基于启动压力梯度与应力敏感的致密气藏多层多级渗流模型
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摘要
致密砂岩气藏具有储层物性差、非均质性强、渗流规律复杂以及开发难度大的特征,因此基于非均质层多级渗流实验,建立多层多级渗流模型,弄清各层渗流规律对该类气藏气井合理压裂设计与压力保持至关重要。首先,进行了滑脱效应、启动压力梯度以及应力敏感3类实验,实验结果表明:储层有效渗透率介于(0.01~1.0)×10-3μm2之间,当气藏压力高于10MPa时,滑脱效应对生产影响程度在3%以内,可忽略;致密气藏单相气体渗流不存在启动压力梯度现象,而两相渗流则存在;对于高含水饱和度储层,为气水两相渗流,由于毛管力作用,宏观表现为启动压力现象;与基质岩心相比,微裂缝岩心的渗透率应力敏感性更强,应力敏感滞后程度也更强。然后,考虑启动压力梯度与应力敏感效应,建立了多层多级渗流模型。最后,利用无因次拟压力和无因次时间的关系曲线进行了模型参数敏感性分析。研究认为,层间参数主要影响晚期阶段,裂缝地层系数之比k越大,晚期压力降越大;另外层内参数中变形介质拟渗透率模数、介质弹性储容比和启动拟压力梯度均影响过渡与晚期阶段,因此合理保持压力对致密气藏开发后期尤为重要。
Tight reservoir with poor physical property,complex seepage characteristics and strong heterogeneity result in the difficulty in the development,so the study of reservoir horizontal and vertical heterogeneity and the establishment of a multi-layered and multi-stage(different scales)seepage model based on multi-stage seepage experiments in heterogeneous layers is essential for improving oil recovery.Firstly,three kinds of experiments are carried out:Slippage effect,starting pressure gradient and stress sensitivity.Experimental results show:when the reservoir effective permeability is between 0.01×10~(-3)μm~2 and 1.0×10~(-3)μm~2 and the gas reservoir pressure is higher than 10 MPa,the effect of slippage effect on the production is less than 3% which can be ignored;there is no starting pressure gradient in single gas flow in tight gas reservoir;for the gas-water two-phase seepage in high water saturation reservoirs,due to the role of capillary force,the macro performance of the reservoir is the starting pressure phenomenon;compared with the matrix core,the stress sensitivity of the micro-crack core permeability is stronger and stress-sensitive lag is also stronger.Then,considering the starting pressure gradient and the stress sensitivity,the Multi-Layered and Multi-Stage seepage model of tight sandstone gas reservoir is established.Finally,the sensitivity analysis of model parameters was carried out by using the relationship between dimensionless quasi-pressure and dimensionless time.Research shows:the interlayer parameters mainly affect the later stage,the larger the ratio of the formation coefficient of the fracture,the greater the later pressure drop,so the fracturing scale is uniform when the production is in several layers,otherwise the pressure between the layers differentiates significantly,likely to cause a single layer of gas overriding and gas flow;in addition,the permeability modulus of the deformed medium,the elasticity ratio of the medium and the starting pressure gradient in inlayer parameters all affect the transition and the late stage.Therefore,it is very important to maintain the pressure at the later stage of gas reservoir development.
Tight reservoir with poor physical property,complex seepage characteristics and strong heterogeneity result in the difficulty in the development,so the study of reservoir horizontal and vertical heterogeneity and the establishment of a multi-layered and multi-stage(different scales)seepage model based on multi-stage seepage experiments in heterogeneous layers is essential for improving oil recovery.Firstly,three kinds of experiments are carried out:Slippage effect,starting pressure gradient and stress sensitivity.Experimental results show:when the reservoir effective permeability is between 0.01×10~(-3)μm~2 and 1.0×10~(-3)μm~2 and the gas reservoir pressure is higher than 10 MPa,the effect of slippage effect on the production is less than 3% which can be ignored;there is no starting pressure gradient in single gas flow in tight gas reservoir;for the gas-water two-phase seepage in high water saturation reservoirs,due to the role of capillary force,the macro performance of the reservoir is the starting pressure phenomenon;compared with the matrix core,the stress sensitivity of the micro-crack core permeability is stronger and stress-sensitive lag is also stronger.Then,considering the starting pressure gradient and the stress sensitivity,the Multi-Layered and Multi-Stage seepage model of tight sandstone gas reservoir is established.Finally,the sensitivity analysis of model parameters was carried out by using the relationship between dimensionless quasi-pressure and dimensionless time.Research shows:the interlayer parameters mainly affect the later stage,the larger the ratio of the formation coefficient of the fracture,the greater the later pressure drop,so the fracturing scale is uniform when the production is in several layers,otherwise the pressure between the layers differentiates significantly,likely to cause a single layer of gas overriding and gas flow;in addition,the permeability modulus of the deformed medium,the elasticity ratio of the medium and the starting pressure gradient in inlayer parameters all affect the transition and the late stage.Therefore,it is very important to maintain the pressure at the later stage of gas reservoir development.
引文
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[2]Li Chengyong,Jiang Yuqiang,Wu Yong,et al.The bottomhole pressure response model solution in multilayer commingled gas reservoir[J].Natural Gas Industry,2010,30(9):39-41.[李成勇,蒋裕强,伍勇,等.多层合采气藏井底压力响应模型通解[J].天然气工业,2010,30(9):39-41.]
