| A composite reservoir is made up of two or more concentric regions with different rock and fluid properties. In a well-test analysis for thermal recovery projects, reservoirs have mostly been idealized as radial, composite systems. This idealization is adequate if the reservoir is homogeneous and isotropic, and the well is vertical and not fractured. However, the increasing scope and complexity of thermal recovery projects, as well as, the general heterogeneity of petroleum reservoirs, have necessitated the consideration of different flow geometries other than radial. Steam injection in a fractured well or an anisotropic reservoir, may result in an elliptical swept region. A partially-completed injection well may create a spherically-shaped swept region, while steam injection in a linear or channel reservoir may result in a linear, composite reservoir.;The main objective of this study is to compare, in a comprehensive and systematic manner, the transient pressure and rate behavior of composite reservoirs in radial, elliptical, linear and spherical flow geometries. Normalizing factors to enable comparison of pressure derivative and rate responses for the various flow geometries have been presented. The effect of mobility and storativity ratio on the pseudosteady state behavior of the various composite reservoirs has been investigated. Conditions have been established for the occurrence of pseudosteady state flow for various flow geometries. As well, a generalized pressure derivative is presented that eases the identification of flow regimes characteristic of the various flow geometries. New design and analysis equations based on the generalized pressure derivative have been developed for well testing of composite reservoirs in the various flow geometries. A comparison of the production decline from the various composite reservoirs has also been undertaken. Some type curves for decline curve analysis of linear and radial composite reservoirs are presented.;Finally, a new analytical model for the transient pressure behavior of a three-region composite reservoir with power law property variation in the intermediate region is presented. This model, which accounts for smooth changes in mobility and storativity ahead of the flood front in thermal recovery processes, offers a significant improvement over the sharp-front idealizations of the composite reservoir models currently available. |
