Authors : Freddy Humberto Escobar , Djebbar Tiab and Lida Vanessa Tovar
Abstract: Elongated reservoirs, resulting mainly from fluvial deposition or faulting, are often found in the three Basins of the Magdalena River Valley in Colombia and several other places around the globe. Since most of these reservoirs are due to parallel stratigraphic or structural features, horizontal permeability anisotropy may occur. Normally, a single horizontal well test is meant to be enough for permeability anisotropy determination. It is not the same situation for vertical wells where interference testing involves at least three active wells. However, in channel-type reservoirs when its width is known from estructural maps or seismic data, the advantage of having, first, radial flow regime which involves two directional permeability and then, linear flow regime related to permeability in one direction, the horizontal anisotropy can be also determined from a single well pressure test. In this study, a detailed analysis of pressure derivative behavior for a vertical well in areally anisotropic long and narrow reservoirs is presented for the case of constant rate production. For this case, the radial flow is distorted into an elliptical flow profile and its shape is determined by the maximum and minimum principle permeabilities. The elliptical nature of the system leads to the determination of a bi-dimensional permeability while the linear flow allows for the estimation of permeability in a single direction. The proposed interpretation method uses the concept of the TDS technique, which relies on characteristic points and straight lines corresponding to flow regimes found on the loglog plot of pressure and pressure derivative to caculate various reservoir parameters directlty, thus avoiding the use of type-curve matching or regression analysis.The technique was successfully verified by interpreting synthetic pressure tests for oil reservoirs.
Freddy Humberto Escobar , Djebbar Tiab and Lida Vanessa Tovar , 2007. Determination of Areal Anisotropy from a Single Vertical Pressure Test and Geological Data in Elongated Reservoirs . Journal of Engineering and Applied Sciences, 2: 1627-1639.