Experimental Investigation of a Niger Delta Hydrocarbon Field for Reservoir Souring Tendency

Abstract

Reservoir souring which occurs due to an increase in hydrogen sulfide (H2S) concentration of a production well stream fluid undergoing water injection for example during secondary recovery, can significantly impact on the economic viability of a deep water project. Souring also raises technical concerns ranging from compromising safety compliance to damaging of infrastructure integrity due to corrosion attack. The activities of Sulfur Reducing Bacteria (SRB) present downhole act on sulfate in the injected water (sea water) to enhance the reproduction and generation of hydrogen sulfide which sours the reservoir. In this work, experimental study was carried out in an XYZ field in the Niger Delta, to evaluate the souring potential of the reservoirs undergoing water flooding. Field test kits were used to determine the temperature, pH and salinity of produced water samples; while colorimetric method was used in the laboratory to determine the sulfate concentration. The strength of stained tubes was used to determine the hydrogen sulfide concentration in the gas phase. The concentration of H2S in one of the wells was as high as 140ppm in the gaseous phase, the salinity concentration ranged between 16,435–24,479mg/l, the sulfate concentration ranged from 0-2200mg/l while the temperature ranged between 31.6°C-62.4°C. The results of the study show a favourable disposition for SRB to thrive and multiply. Also, the reservoirs within the field show different degrees of souring. The outcome of this analysis will be used for proffering cost effective and efficient remedial action.