Forecasting production rates from gas wells has always been of considerable importance to the natural gas industry. The conventional method of predicting the performance of gas reservoirs requires data which are often unavailable. This is particularly the case when dealing with low permeability gas reservoirs. In the absence of complete reservoir data, the production decline type curves are employed to predict the future rates utilizing production history. Generally, the production decline type curves are generated based on assumption that the operating and reservoir conditions which affected gas production in the past will remain unchanged. However, there are many instances when it is necessary to forecast the production rates under conditions which are not similar to those of the past. Typical examples of such cases are: (a) changes encountered in well spacing due to developmental drilling programs and (b) backpressure changes which occur due to compressor installations. This paper introduces a series of production decline type curves and relative methodologies which can be utilized to forecast gas production when the conditions are altered. A gas reservoir model has been utilized to simulate gas production to study the effects of changes relative to reservoir and operating conditions. The model takes into account many factors such as the non-Darcy flow effects, skin factor, and pressure dependent gas properties. The results have been utilized to develop techniques (for type curve applications) to forecast production under different reservoir and operating conditions.

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