考虑天然水平裂缝的页岩气三维运移模型
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摘要
页岩气藏中分布着大量的天然裂缝,天然裂缝既是气体的储集场所也是气体的渗流通道。为了分析天然水平裂缝对页岩气产能的影响,将页岩气藏的基质和裂缝简化为双重介质模型,建立了三维地质渗流模型,并采用有限元程序COMSOL Multiphyscis 5.1进行了求解,同时利用现场测井数据验证了该模型。在此基础上研究了天然水平裂缝的宽度、空间展布情况、充填以及密度等参数对产能的影响。三维地质渗流模型与二维地质模型相比由于考虑了水平向的裂隙更接近于实际情况,当天然水平裂缝的导流能力比人工裂缝导流能力强时,考虑天然水平裂缝时的页岩气产量是不考虑时的两倍。裂缝的宽度实际变化不大,裂缝的导流能力主要取决于其填充情况对渗透率的影响。在本模型的几何尺寸下,人工裂缝比天然裂缝的渗透率高1个数量级,且1 000d时,和不考虑天然裂缝相比,累计产量多出了近3倍。页岩气的累计产量还随天然裂缝垂向分布密度的增加而增加,1 000d时,裂缝由0增加到1条时,累计产量可增加近4倍,裂缝由2条增为3条时,累计产量增加量为5×108 m3。在实际开发过程中,人工裂缝的设计需考虑到储层中天然水平裂缝的相关参数对产能的影响。
Shale gas reservoirs are distributed with a large number of natural fractures.They are both gas storage sites and gas seepage channels.In order to analyze the influence of natural horizontal fractures on shale gas production,the matrix and fracture of shale gas reservoirs are simplified into a dual porous media model.The three-dimensional geological seepage model is then developed and solved by the finite element based program COMSOL Multiphyscis 5.1.The logging data are used to verify the proposed model.On the basis of this,the effect of the parameters including width,spatial distribution,the filling materials and the density of the horizontal fracture on the shale gas productivity is studied.The results show that the predicted results of the proposed three-dimensional geological model are closer to the actual situation than those obtained by the two-dimensional geological model taking the natural horizontal fractures into account.When the conductivity of the natural horizontal fracture is larger than that of the artificial fracture,the production capacity is two times greater than that without considering the effect of the natural horizontal fracture.The diversion capacity of the fracture depends mainly on the effect of the filling on the permeability.Under the geometric size of the model,the artificial fracture is more than an order of magnitude higher than that of natural fractures,and 1 000 days,compared with the natural fractures,the cumulative output is more than 3times the production capacity.The cumulative production of shale gas also increased with the increase of the spatial distribution area and vertical distribution of natural fractures.At 1 000 days,by0increasing to 1,the cumulative production can be increased by nearly 4times.When the number of increases from 2to 3,the cumulative production can be increased by 5×108 m3.In the actual mining process,the design of artificial fractures should take into account the relevant parameters of the natural horizontal fractures in the reservoir.
Shale gas reservoirs are distributed with a large number of natural fractures.They are both gas storage sites and gas seepage channels.In order to analyze the influence of natural horizontal fractures on shale gas production,the matrix and fracture of shale gas reservoirs are simplified into a dual porous media model.The three-dimensional geological seepage model is then developed and solved by the finite element based program COMSOL Multiphyscis 5.1.The logging data are used to verify the proposed model.On the basis of this,the effect of the parameters including width,spatial distribution,the filling materials and the density of the horizontal fracture on the shale gas productivity is studied.The results show that the predicted results of the proposed three-dimensional geological model are closer to the actual situation than those obtained by the two-dimensional geological model taking the natural horizontal fractures into account.When the conductivity of the natural horizontal fracture is larger than that of the artificial fracture,the production capacity is two times greater than that without considering the effect of the natural horizontal fracture.The diversion capacity of the fracture depends mainly on the effect of the filling on the permeability.Under the geometric size of the model,the artificial fracture is more than an order of magnitude higher than that of natural fractures,and 1 000 days,compared with the natural fractures,the cumulative output is more than 3times the production capacity.The cumulative production of shale gas also increased with the increase of the spatial distribution area and vertical distribution of natural fractures.At 1 000 days,by0increasing to 1,the cumulative production can be increased by nearly 4times.When the number of increases from 2to 3,the cumulative production can be increased by 5×108 m3.In the actual mining process,the design of artificial fractures should take into account the relevant parameters of the natural horizontal fractures in the reservoir.
引文
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[27]王玉满,李新景,董大忠,等.海相页岩裂缝孔隙发育机制及地质意义[J].天然气地球科学,2016,27(9):1602-1610.
[28]梁利喜,黄静,刘向君,等.天然裂缝对页岩储层井周诱导缝形成扩展的影响[J].地质科技情报,2014,33(5):160-165.
[29]张金功,黄传卿,修艳敏,等.中国典型盆地页岩层面滑移缝的特征、成因及其与页岩气藏形成的关系[C]∥第376次香山科学会议摘要.2010.
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[32]COMSOL.Multiphysics Model Library,Earth Science Module[M].Version 4.3a.2013.
[33]杨胜来,魏俊之.油层物理学[M].北京:石油工业出版社,2004:36.
