非连续铺砂裂缝支撑机理及形变规律研究
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摘要
为改善致密砂岩等非常规储层压裂裂缝渗流条件及压后长期导流能力,引入缝内非连续多层铺砂理念,通过开展室内支撑剂砂团受压形变实验评价,分析了支撑剂砂团在闭合压力作用下轴向及径向形变特征,结合邓肯—张本构模型拟合得到支撑剂砂团扩展半径与闭合压力及携砂液砂浓度关系方程;根据接触力学中弹性半空间固体形变原理,在考虑支撑剂砂团受压径向形变与裂缝壁面闭合耦合作用的条件下,建立了三维非连续支撑裂缝壁面形变计算模型,以苏里格地区某区块致密砂岩气藏为例,对多因素影响下残余缝宽变化规律进行了计算分析。结果表明:(1)随着脉冲间隔时间与泵注排量增大,相同闭合应力作用下未支撑区域裂缝壁面闭合风险逐渐增高,当脉冲周期超过18 s或者排量高于4.5 m~3/min时,未支撑区域中部出现闭合;(2)随支撑剂砂团浓度增加,支撑剂砂团稳定性提高,可减小裂缝闭合程度;(3)储层岩石有效杨氏模量越高,未支撑区域裂缝形变量越小,裂缝闭合风险越小。
In order to improve the reservoir seepage and long-term conductivity after fracturing, by introducing the concept of discontinuous multilayer sanding in fractures, the experiment evaluates proppant sand group compression and deformation. Simultaneously, the deformation characteristics of proppant column under the action of closure pressure in axial and radial direction have been analyzed. Combined with a Duncan-Chang constitutive model, the relationship equation is fitted which contains the proppant column expansion radius, closure pressure and proppant concentration. According to the principle of contact mechanics of elastic half space solid deformation, a three-dimensional discontinuous propped wall deformation calculation model is established which considers the coupling action between the radial deformation of a proppant sand column under compression and the closure of the fracture wall. Based on the above research results, using the Sulige tight sandstone reservoir for illustration, the transformation of residual width in nonsupported area of discontinuous sanding fracture has been calculated and analyzed, under the condition of different rock mechanical parameters and fracturing treatment parameters. The results obtained in this study indicate that :(1) the volume of the proppant column and non-supported areas increase with the pulse interval and pump rate. Simultaneously the risk of fracture face closure in non-supported areas increases. For low-permeability sand reservoirs, the middle of the surface in non-supported area starts to contact when the pulse interval is larger than 18 s or pump rate is larger than 4.5 m3/min.(2) stability of a proppant column could be improved by increasing the proppant concentration.(3) the deformation in non-supported areas and risk of fracture closure is smaller in rocks with a higher effective Young's modulus
In order to improve the reservoir seepage and long-term conductivity after fracturing, by introducing the concept of discontinuous multilayer sanding in fractures, the experiment evaluates proppant sand group compression and deformation. Simultaneously, the deformation characteristics of proppant column under the action of closure pressure in axial and radial direction have been analyzed. Combined with a Duncan-Chang constitutive model, the relationship equation is fitted which contains the proppant column expansion radius, closure pressure and proppant concentration. According to the principle of contact mechanics of elastic half space solid deformation, a three-dimensional discontinuous propped wall deformation calculation model is established which considers the coupling action between the radial deformation of a proppant sand column under compression and the closure of the fracture wall. Based on the above research results, using the Sulige tight sandstone reservoir for illustration, the transformation of residual width in nonsupported area of discontinuous sanding fracture has been calculated and analyzed, under the condition of different rock mechanical parameters and fracturing treatment parameters. The results obtained in this study indicate that :(1) the volume of the proppant column and non-supported areas increase with the pulse interval and pump rate. Simultaneously the risk of fracture face closure in non-supported areas increases. For low-permeability sand reservoirs, the middle of the surface in non-supported area starts to contact when the pulse interval is larger than 18 s or pump rate is larger than 4.5 m3/min.(2) stability of a proppant column could be improved by increasing the proppant concentration.(3) the deformation in non-supported areas and risk of fracture closure is smaller in rocks with a higher effective Young's modulus
引文
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[12]张嘎,张建民.粗颗粒土的应力应变特性及其数学描述研究[J].岩土力学,2004,25(10):1587-1591.[ZHANG G,ZHANG J M.Study on behavior of coarse grained soil and its modeling[J].Rock and Soil Mechanics,2004,25(10):1587-1591.]
