连续油管井下弯曲段沿程压降计算方法

随着压裂技术的发展，压裂工艺和管柱结构日益复杂，特别是井下弯曲段管柱曲率半径由几米到几千米不等。采用数值模拟的方法，结合连续油管几何特征，建立直管、弯管数值仿真模型，计算不同工况下沿程压降，数值仿真结果与理论计算结果对比，弯管误差小于5%，直管误差小于6%，验证了数值模型的准确性。计算了曲率半径为1.25~1 280 m 的弯管沿程压降， 数值仿真结果与弯管理论计算结果对比表明，弯管曲率半径小于某一临界值时（该临界值与流体介质和排量有关），数值仿真与弯管理论计算结果吻合较好，当曲率半径大于这一临界值时，弯管理论计算结果偏小，甚至小于直管压降。为此，依据数值仿真计算结果，修正了弯管理论压降公式，拓宽了弯管压降计算公式的计算范围，为连续油管等弯管结构压降计算提供了可靠的公式。

Calculation methods for pressure drop along downhole bending section of coiled tubing

With the development of fracturing technologies, fracturing process and string structures become more and more complicated, especially the curvature radius of pipe string in downhole bending section is varying from a few meters to thousands of meters. The numerical simulation model for straight pipes and bends was established by means of numerical simulation based on the geometric characteristics of coiled tubing. Then, the on-way pressure drop in different working conditions was calculated and compared with the theoretical calculation result. It is verified that the numerical model is accurate with the error of bend and straight pipe lower than 5% and 6% respectively. The pressure drop along the bend with curvature radius of 1.25-1 280 m was calculated and then compared with the numerical simulation result. It is shown that the numerical simulation result coincides well with the theoretical calculation result when the curvature radius of bend is shorter than a certain critical value which is related to fluid medium and displacement. When the curvature radius of bend is longer than the certain critical value, the theoretical calculation result of bend is lower, and even lower than the pressure drop of straight pipe. Finally, the theoretical pressure drop formula of bend was corrected according to the numerical simulation results. It broadens the calculation range of pressure drop calculation formula of bends, and provides the reliable calculation formula for the pressure drop of bent structures, such as coiled tubing.