IMPACT OF MICROBIAL IRON REDUCTION ON RESERVOIR SOURING DURING WATERFLOODING

Open Access
Author:
Alsaffar, Mohammed Ahmed
Graduate Program:
Petroleum and Mineral Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
August 30, 2017
Committee Members:
  • Russell T. Johns, Thesis Advisor
  • Li Li, Thesis Advisor
  • Turgay Ertekin, Committee Member
Keywords:
  • Reservoir Souring
  • SRB
  • FeRB
  • Iron Reduction
  • Sulfate Reduction
Abstract:
Water-injection is widely practiced in petroleum reservoirs to improve oil recovery, maintain reservoir pressure and re-inject produced water. This practice can lead to microbial reservoir souring, which generates hydrogen sulfide via sulfate-reducing bacteria. Hydrogen sulfide adversely impacts the health and safety of employees, reduces oil quality and thus demands more processing requirements, corrodes pipeline and facilities, and plugs permeable formations. Reservoir souring costs the industry millions of dollars annually. Laboratory experiments that have been made to study microbial souring mechanisms and growth, while published mathematical models simulate and forecast the souring process. In spite of the diverse microbial communities in oil reservoirs, current studies have been limited to selective microbes that mostly include sulfate-reducers and nitrate-reducers. One of the processes that has not yet been considered is microbial iron reduction. Current reservoir souring studies narrow the impact of iron minerals to the adsorption of hydrogen sulfide, namely through abiotic reactions to precipitate iron sulfides. Studies show that ferric iron can exist as iron oxides in natural systems within clay minerals and coating grains, a fraction of which would be bio-available for microbial reduction. In this research, we have utilized the published results of microbial experiments conducted in upflow porous reactors to comprehend microbial processes and growth parameters. We used CrunchFlow, a reactive transport model, to simulate those processes in seawater injection for 1D homogeneous media at various ferric iron concentrations, and 2D heterogeneous media where ferric iron distribution was correlated with permeability reduction. Random heterogeneous fields were generated using a Fast Fourier Transform simulator at differing correlation lengths and Dykstra- Parson coefficients. iii iv The analysis of microbial experiments by simulation indicate that microbial iron reduction inhibits sulfate reduction, imposing a delay on microbial souring by several pore volumes injected after seawater breakthrough. The results also show that higher concentrations of bio-available ferric iron would impose further delay on the microbial souring process in oil reservoirs. Formations with higher heterogeneity experience earlier hydrogen sulfide breakthrough than those that are more homogenous. In more heterogeneous reservoirs, the microbial reductions of sulfate and ferric iron are more isolated from one another than in homogenous reservoirs. Sulfate reduction prevails in permeable formations, while ferric iron reduction is limited to tight formations in which there are higher concentrations of iron minerals. Our research demonstrates the benefits of understanding potential microbial iron reduction and ferric iron bio-availability in oil fields. This knowledge will enhance the prediction and forecast regarding biogenic hydrogen sulfide breakthrough, leading to improvements in the field and further developments.