考虑变渗透率模量的异常高压气藏产能计算新方法

在异常高压气藏开发过程中，储层岩石常常表现出应力敏感特征。由于压敏储层在有效应力变化范围较大时，渗透率模量将随着有效应力的变化而变化，这样基于常渗透率模量的产能方程很难准确评价异常高压气藏的产能特征。为此，针对异常高压气藏的渗流规律，建立了考虑变渗透率模量和高速非达西效应的产能计算模型，并用Newton Raphson方法对模型进行求解。研究及实例分析结果表明：应力敏感作用会使异常高压气藏气井的产量降低，尤其是在井底流压较低时，其产量降低得更为严重；在井底流压较小时，用传统的常渗透率模量计算的产量可能会错误评价应力敏感作用对气井产量的影响；而高速非达西效应将会使异常高压气藏气井的产量降低，随着井底流压的减小，高速非达西效应使气井产量降低的程度更为严重。结论认为：在开发异常高压气藏的过程中应考虑变渗透率模量和高速非达西效应对气井产能的影响。

A new method for calculating the productivity of abnormally high-pressure gas reservoirs considering variable permeability modulus

In the development of abnormally high pressure gas reservoirs, the reservoir rock generally exhibits the characteristic of stress sensitivity. For such stress sensitive reservoirs, the permeability modulus changes with the stress if the effective stress is of a large variation range. Therefore, the productivity formula based on the constant permeability modulus is unlikely to accurately evaluate the productivity of such gas reservoirs. In view of this, a productivity calculation model was established considering both the variable permeability model and high velocity non Darcy flow effect according to the permeability rule of abnormally high pressure gas reservoirs; The Newton Raphson method was adopted for solving the model. The study results and case analysis showed that the stress sensitivity has the effect of reducing the production of abnormally high pressure gas reservoirs. Particularly, the production decreases heavily when the FBHP (flowing bottomhole pressure) is low. Thus if the traditional calculation method based on the constant permeability modulus is adopted, the evaluated productivity will probably provide unreliable basis for assessing the stress sensitive effect on the gas well production. Moreover, the high velocity non Darcy flow effect will reduce the productivity of abnormally high pressure gas reservoirs, and the reduction becomes severer with the decrease of FBHP. Therefore, the effect of such factors as the variable permeability modulus and the high velocity non Darcy flow effect on well productivity should be considered in the development of abnormally high pressure gas reservoirs.