Technology Update Improving oil production from mature fields is a significant challenge because of rising recovery costs and fluctuating crude oil prices. Although large investments are made in finding new reserves, typically more than 60% of discovered oil is left behind. Thus, the use of enhanced oil recovery (EOR) technologies is necessary to bring more of this oil into production. This article describes how the use of a biological EOR technique that applied produced water for reservoir flooding in a mature field led to rapid and substantial increases in oil production. Glori Energy’s Activated Environment for Recovery of Oil (AERO) technology is a biological EOR method in which customized nutrients are injected into the reservoir to activate native microbes. The ensuing microbial activity improves oil mobility and leads to increased production in waterflooded sandstone reservoirs. Use of the technology involves minimal capital spending and low operating costs, and applications can use existing field infrastructure. Reservoirs respond quickly to the use of the method, showing higher oil rates and increased oil cuts. Recovery is increased, and the economic life of the field is extended. Oil fields are screened in a two-step process that includes reservoir analysis and treatment design. Reservoir analysis involves geological assessment to determine key characteristics such as porosity, permeability, structural alignment, net pay, oil gravity, injector/producer continuity, and historical production response. The analysis allows for a quick review of multiple fields to select the one predicted to benefit most from biological EOR. Treatment design comprises biochemical testing and nutrient formulation. The process starts with the sampling of reservoir fluids under controlled conditions, using specialized equipment from pertinent locations such as injection, production, and source-water wells. Chemical analysis is begun immediately upon the sample’s arrival to determine the physicochemical characteristics of oil and water. Biological testing comprises assessing the viability of native microbial populations, developing a customized nutrient blend tailored to the field, and confirming the suitability of injection water for supporting microbial activity.
Enhanced oil recovery operations are less common offshore in comparison to their mature counterparts onshore. Large inter-well distances, facilities and weight constraints as well as capital expenditure limitations due to declining production greatly restrict choices for tertiary recovery strategies. Moreover, as oil cut continues to fall, maintaining economic production requires processing ever-increasing water volumes eventually requiring plugging and abandonment (P&A), even though typically 45 to 70% of the original oil remains in the formation. Ideally, the economic life of mature offshore facilities would be extended by incremental oil production at a reduced, per-barrel cost to lower the overall lifting expense. As fluid processing and pumping rates are usually already optimized at maximum rates, an ideal enhanced oil recovery method would, in addition to increasing the oil production, also improve the oil-to-water ratio and reduce the per-barrel operating expenditure, or OPEX. A biological enhanced oil recovery (EOR) solution initially deployed offshore in the North Sea has been validated with multiple onshore demonstrations and is now available for mature, offshore facilities to promote preferential oil flow in water-flooded sandstone reservoirs. The method makes use of the existing biology in the formation, which is activated from its dormant state by continuous addition of a low-dose (ca. 100 ppm) nutrient solution from a small footprint injection unit. The resulting biological growth reduces interfacial tension (IFT) and mobilizes otherwise trapped oil. This paper shows the rapid improvements of oil production and oil-water ratios over large injector- producer well distances in as little as 2-4 months following initiation of biological EOR. Recommendations are offered that are relevant for extracting otherwise trapped oil and recovering significantly more of the oil-in-place prior to P&A. Strategies are also offered for field-wide implementation to enhance oil recovery and reduce OPEX with minimal capital investment and equipment installation.
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