压裂后焖井期间页岩吸水起裂扩展研究——以四川盆地长宁区块龙马溪组某平台井为例
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摘要
为了确定页岩气井压后的焖井时间,需要预测关井期间储层条件下页岩自吸压裂液对裂缝起裂扩展的影响。为此,基于裂缝闭合判断准则,针对四川盆地长宁区块三轴地应力测试结果,判定裂缝的闭合状态,然后基于张开裂缝的拉伸和剪切起裂准则,计算拉伸破坏和剪切破坏情况下的最大周向应力和最大有效剪切应力,并结合三轴及单轴岩石抗压力学实验和单轴巴西劈裂抗拉强度实验结果,获得裂缝起裂阈值压力,进而探讨了该区块下志留统龙马溪组页岩气井的合理焖井时间。研究结果表明:(1)该区块龙马溪组页岩气井压裂后,在焖井期间储层中的微裂缝总是保持开启的;(2)储层条件下裂缝所处的应力状态十分复杂,即使是张开裂缝,也有可能发生剪切破坏;(3)当裂缝倾角为0°时,裂缝尖端获得最大周向应力值,对应裂缝起裂角为0°,即裂缝会沿着最大水平主应力方向起裂延伸,当缝内流体压力低于70 MPa后,裂缝不会再产生拉伸起裂;(4)当裂缝倾角为0°时,对应最大有效剪切应力,此时裂缝起裂角为55°,当缝内流体压力低于60 MPa后,裂缝不再产生剪切起裂;(5)若要充分发挥页岩气井压裂后焖井期间压裂液的改造作用,该区块龙马溪组气井压裂后的合理焖井时间为5～10天。
In order to determine the soak time of shale gas wells after fracturing, it is necessary to predict the influence of shale's fracturing fluid imbibition capacity on the fracture initiation and propagation under reservoir conditions during well shut-in. In this paper, according to the fracture closure criterion, the closure state of fracture was analyzed based on the triaxial stress test results of Changning Block. Then, the maximum circumferential stress and the maximum effective shear stress under tensile failure and shear failure were calculated according to the tensile and shear initiation criteria of open fracture. And combined with the results of the triaxial and uniaxial compressive strength tests and the uniaxial Brazilian splitting tensile strength test, the threshold pressure of fracture initiation was obtained. Finally, the reasonable soak time of shale gas wells in the Longmaxi Fm of Lower Silurian in Changning Block, Sichuan Basin was discussed. And the following research results were obtained. First, after the fracturing of shale gas well in the Longmaxi Fm in Changning Block, the micro-fractures in the reservoir remain open during well shut in. Second, the stress state of the fractures under reservoir conditions is very complicated, and even the open fractures may suffer shear failure. Third, when the fracture dip is 0°, the maximum circumferential stress value is obtained at the fracture tip, and the corresponding fracture initiation angle is 0°, which means that fracture initiation and propagation will be along the direction of the maximum horizontal principal stress, and that when the fluid pressure inside the fracture is lower than 70 MPa, tensile fracturing will not happen any longer. Fourth, when the fracture dip is 0°, the corresponding maximum effective shear stress is, obtained and the fracture initiation angle is 55°. When the fluid pressure inside the fracture is lower than 60 MPa, shear fracturing will not occur any longer. Fifth, if full play should be given to the stimulation effect of fracturing fluid during well shut-in after fracturing, the reasonable soak time after fracturing in the Longmaxi Fm of the Changning Block shall be 5–10 days.
