| Reservoir deposition occurs over geologic periods of time and, thus, most reservoirs are heterogeneous in nature. Some common forms of heterogeneity are the presence of layers and the presence of different zones of fluids and/or rocks in the formation. When an enhanced recovery method, such as steam-flooding, is implemented for a heavy-oil reservoir, the reservoir resembles a composite reservoir. Because of the gravity override effect, the fluid front of the swept region is not vertical, but tilted or inclined. Sometimes, reservoirs are accompanied by a bottom-water or a gas-cap zone of various sizes. In the presence of a bottom-water or a gas-cap zone, the well is partly-penetrated to avoid or delay the water or gas coning problem.; In this study, a new analytical solution for multi-layer, composite reservoirs with pseudosteady state interlayer crossflow has been developed. Fluid flow in the reservoir has been treated as a generalized eigenvalue problem. The developed analytical solution for an n-layer composite reservoir is applicable for a tilted or irregularly-shaped discontinuity boundary, and for closed, constant-pressure, and infinite outer-boundary conditions. For tilted front cases, a pseudosteady-state (pss) flow period exists in some average sense and pss analysis will result in considerable underestimation of the swept volume for tilted front reservoirs. A correction factor has been developed to correct the estimated swept volume from pss analysis. Well-test analysis under infinite and finite bottom-water conditions has been considered and the effect of aquifer size on well-test analysis has been investigated.; For partially-penetrating wells in multi-layer reservoirs, new analytical expressions for the pseudoskin factor have been developed for both closed top and bottom boundaries, and with bottom-water zones and/or gas caps. Evaluation of the pseudoskin factor using these expressions requires a knowledge of two parameters when the top and the bottom boundaries are closed, and three parameters in the presence of a bottom-water zone or a gas cap, regardless of the number of layers. The estimated pseudoskin factor is very close to the actual pseudoskin obtained from the complete analytical solution. |
