Mathematical Geology, Vol. 34, No. 6, August 2002 ( C  2002) Evaluation of the Reduction in Uncertainty Obtained by Conditioning a 3D Stochastic Channel to Multiwell Pressure Data 1 Fengjun Zhang, 2 Albert C. Reynolds, 2 and Dean S. Oliver 2 A stochastic channel embedded in a background facies is conditioned to data observed at wells. The background facies is a fixed rectangular box. The model parameters consist of geometric parameters that describe the shape, size, and location of the channel, and permeability and porosity in the channel and nonchannel facies. We extend methodology previously developed to condition a stochastic channel to well-test pressure data, and well observations of the channel thickness and the depth of the top of the channel. The main objective of this work is to characterize the reduction in uncertainty in channel model parameters and predicted reservoir performance that can be achieved by conditioning to well- test pressure data at one or more wells. Multiple conditional realizations of the geometric parameters and rock properties are generated to evaluate the uncertainty in model parameters. The ensemble of predictions of reservoir performance generated from the suite of realizations provides a Monte Carlo estimate of the uncertainty in future performance predictions. In addition, we provide some insight on how prior variances, data measurement errors, and sensitivity coefficients interact to determine the reduction in model parameters obtained by conditioning to pressure data and examine the value of active and observation well data in resolving model parameters. KEY WORDS: conditional simulation, stochastic channel, uncertainty evaluation, pressure transient analysis. INTRODUCTION The problem of conditioning a channel to well-test pressure data has been con- sidered previously by Rahon, Edoa, and Masmoudi (1997), Landa and Horne (1997), and Bi, Oliver, and Reynolds (2000). Landa and Horne, considered only two-dimensional channels of constant width, represented channel boundaries with simple trigonometric functions and assumed that channel width is constant. Chan- nel and nonchannel permeability were assumed to be unknown, but porosity was assumed to be a known function of permeability. They applied various optimization 1 Received 26 December 2000; accepted 28 October 2001. 2 Petroleum Engineering Department, University of Tulsa, 600 South College Avenue, Tulsa, Oklahoma 74104; e-mail: reynolds@utulsa.edu 715 0882-8121/02/0800-0715/1 C  2002 International Association for Mathematical Geology