[3]Cai Zhenghua,Liao Xinwei,Shang Baobing,et al.Percolation model of stress sensitive effect of tight sandstone gas well[J].Science&Technology Review,2014,32(31):50-54.[蔡振华,廖新维,尚宝兵,等.致密砂岩气井的应力敏感效应渗流模型[J].科技导报,2014,32(31):50-54.]
[4]Li Chen,Xia Zhaohui,Wang Ping.Flow Mechanism in Major Production Stages of Tight Sandstone Gas Reservoir[J].Special Oil and Gas Reservoirs,2016,23(3):94-96.[李陈,夏朝晖,汪萍.致密砂岩气藏主要产气阶段渗流特征[J].特种油气藏,2016,23(3):94-96.]
[5]Wang Jing,Liu Huiqing,Liu Renjing,et al.Numerical simulation for low-permeability and extra-low permeability reservoirs with considering starting pressure and stress sensitivity effects[J].Chinese Journal of Rock Mechanics and Engineering,2013,32(supplement 2):3317-3327.[王敬,刘慧卿,刘仁静,等.考虑启动压力和应力敏感效应的低渗、特低渗油藏数值模拟研究[J].岩石力学与工程学报,2013,32(增刊2):3317-3327.]
[6]Sun Hedong,Zhou Fangde,Gao Chengtai.Study on semi permeable wall model and numerical simulation of partially open unstable gas reservoir[J].Natural Gas Industry,2001,21(4):77-80.[孙贺东,周芳德,高承泰.部分打开的多层气藏不稳定试井的半透壁模型及数值模拟研究[J].天然气工业,2001,21(4):77-80.]
[7]Jalali Y,Ershaghi I.Pressure Transient Analysis of Heterogeneous Naturally Fractured Reservoirs[J].Spe California Regional Meeting,1987.
[8]Abdullah A G,Iraj E.Pressure transient analysis of dually fractured reservoirs[J].Spe Journal,1996,1(1):93-100.
[9]Velazquez R C,Vasquez-Cruz M A,Castrejon-Aivar R,et al.Pressure transient and decline curve behaviors in naturally fractured vuggy carbonate reservoirs[J].Spe Reservoir Evaluation&Engineering,2005,8(2):95-112.
[10]Yan Tao,Jia Yonglu.Vertical well test model for low velocity non darcy flow[J].Natural Gas Industry,2005,25(2):l30-132.[严涛,贾永禄.低速非达西流垂直裂缝试井模型[J].天然气工业,2005,25(2):130-132.]
[11]Chavez M G,Ley H C.Effect of pressure in a well with a vertical fracture with variable conductivity and skin fracture[J].Revista De Sociologia E Politica,2006(25):63-82.
[12]Nooruddin H,Hossain M E,Sudirman S B,et al.Field Application of a Modified Kozeny-Carmen Correlation to Characterize Hydraulic Flow Units[C].[s.n.].2011.
[13]Aguilera R.Flow units:From conventional to Tight-Gas to Shale-Gas to Tight-Oil to Shale-Oil reservoirs[J].Spe Reservoir Evaluation&Engineering,2014,17(2):190-208.
[14]Guo Xiao,Wu Yong.Influence of start-up pressure gradient and stress sensitivity on productivity of low-permeability gas reservoirs[J].Oil&Gas Geology,2007,28(4):539-543.[郭肖,伍勇.启动压力梯度和应力敏感效应对低渗透气藏水平井产能的影响[J].石油与天然气地质,2007,28(4):539-543.]
[15]Wang Yining,Wang Hui,Cao Shuhui,et al.Effect of nonlinear percolation on recovery factor of low permeability gas reservoirs[J].Science&Technology Review,2016,34(2):147-151.[汪益宁,王晖,曹淑慧,等.非线性渗流对低渗气藏采收率的影响[J].科技导报,2016,34(2):147-151.]
[16]Yang Kai,Guo Xiao,Xiao Xiqing,et al.The modified deliverability equation of low permeability gas reservoirs[J].Natural Gas Industry,2009,29(4):68-70.[杨凯,郭肖,肖喜庆,等.修正的低渗透气藏产能方程[J].天然气工业,2009,29(4):68-70.]
[17]Zhang Qiang,Wang Yongqing,Zhang Nan,et al.Analysis of fractured well productivity in low-permeability stress-sensitive gas reservoir[J].Special Oil&Gas Reservoirs,2012,19(3):74-76.[张强,王永清,张楠,等.低渗透应力敏感气藏压裂井产能分析[J].特种油气藏,2012,19(3):74-76.]
[18]Qiu Xianqiang,Li Zhiping,Liu Yinshan,et al.Analysis of productivity equation and influence factors of horizontal wells in tight sand gas reservoir[J].Journal of Southwest Petroleum University,2013,15(12):2337-2350.[邱先强,李治平,刘银山,等.致密气藏水平井产量预测及影响因素分析[J].西南石油大学学报,2013,15(12):2337-2350.]
[19]Yan J,Liang X B,Wu Q,et al.Stress sensitivity of low permeable and water-bearing gas reservoir without gas slippage effect[J].Advanced Materials Research,2014,962(965):570-573.
[20]Hou Yong,Tang Rui.Productivity model of fractured gas well considering stress sensitivity in low permeability gas reservoirs[J].Science&Technology Review,2016,34(2):152-155.[侯勇,汤睿.考虑应力敏感性的低渗气藏压裂气井产能模型[J].科技导报,2016,34(2):152-155.]