流量对水力压裂破裂压力和增压率的影响研究

水力压裂现场原位测试试验的破裂压力是计算构造地应力的重要参数。为了探究流量对水力压裂破裂压力和增压率的影响，设计4种不同恒定流量情况的低渗透硬脆灰岩室内大型水力压裂试验，结合声发射监测技术分析不同流量下水力裂缝破裂压力、破坏模式和缝网复杂程度的规律以及流量与增压率的内在关系。试验结果表明：流量越大，破裂压力越高，缝网复杂程度越低；典型压力?时间曲线分为缓慢增压段、急速增压段、稳定增压段和突然下降段；稳定增压段增压率保持不变，压力随时间线性增长，其增压率的大小和流量存在明显的线性关系；基于流量与稳定增压段增压率的线性关系，考虑流量因素的Ito理论可以很好地定量解释流量对破裂压力的影响，试验结果与理论预测吻合度较高。

Effect of pumping rate on hydraulic fracturing breakdown pressure and pressurization rate

The breakdown pressure of the pressure-time curve obtained from the in-situ test is an important parameter for calculating the tectonic stress. In order to investigate the influence of pumping rate on breakdown pressure and pressurization rate, four large-scale hydraulic fracturing experiments on low-permeability hard and brittle limestone with varying constant pumping rate were conducted. Acoustic emission monitoring technique was used to investigate how varying pumping rate affected breakdown pressure, failure mode and complexity of fracture network as well as internal relationship between pumping rate and pressurization rate. The experimental results show that the pumping rate has a significant effect on the breakdown pressure. A larger pumping rate results in a higher breakdown pressure and a lower complexity of fracture network. The typical pressure-time curve consists of a slow boosting stage, a rapid boosting stage, a stable boosting stage and a sudden drop stage. Pressure increases linearly with time during the stable boosting stage, and there is a clear linear relationship between the pressurization rate and the pumping rate. Using the linear relationship between the pumping rate and the steady-state pressurization rate, the Ito theory can quantitatively explain the dependence of the breakdown pressure on the pumping rate. The theoretical predictions are in good agreement with the experimental results.