气井复合工作制度生产动态预测

Production Performance Prediction of Gas Wells with Compound Working System

实际开采过程中,一些气井往往以复合工作制度进行生产,为了研究这一生产动态过程,采用有限差分和半解析法求解复合工作制度下非齐次、非线性天然气渗流数学模型。有限差分法单步长中对非线性系数(β)差分计算,循环计算内边界条件至收敛,以保证获得高阶精度的数值解。在实例计算中,数值解和半解析解的预测结果符合良好,相互印证,可精确预测出气井从稳产期到递减期的产量、井底压力和采收率等重要生产数据随时间的变化规律。研究结果表明,当产量递减至经济极限产量时,在相同转制压力下,稳产期的生产速度对采收率基本无影响,转制压力会在提高采收率的基础上,有效延长稳产期。生产速度和转制压力的合理设置可优化气井生产工作制度,为制订开发方案提供理论依据。

Some gas wells are actually produced in the pattern of compound working system. To investigate their production performance, the inhomogeneous and nonlinear mathematical model of natural gas flowing in compound working system was solved by means of finite difference and semi- analytic methods. When the finite difference method is adopted, difference calculation is performed on nonlinearity coefficient （fl } in single step length and loop calculation is conducted on inner boundary condition to the convergence so as to obtain the numerical solution of higher order accuracy. In the actual calculation, the prediction result of numerical solution is well accor＆mt with that of semi-analytic solution and they are confirmed mutually. Therefore, the change laws of important production data of gas wells from the stable production period to the decline period can be predicted accurately, including pro- duction rate, bottom hole pressure and recovery factor. It is indicated that when the production rate declines to the economic limit rate, the production velocity in the stable production period has rare effect on the recovery factor in the same transformation pressure, and transformation pressure can extend the stable production period effectively while increasing the recovery factor. The working system of gas wells can be optimized by setting production velocity and transformation pressure rationally. The research results provide the theoretical basis for the formulation of devel- opment plans.