偏差因子在富含CO2天然气井计算中应用

THE APPLICATION OF Z-FACTOR TO THE CALCULATION FOR GAS WELLS ABUNDANT WITH CO2

井筒压力、温度分布在气井的日常管理及气井设计、动态分析中是两个重要的参数，直接用烃类气井压力、温度模型计算富含CO2气井的压力温度，因CO2的性质和烃类差异较大导致计算结果不准确。为此，通过针对富含CO2气修正相应偏差因子，考虑CO2性质影响，基于质量、动量、能量守恒原理及传热学理论，建立预测井筒流体压力、温度分布的数学模型，进行井筒计算。通过计算，分析不同CO2含量情况下偏差因子、压力、温度及密度变化井筒中天然气相态变化情况，得出同一深度时压力随CO2含量的增加而变小，温度随深度增加趋于气藏温度，沿井筒向井口流速增高，向地层传热减少，井口温度增高，井口差异较大，在井口密度接近液相，即密度较大，越到井底密度越小，总的有从液相向气相过渡的趋势。

The borehole pressure and temperature distribution are 2 important parameters for the daily management, design and dynamic analysis of gas wells. If calculating the pressure and temperature of the gas wells abundant with CO2 with the direct application of the pressure and temperature model for hydrocarbon gas wells, the cal- culation results are not correct due to the large difference between the properties of CO2 and those of hydrocarbon gas. So, the mathematical model to predict the borehole fluid pressure and temperature distribution is established for the calculation. For the model, the relevant Z-factor has been revised focusing on being abundant with CO2 , the effect of C02 properties has been considered, and the principle of conservation of energy, mass and momentum, and theories about thermal conduction study have also been based on. According to the calculation, the gas phase variation in the bore hole where Z-factor, pressure, temperature and density change under different CO2 content can be analyzed. Based on the calculation, it can be obtained that at the same depth the pressure declines with the in-crease of CO2 content, the temperature tends to reach the gas reservoir temperature＇with the increase of depth, the flow rate at the well head along the bore hole increases, and the temperature at the well head increases due to less thermal conduction to the formation. It can be also obtained that, the difference at the well head is obvious： the density at the well head is near liquid phase with higher density; the density towards the bottom hole is lower, and the change tendency is presented as transiting from liquid phase to gas phase.