超临界CO2压裂起裂压力预测方法

Prediction method of fracture initiation pressure for supercritical CO2 fracturing

马建民 马可欣 张富美 李小娜 杜玉昆 赵博 赵玉明

中国石油大学（华东）石油工业训练中心，山东 青岛 266580 中国海洋大学工程训练中心，山东 青岛 266100 中国石油青海油田分公司
采油一厂，青海 海西 817000 中国石油大学（华东）石油工程学院，山东 青岛 266580

Oil Industry Training Centre, China University of Petroleum, Qingdao 266580, China Engineering Training Centre, Ocean University of China, Qingdao 266100, China No.1 Oil Production Plant, Qinghai Oilfield Company, PetroChina, Haixi 817000, China School of Petroleum Engineering, China University of Petroleum, Qingdao 266580, China

超临界CO2压裂具有降低起裂压力、低伤害等特点，并兼顾温室气体埋存等优势，在非常规油气资源的开发中具有广阔的应用前景。为弄清超临界CO2侵入条件下的储层起裂机制，基于岩石的拉伸破坏机理，考虑CO2侵入地层引起的近井地层温度和孔隙压力变化对储层岩石切向应力的影响，建立了热流固耦合的超临界CO2压裂起裂压力模型，并应用致密气井超临界CO2压裂现场数据进行了模型验证。结果表明：超临界CO2压裂可显著降低起裂压力，且起裂压力随着排量增大而降低；井底压力的波及速度高于井底温度，排量对波及速度影响不大；切向应力最小值位于井壁处，地层温度和孔隙压力引起的井壁切向应力方向相反，前者大于后者；泊松比增大、弹性模量增大、井底温度降低均可使储层起裂压力降低。

Supercritical CO2 fracturing technology has the advantages of reducing fracture initiation pressure, low damage to the formation and greenhouse gas storage, so it has broad application prospects in unconventional reservoir development. To investigate the fracture initiation mechanism with supercritical CO2 invasion, considering the influence of variation of formation temperature and pore pressure near the well caused by CO2 invasion on rock tangential stress, a fracture initiation pressure model of supercritical CO2 fracturing with thermo-fluid-solid coupling is established based on the tensile failure mechanism of rock. And supercritical CO2 fracturing field data for tight gas well is applied to verify the model. The results show that supercritical CO2 fracturing can significantly reduce the initiation pressure, and the initiation pressure decreases with pump rate increasing. Moreover, the propagation velocity of bottom hole pressure is higher than that of bottom hole temperature, and pump rate has little effect on the propagation velocity. The minimum tangential stress is at the borehole wall, and the tangential stress at the borehole wall caused by formation temperature and pore pressure are in opposite direction and the former is larger. With the increase of Poisson′s ratio and Young modulus, and the decrease of bottom hole temperature, the initiation pressure decreases.

10.6056/dkyqt202203002