井下管柱的真实轴向力计算与应用

Calculation and Application of Real Axial Force of Downhole Pipe String

摘要: 管柱的摩阻计算精度直接关系到完井的质量。国内外学者已经建立了许多管柱摩阻计算模型，其中“刚杆模型”是较为常用的计算模型，但是该模型在计算管柱微元体所受的浮力时，没有考虑到微元体的端面不受液体的静压力，导致所计算的轴向力为有效轴向力。对于只有侧面与液体接触的管柱单元，如果仍把排开液体的重力作为浮力，此时会在管柱单元的两端产生附加轴向力，将在此基础上计算管柱的真实轴向力，得出新的计算公式，提高管柱摩阻的计算精度。为验证模型的准确性，同时采用现有的刚杆模型和笔者所建立的模型，利用Matlab编程求解某一实际井的注水管柱在上提时的受力情况，并将两个模型所求的结果进行比较，发现建立的模型计算结果显示管柱存在中性点，中性点以下受压，中性点以上受拉，该结果与管柱的实际受力情况相符。

Abstract: The calculation precision of pipe string’s fraction was directly related to the quality of well com-pletion. Domestic and foreign scholars have established a lot of models to calculate the friction of pipe string, of which the “rigid rod model” was more frequently used, but the static pressure without liquid at ends of micro-unit was not taken into account when the buoyancy of pipe string on the unit is calculated, thus the calculation of axial force was the effective axial force. For the pipe string unit that only side is contacted with liquid, if the displaced fluid gravity is used as its buoyancy, additional axial force would be generated at the ends of the unit, the real axial force of pipe string is calculated based on the study above, a new calculation formula is established for improving the accuracy of calculation of pipe string friction. To verify the accuracy of the model, the existing rigid rod model and the model established in this paper are used to solve the stress of water injection string when it is lifted in a actual well, and Matlab program is used to solve it. By comparing the results of the two models, the results of the model of this paper show that the pipe string exists neutral point, the pipe string above the neutral point is subjected to tension and the pipe string below the neutral point is subjected to pressure, this result is closer to the actual stress state of pipe string.