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[15]钱斌,尹丛彬,朱炬辉,等.高效脉冲式加砂压裂技术研究与实践[J].天然气工业,2015,35(5):39-45.[QIAN B,YIN C B,ZHU JH,et al.Research and practice of the impulse sand fracturing technology[J].Natural gas industry,2015,35(5):39-45.]
[2]TINSLEY J M,WILLIAMS J R.A new method for providing increased fracture conductivity and improving stimulation results[C].Paper SPE4676 presented at the SPE-AIME annual fall meeting,Las Vegas,Nevada,USA,30 September-3 October.
[3]NGUYEN P D.Evaluation of low-quality sand for proppant-free channel fracturing method[R].IPTC17937,2014.
[4]HOU B,ZHENG X,CHEN M,et al.Parameter simulation and optimization in channel fracturing[J].Journal of Natural Gas Science&Engineering,2016,35:122-130.
[5]ZHENG X,CHEN M,HOU B,et al.Effect of proppant distribution pattern on fracture conductivity and permeability in channel fracturing[J].Journal of Petroleum Science&Engineering,2016.
[6]侯冰,陈勉,张保卫,等.裂缝性页岩储层多级水力裂缝扩展规律研究[J].岩土工程学报,2015,37(6):1041-1046.[HOU B,CHEN M,ZHANG B,et al.Propagation of multiple hydraulic fractures in fractured shale reservoir[J].Chinese Journal of Geotechnical Engineering,2015,37(6):1041-1046.]
[7]侯冰,程万,陈勉,等.裂缝性页岩储层水力裂缝非平面扩展实验[J].天然气工业,2014,34(12):81-86.[HOU B,CHENG W,CHEN M,et al.Experiments on the non-planar extension of hydraulic fractures in fractured shale gas reservoirs[J].Natural Gas Industry,2014,34(12):81-86.]
[8]侯冰,陈勉,李志猛,等.页岩储集层水力裂缝网络扩展规模评价方法[J].石油勘探与开发,2014,41(6):763-768.[HOU B,CHEN M,LI Z M,et al.Propagation area evaluation of hydraulic fracture networks in shale gas reservoirs[J].Petroleum Exploration and Development,2014,41(6):833-838.]
[9]MANSOOR A,AMJAD H S,et al.Optimizing production of tight gas wells by revolutionizing hydraulic fracturing[C].SPE 141708presented at the SPE Projects and Facilities Challenges Conference at METS held in Doha,Qatar,13-16 February 2011
[10]PARKER M,GLASBERGEN G V,BATENBURG D,et al.High-porosity fractures yield high conductivity[C].Paper SPE 96848presented at the SPE annual technical conference and exhibition,Dallas,Texas,USA,9-12 October.
[11]HOU B,CHEN M,WANG Z,et al.Hydraulic fracture initiation theory for a horizontal well in a coal seam[J].Petroleum Science,2013,10(2):219-225.
[12]张嘎,张建民.粗颗粒土的应力应变特性及其数学描述研究[J].岩土力学,2004,25(10):1587-1591.[ZHANG G,ZHANG J M.Study on behavior of coarse grained soil and its modeling[J].Rock and Soil Mechanics,2004,25(10):1587-1591.]
[13]JOHNSON K L.Contact mechanics[M].London:Cambridge University Press,1985:56-63.
[14]BRUCE R M,LUCAS W B,DOUG E W,et al.Theoretical foundation and design formulae for channel and pillar type propped fractures-a method to increase fracture conductivity[C].Paper SPE170781 presented at SPE Annual Technical Conference and Exhibition held in Amsterdam,The Netherlands,27-29 October,2014.
[15]钱斌,尹丛彬,朱炬辉,等.高效脉冲式加砂压裂技术研究与实践[J].天然气工业,2015,35(5):39-45.[QIAN B,YIN C B,ZHU JH,et al.Research and practice of the impulse sand fracturing technology[J].Natural gas industry,2015,35(5):39-45.]