In order to determine the soak time of shale gas wells after fracturing, it is necessary to predict the influence of shale's fracturing fluid imbibition capacity on the fracture initiation and propagation under reservoir conditions during well shut-in. In this paper, according to the fracture closure criterion, the closure state of fracture was analyzed based on the triaxial stress test results of Changning Block. Then, the maximum circumferential stress and the maximum effective shear stress under tensile failure and shear failure were calculated according to the tensile and shear initiation criteria of open fracture. And combined with the results of the triaxial and uniaxial compressive strength tests and the uniaxial Brazilian splitting tensile strength test, the threshold pressure of fracture initiation was obtained. Finally, the reasonable soak time of shale gas wells in the Longmaxi Fm of Lower Silurian in Changning Block, Sichuan Basin was discussed. And the following research results were obtained. First, after the fracturing of shale gas well in the Longmaxi Fm in Changning Block, the micro-fractures in the reservoir remain open during well shut in. Second, the stress state of the fractures under reservoir conditions is very complicated, and even the open fractures may suffer shear failure. Third, when the fracture dip is 0°, the maximum circumferential stress value is obtained at the fracture tip, and the corresponding fracture initiation angle is 0°, which means that fracture initiation and propagation will be along the direction of the maximum horizontal principal stress, and that when the fluid pressure inside the fracture is lower than 70 MPa, tensile fracturing will not happen any longer. Fourth, when the fracture dip is 0°, the corresponding maximum effective shear stress is, obtained and the fracture initiation angle is 55°. When the fluid pressure inside the fracture is lower than 60 MPa, shear fracturing will not occur any longer. Fifth, if full play should be given to the stimulation effect of fracturing fluid during well shut-in after fracturing, the reasonable soak time after fracturing in the Longmaxi Fm of the Changning Block shall be 5–10 days.
引文
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[5]钱斌,朱炬辉,杨海,梁兴,尹丛彬,石孝志,等.页岩储集层岩心水化作用实验[J].石油勘探与开发,2017,44(4):615-621.Qian Bin,Zhu Juhui,Yang Hai,Liang Xing,Yin Congbin,Shi Xiaozhi,et al.Experiments on shale reservoirs plugs hydration[J].Petroleum Exploration and Development,2017,44(4):615-621.
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[8]韩慧芬,贺秋云,王良.长宁区块页岩气井排液技术现状及攻关方向探讨[J].钻采工艺,2017,40(4):69-71.Han Huifen,He Qiuyun&Wang Liang.The current situation of flowback technology and its further development research for shale-gas wells in Changning Block[J].Drilling&Production Technology,2017,40(4):69-71.
[9]马俯波,周正武,王延忠,鲁东升,陈宏亮.页岩储层中黏土对压裂液吸收能力的影响及其因素分析[J].科学技术与工程,2016,16(12):260-263.Ma Fubo,Zhou Zhengwu,Wang Yanzhong,Lu Dongsheng&Chen Hongliang.Shale reservoir fracturing fluid absorption capacity and influencing factors of research[J].Science Technology and Engineering,2016,16(12):260-263.
[10]Dehghanpour H,Lan Q,Saeed Y,Fei H&Qi Z.Spontaneous imbibition of brine and oil in gas shales:Effect of water adsorption and resulting microfractures[J].Energy Fuels,2013,27(6):3039-3049.
[11]张涛,李相方,杨立峰,李靖,王永辉,冯东,等.关井时机对页岩气井返排率和产能的影响[J].天然气工业,2017,37(8):48-60.Zhang Tao,Li Xiangfang,Yang Lifeng,Li Jing,Wang Yonghui,Feng Dong,et al.Effects of shut-in timing on flowback rate and productivity of shale gas wells[J].Natural Gas Industry,2017,37(8):48-60.
[12]李强,杨庆.压缩作用下岩石裂纹闭合判据的研究[J].岩石力学与工程学报,2009,28(增刊1):2722-2728.Li Qiang&Yang Qing.Study on closing law of crack in rock mass under compression[J].Chinese Journal of Rock Mechanics and Engineering,2009,28(S1):2722-2728.
[13]唐世斌,张恒.岩石材料裂纹尖端起裂特性研究[J].岩石力学与工程学报,2017,36(3):552-559.Tang Shibin&Zhang Heng.The characteristics of crack initiation at the crack tip in rock material[J].Chinese Journal of Rock Mechanics and Engineering,2017,36(3):552-559.
[14]陈勉,金衍,卢运虎.页岩气开发:岩石力学的机遇与挑战[J].中国科学:物理学力学天文学,2017,47(11):16-18.Chen Mian,Jin Yan&Lu Yunhu.Shale gas development:Opportunities and challenges for rock mechanics[J].Scientia Sinica(Physica,Mechanica&Astronomica),2017,47(11):16-18.
[15]赵金洲,许文俊,李勇明,胡晋阳,李晋秦.页岩气储层可压性评价新方法[J].天然气地球科学,2015,26(6):1165-1170.Zhao Jinzhou,Xu Wenjun,Li Yongming,Hu Jinyang&Li Jinqin.A new method for fracability evaluation of shale gas reservoirs[J].Natural Gas Geoscience,2015,26(6):1165-1170.
