geology.2009,11.
[11]Julia F W G,Robert M R,Jon H.Natural fractures in the Barnett shale and their importance for hydraulic fracture treatments[J].AAPG Bulletin,2007,91(4):603-622.
[12]李玉梅,吕炜,宋杰,等.层理性页岩气储层复杂网络裂缝数值模拟研究[J].石油钻探技术,2016,44(4):108-113.