[2]Montgomery S L,Jarvie D M,Bowker K A,et al.Mississippian Barnett Shale,Fort Worth Basin,north-central Texas:Gasshale play with multi-trillion cubic foot potential[J].AAPGBulletin,2005,90(6):963-966.
[3]Loucks R G,Reed R M,Ruppel S C,et al.Morphology,genesis,and distribution of nanometer-scale pores in siliceous mudstones of the Mississippian Barnett Shale[J].Journal of Sedimentary Research,2009,79(12):848-861.
[4]Casey J A,Savitz D A,Rasmussen S G,et al.Unconventional natural gas development and birth outcomes in Pennsylvania,USA[J].Epidemiology,2016,27(2):163.
[5]巩磊,王超勇,杨永国,等.川西南与川东北地区下志留统龙马溪组页岩气成藏条件对比及目标区分析[J].地质科技情报,2014,33(5):128-133.
[6]杨振恒,李志明,王果寿,等.北美典型页岩气藏岩石学特征、沉积环境和沉积模式及启示[J].地质科技情报,2010,29(6):59-65.
[7]董大忠,邹才能,杨桦,等.中国页岩气勘探开发进展与发展前景[J].石油学报,2012(增刊1):107-114.
[8]冀昆,郭少斌,余春昊,等.威信凹陷龙马溪组页岩成藏条件分析[J].地质科技情报,2017,36(3):130-136.
[9]陕亮,张万益,罗晓玲,等.页岩气储层压裂改造关键技术及发展趋势[J].地质科技情报,2013,32(2):156-162.
[10]蒲泊伶,董大忠,牛嘉玉,等.页岩气储层研究新进展[J].地质科技情报,2014,33(2):98-104.
[11]刘洪平,赵彦超,孟俊,等.压裂水平井产能预测方法研究综述[J].地质科技情报,2015,34(1):131-139.
[12]Freeman C M,Moridis G,Ilk D,et al.A numerical study of performance for tight gas and shale gas reservoir systems[J].Journal of Petroleum Science&Engineering,2013,108(3):22-39.
[13]于炳松.页岩气储层的特殊性及其评价思路和内容[J].地学前缘,2012,19(3):252-258.
[14]李治平,李智峰.页岩气纳米级孔隙渗流动态特征[J].天然气工业,2012,32(4):50-53.
[15]邹才能,董大忠,王社教,等.中国页岩气形成机理、地质特征及资源潜力[J].石油勘探与开发,2010,37(6):641-653.
[16]Javadpour F,Fisher D,Unsworth M.Nanoscale gas flow in shale gas sediments[J].Journal of Canadian Petroleum Technology,2007,46(10):54-61.
[17]Javadpour F.Nanopores and apparent permeability of pas flow in mudrocks(Shales and Siltstone)[J].Journal of Canadian Petroleum Technology,2009,48(8):16-21.
[18]Civan F.Effective correlation of apparent gas permeability in tight porous media[J].Transport in Porous Media,2010,82(2):375-384.
[19]Florence F,Rushing J,Newsham K,et al.Improved permeability prediction relations for low permeability sands[C]∥Anon.Rocky Mountain Oil&Gas Technology Symposium.2007.
[20]Sahimi M.Flow and transport in porous media and crackd rock:From classical methods to modern approaches[M].[S.l.]:VCH,2011.
[21]Kim J G,Deo M D.Finite element,discrete-crack model for multiphase flow in porous media[J].Aiche Journal,2000,46(6):1120-1130.
[22]Mary2ka J,Severn O,Vohralík M.Numerical simulation of crack flow with a mixed-hybrid FEM stochastic discrete crack network model[J].Computational Geosciences,2005,8(3):217-234.
[23]Yan B,Wang Y,Killough J E.Beyond dual-porosity modeling for the simulation of complex flow mechanisms in shale reservoirs[J].Computational Geosciences,2016,20(1):69-91.
[24]Mi L,Jiang H,Li J,et al.The investigation of fracture aperture effect on shale gas transport using discrete fracture model[J].Journal of Natural Gas Science&Engineering,2014,1:631-635.
[25]糜利栋,姜汉桥,李俊键.页岩气离散裂缝网络模型数值模拟方法研究[J].天然气地球科学,2014,25(11),1795-1803.
[26]张士诚,牟松茹,崔勇.页岩气压裂数值模型分析[J].天然气工业,2011,31(12):81-84.
[27]王玉满,李新景,董大忠,等.海相页岩裂缝孔隙发育机制及地质意义[J].天然气地球科学,2016,27(9):1602-1610.
[28]梁利喜,黄静,刘向君,等.天然裂缝对页岩储层井周诱导缝形成扩展的影响[J].地质科技情报,2014,33(5):160-165.
[29]张金功,黄传卿,修艳敏,等.中国典型盆地页岩层面滑移缝的特征、成因及其与页岩气藏形成的关系[C]∥第376次香山科学会议摘要.2010.
[30]郭旭升.涪陵页岩气田焦石坝区块富集机理与勘探技术[M].北京:科学出版社,2014:33-45,86,312-315.
[31]Walton J C,Seitz R R.Fluid flow through fractures in below ground concrete vaults[J].Waste Management,1992,12(2/3):179-187.
[32]COMSOL.Multiphysics Model Library,Earth Science Module[M].Version 4.3a.2013.
[33]杨胜来,魏俊之.油层物理学[M].北京:石油工业出版社,2004:36.