超临界CO_2压裂起裂压力模型与参数敏感性研究

Initiation pressure models for supercritical CO_2 fracturing and sensitivity analysis

超临界CO2流体具有低黏度、无表面张力的特性,若应用于非常规油气储层压裂可望实现一种无污染的新型无水压裂方法。通过建立流体在井筒内的增压速率模型,得到了考虑超临界CO2流体黏度、压缩性及增压速率的裂缝起裂压力预测模型,并与水力压裂、液态CO2压裂起裂压力进行了对比分析。结果表明,超临界CO2流体的起裂压力比液态CO2流体低20.5%,比常规水力压裂起裂压力低75.5%;超临界CO2流体的黏度、压缩性及增压速率对裂缝起裂压力影响显著。模型与文献中试验数据对比,误差在3%以内,可为超临界CO2压裂起裂压力预测提供指导。

Considering the supercritical CO2's characteristics of low viscosity and no surface tension, it is expected to be a new type of fracturing method for unconventional oil and gas reservoir. In this paper, we finally build the initiation pressure models for supercritical CO2 fracturing through the establishment of pressurization rate model of fluid in the wellbore, and compare with the breakdown pressure of water and liquid CO2. The results show that: the breakdown pressure of supercritical CO2 fluid is 20.5% less than liquid CO2 fluid, which is 75.5% less than conventional hydraulic fracturing breakdown pressure, which shows that breakdown pressure is significantly affected by the low viscosity and low pressurization rate of supercritical CO2. The error of this model is only less than 3% compared with experimental data in the literature, so as to indicate that the model can provide guidance for the prediction of supercritical CO2 fracturing initiation pressure.