Diversity and abundance of Sulfate-reducing bacteria in oil fields of India

Oil exploration is the major activity energizing human needs; however, it confronts operational hindrance and economic run-offs. These hindrances arise due to extreme conditions such as deep dwelling sites, high salinity and high temperature, high pressure and anoxic conditions. The oil recovery processes is divided in three classical steps. First step is Primary recovery; the initial reservoir pressure is often high enough that when well is opened, the oil and gas in the reservoir flows freely to the surface. During production, pressure in the reservoir drops progressively which negatively influence production level. This make primary recovery no more feasible and only about 10% of the oil initially in place at the field can be produced by this method. The next step of recovery is secondary recovery; where injection of water is carried out with the objectives to maintain pressure and to push oil towards producing wells. Water can be injected into the aquifer through injection well. This phenomenon is known as water flooding; creates a zone of fluid around the injection well. With subsequent injections, these zones extend until oil production restarts at the producer well. The third step to improve oil recovery is by more sophisticated technologies. Enhanced oil recovery (EOR) composed of four methods: thermal, chemical, miscible and microbial. Water injection is very useful technique in secondary oil recovery process and up to 60% of the oil initially in place in the field can be recovered. The water injection leads to detrimental effects of reservoir souring. Oil industries faces problem of reservoir souring during the production life time of a field. Reservoir souring is characterized by an increasing concentration of the hydrogen sulfide (H₂S) in production gas, typically after the initiation of secondary recovery by water injection and some time the breakthrough of injected water at the producing wells. Reservoir souring is an example of a process that is initiated at the microbiological level, yet exerts an effect over an entire reservoir and its produced fluids. It is now widely accepted that the reduction of sulfate by SRB is the most significant mechanism of oil reservoir souring as a result of water flooding (Ligthelm et al., 1991; Sunde et al., 1993). The harmful effect of reservoir souring are localized pitting corrosion, cracking of susceptible steels (pipes and external units) and hydrogen sulfide is toxic to life (Bob Eden et al., 1993). Decreased oil production and underground crude oil leakage add to more economical loss and environmental hazards.;Biocorrosion negatively impacts the integrity, safety and reliability of the pipes in oil and gas industry throughout the world. Studies estimate that corrosion caused due to various mechanism in recovery wells cost U.S. companies ;The overall economic impact of the reservoir souring by microbial activity can be significant, yet there are few technologies aimed at preventing the initiation of reservoir souring, and these have shown limited success. The two important factors affect the treatment process are the species and quantity of sulfidogenic bacteria present. Higher the quantity of sulfidogenic bacteria, higher the amount of sulfide produced.;The overall aim of this study was to know the diversity and abundance of SRB in various oil fields. The first objective of this research was assessment and documentation of diversity of sulfidogenic bacteria in five different oil fields of India from geographically distinct locations. Both culturable and total diversity of SRB was investigated using various microbiological and molecular tools. SRB diversity and accurate quantification is very important to determine treatment type and biocide to be dosed in external facilities. The second part of this study, therefore, was to develop a quick and reliable method to detect and quantify SRB. A real time quantitative PCR assay using dsr gene beta subunit (dsrB) was developed towards this aim. Further, investigations were done to check the efficacy of the biocide against the production water enriched cultures employing dsr gene based real-time quantitative PCR. (Abstract shortened by UMI.).