Online Water-Injection Optimization and Prevention of Reservoir Damage

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractWaterflood injection on the Shell Bonga field offshore Nigeria is accomplished via a network of subsea flowlines and 15 subsea injection wells. Maximizing water injection volume is an important economic objective for Bonga. Water injection is used for maintaining the reservoir pressure and thereby maximize oil production. The water injection flowrate to each well is limited by the fracture pressure of the overlying shale layer. Fracture of overlying shale could significantly reduce oil recovery from the damaged reservoir.Hence, it is important to accurately control the reservoir injection pressure such that volume of injected water is maximized without excessive risk of damaging the overlying shales. Since there are no downhole pressure gauges in the injection wells, the downhole injection pressure must be estimated from other measured variables.For this, we developed a novel technology, WRIPS (Waterflood Reservoir Injection Pressure System). The WRIPS algorithm is used to:Estimate downhole injection pressure based on the model and available measurements Estimate injection pressure uncertainty as a function of available measurements Calculate an injection pressure target as a function of system conditions Calculate injection rates for wells where the venturi has failed Data reconciliation: calculate the most probable pressures and flowrates based on model, measurements, and sensor accuracies Set conditioned alarm flagsThe paper gives a brief description and the experience gained with WRIPS applied to water injection wells. The main contribution from the paper is to demonstrate the benefits with such a system and that the WRIPS is an attractive solution compared to expensive downhole pressure gauges.