Engineered fractures play a critical role in enhancing energy extraction efficiency. In this study, energised fracturing with CO, as an alternative approach to conventional water-based hydraulic fracturing, is investigated via numerical simulations. We validated the CO finite element-based fracturing model against analytical as well as CO-fracturing laboratory experiments, then utilised the model to investigate the effects of pressure-temperature dependent properties of CO on energised fracturing process. To account for the temperatures expected in a real field, four cases with injection temperatures of CO varying between 250 K and 350K, under both isothermal and adiabatic conditions have been considered. In the adiabatic conditions, the temperature variation during compression of CO is captured using the Joule-Thompson coefficient, assuming no thermal exchange between the CO and the surrounding medium. The results highlight the significant influence of CO phase on the fracturing process, during the pressurisation stage, as well as post-breakdown, the speed of fracture growth after the breakdown and subsequent depressurisation and associated cooling of CO. In the designed cases, the phase-change from gas to liquid or supercritical occurs during the pressurisation and prior to breakdown, while the phase remains unchanged post breakdown and during fracture propagation. Liquid CO presents a fast-pressurising process while gaseous CO undergoes a lengthy compression stage. Supercritical CO is the best performing as the pressurisation is not too lengthy, while the instantaneous post breakdown fracturing is significant. Results show that higher temperature of supercritical CO is causing larger instantaneous fracture propagation as it has lower viscosity for the given in situ stresses (>10 MPa).

中文翻译：

---

CO2 赋能压裂的 3D 耦合数值模拟：CO2 相对压裂过程的影响


工程裂缝在提高能量提取效率方面发挥着关键作用。在这项研究中，通过数值模拟研究了二氧化碳赋能压裂作为传统水基水力压裂的替代方法。我们根据分析和 CO 压裂实验室实验验证了基于 CO 有限元的压裂模型，然后利用该模型研究 CO 的压力-温度依赖性特性对通电压裂过程的影响。为了考虑实际油田中的预期温度，考虑了在等温和绝热条件下 CO 注入温度在 250 K 至 350 K 之间变化的四种情况。在绝热条件下，假设 CO 与周围介质之间没有热交换，则使用焦耳-汤普森系数捕获 CO 压缩期间的温度变化。结果强调了CO相对压裂过程的显着影响，在加压阶段以及破裂后，破裂后裂缝扩展的速度以及随后的减压和相关的CO冷却。在设计的情况下，该相-在加压期间和破裂之前发生从气体到液体或超临界的变化，而在破裂后和裂缝扩展期间相保持不变。液态二氧化碳呈现快速加压过程，而气态二氧化碳则经历漫长的压缩阶段。超临界 CO 的性能最好，因为加压时间不太长，而瞬时击穿后压裂效果显着。 结果表明，超临界 CO 的较高温度会导致较大的瞬时断裂扩展，因为它对于给定的原位应力 (>10 MPa) 具有较低的粘度。