Research On Chemicals Assistant Bacteria Treatment For Hydrogen Sulfide In Oil Reservoir

Hydrogen sulfide is an important reason for corrosion production environment in oilfield. It also may increase the cost but reduce the quality of downstream productions. The treatment of hydrogen sulfide plays an important role in guarantees for personal live and production safety.In this paper, we will focus on the complete removal of hydrogen sulfide. The mechanism is to inject nutrients into reservoir in order to activate and promote the growth of nitrate reducing bacteria(NRB), then to gradually eliminate native sulfate reducing bacteria(SRB) which can produce hydrogen sulfide in reservoir by the principle of biological competition. Thus the growth of sulfide sulfate can be effectively controlled at its source. In the laboratory, we have taken experiments on the nutrients injected into reservoir to choose the most appropriate microbial promoter. The experiment included the following contents:(1) The physical and chemical analysis as well as bacterial culture test were carried out on the oilfield produced fluid. It showed that there were native NRB in reservoir. According to the results of the bottle test, appropriate promoters for NRB and inhibitors for SRB were selected for the next step bottle tests.(2) Two kinds of agents produced by different companies were collected and tested. According to the results of the bottle test, the best promoter for NRB and inhibitors for SRB were chosen. It indicated that it was best to use 300mg/L promoter for NRB with 500mg/L inhibitors.After bottle tests, productive tests in Cnooc Bohai branch of Chengbei oil field were carried out. Tests for the concentration of hydrogen sulfide gas concentration and microbial detection in each well and key production equipment were conducted to verify productive tests' results. Productive tests' results revealed:(1) In Chengbei, each single well in A/B oilfield has significantly reduced before governance and the average rate of reduction is above 80%. The content of hydrogen sulfide in main production equipments has also greatly reduced and the average rate of reduction is over 90%. The results confirm the removal of hydrogen sulfide is effective.(2) In A/B oilfield in Chengbei, the number of hydrogen sulfate in the single well and the main production equipments is reduced, which proves that the hydrogen sulfide problem has been solved at its source.(3) Through the analysis of the water samples from the wellhead and the system and monitoring for the thickness of pipe wall, it proves that corrosion of the main production equipments and pipeline has been controlled with the reduction of hydrogen sulfide.(4) The productive experiment results has proved the method is workable. And the above method has been spread in the Bohai oilfields.