气藏平均地层压力跟踪计算新方法

平均地层压力是产能评价和动态分析的基础，准确、快速获取平均地层压力对高效开发气藏意义重大。基于地层压力随时间变化的规律，分析了平均地层压力的变化规律。研究结果表明：平均地层压力等效点仅随时间发生改变，平均地层压力的下降速率等于或者近似等于井底流压的下降速率。从封闭弹性驱动气藏的物质平衡方程出发，考虑偏差系数和井底流压随平均地层压力的变化，推导建立了平均地层压力跟踪计算新方法，根据生产数据可迭代计算平均地层压力。方法验证结果显示，采气速度和采出程度共同影响模型的计算结果。应用实例表明，跟踪计算法与压力恢复试井和物质平衡法之间的相对误差均较小，满足工程计算精度要求，且跟踪计算法不需依托生产测试数据，节约了测试费用，避免了测试占产。

A new method for tracking and calculating average formation pressure of gas reservoirs

Average formation pressure is a fundamental parameter for productivity evaluation and dynamic analysis. To accurately and rapidly acquire the average formation pressure is of great significance to the efficient development of gas reservoirs. This paper analyzes the change rule of average formation pressure based on its variation with time. The research shows that the equivalent point of average formation pressure only changes with time, and the decline rate of average formation pressure is equal to or approximately equal to that of bottom-hole flow pressure. According to the material balance equation of a closed elastically-driven gas reservoir, considering the variation of the deviation coefficient and bottom hole flow pressure with the average formation pressure, this paper derives and establishes a new method for tracking and calculating the average formation pressure, which can be iteratively calculated by substituting the production data. Method verification shows that gas production rate and recovery percent together affect the calculation results. Application examples show that there is a small relative error between the tracking calculation method and the pressure buildup test and material balance method, thus meeting the accuracy requirements for engineering calculation, and the tracking calculation method is really independent of production test data, which saves test costs and avoids the impact of tests on production.