On the accuracy of dimensionless inflow performance relationships for gas wells

Usually four-point backpressure test, an isochronal test or a modified isochronal test is conducted to predict gas well deliverability. During past decades several simple dimensionless inflow performance relationships (IPRs) have been developed to eliminate the need for conducting multi-point test by using only data from a single drawdown or build-up test. The capability and accuracy of these models should be evaluated with measured field data using wide range of fluid and rock properties. This paper addresses the limitations, accuracy and optimal use of proposed dimensionless inflow performance correlations (Mishra and Caudle, 1984, Al-Attar and Al-Zuhair, 2009) based on back-pressure field test data of 53 wells that cover a broad range of AOF, reservoir pressure, well stabilized rate and pressure. The results show that both methods lose their accuracy at high rate and low drawdown conditions with unacceptable overprediction of AOFs. None of the studied models are recommended to use when dimensionless pressure (ratio of the well pressure to the reservoir pressure) is above 0.9. Advantages and ranges of optimal use of different models are discussed through error analysis.