Natural influx of water in oil reservoirs surrounded by water bearing rocks (aquifers) play a very important role in increasing oil recovery. Such reservoirs are referred as water drive reservoirs. The pressure drop in reservoir caused by production of hydrocarbons prompts the influx of water from surrounding aquifer to offset it. This pushes more hydrocarbons towards the surface thus enhancing the oil recovery.
Correct prediction of amount of water influx is very important to find the recovery factor associated with a reservoir. Various models like Schilthius, Van Everdingen & hurt and Fetkowich have been proposed for water influx calculation. In this study attempts are made for using these models for calculating the water influx for a sample reservoir from Niger delta using the pressure history data. A MATLAB program is developed for this purpose. The effectiveness of each model is studied in explaining the behavior of given reservoir. The water influx calculated is used in material balance analysis to characterize the aquifer and find the value of initial oil in place (OOIP).
The water influx values obtained from VEH model and Fetkowich model are similar, with the only advantage of Fetkowich model being that it is computationally easier. The Schilthius model gives incorrect value of water influx for our case as the amount water influx given by Schilthius model does not give straight line when used in material balance analyses. The values of cumulative water influx obtained from VEH and Fetkowich model are in accordance with the year wise oil production data. Both year wise water influx and oil production reaches peak at around 4 years. This shows that the VEH & Fetkowich models are valid.
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