煤层气井完井用PE筛管的地质适应性分析
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摘要
煤层气井水平井段易垮塌是导致煤层气开发过程中产量难以提升的重要原因之一,出于煤层气开采之后的采煤作业安全考虑,金属材质的筛管被禁止下入煤层,采用PE筛管完井则成为解决上述问题的重要途径。为分析PE筛管能否适用于易垮塌的煤层中,利用断裂力学方法开展了煤层的井壁失稳机理分析,并基于时间延迟效应原理分析了近井壁地带的煤岩裂纹尖端应力强度因子,提出了在孔隙压力压降漏斗存在的情况下裂纹延展范围的判定方法。通过实例计算分析了煤岩垮塌可能对PE筛管造成的最大压力。利用室内单轴压缩机模拟大块煤岩掉落时PE筛管(外径50.8mm,壁厚4.6mm)单轴受压变形工况,得到了管体抗挤性能和PE管体挤压破坏判别标准;以实验结果为基础,采用数值模拟软件分析了直径分别为50.8、63.5、76.2、88.9、101.6mm筛管的抗挤性能,从而优选出了不同尺寸筛管的合理壁厚,对煤层气井完井用的PE筛管的研制和应用具有一定的指导意义。
The collapse-proneness of coal beds in horizontal sections of a CBM well is one of the main inhibiting factors for CBM production enhancement.In view of the safety of following coal mining operation,metal pipes are not allowed to run under the coal beds.As a result,PE screen completion is an important solution to the above problem.In order to determine whether PE screen pipes are applicable or not to the coal beds susceptible to collapse,the wellbore instability mechanism of coal beds was analyzed by means of fracture mechanics,and the stress intensity factors at the fracture end of the coal rocks close to wellbore was discussed based on time delay effect,a method was further developed to judge the crack extension range in the presence of pore pressure drop funnel.The greatest potential compression force exerted on PE screen by collapsed coal rocks was investigated by example calculation.The uniaxial compressor was used in the laboratory to simulate the deformation of PE screen(outer diameter: 50.8 mm;wall thickness: 4.6 mm) caused by the falling of large coal rock blocks.The compression resistance and compression rupture judgment criteria of PE screen were determined in the test.Based on the test results,the simulation software was applied to analyze the compression resistance of screens with diameters of 50.8,63.5,76.2,88.9,and 101.6 mm respectively.Finally,the optimal wall thickness of different-sized PE screen pipes was determined,which gives certain instructions to the development and application of PE screen pipes in CBM well completion.
The collapse-proneness of coal beds in horizontal sections of a CBM well is one of the main inhibiting factors for CBM production enhancement.In view of the safety of following coal mining operation,metal pipes are not allowed to run under the coal beds.As a result,PE screen completion is an important solution to the above problem.In order to determine whether PE screen pipes are applicable or not to the coal beds susceptible to collapse,the wellbore instability mechanism of coal beds was analyzed by means of fracture mechanics,and the stress intensity factors at the fracture end of the coal rocks close to wellbore was discussed based on time delay effect,a method was further developed to judge the crack extension range in the presence of pore pressure drop funnel.The greatest potential compression force exerted on PE screen by collapsed coal rocks was investigated by example calculation.The uniaxial compressor was used in the laboratory to simulate the deformation of PE screen(outer diameter: 50.8 mm;wall thickness: 4.6 mm) caused by the falling of large coal rock blocks.The compression resistance and compression rupture judgment criteria of PE screen were determined in the test.Based on the test results,the simulation software was applied to analyze the compression resistance of screens with diameters of 50.8,63.5,76.2,88.9,and 101.6 mm respectively.Finally,the optimal wall thickness of different-sized PE screen pipes was determined,which gives certain instructions to the development and application of PE screen pipes in CBM well completion.
引文
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[2]屈平.煤岩井壁稳定力学机理及工程应用研究[D].北京:中国石油勘探开发研究院,2011.QU Ping.Mechanical analysis on borehole stability and ap-plication[D].Beijing:Research Institute of Petroleum Ex-ploration and Development,2011.
[3]李庆芬.断裂力学及其工程应用[M].哈尔滨:哈尔滨工程大学出版社,1998:17-25.LI Qingfen.Application of fracturing mechanics[M].Har-bin:Harbin Engineering University Press,1998:17-25.
[4]QU Ping,SHEN Ruichen,FU Li,et al.Time delay effectdue to pore pressure changes and existence of cleats onborehole stability in coal seam[J].International Journal ofCoal Geology,2011,85(2):212-218.
[5]GENTZIS T.Stability analysis of a horizontal coalbedmethane well in the rocky mountain front ranges of south-east British Columbia,Canada[J].International Journal ofCoal Geology,2009,77(3/4):328-337.
[6]尹祥础.固体力学[M].北京:地震出版社,2011.YIN Xiangchu.Solid mechanics[M].Beijing:SeismologicalPress,2011.
[7]袁小平,李波涛,刘红岩,等.基于压缩载荷下微裂纹扩展的微观力学岩石弹塑性损伤模型研究[J].中南大学学报:自然科学版,2012,43(8):3201-3208.YUAN Xiaoping,LI Botao,LIU Hongyan,et al.Elasto-plastic damage model of rock based on micro-crack propa-gation under compression[J].Journal of Central South Uni-versity:Science and Technology Edition,2012,43(8):3201-3208.
[8]刘新福,綦耀光,刘春花,等.气水两相煤层气井井底流压预测方法[J].石油学报,2010,31(6):998-1003.LIU Xinfu,QI Yaoguang,LIU Chunhua,et al.Predictionof flowing bottomhole pressures for two-phase coalbedmethane wells[J].Acta Petrolei Sinica,2010,31(6):998-1003.
[9]KARL ZIPF R,Jr.BIENIAWSKI Z T.Mixed mode testingfor fracture toughness of coal based on critical-energy-den-sity[C]∥paper 86-0016presented at the 27th U.S.Sympo-sium on Rock Mechanics(USRMS),23-25June 1986,Tus-caloosa,Alabama,USA.New York:SPE,1986.
[10]殷有泉,李平恩.非均匀载荷下套管强度的计算[J].石油学报,2007,28(6):138-146.YIN Youquan,LI Ping'en.Computation of casing strengthunder non-uniform load[J].Acta Petrolei Sinica,2007,28(6):138-146.
[11]王同涛,闫相祯,杨秀娟.基于塑性铰模型的煤层气完井筛管抗挤强度分析[J].煤炭学报,2010,35(2):273-277.WANG Tongtao,YAN Xiangzhen,YANG Xiujuan.Col-lapse pressure of perforated liner casing in CBM explora-tion based on plastic hinge model[J].Journal of ChinaCoal Society,2010,35(2):273-277.
[12]樊生利.沁水盆地南部煤层气勘探成果与地质分析[J].天然气工业,2001,21(4):35-38.FAN Shengli.Exploration result and geological analysis ofcoal-bed gas in the south part of Qinshui Basin[J].Natu-ral Gas Industry,2001,21(4):35-38.
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