Microbial hydrogen sulfide (H2S) production is a complication in the oil and gas industry. Production of H2S by bacteria within oil reservoir is detrimental to both injection and production. This study determines the root cause of the problem with a scientific approach to control H2S content – in a mature field in Gulf of Suez (GOS) – by applying different methods of chemical treatments in injectors, subsequently leading to production of fluids and gases with sustaining lower H2S content. The field depends on injection of sulfate-rich seawater into hydrocarbon containing reservoirs for pressure maintenance for 50 years. H2S content in the reservoir was relatively low before proceeding the water-flooding project. Initially, microbiological induced corrosion in oil production and water injection pipping were detected, then a strategy for monitoring the process of microbial production of H2S and its build-up within a reservoir and mitigation of induced scale by bacterial action was created. Finally, chemical injection approaches were implemented to reduce sulfate reducing bacteria (SRB) activity in the reservoir and to control / decrease H2S content in production fluids and gases.
Sharp increase in H2S content in production fluids and gases parallel with a decline in injection rate of water injection wells were the first signs of microbiological bacterial activity in piping and reservoir. In situ injection of biocide in production wells followed by soaking for 24 hours failed to decrease H2S content in production fluids. Continuous injection of oxygen scavenger with water stream in injection wells was the second trial that succeeded in decreasing H2S content in production wells, but only for short time, and then it increased yet again. This trial was the highest cost with low to moderate results. Last trial was to inject biocide with water stream in injection wells for three months, followed by H2S content observation in production wells. Chemical lab tests showed dramatic reduction of H2S content by 30 to 40% in some production wells in addition to tremendous improvement in injection rate of the injectors.
The case signifies the importance of root cause analysis and engineering problem solving techniques in finding a solution to reduce microbial hydrogen sulfide content caused by SRB action. Reduction of H2S allows opening of many shut-in producers that were producing high H2S content fluids and resulted in severe corrosion in addition to health, safety and environment (HSE) issues, particularly when assets were not designed to be operated in souring conditions.