CO_2干法压裂井筒压力与相态控制研究
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摘要
液态CO_2干法压裂过程中井筒压力与相态显著影响裂缝起裂和延伸。鉴于此,根据Span-Wagner状态方程,建立了CO_2干法压裂井筒流动传热模型,揭示了CO_2干法压裂过程中井筒压力与相态的变化规律。研究结果表明:CO_2摩阻非常高,在常规施工条件下其摩阻每1 000 m超过10 MPa;排量和油管内径对井筒压降影响非常大,在满足携砂情况下可通过适当降低排量或选用较大管径油管降低摩阻;干法压裂过程中相态转变取决于井底CO_2温度,而井底温度受注入温度影响最大,其次为注入排量和地温梯度,并且几乎不受油管内径影响; CO_2流体密度和黏度与温度成反相关关系,井筒内CO_2黏度仅为0. 08～0. 25 m Pa·s,携砂能力差,加之滤失大,不利于压裂造缝是压裂施工失败的主要原因。研究结果可为CO_2干法压裂和CO_2增能压裂提供理论指导和现场借鉴。
The wellbore pressure and phase state of the liquid CO_2 significantly affect crack initiation and propagation during fracturing. Based on the Span-Wagner equation of state,the wellbore flow and heat transfer model of CO_2 fracturing is established to study the variation of wellbore pressure and phase state in CO_2 fracturing.The study shows that the friction resistance of CO_2 is very high. Under normal operation conditions,the frictional resistance exceeds 10 MPa per 1 000 m. The displacement and the inner diameter of the tubing have a great influence on the pressure drop of the wellbore. Under the premise of carrying sand,appropriate reduced displacement and larger tubing diameter could be options to reduce the friction. The phase transition during fracturing depends on the CO_2 temperature at the bottom of the well,which is most affected by the injection temperature,followed by the injection displacement and geothermal gradient,and is almost independent of the tubing inner diameter. The CO_2 fluid density and viscosity is inversely related to temperature. The viscosity of 0. 08 ～ 0. 25 m Pa·s in the wellbore,poor sand carrying capacity and large fluid loss of CO_2 makes it inferior for fracturing,which is the main causes of fracturing failure. The study could provide theoretical guidance and on-site reference for CO_2 fracturing and CO_2 energized fracturing.
The wellbore pressure and phase state of the liquid CO_2 significantly affect crack initiation and propagation during fracturing. Based on the Span-Wagner equation of state,the wellbore flow and heat transfer model of CO_2 fracturing is established to study the variation of wellbore pressure and phase state in CO_2 fracturing.The study shows that the friction resistance of CO_2 is very high. Under normal operation conditions,the frictional resistance exceeds 10 MPa per 1 000 m. The displacement and the inner diameter of the tubing have a great influence on the pressure drop of the wellbore. Under the premise of carrying sand,appropriate reduced displacement and larger tubing diameter could be options to reduce the friction. The phase transition during fracturing depends on the CO_2 temperature at the bottom of the well,which is most affected by the injection temperature,followed by the injection displacement and geothermal gradient,and is almost independent of the tubing inner diameter. The CO_2 fluid density and viscosity is inversely related to temperature. The viscosity of 0. 08 ～ 0. 25 m Pa·s in the wellbore,poor sand carrying capacity and large fluid loss of CO_2 makes it inferior for fracturing,which is the main causes of fracturing failure. The study could provide theoretical guidance and on-site reference for CO_2 fracturing and CO_2 energized fracturing.
引文
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[15]VESOVIC V,WAKEHAM W,OLCHOWY G,et al.The transport properties of carbon dioxide[J].Journal of Physical and Chemical Reference Data,1990,19(3):763-808.
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[2]刘合,王峰,张劲,等.二氧化碳干法压裂技术应用现状与发展趋势[J].石油勘探与开发,2014,41(4):466-472.LIU H,WANG F,ZHANG J,et al.Fracturing with carbon dioxide:application status and development trend[J].Petroleum Exploration and Development,2014,41(4):466-472.
