Uncertainty analysis of well test data

Abstract

During a well test a transient pressure response is created by a temporary change in production rate. The well response is usually monitored during a relatively short period of time, depending upon the test objectives. Reservoir properties are determined from well test data via an inverse problem approach. Uncertainty is inherent in any nonlinear inverse problem. Unfortunately, well test interpretation suffers particularly from a variety of uncertainties that, when combined, reduce the confidence that can be associated with the estimated reservoir properties. The specific factors that have been analyzed in this work are: 1. Pressure noise (random noise) 2. Pressure drift (systematic variation) 3. Rate history effects Our work is based on the analysis of the effects of random pressure noise, the drift error, and the rate history on the estimation of typical reservoir parameters for two common reservoir models: A vertical well with a constant wellbore storage and skin in a homogeneous reservoir. A vertical well with a finite conductivity vertical fracture including wellbore effects in a homogeneous reservoir. This work represents a sensitivity study of the impact of pressure and rate uncertainty on parameter estimation and the confidence intervals associated with these results. In this work we statistically analyze the calculated reservoir parameters to quantify the impact of pressure and rate uncertainty on them.