Acidithobacillus ferrooxidans (A. ferrooxidans) is a gram-negative, acidophilic and chemolithotropic bacterium that utilizes oxidation of ferrous ions, hydrogen and reduced inorganic sulfur compounds, such as H2S, as sources of energy. Sulfur oxidation in A. ferroxidans is catalyzed by the Sulfide Quinone Reductase (SQR) enzyme system. The initial step of the SQR reaction is the oxidation of sulfide to elemental sulfur or to the less-toxic polysulfide. SQR can eliminate the accumulation and persistence of H2S in waters and reservoirs contaminated with sulfur-reducing bacteria (SRB). H2S causes reservoir souring, corrosion problems, and presents a danger to oilfield personnel because of its inherent toxicity. SQR does not destroy the SRBs present in the system, but it does catalytically attack the H2S and H2S precursors produced by SRBs. As an enzyme, SQR is an environmentally compliant, sustainable, and catalytic solution to the growing H2S problem. The Sulfide Quinone Reductase enzyme (Bio-molecular scavenger-BMS) was evaluated for its efficacy as an H2S mitigation strategy. The evaluation showed that the BMS could convert H2S from different sources in liquid and gaseous phases in to nontoxic polysulfide. The studies also showed that the BMS-based H2S mitigation reactions did not cause corrosion, and the formulations are compatible with oilfield metals, plastics and elastomers.

The oil and gas industry uses chemicals like acids and oxidizers as polymer breakers in hydraulic fracturing and triazene and glyoxal for H2S mitigation. In addition to serving the intended purpose, the chemicals cause secondary effects like non-specific oxidation, acid corrosion, precipitation and danger to oil field personal. We present novel, environmentally preferable chemistries to address various issues in the oil and gas industry. The studies using -Mannanase HT enzyme as polymer breaker showed breaking of cross-linked guar polymers at elevated pH (7-12) and temperature ( 175°F) ranges. Chlorophyll-treated cross-linked fluids showed more than 90% viscosity reduction. The chlorophyll worked efficiently up to 250°F, but the optimum temperatures are at 175 to 200°F. The chlorophyll treatment also showed a reduction of molecular weights of a linear polymer from 1,472,000 to 6,000. Further, H2S mitigation was addressed using a novel recombinant Sulfide Quinone Reductase enzyme (SQR). Functional studies conducted by treatment of soured brine and oil revealed 72% and 90% reduction in H2S concentration, respectively. The scavenger showed 75% reduction of sulfide in simulated mixed production samples containing a 30:70 ratio of brine to oil. Field testing of SQR showed a reduction of headspace sulfide from 400 ppm to 2 ppm and BS&W values less than 0.5%. These studies confirm that this novel biotechnology based environmentally preferable tools can be successfully used to break polymers and mitigate H2S in various systems. Further, the biotechnology solutions have several advantages such as meeting environmental regulations, reducing, or eliminating secondary effects and health hazards that are associated with current chemical treatments.

The objective of this study was to develop and apply a non-chemical based environmentally preferable hydrogen sulfide scavenger that addresses secondary issues caused by current chemical scavengers like triazine and glyoxal and to confirm its ability to mitigate sulfide in different applications. Recombinant DNA and protein expression technologies were exploited to develop this novel H2S scavenger. This non-chemical scavenger (NCS) is generated by cloning the cDNA sequence from a thermophilic organism and expression of the encoded protein in suitable vector. Non-chemical based formulation was developed and blended in a pilot plant. The efficacy of the scavenger was evaluated in sour brine, crude oil and mixed production fluids from different sources. Sulfide concentrations before and after reactions in headspace were measured by using Dräger gas detection tubes (ASTM D5705). Corrosion testing was performed using kettle tests. Field assessment of the scavenger was carried out by treating sour oil at the Bakken oil field as per the field testing plan. In this study, H2S mitigation was addressed using a novel non-chemical scavenger generated from thermophilic bacteria from lab scale to pilot scale. Functional studies conducted by treatment of soured brine and oil revealed 72% and 90% reduction in H2S concentration respectively. The scavenger showed a 75% reduction of sulfide in simulated mixed production samples containing 30:70 ratio of brine and oil. Limited testing of this scavenger in field showed reduction of headspace sulfide from 400 ppm to 2 ppm. In addition, the field data showed less than 0.5% BS&W. The scavenger also showed no significant increase in corrosion during the scavenging reaction. These studies confirm that this novel non-chemical scavenger can be successfully used to mitigate H2S in various systems without causing adverse effects that were seen with chemical scavengers. A non-chemical scavenger has several advantages such as meeting environmental regulations, reducing, or eliminating secondary effects like solids formation, corrosion, scaling, and health hazards that are associated with current chemical scavengers.