深部煤层力学参数反演和气体钻井井壁稳定性
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摘要
如何确定深部煤层的地质力学参数是气体钻井井壁稳定评价的关键。基于量化的地质强度指标GSI和Hoek-Brown强度准则分析了反演深部煤层地质力学参数的方法,结合DB1井氮气钻井,以弹塑性方法分析了侏罗系炭质泥岩和煤层的井壁稳定性。研究表明,塔里木盆地依奇克里克区块侏罗系煤GSI介于45~55,变形模量约在1 560~2 850 MPa之间。井眼钻开后炭质泥岩和煤层井周存在塑性区,炭质泥岩层井周塑性区约为1.37倍井眼半径,煤层井周塑性区约为2.07~2.59倍井眼半径。塑性区应力松弛造成围压减小,导致节理岩体抵抗工程扰动的能力减弱。以工程允许塑性半径等于1.5倍井眼半径为临界稳定条件,井眼钻开后煤层会出现大面积坍塌失稳,不宜采用气体钻井;工程扰动造成炭质泥岩井眼扩径,扩径后井眼仍能保持稳定。
How to assess the geomechanical properties of deep coal bed is a key issue for wellbore stability analysis of gas drilling. Geomechanical properties inversion method of deep coal bed is proposed in this work based on the quantitative geological strength index(GSI) and Hoek-Brown strength criterion. The strength and deformation parameters of Jurassic coal were estimated. Taking nitrogen drilling well DB1 in Yiqikelike region as an example,wellbore stabilities of Jurassic carbonaceous mudstone and coal bed were investigated with FLAC. Analysis indicates that GSI of coal bed at Yiqikelike region in Tarim Basin ranges from 45 to 55,and deformation modulus is from 1 560 MPa to 2 850 MPa. The results also reveal that carbonaceous mudstone and coal bed exhibit elastoplastic behavior during gas drilling. The plastic zone radius of carbonaceous mudstone is about 1. 37 times of wellbore radius,while that of coal bed is 2. 07 to 2. 59 times of wellbore radius. Stress relaxation in the plastic zone is captured,thereby leading to a decrease in confining stress,and reducing the anti-disturbance ability of jointed rock mass with respect to excavation. The plastic zone radius of carbonaceous mudstone that results from drilling is less than 1. 5 times of wellbore radius,which shows a stable hole. While that of coal bed is far more than the plastic radius permitted by project,thus predicting borehole collapse,therefore gas drilling should not be used. Borehole enlargement of carbonaceous mudstone may be encountered as a result of engineering disturbance,and the borehole can remain stable during gas drilling.
How to assess the geomechanical properties of deep coal bed is a key issue for wellbore stability analysis of gas drilling. Geomechanical properties inversion method of deep coal bed is proposed in this work based on the quantitative geological strength index(GSI) and Hoek-Brown strength criterion. The strength and deformation parameters of Jurassic coal were estimated. Taking nitrogen drilling well DB1 in Yiqikelike region as an example,wellbore stabilities of Jurassic carbonaceous mudstone and coal bed were investigated with FLAC. Analysis indicates that GSI of coal bed at Yiqikelike region in Tarim Basin ranges from 45 to 55,and deformation modulus is from 1 560 MPa to 2 850 MPa. The results also reveal that carbonaceous mudstone and coal bed exhibit elastoplastic behavior during gas drilling. The plastic zone radius of carbonaceous mudstone is about 1. 37 times of wellbore radius,while that of coal bed is 2. 07 to 2. 59 times of wellbore radius. Stress relaxation in the plastic zone is captured,thereby leading to a decrease in confining stress,and reducing the anti-disturbance ability of jointed rock mass with respect to excavation. The plastic zone radius of carbonaceous mudstone that results from drilling is less than 1. 5 times of wellbore radius,which shows a stable hole. While that of coal bed is far more than the plastic radius permitted by project,thus predicting borehole collapse,therefore gas drilling should not be used. Borehole enlargement of carbonaceous mudstone may be encountered as a result of engineering disturbance,and the borehole can remain stable during gas drilling.
引文
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[8]Hoek E,Carranza-Torres C,Corkum B.Hoek-Brown failure criterion:2002 edition[A]//Proc.NARMSTAC Conference[C].Toronto:University of Toronto,2002:267-273.
