Capacitance–Resistance Model Application to Reservoirs Primarily Under Aquifer Influx

Abstract

Previous Capacitance – Resistance Models that have been developed to characterise black oil reservoirs undergoing waterflooding do not apply to waterflooding of reservoirs primarily under aquifer influxresulting in significant error. This paper has attempted to overcome this limitation by presenting the aquifer influx as a pseudo injector whose injection rate is represented by an existing aquifer model.

The influencing parameters of the model have been modified to include an aquifer influx factor. The equation was developed from the mass balance equation into a partial differential equation which included the reservoir connectivity parameters. The developed equation was solved based on assumption of linear variation in injection rate and bottom hole pressure as a single producer, n+1 injectors’ reservoir system. The Leung’s modified pseudo steady state aquifer model was incorporated as the aquifer influx factor into the final equation. A stand-alone software was developed for the computation and validation of the developed model. The model was validated by establishing the interwell connectivity over part of the historical data and then using the fitted model to predict the other part of the data.

Comparison of this study to the existing models indicated error margin decline towards the end of the production table where the aquifer influx rate is much lower indicating the importance of the addition of the aquifer influx factor.This model is accurate and proves to be a simple and useful tool in waterflood planning and monitoring and general reservoir characterisation.