On the Modeling of Vertical Permeability Barriers in Single-Well Simulation Models

Abstract

Summary This paper presents stochastic descriptive schemes for explicit and implicit modeling of vertical permeability barriers in single-well simulation studies. The drainage volume of the well to be simulated is first partitioned into two regions: one explicit region ("explicit" because actual barriers—e.g., shales of various sizes—are placed within the grid) and one implicit region ("implicit" because the effects of the discontinuous shales are averaged into an effective vertical permeability). Second, the shales are converted into vertical transmissibility modifiers and included in the data-input stream, along with the effective vertical permeabilities calculated for the implicit regions. The methodology developed is illustrated by application to a North Sea reservoir with a thin oil column sandwiched between a gas cap and an active aquifer. In this reservoir, trustworthy predictions of oil, gas, and water production rates through time are of fundamental importance. In fact, the field-development decision may be swayed one way or another, depending on how long the gas and water production may be suppressed (aided by shales) for a reasonably high (and sustainable) oil-production rate.