Reservoir Souring Modelling, Prediction and Mitigation

The prediction of reservoir souring due to the activity of sulphate-reducing bacteria (SRB) during water injection is an important consideration in material selection for wells and production facilities. A number of reservoir souring models have been developed in the past 16 years or so, with the objective of predicting the timing and magnitude of H₂S production. The results of the reservoir souring models are dependent on a number of reservoir geometry, geochemical, microbiological and reservoir geology parameters. For example, the SRB activity is dependent on the availability of essential nutrients such as sulphate and dissolved hydrocarbons in the injection and formation waters. Environmental parameters such as temperature and pressure control in which parts of the reservoir SRB can be active. Water flow path and extent of water breakthrough has a major impact on H₂S production. Very low reservoir permeabilities will restrict the movement of SRB into the rock matrix and certain minerals have the ability to scavenge H₂S within the reservoir. All of these parameters must be accounted for in a reservoir souring simulation, and this requires the cooperation of reservoir engineers, geologists, production chemists and facilities engineers. Several techniques have been employed in the oil industry to try to control the generation of H₂S within the reservoir. These include the application of biocides to control SRB activity, the injection of nitrate to stimulate other bacterial populations to out compete SRB for available food sources and the use of sulphate removal technologies to minimize sulphide production.