连续油管管内摩擦压降计算模型与敏感性分析

连续油管压裂作业过程中,压裂液除了在连续油管井下直管段流动,同时也会流入缠绕在滚筒上的那部分连续管,螺旋段的流动非常复杂,现有模型的计算结果与工程实际有一定的差距,基于流体力学基本原理,结合直管段摩擦因数公式和螺旋段几何特征,给出了连续油管螺旋段摩擦因数的一般关系式,最后经理论推导建立了完整的连续油管压裂作业管内压降的计算模型。分析了连续油管管径、滚筒直径、排量、黏度和流性指数等参数对管内压降的影响规律。结果表明:该模型的计算结果精度较高;相同条件下,螺旋段的压降总是大于直管段的压降;连续油管管径对压降的影响最大,管径增大近1倍,压降却减小了13倍,而滚筒直径对压降的影响最小,选择不同的滚筒直径,压降几乎未发生变化。

Calculation model for internal frictional pressure drop in coiled tubing and analysis of sensitivity

Unlike the conventional fracturing operation, the fracturing fluid not only flows in straight section of downhole coiled tubing, but also flows into the part of coiled tubing which is wound on the reel. The flow in spiral section is very complex, and the calculation results from existing model is somewhat different from the actual engineering practice, so a general relation was given to the friction factor in the spiral section of the coiled tubing based on principle of flow mechanics and in combination with friction factor equation of the straight section and the geometric characteristics of the spiral section; finally a complete calculation model for internal pressure drop during fracturing operation in coiled tubing was built with theoretical derivation. Analysis was conducted of the effect law of parameters like coiled tubing diameter, drum diameter, displacement, viscosity and flow index on internal pressure drop. The result shows that the accuracy of the calculations by this model is high; under the same conditions, the pressure drop in spiral section is always greater than that in straight section; the diameter of coiled tubing poses the greatest impact on pressure drop; when the diameter is increased by 1 time, the pressure drop reduces by 13 times, while the drum’s diameter has the smallest impact on pressure drop, so no matter what size of the drum is, the pressure drop almost remains the same.