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Effects of super-critical CO_2 phase change on dynamic multi-fracturing process in reservoir stimulation

机译:超关键CO_2相变对水库刺激动态多压裂过程的影响

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To investigate the effects of carbon dioxide phase change on dynamic multi-fracturing process during supercritical carbon dioxide (SC-CO2) fracturing, polymethyl methacrylate (PMMA) specimens of 20 X 20 X 10cm~3 are used in experiments with SC-CO2 and water as fracturing fluids, respectively. The process of fracture propagation is recorded using high speed camera to determine fracture propagation velocity and morphology. Simple models related to expansion work and heat energy caused by SC-CO2 phase change are to explain the experimental observations and results. The experimental results show that, due to strength weakening from CO2 adsorbed into the nano-scale fracture surface, the magnitude of fracture initiation pressure of SC-CO2 fracturing is lower than that of water-based fracturing. It is of interest that fracture propagation velocity of SC-CO2 fracturing is two order greater in magnitude than that of water-based fracturing, which shows that the energy release rate maybe sufficient for fracture branching. The expansion and thermal stresses induced by CO2 phase change, when the fracture instability occurs, further extend the fractures or even create multi-fractures. Eventually, the intermittent dynamic growth of multi-fractures occurs under the effect of CO2 phase change in SC-CO2 fracturing.
机译:为了研究二氧化碳相变对超临界二氧化碳(SC-CO2)压裂期间对动态多压裂过程的影响,将20×20×10CM〜3的聚甲基丙烯酸甲酯(PMMA)标本用于SC-CO2和水的实验中使用分别作为压裂液。使用高速摄像机记录断裂传播的过程,以确定裂缝繁殖速度和形态。与SC-CO2相变导致的扩展工作和热能相关的简单模型是解释实验观察和结果。实验结果表明,由于强度从吸附到纳米裂缝表面中的CO 2的强度弱化,SC-CO2压裂的裂缝起始压力的大小低于水性压裂。感兴趣的是,SC-CO2压裂的断裂繁殖速度的幅度幅度大于水基压裂的额定大于,这表明能量释放速率可能足以用于裂缝支化。当发生断裂不稳定性时,CO2相变诱导的膨胀和热应力,进一步延长裂缝或甚至产生多骨折。最终,在SC-CO2压裂中的CO2相变的影响下发生多骨折的间歇动态生长。

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