Production Forecasting for Gas Wells Under Variable Conditions

Abstract

ABSTRACT Forecasting production rates from gas wells has always been of considerable importance to the natural gas industry. The conventional method to predict the performance of gas reservoirs requires data which are often unavailable. This is especially true for low permeability reservoirs. In the absence of complete reservoir data, production decline type curves are employed to predict future production rates utilizing past production data. The general assumption behind this technique is that the reservoir parameters such as drainage area, skin factor, etc., and operating conditions (back pressure) affecting gas production in the past will remain unchanged. There are, however, many occasions where it is necessary to forecast production rates under conditions which are not similar to those of the past. This paper introduces a series of production decline type curves which can be utilized to forecast gas production rates under conditions which are different from those affecting well performance in the past. A gas reservoir model has been utilized to generate the type curves through changing the operating conditions and reservoir parameters. The model takes into account many factors which are usually ignored. These include the non-Darcy flow effects, skin factor, and pressure dependent gas properties.