摘要: |
超临界CO2压裂是种新型的无水压裂技术,井筒温度和压力准确预测是该技术成功实施的关键。基于Span-Wagner状态方程和Fenghour输运性质模型,结合质量、动量和能量守恒方程,建立考虑热量源汇的超临界CO2压裂井筒流动解析模型,采用压力和温度以及油管-环空-地层的迭代计算,实现井深和径向方向的双重耦合数值求解。通过对比分析经典模型和现场实测数据,分别验证模型的推导过程和精度。结果表明:气体膨胀或压缩做功对井筒温度和压力的影响不能忽略;大排量超临界CO2压裂过程中,须考虑摩擦生热对井筒温度和压力的影响;焦耳-汤姆逊效应对井筒温度和压力影响较小,工程计算中可忽略。 |
关键词: 超临界CO2 压裂 井筒流动模型 耦合求解 热量源汇 |
DOI:10.3969/j.issn.1673-5005.2018.02.010 |
分类号:TE357 |
基金项目:国家自然科学基金项目(U1562212);国家"973"重点基础研究发展规划项目(2014CB239203) |
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A wellbore flow model and coupling solution for supercritical CO2 fracturing |
LI Xiaojiang, LI Gensheng, WANG Haizhu, TIAN Shouceng, SONG Xianzhi, LU Peiqing, LIU Qingling1,2
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1. State Key Laboratory of Petroleum Resource and Prospecting in China University of Petroleum, Beijing 102249, China;2. Research Institute of Petroleum Engineering, SINOPEC, Beijing 100101, China
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Abstract: |
Supercritical carbon dioxide (CO2) can be applied as a new type of non-aqueous fracturing fluid. Precise prediction of the bottomhole temperature and pressure is the key requirement for the design and operation of supercritical CO2 fracturing. In this paper, a theoretical CO2 wellbore flow model was developed based on the conservation laws of mass, momentum and energy balance. The equation of state for CO2 proposed by Span and Wagner and a model proposed by Fenghour et al. were adopted to calculate the in-situ thermodynamic and transport properties of CO2 at wellbore conditions. The model was solved by coupling pressure and temperature along the wellbore and coupling tubing-annulus-formation in the radial direction. The derivation of the model was validated by comparing with the classical models, and the accuracy of model was verified using data from a CO2 injection well, in which the relative errors are below 1%. The results indicate that heat generated by gas expansion or compression should be considered in the process of CO2 injection at a low rate. Moreover, the heat generated by gas expansion and friction should be considered for the CO2 fracturing at high injection rates, while the Joule-Thompson effect can be neglected at most operating conditions. |
Key words: supercritical CO2 fracturing wellbore flow model coupling solution heat source/sink |