超临界CO_(2)压裂井筒传热规律

Heat Transfer in Wellbores Fractured with Supercritical CO_(2) Fracturing Fluid

为了优化超临界CO_(2)压裂工艺技术和施工参数,考虑到井筒温压变化与CO_(2)物性之间的相互影响与作用,基于CO_(2)物性模型,建立CO_(2)压裂井筒压降、传热耦合数学模型,通过现场压裂施工数据验证模型准确性,进行耦合计算和井筒传热规律分析。研究表明:不同排量下,油管内温度分布均明显低于地层原始温度,且随着排量增加,井筒温度出现了先减小后增加的变化趋势;井底温度随着注入温度的增大而增大,且较高排量下,井底温度随注入温度的变化更加显著;井口压力增加对井底温度的影响很小,在工程上可以忽略其影响;不同排量下,井底温度均随着注入时间的增大而降低,且降幅随着注入时间增大逐渐减小;加入降阻剂会显著降低油管内温度,且不同排量下,降阻后井筒温度差异较小。该研究对于CO_(2)压裂设计优化及现场施工具有重要指导意义。

To optimize the techniques and operational parameters of well fracturing with supercritical CO_(2)fracturing fluid, a mathematical model coupling the pressure drawdown and heat transfer of a well fractured with CO_(2)fracturing fluid is established based on the physical properties of CO_(2), taking into account the mutual influence and interaction between the changes in temperature and pressure of the well and the properties of CO_(2). The accuracy of the model is verified with data collected from field fracturing operations. Using this model, the effect of coupled temperature and pressure is calculated, and heat transfer pattern in the wellbore analyzed. Laboratory studies have shown that the temperature distribution inside the tubing is significantly lower than the in-situ formation temperature at different flow rates of the fracturing fluid. With the increase in flow rate, the wellbore temperature is first decreasing and then increasing. The bottomhole temperature is increasing with the increase in the temperature of the injected fluid,and the change in the bottomhole temperature becomes more significant with the temperature of the injected fluid at higher flow rates. Increase in the wellhead pressure has little, if any, influence on the bottomhole temperature, and its effect can be ignored in engineering calculations. The bottom hole temperature is always decreasing with time at different flow rates, and the amplitude of this temperature decrease is gradually decreasing with time. The tubing temperature can be significantly reduced if drag reducer is added into the fracturing fluid. At any flow rate, the changes in the wellbore temperatures are becoming smaller in a wellbore fractured with a fracturing fluid containing drag reducers. This research has important guiding significance to CO_(2)fracturing design optimization and field operations.