Pressure transient analysis of reservoirs with a high permeability lens intersected by the Wellbore

This paper presents new insights of pressure response of reservoirs in which the well intersects a high permeability lens. The lens is of a limited lateral extent and is embedded within a reservoir matrix. Such situations are observed to result from depositional processes in a variety of geological environments (e.g., fluvial and turbidite) where textural variations lead to large contrasts in permeability. A published analytical multi-layered composite model is adopted to calculate the pressure response of reservoirs including the high permeability lens. Close examination of pressure derivative curves reveals the response is identical to that of the layered reservoir at early times. However, once the pressure disturbance reaches the edge of the lens, the response shows characteristic flow periods. The response shows similarities to that of the layered reservoir, radial composite reservoir, or horizontal hydraulically fractured reservoir according to the lens properties. Wellbore storage may mask the flow periods in the early time period causing difficulties in the analysis of welltest data. Dimensionless variables are deduced, and sensitivities to those variables are investigated, which facilitates pressure-pressure derivative curve matching. The method to calculate a well productivity is presented. A field case is analyzed for estimating various reservoir properties (e.g., the size of the lens). This example illustrates that the high permeability lens reduces total skin and provides "enhanced" well productivity. (C) 2000 Elsevier Science B.V. All rights reserved.