A method to match and forecast production rates for commingled gas wells has been developed. In this paper, the method previously developed by El-Banbi and Wattenbarger1,2 , was improved and extended to allow modeling of recompletions and different initial pressures in the layers. This new method is based on a layered model that couples the material balance gas equation with the real gas boundary dominated flow equation for each layer of the multilayer-commingled system.

A spreadsheet-based computer program was developed and used to analyze the production history of commingled wells. The program calculates the individual original gas in place, OGIP, productivity index, Jg, and production rates for each layer. It also forecast the production rates of individual layers and the total well. Bottom-hole flowing pressure, pwf, total gas rate history, gas properties, and initial reservoir pressure for each layer are required.

The parameters OGIP and Jg for each layer are determined by history-matching the total gas rate using a nonlinear optimization procedure. This new method gives excellent results for cases dominated by stabilized flow, with occasional shut-ins and substantial pwf variations. The method calculates back-flow between layers during shut-in periods. Although this method is based on using stabilized flow in history-calibration data, validation against numerical simulation shows that the method can tolerate many transient flow periods caused by variations in producing conditions. Several wells were used in testing this method. Five Mexican wells are included in this paper.

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