[16]金衍,陈勉,张旭东.利用测井资料预测深部地层岩石断裂韧性[J].岩石力学与工程学报,2001,20(4):454-456.Jin Yan,Chen Mian&Zhang Xudong.Determination of fracture toughness for deep well rock with geophysical logging data[J].Chinese Journal of Rock Mechanics and Engineering,2001,20(4):454-456.
[17]金衍,陈勉,王怀英,阮洋.利用测井资料预测岩石Ⅱ型断裂韧性的方法研究[J].岩石力学与工程学报,2008,27(增刊2):3630-3635.Jin Yan,Chen Mian,Wang Huaiying&Ruan Yang.Study on prediction method of fracture toughness of rock modeⅡby logging data[J].Chinese Journal of Rock Mechanics and Engineering,2008,27(S2):3630-3635.
[18]唐世斌,刘向君,罗江,董卓.水压诱发裂缝拉伸与剪切破裂的理论模型研究[J].岩石力学与工程学报,2017,36(9):2124-2133.Tang Shibin,Liu Xiangjun,Luo Jiang&Dong Zhuo.Theoretical model for tensile and shear crack initiation at the crack tip in rock subjected to hydraulic pressure[J].Chinese Journal of Rock Mechanics and Engineering,2017,36(9):2124-2133.
[19]李敏,练章华,陈世春,魏臣兴,林铁军,李孝军.岩石力学参数试验与地层破裂压力预测研究[J].石油钻采工艺,2009,31(5):15-18.Li Min,Lian Zhanghua,Chen Shichun,Wei Chenxing,Lin Tiejun&Li Xiaojun.Rock mechanical parametric experiments and the research of formation fracture pressure prediction[J].Oil Drilling&Production Technology,2009,31(5):15-18.
[2]孙雷,高玉琼,潘毅,欧成华.页岩纳米孔隙表面分形特征及其影响因素[J].西南石油大学学报(自然科学版),2017,39(6):85-91.Sun Lei,Gao Yuqiong,Pan Yi&Ou Chenghua.Surface fractal characteristics and their Influence on shale nanopores[J].Journal of Southwest Petroleum University(Science&Technology Edition),2017,39(6):85-91.
[3]卢拥军,王海燕,管保山,刘萍,郭丽梅,吴家全,等.海相页岩压裂液低返排率成因[J].天然气工业,2017,37(7):46-51.Lu Yongjun,Wang Haiyan,Guan Baoshan,Liu Ping,Guo Limei,Wu Jiaquan,et al.Reasons for the low flowback rates of fracturing fluids in marine shale[J].Natural Gas Industry,2017,37(7):46-51.
[4]马天寿,陈平.基于CT扫描技术研究页岩水化细观损伤特性[J].石油勘探与开发,2014,41(2):227-232.Ma Tianshou&Chen Ping.Study of meso-damage characteristics of shale hydration based on CT scanning technology[J].Petroleum Exploration and Development,2014,41(2):227-232.
[5]钱斌,朱炬辉,杨海,梁兴,尹丛彬,石孝志,等.页岩储集层岩心水化作用实验[J].石油勘探与开发,2017,44(4):615-621.Qian Bin,Zhu Juhui,Yang Hai,Liang Xing,Yin Congbin,Shi Xiaozhi,et al.Experiments on shale reservoirs plugs hydration[J].Petroleum Exploration and Development,2017,44(4):615-621.
[6]隋微波,田英英,姚晨昊.页岩水化微观孔隙结构变化定点观测实验研究[J].石油勘探与开发,2018,45(5):1-7.Sui Weibo,Tian Yingying&Yao Chenhao.Investigation of microscopic pore structure variations of shale due to hydration effects through SEM fixed-point observation experiments[J].Petroleum Exploration and Development,2018,45(5):1-7.
[7]Wattenbarger RA&Alkouh AB.New advances in shale reservoir analysis using flowback data[C]//Paper 165721-MS presented at the SPE Eastern Regional Meeting,20-22 August 2013,Pittsburgh,Pennsylvania,USA.
[8]韩慧芬,贺秋云,王良.长宁区块页岩气井排液技术现状及攻关方向探讨[J].钻采工艺,2017,40(4):69-71.Han Huifen,He Qiuyun&Wang Liang.The current situation of flowback technology and its further development research for shale-gas wells in Changning Block[J].Drilling&Production Technology,2017,40(4):69-71.
