Field-Related Mathematical Model to Predict and Reduce Reservoir Souring

Abstract

ABSTRACT A mathematical model for reservoir souring caused by growth of sulfate reducing bacteria (SRB) in the reservoir has been developed. The model is a 1D numerical transport model based on conservation equations and includes bacterial growth rates, the effect of nutrients, water mixing, transport and adsorption of H2S in the reservoir formation. Two basic concepts for microbial H2S production were tested using the model: H2S production in the mixing zone between formation water and injection water (mixing zone model), and H2S production due to SRB growth in a biofilm in the reservoir rock close to the injection well (biofilm model). In both cases H2S adsorption by reservoir rock was considered. Field data obtained from three oil producing wells on the Gullfaks field correlated with H2S production profiles obtained using the biofilm model, but could not be explained by the mixing model. The biofilm model implies that H2S production is correlated to the quality of the injection water, especially nitrogen (N) and phosphorous (P). The use of chemicals (containing N and P) in injection water treatment should therefore be reduced to a minimum.