Summary Bulk-phase CO2 injection into saline aquifers can provide substantive reduction in CO2 emissions if the risk arising from aquifer pressurization is addressed adequately through mechanisms such as brine production out of the system (Anchliya 2009). While this approach addresses the risks associated with aquifer pressurization it does not address the problem of ensuring CO2 trapping as an immobile phase and its accumulation at the top of the aquifer. The performance of bulk-CO2-injection schemes highly depends on the seal-integrity assessment and presence of thief zones. The accumulated pocket of free CO2 can readily leak through a breach in the aquifer seal. Ideally, the aquifer should be monitored as long as the free CO2 is present, but if the CO2 is not immobilized, it is expected to remain underneath the seal rock for more than 1,000 years. Therefore, long-term monitoring of the seal integrity and avoiding leakage will be very costly. To minimize the free CO2 below the caprock, we propose an engineered system to reduce aquifer pressurization and accelerate CO2 dissolution and trapping. We achieve these objectives through effective placement of brine injection and production wells to facilitate the lateral movement (hence, residual and solubility trapping) of CO2 in the aquifer and impede its upward movement. The simulation results for example engineered well configurations in this paper suggest that substantial improvements in immobilizing CO2 can be achieved through increasing enhanced solubility and residual trapping that result from better CO2-injection sweep efficiency. This approach has the potential to greatly reduce the risk of CO2 leakage both during and after injection. The controlled injection of CO2 with this technique reduces the uncertainty about the long-term fate of the injected CO2, prevents CO2 from migrating toward potential outlets or sensitive areas, and increases the volume of CO2 that can be stored in a closed aquifer volume during the CO2-injection period. Field-scale compositional simulation cases are discussed, and sensitivity studies are used to provide guidelines for well spacing and flow rates depending on aquifer properties and the volume of CO2 to be stored. Although it requires additional drilled wells, the active engineered configuration proposed for CO2 injection significantly reduces the reservoir volume required to effectively sequester a given volume of CO2, and the increase in the cost caused by additional wells is recovered by dramatic reduction in monitoring cost.

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.

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