[3]邹才能,张国生,杨智,等.非常规油气概念、特征、潜力及技术---兼论非常规油气地质学[J].石油勘探与开发,2013,40(4):385-399.ZOU C N,ZHANG G S,YANG Z,et al.Geological concepts,characteristics,resource potential and key techniques of unconventional hydrocarbon:on unconventional petroleum geology[J].Petroleum Exploration and Development,2013,40(4):385-399.
[4]卢义玉,廖引,汤积仁,等.页岩超临界CO2压裂起裂压力与裂缝形态试验研究[J].煤炭学报,2018,43(1):175-180.LU Y Y,LIAO Y,TANG J R,et al.Experimental study on fracture initiation pressure and morphology in shale using supercritical CO2fracturing[J].Journal of China Coal Society,2018,43(1):175-180.
[5]程宇雄,李根生,王海柱,等.超临界二氧化碳喷射压裂井筒流体相态控制[J].石油学报,2014,35(6):1182-1187.CHENG Y X,LI G S,WANG H Z,et al.Phase control of wellbore fluid during supercritical CO2jet fracturing[J].Acta Petrolei Sinica,2014,35(6):1182-1187.
[6]陈立强,田守嶒,李根生,等.超临界CO2压裂起裂压力模型与参数敏感性研究[J].岩土力学,2015,36(增刊2):125-131.CHEN L Q,TIAN S C,LI G S,et al.Initiation pressure models for supercritical CO2fracturing and sensitivity analysis[J].Rock and Soil Mechanics,2015,36(S2):125-131.
[7]ISHIDA T,AOYAGI K,NIWA T,et al.Acoustic emission monitoring of hydraulic fracturing laboratory experiment with supercritical and liquid CO2[J].Geophysical Research Letters,2012,39(16):1-6.
[8]郭建春,曾冀.超临界二氧化碳压裂井筒非稳态温度-压力耦合模型[J].石油学报,2015,36(2):203-209.GUO J C,ZENG J.A coupling model for wellbore transient temperature and pressure of fracturing with supercritical carbon dioxide[J].Acta Petrolei Sinica,2015,36(2):203-209.
[9]窦亮彬,李根生,沈忠厚,等.注CO2井筒温度压力预测模型及影响因素研究[J].石油钻探技术,2013,41(1):76-81.DOU L B,LI G S,SHEN Z H,et al.Wellbore pressure and temperature prediction model and its affecting factors for CO2injection well[J].Petroleum Drilling Techniques,2013,41(1):76-81.
[10]赖力,龙伟.超临界CO2管道泄压过程中管内动态应力分布[J].油气储运,2018,37(3):276-280.LAI L,LONG W.Distribution of dynamic stress on the supercritical CO2pipeline in the process of its pressure relief[J].Oil&Gas Storage and Transportation,2018,37(3):276-280.
[11]KABIR C S,HASAN A R,KOUBA G E,et al.Determining circulating fluid temperature in drilling,workover,and well control operations[R].SPE 24581,1992.
[12]HASAN A R,KABIR C S.Aspects of wellbore heat transfer during two-phase flow[R].SPE 22948-P4,1994.
[13]SPAN R,WAGNER W.A new equation of state for carbon dioxide covering the fluid region from the triplepoint temperature to 1100 K at pressures up to 800MPa[J].Journal of Physical and Chemical Reference Data,1996,25(6):1509-1596.
[14]FENGHOUR A,WAKEHAM W A,VESOVIC V.The viscosity of carbon dioxide[J].Journal of Physical and Chemical Reference Data,1998,27(1):31-43.
[15]VESOVIC V,WAKEHAM W,OLCHOWY G,et al.The transport properties of carbon dioxide[J].Journal of Physical and Chemical Reference Data,1990,19(3):763-808.
[16]CHEN N H.An explicit equation for friction factor in pipe[J].Industrial and Engineering Chemistry Research Fundamentals,1979,18(3):296-297.