Study On Transient Temperature And Pressure Coupling Model Of Gas Well

The storage of natural gas is rich in China. In order to achieve the high-efficient development, dynamic monitoring for the natural gas reservoir is required. The fundamental targets of which include wellbore pressure and temperature data. There are two approaches of data acquisition: The first one is to calculate the distribution directly based on pressure data observed by manometer and temperature data observed by thermometer. The second one is to calculate the distribution by building models of wellbore temperature and pressure based on related data such as wellbore data and output fluids parameters. It is currently difficult to place test instruments down to gas wells in many situations so that we have to choose the second approach to obtain the related data for well bottom. Nevertheless, it is hard, for the traditional model of the steady-state models of wellbore temperature and pressure, to solve complex problems, the research, therefore, becomes necessary for the wellbore transient temperature stress model.This paper focus on the problem that wellbore temperature and pressure changes with time in a producting gas well. The main works are as follows. Firstly, based on the heat transfer and thermodynamic theories, the thermal properties such as solid, liquid, and solid-liquid were introduced. Secondly, because of the defect of the traditional wellbore temperature and pressure model, a new composite model was established to perform the process of hear transfer from wellbore to formation. And the wellbore transient temperature model was established by combining this composite model with the energy conservation equation. Thirdly, the pipeline flow model of single phase was introduced, and a pipeline flow model of gas-liquid phase was improved. Then, a program was also programed to realize the function. And last, works on comparison, sensitivity analysis and application example analysis were also done, and conclusions were as follows.(1) the thermal parameters changes greatly along the well depth, which cannot be considered as a constant.(2) The process that heat transfer from wellbore to formation was not steady, and the new model could solve this problem.(3) There were5typical stages of heat transfer from wellbore to formation, early stage, steady radial heat transfer stage in wellbore, the stage of heat transfer from wellbore to formation, steady radial heat transfer stage in formation, and the outer boundary condition stage. And the sensitivity analysis shows that the dimensionless distance, dimensionless thermal conductivity coefficient and the dimensionless heat capacity per unit volume influence the heat transfer from wellbore to formation.(4) The pressure data show that the improved pipeline flow model of gas-liquid phase was accurate.(5) Works on comparison, sensitivity analysis and application example analysis showed:①the result calculated by PIPESIM, COMSOL, and the new model were closed,②while decoupling the temperature and pressure model, the accuracy of result will reduced.③the Ramey model and Hasan&Kabir model were less accurate than the new model.④The wellbore temperature data were strong sensitive to gas production, water production, liquid specific heat, thermal conductivity of cement, and the wellbore temperature data were sensitive to natural convection heat transfer coefficient of annular, and the opposite, the data were less sensitive to thermal conductivity coefficient of formation, thermal conductivity coefficient of liquid, forced convection heat transfer coefficient of the tubing-liquid and radiation heat transfer coefficient of annular. The wellbore pressure data were strong sensitive to gas production and water production, and the data were less sensitive to the others.⑤A new method was provided to solve the unsteady situation in the production test for high temperature and high pressure gas well.