Reservoir souring is an increase in hydrogen sulfide concentration during water injection operations. H2S content reduces the value of produced hydrocarbon, in addition to being a health and safety issue. Nitrate injection is an effective method to prevent the formation of H2S. This project includes the modeling and simulation of biological reactions associated with reservoir souring and nitrate injection for remediation. The model is implemented in GPAS.
There are proposed mechanisms that describe the effect of nitrate injection on souring in the reservoir. Depending on the circumstances, more than one mechanism may be involved. For each mechanism, we specify the biological species and chemical components and determine the role of each component in the biological reaction. For every biological reaction a set of ordinary differential equations are solved along with the mass conservation equations for the transport of chemical and biological species.
Biological reactions occur in the mixing zone developed between injection and formation water. Dispersion can have a significant effect on the development of the mixing zone in the reservoir. To study this effect, a dispersion term is implemented in the species mass balance equations. This term consists of molecular diffusion and mechanical dispersion. The biological model can predict the onset of souring and the effectiveness of nitrate injection in remediating the souring.