New Nitrate-Based Treatments—A Novel Approach To Control Hydrogen Sulfide in Reservoir and to Increase Oil Recovery

Abstract

Biogenic formation of hydrogen sulfide has, and will, occur in most oil and gas reservoirs - particularly those flooded with sea water. Hydrogen sulfide causes high costs and serious operational problems, including reservoir souring, sulfide corrosion, iron sulfide plugging, reduced product value, and health and environmental hazards. Historically, the sulfide problem has been treated with toxic biocides, which have proven to be costly and mostly ineffective. The petroleum industry is now implementing a nitrate-based microbial treatment technology for both the prevention and removal of sulfide from reservoirs, produced water, surface facilities, pipelines and gas storage reservoirs, as well as increasing oil recovery. This innovative reservoir treatment technology recognizes that detrimental sulfate reducing bacteria (SRB), which produce sulfide, can be replaced by a naturally occurring suite of beneficial microorganisms enhanced by the introduction of an inorganic nitrate-based formulation. This designed manipulation of the reservoir ecology has been termed Bio-competitive Exclusion (BCX) technology. The Bio-Competitive Exclusion (BCX) biological process has also demonstrated significant application in the field of tertiary oil recovery. This is possible through the use of nitrate-based formulae as alternate electron acceptors and microbial nutrient. This nitrate based formulation is environment friendly and complement the naturally occurring volatile fatty acids (VFA) in the reservoir, selectively stimulating and increasing the targeted Nitrate-Reducing Bacteria (NRB). This paper discusses novel action and advantages of BCX Technology for effective sulfide suppression when compared to previous biocide treatments. It also brings into light the two main approaches to solving the sulfide problem: proactive and reactive. Several examples of the BCX technology to treat sulfide problems are illustrated These results are reinforced by reports that both proactive and reactive nitrate treatment projects are now operational at several North Sea platforms, Such reported successes have resulted in the nitrate technology being applied to other North Sea fields including Norne, Statfjord, Valhall. The BCX technology offers a cost effective technique of sulfide removal and increased oil recovery. Introduction Need for BCX - Reservoirs that produce hydrogen sulfide (H2S) and iron sulfide (FeS) can cause significant production problems and safety hazards for producers. Hydrogen sulfide gas even in relatively small concentrations can be deadly when encountered unexpectedly in the field. It can also cause rapid corrosion of downhole and surface equipment. Iron sulfide scale often causes restricted production by plugging flow paths in the reservoir, perforations, pump intakes, and tubulars. This problem may be especially acute in reservoirs flooded with water containing significant sulfates. The influx of sulfate can stimulate indigenous sulfate reducing bacteria (SRB), which metabolize the sulfate into hydrogen sulfide gas. The hydrogen sulfide then reacts with metallic compounds such as iron to form iron sulfide, which appears as a black scale. These bacteria are commonly found and are active in aqueous systems throughout the world.[1] Detrimental effects of SRB could be summarized as follows-Souring of oil and gas reservoirs and wells.Souring of surface vessels of many types.Reservoir and well plugging those results in reduced production.Corrosion and scaling of metals.Serious hazard to personnel and the environment.Cost of replacing the equipment and cost involved in conventional biocide treatment for preventing sulfide production.

Assessment of the Biogenic Souring in Oil Reservoirs Under Secondary and Tertiary Oil Recovery

“…Biogenic souring is commonly inhibited by adding biocides to surface water loops or injection fluids. However, these are often environmentally questionable and associated with excessive costs versus a limited efficiency [3,34]. Furthermore, their usage is heavily regulated.…”

“…Independent from its source, production of H2S is always an unwelcome issue in the oil and gas industry as the compound is extremely toxic, flammable, and corrosive. Damage to reservoir and associated surface facilities caused by biogenic souring remains one of the largest techno-economic risks in all water/chemical injection oil recovery operations, estimated to cause over $100 billion in annual economic damage [2][3][4]. A number of studies from a wide range of disciplines have been published to investigate various aspects of its generation, transport in porous media, rock and fluid interaction, mitigation, and production-corrosion characteristics.…”

“…Several books and publications describe the microbial aspects of souring [7][8][9][10][11] and well-established expertise is existing on the issue, including methods of comprehensive analyses of key parameters. The efforts on the modelling and mitigation in the reservoir as well as in production systems are also subject of various publications [3,[12][13][14][15][16]. Based on the theoretical, laboratory, and field results, for example, the use of nitrate to mitigate the reservoir souring has been proposed [8,[17][18][19][20].…”

Assessment of the Biogenic Souring in Oil Reservoirs under Secondary and Tertiary Oil Recovery

“…Independent from its source, production of H2S is always an unwelcome issue in the oil and gas industry as the compound is extremely toxic, flammable, and corrosive. Damage to reservoir and associated surface facilities caused by biogenic souring remains one of the largest techno-economic risks in all water/chemical injection oil recovery operations, estimated to cause over USD 100 billion in annual economic damage [2][3][4]. A number of studies from a wide range of disciplines have been published to investigate various aspects of its generation, transport in porous media, rock and fluid interaction, mitigation, and production-corrosion characteristics.…”

Water Compatibility Study: Detecting Souring Potential

“…Reservoir souring has also been reported in the Bonga field of the Gulf of Guinea where reservoir temperatures are around 63 o C and TDS is well below the maximum limit of 15 to 20% [9]. Methods of militating against reservoir souring have been discussed [10,11]. The Mechanisms of controlling reservoir souring using nitrate and biocide have been studied and simulated [12].…”