Reservoir Simulation of Sulfate-Reducing Bacteria Activity in the Deep Sub-Surface

Abstract

Reservoir Simulation of Sulfate-Reducing Bacteria Activity in the Deep Sub-Surface

Accurate predictions of reservoir souring due to sulfate-reducing bacteria (SRB) are essential for multi-million dollar decisions on oilfield development and materials selection. Laboratory experiments have been conducted to investigate the effects of pressure, salinity, pH, temperature and nutrient availability on various environmental isolates of oilfield SRB. In laboratory tests, high pressure, high salinity, high temperature and extreme pH all inhibited growth and H2S generation. The data on growth rates and nutrient consumption at various environmental conditions has been incorporated into reservoir souring models. The availability of sulfate and nutrients can also limit the growth of SRB biomass and the generation of H2S. A 2D souring model has been developed and used in excess of 30 reservoir cases. Within this model, SRB activity occurs in reservoir regions with favourable environmental conditions and H2S is then partitioned between and transported with the reservoir fluids. The 2D model has been used in the simulation of reservoir souring due to seawater injection in the Alba Field, North Sea. Analysis of Alba field and laboratory data indicates that souring predominantly occurs deep within the reservoir in the mixing zone between seawater and formation water. A 3D model is currently being developed that is run in a loosely coupled manner with reservoir simulators. The loose coupling means that there is only a one-way flow of reservoir data (pressures, saturations, etc.) from the reservoir simulation to the souring model. The 3D model is being validated against field data, with a comparison of historical and predicted H2S breakthrough and mass flow rates from production wells. This tool will help operators trying to predict subsurface microbial activity on a large scale.