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[11]孙明波,樊泽霞,王书琪,等.塔里木盆地煤层坍塌机理研究[J].石油大学学报(自然科学版),2004,28(2):49-51.(Sun Mingbo,Fan Zexia,Wang Shuqi,et al.Synthetic sloughing mechanism of coal beds in Tarim basin[J].Journal of the University of Petroleum(Science&Technology Edition),2004,28(2):49-51.(in Chinese))
[12]吕开河,孙明波,邱正松.塔里木盆地依奇克里克区块煤层钻井技术研究[J].石油学报,2006,27(5):108-111.(LüKaihe,Sun Mingbo,Qiu Zhengsong.Drilling techniques for coal bed in Yiqikelike area of Tarim basin[J].Acta Petrolei Sinica,2006,27(5):108-111.(in Chinese))
[13]张建国,程远方,孙明波.塔里木煤层坍塌力学机理的实验研究[J].石油钻探技术,2000,28(3):21-23.(Zhang Jianguo,Cheng Yuanfang,Sun Mingbo.Experimental study on sloughing mechanism of coal beds in Tarim oilfield[J].Petroleum Drilling Techniques,2000,28(3):21-23.(in Chinese))
[14]聂臻,夏柏如,邹灵战,等.气体钻井井壁稳定性模型的建立[J].天然气工业,2011,31(6):71-76.(Nie Zhen,Xia Bairu,Zhou Lingzhan,et al.Modeling of wellbore stability for gas drilling[J].Natural Gas Industry,2011,31(6):71-76.(in Chinese))
[15]鞠玮,侯贵廷,黄少英,等.库车坳陷依南-吐孜地区下侏罗统阿合组砂岩构造裂缝分布预测[J].大地构造与成矿学,2013,37(4):592-602.(Ju Wei,Hou Guiting,Huang Shaoying,et al.Structural fracture distribution and prediction of the lower Jurassic ahe formation sandstone in the yinan-tuzi area,kuqa depression[J].Geotectonica et Metallogenia,2013,37(4):592-602.(in Chinese))
[2]Gentzis T,Deisman N,Chalaturnyk R J.A method to predict geomechanical properties and model well stability in horizontal boreholes[J].International Journal of Coal Geology,2009,78(2):149-160.
[3]Deisman N,Mas Ivars D,Darcel C,et al.Empirical and numerical approaches for geomechanical characterization of coal seam reservoirs[J].International Journal of Coal Geology,2010,82(3):204-212.
[4]Deisman N,Khajeh M,Chalaturnyk R J.Using geological strength index(GSI)to model uncertainty in rock mass properties of coal for CBM/ECBM reservoir geomechanics[J].International Journal of Coal Geology,2013,112(1):76-86.
[5]Hawkes C,Mclellan P.Borehole stability analysis for underbalanced drilling[J].Canadian Journal of Petroleum Technology,2001,40(5):31-38.
[6]张立松,闫相祯,杨秀娟,等.基于Hoek-Brown准则的深部煤层钻井坍塌压力弹塑性分析[J].煤炭学报,2013,38(1):85-90.(Zhang Lisong,Yan Xiangzhen,Yang Xiujuan,et al.Elasto-plastic analysis of collapse pressure for deep coal seam drilling based on Hoek-Brown cirterion[J].Journal of China Coal Society,2013,38(1):85-90.(in Chinese))
[7]Hoek E,Diederichs M S.Empirical estimation of rock mass modulus[J].International Journal of Rock Mechanics and Mining Sciences,2006,43(2):203-215.
[8]Hoek E,Carranza-Torres C,Corkum B.Hoek-Brown failure criterion:2002 edition[A]//Proc.NARMSTAC Conference[C].Toronto:University of Toronto,2002:267-273.
[9]Cai M,Kaiser P K,Uno H,et al.Estimation of rock mass deformation modulus and strength of jointed hard rock masses using the GSI system[J].International Journal of Rock Mechanics and Mining Sciences,2004,41(1):3-19.
[10]胡盛明,胡修文.基于量化的GSI系统和HoekBrown准则的岩体力学参数的估计[J].岩土力学,2011,32(3):861-866.(Hu Shengming,Hu Xiuwen.Estimation of rock mass parameters based on quantitative GSI system and Hoek-Brown criterion[J].Rock and Soil Mechanics,2011,32(3):861-866.(in Chinese))
[11]孙明波,樊泽霞,王书琪,等.塔里木盆地煤层坍塌机理研究[J].石油大学学报(自然科学版),2004,28(2):49-51.(Sun Mingbo,Fan Zexia,Wang Shuqi,et al.Synthetic sloughing mechanism of coal beds in Tarim basin[J].Journal of the University of Petroleum(Science&Technology Edition),2004,28(2):49-51.(in Chinese))
[12]吕开河,孙明波,邱正松.塔里木盆地依奇克里克区块煤层钻井技术研究[J].石油学报,2006,27(5):108-111.(LüKaihe,Sun Mingbo,Qiu Zhengsong.Drilling techniques for coal bed in Yiqikelike area of Tarim basin[J].Acta Petrolei Sinica,2006,27(5):108-111.(in Chinese))
[13]张建国,程远方,孙明波.塔里木煤层坍塌力学机理的实验研究[J].石油钻探技术,2000,28(3):21-23.(Zhang Jianguo,Cheng Yuanfang,Sun Mingbo.Experimental study on sloughing mechanism of coal beds in Tarim oilfield[J].Petroleum Drilling Techniques,2000,28(3):21-23.(in Chinese))
[14]聂臻,夏柏如,邹灵战,等.气体钻井井壁稳定性模型的建立[J].天然气工业,2011,31(6):71-76.(Nie Zhen,Xia Bairu,Zhou Lingzhan,et al.Modeling of wellbore stability for gas drilling[J].Natural Gas Industry,2011,31(6):71-76.(in Chinese))
[15]鞠玮,侯贵廷,黄少英,等.库车坳陷依南-吐孜地区下侏罗统阿合组砂岩构造裂缝分布预测[J].大地构造与成矿学,2013,37(4):592-602.(Ju Wei,Hou Guiting,Huang Shaoying,et al.Structural fracture distribution and prediction of the lower Jurassic ahe formation sandstone in the yinan-tuzi area,kuqa depression[J].Geotectonica et Metallogenia,2013,37(4):592-602.(in Chinese))