Professional Analysis of Produced Water Reinjection Feasibility and Injectivity Decline Management in Mature Niger Delta Onshore Fields

Produced water reinjection has emerged as both an environmental management obligation and a pressure maintenance strategy in mature Niger Delta onshore fields, but sustained injectivity over multi-decade operations presents significant technical management challenges. This study professionally analyses the feasibility of produced water reinjection and develops injectivity decline management strategies for selected mature onshore Niger Delta fields operated by indigenous producers. Produced water volumes from four candidate fields were projected over ten years using decline curve analysis of water production trends, establishing daily injection volume requirements of 25,000 to 80,000 barrels per day by the forecast period end. Reservoir candidate screening for injection disposal evaluated formation permeability, depth, pore pressure capacity, and risk of hydrocarbon contact. The Hall plot analysis methodology was applied to historical injection well pressure and rate data to diagnose injectivity decline mechanisms: plugging by suspended solids accounted for 68 percent of observed injectivity decline events, with reservoir fluid incompatibility scale deposition responsible for the remainder. Filtration train design standards aligned with the modified Almond criterion for injection water quality are developed for each candidate field, specifying maximum suspended solids concentrations and maximum particle sizes for the target injection formation permeability. An economic comparison confirms that produced water reinjection is cost-competitive with surface disposal treatment alternatives at produced water volumes above 15,000 barrels per day. Keywords: produced water reinjection, injectivity decline, Niger Delta, mature fields, Hall plot.