Scott Christopher Jackson

Characterizing microbial diversity in production water from an Alaskan mesothermic petroleum reservoir with two independent molecular methods

The phylogenetic diversity of Bacteria and Archaea within a biodegraded, mesothermic petroleum reservoir in the Schrader Bluff Formation of Alaska was examined by two culture-independent methods based on fosmid and small-subunit rRNA gene PCR clone libraries. Despite the exclusion of certain groups by each method, there was overall no significant qualitative difference in the diversity of phylotypes recovered by the two methods. The resident Bacteria belonged to at least 14 phylum-level lineages, including the polyphyletic Firmicutes, which accounted for 36.2% of all small-subunit rRNA gene-containing (SSU(+)) fosmid clones identified. Members of uncultured divisions were also numerous and made up 35.2% of the SSU(+) fosmid clones. Clones from domain Archaea accounted for about half of all SSU(+) fosmids, suggesting that their cell numbers were comparable to those of the Bacteria in this microbial community. In contrast to the Bacteria, however, nearly all archaeal clones recovered by both methods were related to methanogens, especially acetoclastic methanogens, while the plurality of bacterial fosmid clones was affiliated with Synergistes-like acetogenic Firmicutes that possibly degrade longer-chain carboxylic acid components in the crude oil to acetate. These data suggest that acetate may be a key intermediary metabolite in this subsurface anaerobic food chain, which leads to methane production as the primary terminal electron sink.

Microbial EOR -- Critical Aspects Learned From The Lab

DuPont and BP have been working together to develop Microbial EOR targeted at viscous oil in the Schrader Bluff formation on the North Slope of Alaska. The goal of this program was a 5% increase in the recovery factor. Mechanisms to be assessed in the original agreement included 1. Viscosity reduction of the oil by transformation or degradation of heavy components in the oil – thus improving the oil water mobility ratio. 2. Drastic reduction (to ~<0.01 dynes/cm) in the interfacial tension between water and the oil After extensive fundamental research we have learned many critical aspects of microbial EOR that made the application of these two mechanisms to the Schrader Bluff formation impractical. Instead, we have demonstrated two site appropriate mechanisms that achieved, in the lab, the targeted increase in the recovery factor. 1. Improved flow conformance and increased sweep efficiency by preferential plugging of high permeable zones thereby forcing water to produce oil from previously unswept parts of the reservoir. 2. Reduced oil / rock surface tension and a subsequent reduction in the oil “wetting” the rock. This results in changes in the relative permeability of the oil and the water and ultimately lower residual oil saturation. This paper describes the key laboratory tests used to evaluate these four mechanisms. The cornerstones of our work have been the detailed characterization of the waters, the oil, the formation matrix and the microbial community. In addition we describe our search for useful microbes isolated from a variety of environmental samples collected from the Milne Point Unit (MPU) of the Alaskan North Slope. These samples were taken over several years and included injection, production and power fluid waters. These samples were used to understand the temporal changes in the microbial populations and to provide inoculum for our enrichment cultures. Our ongoing research has provided many insights into the appropriate application of microbial EOR. The unique aspects of each production area, the nature of the oil, the water, the formation matrix, and the background microbial population and their complex interactions must all be assessed when considering the potential application of microbial EOR. The amount of work discribed below for assessing potential MEOR mechanisms is extensive. However, this process has been streamlined and we have been able to assess new target reservoirs for potential MEOR treatments in about 6 months.

Considerations for Field Implementation of Microbial Enhanced Oil Recovery

For the last 6 years DuPont with different partners has done extensive fundamental research into the application of Microbial Enhanced Oil Recovery technology (MEOR). We have demonstrated two mechanisms that have shown in the lab, more than a 10% increase in the recovery factor. 1. Increased sweep efficiency by plugging of high permeable zones thereby forcing water to produce oil from previously unswept parts of the reservoir. 2. Reduced oil / rock surface tension resulting in lower residual oil saturation. This paper describes the key laboratory tests and preliminary field data used to evaluate these two mechanisms. Our approach has been to inoculate the reservoir with a microbe that under the optimal nutrient conditions will expressed the needed function -- bioplugging or reduced oil saturation. The microbe and the nutrients are tailored to the conditions of each reservoir thus giving MEOR the greatest chance for success. This paper presents challenges that were raised as a result of extensive lab work that are relevant to the implementation of MEOR on a field level. Our ongoing research has provided many insights into the appropriate application of microbial EOR. The unique

Increased Oil Recovery by Permeability Modification in High Perm Contrast Slim Tubes

Biofilm and biopolymers produced from microbes have been shown to reduce the permeability of high perm streaks which can result in improved sweep efficiency. The rate of permeability modification is very reproducible but can vary depending on the specific treatments used. Our approach has been to inoculate the reservoir with a microbe that under the optimal nutrient conditions will express a biopolymer as a film, reduce the size of pore throats and reduce the apparent permeability. The microbe and the nutrients are tailored to the conditions of each reservoir thus giving MEOR the greatest chance for success. In this paper we describe the use of a high permeability contrast composite slim tube to demonstrate increased oil recovery using microbes that generate biofilms to reduce the permeability contrast and thus improve sweep efficiency. In this setup, three hydraulically constrained slim tubes ‐ working as very long sand packs ‐ were constructed from different sources of sand with a range of particle size distributions. Absolute and differential pressure transducers were used to monitor the pressure drop across individual slim tubes and across the composite configuration of the three slim tubes. Oil traps were located at the exit of each slim tube to measure the oil production from each tube. The permeabilities of the slim tubes against a high salt injection brine (TDS ~ 85,000 ppm) were measured to be 45, 4.5 and 2.6 Darcy. This presented a challenging system with a slim tube at a very high permeability that would need to be reduced by the MEOR treatment. Oil (viscosity of ~58 cp) was pumped independently into each slim tube to assure that each slim tube was at residual water saturation. The slim tubes were allowed to age before the start of the test. Once working in composite mode the flows of the injected brine and MEOR treatments were dictated only by the hydraulics of the composite slim tube. The produced fluids from all three slim tubes were sent to a single back pressure regulator. In the composite mode, oil was readily produced only from the high permeability slim tube during the initial (non-MEOR) flooding sequence. A salt tolerant microbe present in the target oil reservoir capable of producing biofilms and altering the permeability was inoculated into the composite slim tube. The inoculated microbes were batch fed periodically using a protocol that was scaled down from one that would be used in a field test. An increase in the pressure drop and corresponding increase in oil production from the lower permeable slim tubes was observed as a result of the treatment. This resulted in a dramatic increase in the recovery factor from the composite slim tube. This work is a continuation of tests described in earlier papers (SPE129657, SPE146483 and SPE159128 ‐ references 4, 5 and 6).