[9]马俯波,周正武,王延忠,鲁东升,陈宏亮.页岩储层中黏土对压裂液吸收能力的影响及其因素分析[J].科学技术与工程,2016,16(12):260-263.Ma Fubo,Zhou Zhengwu,Wang Yanzhong,Lu Dongsheng&Chen Hongliang.Shale reservoir fracturing fluid absorption capacity and influencing factors of research[J].Science Technology and Engineering,2016,16(12):260-263.
[10]Dehghanpour H,Lan Q,Saeed Y,Fei H&Qi Z.Spontaneous imbibition of brine and oil in gas shales:Effect of water adsorption and resulting microfractures[J].Energy Fuels,2013,27(6):3039-3049.
[11]张涛,李相方,杨立峰,李靖,王永辉,冯东,等.关井时机对页岩气井返排率和产能的影响[J].天然气工业,2017,37(8):48-60.Zhang Tao,Li Xiangfang,Yang Lifeng,Li Jing,Wang Yonghui,Feng Dong,et al.Effects of shut-in timing on flowback rate and productivity of shale gas wells[J].Natural Gas Industry,2017,37(8):48-60.
[12]李强,杨庆.压缩作用下岩石裂纹闭合判据的研究[J].岩石力学与工程学报,2009,28(增刊1):2722-2728.Li Qiang&Yang Qing.Study on closing law of crack in rock mass under compression[J].Chinese Journal of Rock Mechanics and Engineering,2009,28(S1):2722-2728.
[13]唐世斌,张恒.岩石材料裂纹尖端起裂特性研究[J].岩石力学与工程学报,2017,36(3):552-559.Tang Shibin&Zhang Heng.The characteristics of crack initiation at the crack tip in rock material[J].Chinese Journal of Rock Mechanics and Engineering,2017,36(3):552-559.
[14]陈勉,金衍,卢运虎.页岩气开发:岩石力学的机遇与挑战[J].中国科学:物理学力学天文学,2017,47(11):16-18.Chen Mian,Jin Yan&Lu Yunhu.Shale gas development:Opportunities and challenges for rock mechanics[J].Scientia Sinica(Physica,Mechanica&Astronomica),2017,47(11):16-18.
[15]赵金洲,许文俊,李勇明,胡晋阳,李晋秦.页岩气储层可压性评价新方法[J].天然气地球科学,2015,26(6):1165-1170.Zhao Jinzhou,Xu Wenjun,Li Yongming,Hu Jinyang&Li Jinqin.A new method for fracability evaluation of shale gas reservoirs[J].Natural Gas Geoscience,2015,26(6):1165-1170.
[16]金衍,陈勉,张旭东.利用测井资料预测深部地层岩石断裂韧性[J].岩石力学与工程学报,2001,20(4):454-456.Jin Yan,Chen Mian&Zhang Xudong.Determination of fracture toughness for deep well rock with geophysical logging data[J].Chinese Journal of Rock Mechanics and Engineering,2001,20(4):454-456.
[17]金衍,陈勉,王怀英,阮洋.利用测井资料预测岩石Ⅱ型断裂韧性的方法研究[J].岩石力学与工程学报,2008,27(增刊2):3630-3635.Jin Yan,Chen Mian,Wang Huaiying&Ruan Yang.Study on prediction method of fracture toughness of rock modeⅡby logging data[J].Chinese Journal of Rock Mechanics and Engineering,2008,27(S2):3630-3635.
[18]唐世斌,刘向君,罗江,董卓.水压诱发裂缝拉伸与剪切破裂的理论模型研究[J].岩石力学与工程学报,2017,36(9):2124-2133.Tang Shibin,Liu Xiangjun,Luo Jiang&Dong Zhuo.Theoretical model for tensile and shear crack initiation at the crack tip in rock subjected to hydraulic pressure[J].Chinese Journal of Rock Mechanics and Engineering,2017,36(9):2124-2133.
[19]李敏,练章华,陈世春,魏臣兴,林铁军,李孝军.岩石力学参数试验与地层破裂压力预测研究[J].石油钻采工艺,2009,31(5):15-18.Li Min,Lian Zhanghua,Chen Shichun,Wei Chenxing,Lin Tiejun&Li Xiaojun.Rock mechanical parametric experiments and the research of formation fracture pressure prediction[J].Oil Drilling&Production Technology,2009,31(5):15-18.