超临界二氧化碳喷射压裂孔内流场特性

Flow field character in cavity during supercritical carbon dioxide jet fracturing

为了证实利用超临界二氧化碳(CO2)流体进行喷射压裂的可行性,利用Span-Wagner气体状态方程建立超临界CO2流场的计算流体力学模型,模拟超临界CO2喷射压裂过程中的孔内流场。结果表明:在喷嘴压降相同的条件下,与水射流相比,超临界CO2射流的射流速度更高,射流核心区更长;超临界CO2喷射压裂具有比水力喷射压裂更强的射流增压效果,更容易压开地层;超临界CO2射流具有显著的焦耳-汤姆逊效应,会导致温度下降,在压裂施工中应合理控制喷嘴压降,以防发生冰堵事故;超临界CO2的密度主要受压力影响,通过调节压力就能有效控制,可适应不同的地层温度条件。

To verify the feasibility of supercritical carbon dioxide（ SC-CO2） jet fracturing,a computational fluid dynamic model was established based on Span-Wagner state equation to simulate the flow field in the cavity during SC-CO2 jet fracturing. The results show that in comparison with water jet,the SC-CO2 jet has higher jet energy and experiences less energy attenuation. It also has higher pressure boosting effect than water jet fracturing. Joule-Thomson effect can happen during SCCO2 jet and lead to temperature decrease. Therefore nozzle pressure drop should be reasonably controlled during the jet fracturing process to avoid ice block. The density of SC-CO2 is mainly influenced by pressure instead of temperature. So it can be controlled by adjusting pressure for it to work under different formation temperatures.