二氧化碳无水蓄能压裂参数优化

二氧化碳无水蓄能压裂技术在形成地层高导流裂缝的同时，通过与原油相互作用表现出了一系列有别于常规压裂的增产特性，包括降黏、体积膨胀和混相等。因此其优化设计过程也不同于常规压裂优化设计。首先利用地层原油取样进行室内二氧化碳与原油相互作用实验，获取最小混相压力；利用液态二氧化碳压裂时裂缝长度与储层物性参数关系模板，确定裂缝参数；以最小混相压力为条件，以裂缝参数和井底注入压力为基础，利用三维油藏数值模拟方法预测二氧化碳波及范围、混相带范围，最后确定最优的二氧化碳用液量。利用FracProPT拟三维压裂裂缝模拟软件，结合沿程摩阻损失，以保证井口和井下管柱结构安全稳定为设计前提，从水马力效率和经济效益角度优化施工排量；建立压后地层温度压力计算模型，模拟关井后混相带面积，确定最优关井时间为混相带面积最大时即压后井底压力大于最小混相压力的时间。吉林油田二氧化碳无水蓄能压裂技术已成功应用于致密油井，二氧化碳无水蓄能压裂后产油量均较压前有显著提高，6口井压后平均日产油是同区块常规重复压裂的2.7倍。研究结果表明，该二氧化碳无水蓄能压裂参数优化设计方法是合理可行的。 

Parameter Optimization for CO2 Water-free Energy-storing Fracturing

In CO2 water-free energy-storing fracturing, the fracturing fluid generates fractures of high flow conductivity in formations. By interacting with crude oil, the fracturing fluid also shows some special stimulation characteristics that are different with those of the conventional fracturing fluids, such as viscosity reducing, volume expansion and phase mixing etc. Thus, the optimization design process of the CO2 water-free energy-storing fracturing fluid is different with that of the conventional fracturing fluids. In CO2 waterfree energy-storing fracturing fluid design, the interaction between crude oil and CO2 is tested to obtain the minimum miscibility pressure. Using the relation pattern between the length of fractures caused by liquid CO2 fracturing and the physical parameters of the reservoir, the fracture parameters can be determined. Using 3-D reservoir numerical simulation method, the sweep area of CO2 and the area of miscible zone can be determined based on the value of minimum miscibility pressure, the fracture parameters and the injection pressure of the bottom of the wellbore, and finally the optimum amount of CO2 can be determined. Using FracProPT, a virtual 3-D fracture simulation software, with the friction loss along the flowline, the operational flow rate can be determined from the perspective of hydraulic power efficiency and economic benefits and the prerequisite of ensuring the safety and stability of wellhead and downhole string. Using the formation temperature-pressure computational model established after fracturing operation, the area of the miscible zone after well shut-in can be simulated, and from the simulation it can be determined that the optimum well shut-in time is the time spent for the miscible zone to become maximized, that is to say, the time spent when the bottom hole pressure after fracturing is greater than the minimum miscibility pressure. CO2 water-free energy-storing fracturing technology has been successfully applied in Jilin Oilfield to fracture tight reservoirs. Oil production rate was obviously enhanced after reservoir fracturing. 6 wells fractured with the CO2 water-free energy-storing fracturing technology have oil production rates that are at least one time of those wells fractured with conventional fracturing technology. Study results have shown that CO2 water-free energy-storing fracturing is able to substantially enhance oil recovery, and the method for the parameter optimization design of the CO2 water-free energy-storing fracturing is reasonably practical.