致密砂岩储层CO2压裂裂缝扩展实验研究

为提高天然裂缝和层理不发育致密储层压裂裂缝的复杂性，基于真三轴压裂模拟实验系统，开展了致密砂岩储层CO₂压裂实验研究，分析了水平应力差、压裂液类型和排量对压裂裂缝扩展规律的影响。研究表明，超临界CO₂压裂形成的水力裂缝形态最复杂，液态CO₂次之，滑溜水压裂产生的水力裂缝形态简单；采用液态CO₂压裂时，低水平应力差（≤3 MPa）有利于提高水力裂缝的复杂程度；液态CO₂压裂的起裂压力相比于滑溜水压裂降低22.1%，超临界CO₂压裂的起裂压力相比于滑溜水压裂降低28.2%；提高排量会加快井筒内流体增压速率，起裂压力升高。实验证明超临界CO₂压裂能够有效提高裂缝复杂性。

Experiment research on the CO2 fracturing fracture propagation laws of tight sandstone

In order to improve the complexity of hydraulic fractures in the tight reservoirs with undeveloped natural fractures and beddings, CO₂ based tight sandstone fracturing was experimentally studied in the true triaxial fracturing simulation experiment system to analyze the effects of horizontal stress difference, fracturing fluid type and displacement on the propagation laws of hydraulic fractures. It is shown that the hydraulic fractures generated by supercritical CO₂ fracturing are morphologically the most complex, followed by those generated by liquid CO₂ fracturing and those generated by slick-water fracturing are the simplest. When liquid CO₂ fracturing is carried out, low horizontal stress difference (≤3 MPa) is beneficial to increasing the complexity of hydraulic fractures. Compared with the initial pressure of slick-water fracturing, that of liquid CO₂ fracturing is 22.1% lower and that of supercritical CO₂ fracturing is 28.2% lower. The fluid pressure increasing rate inside the wellbore and the initial pressure can be increased by increasing the displacement. It is experimentally proved that supercritical CO₂ fracturing can improve the complexity of fractures effectively.