Unlocking Oil Production Through Debottlenecking Water Facilities by Implementation of a Novel PWRI Solution

Abstract

Abstract An onshore oilfield producing more than 200 MBD from carbonate reservoirs has been facing production constraints, due to increasing water cut and produced water (PW) disposal limitations caused by surface flow line integrity issues. Traditionally, PW is disposed in water aquifers without treatment other than water settling tanks. Aquifer water is used for reservoir pressure maintenance. To reduce the water disposal volumes and hence debottleneck oil production, and to limit the intake of water from environmentally sensitive aquifers it was evaluated if PW could replace aquifer water for injection. A comprehensive laboratory study, with water analysis and core flooding demonstrated that PW alone, without treatment, is likely to cause significant formation damage. However, additional modeling indicated that PW reinjection (PWRI) was feasible if mixed with aquifer water without the need for further treatment. It was estimated that 35% PW could be mixed with 65% aquifer water for matrix injection in tight reservoirs (<10 md). The risk for inorganic scale formation due to water incompatibility and the risk for corrosion or pitting was assessed to be low. After a facility engineering study it was decided to expedite routing of PW to the injection water manifold via a temporary flexible line. A surveillance program was put in place to monitor the water quality and injection well performance. PW reinjection has been implemented without any recorded instances of increased injection pressure since the start. This ‘reversed engineering’ approach, in which critical oil-in-water (OIW) and total suspended solids (TSS) specifications were first established for different reservoirs, followed by modelling of mixing scenarios that meet these specifications, resulted in a successful PW/aquifer mixing pilot project. The increased produced water handling capacity has unlocked 3,000 t0 5,000 BOPD, resulted in further cost reductions by eliminating drilling of disposal wells and contributed to the overall goals of eliminating water intake from vulnerable aquifers.