Summary
This paper presents a new general analytic formulation for pressure-transient behavior of commingled systems (layered reservoirs without crossflow). The formulation includes the effects of surface and downhole flow-rate variations and of wellbore storage resulting from the wellbore volume's location below the flow-rate measuring point (at any location in the wellbore, including the surface and sandface). The method can be applied to a variety of layered reservoirs. Each individual subzone (reservoir) in the system can be different, with different initial and outer-boundary conditions, and each zone can start to produce at a different time. The well completion for each layer can also be different.
New Laplace-domain solutions are presented for partially penetrating slanted wells and partially penetrated wells with and without a gas cap. The solution for slanted wells is based on that of Cinco-Ley et al. but includes the correct effective wellbore radius for the case of an anisotropic formation. Solutions to a few selected commingled systems are also presented to explore the application of the formulation.
