This paper presents a simple, but reliable, method for predicting the performance of multiple gas wells in complex reservoir shapes. Using an approximation of the traditional "image well" method, pressure and production profiles can be generated for arbitrary shaped reservoirs, with internal boundaries and similar heterogeneity, as well as multiple well completions. The procedure will allow for modeling and analysis, as well as forecasting of complex operating conditions including varying rate and flowing pressure schedules (including shut-in) for conventional and unconventional gas systems without the need of advanced engineering mathematics or computational libraries.
The approach overcomes many limitations of conventional analytical methods (i.e. single well solutions or limited reservoir shapes) which are generally unsuitable for multi-well planning, in-fill drilling, or full field development. But, it also allows for petroleum engineers, without numerical simulation resources or skills, to perform field wide evaluations on reservoirs and wells with a variety of operating conditions. A number of computational and quality issues are addressed including Laplace space inversion methods; addition of wellbore storage and skin (at wellbore and observation points); incorporation of absorbed gas for unconventional gas systems; pressure dependant fluid properties; reservoir heterogeneity; and rate forecasting. The methodology is validated by comparison to both analytical solutions and commercial numerical tools.
In short, a new mathematical approach for production modeling and forecasting has been introduced. Mathematical adaptations for reservoir heterogeneity, complex reservoir shapes, multiple completions and rate forecasting are discussed. Adaptations and applications for both conventional and unconventional gas (including coal and shale gas) are demonstrated. Finally, a simple solution process is presented for quick and easy implementation in MS Excel or other common tools.