Identifiability of Estimates of Two-Phase Reservoir Properties in History Matching

Abstract

Since the number of parameters to be estimated in a reservoir history match is potentially quite large, it is important to determine which parameters can be estimated with reasonable accuracy from the available data. This aspect can be called determining the identifiability of the parameters. The identifiability of porosity and absolute and relative permeabilities on the basis of flow and pressure data in a two-phase (oil/water) reservoir is considered. The question posed is: How accurately can one expect to estimate spatially variable porosity and absolute permeability and relative permeabilities given typical production and pressure data? To gain insight into this question, analytical solutions for pressure and saturation in a one-dimensional (ID) waterflood are used. The following conclusions are obtained. 1. Only the average value of the porosity can be determined on the basis of water/oil flow measurements. 2. The permeability distribution can be determined from pressure drop data with an accuracy depending on the mobility ratio. 3. Exponents in a power function representation of the relative permeabilities can be determined from WOR data alone but not nearly so accurately as when pressure drop and flow data are used simultaneously.

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