Evaluation of Injection Water Quality Requirements and Reservoir Souring Risk at the Qua Iboe Field Water Injection Scheme, Akwa Ibom State

Water injection is the primary pressure maintenance mechanism in the Qua Iboe Field, Akwa Ibom State, South South Nigeria, and the quality of injection water has direct implications for both injectivity maintenance and reservoir souring through bacterial sulphate reduction. This study evaluates injection water quality requirements and assesses the reservoir souring risk associated with the current water injection scheme at the Qua Iboe Field. Injection water samples from the seawater filtration plant and formation water samples from three producing wells were characterised for total suspended solids, dissolved oxygen, iron content, sulphate concentration, and bacterial activity using adenosine triphosphate bioluminescence assays. Membrane filter plugging indices were measured to assess particulate loading relative to formation permeability. Thermodynamic compatibility modelling of injection seawater with formation water indicates a high scaling tendency for barium sulphate due to the elevated barium content of the formation water. Reservoir souring risk is assessed using the Voordouw-type Monod kinetic model to predict hydrogen sulphide generation rates as a function of sulphate availability, temperature, and in situ bacterial populations. Results indicate that the current sulphate concentration of 2,400 milligrams per litre in injected seawater, combined with active sulphate-reducing bacteria populations detected in produced water, creates a measurable souring risk in the swept zones of the reservoir. Recommendations for sulphate removal desulphation plant installation are provided. Keywords: injection water quality, reservoir souring, water injection, Qua Iboe Field, Akwa Ibom State.