Jerry Lee takes a look at some of the research surrounding microbial enhanced oil recovery (MEOR), and how it could be a viable solution for increasing recovery efforts.
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A Glori scientist observes microbial growth and behavior at the company’s Houston laboratory. Photos from Glori Energy. |
Exploration and new field development can require a considerable amount of CAPEX before the first drop of oil is ever produced. Mature or aging fields, however, have proven oil that is already producing. Thus in this oil economy, it may be more cost effective to turn to these fields and seek methods of increasing recovery and profitability. Enhanced oil recovery (EOR) techniques have been developed for this purpose, to decrease the amount of residual oil in a reservoir.
Microbial enhanced oil recovery (MEOR) is a type of EOR that has been refined over the decades, and with an incremental cost around US$10/bbl, it is cost effective and can be seen as a viable solution for today’s oil economy.
“Low CAPEX and low OPEX means low risk for oil producers, so it’s a very attractive technology. In current oil times it may be the only economic alternative, so without a lot of overhead it’s going to be the competition in EOR now,” says Mike Pavia, CTO of Glori Energy.
MEOR is the process whereby microbes in a reservoir can affect the production in the producer wells by producing gas, acids, surfactant, and change water flow patterns. In the past, efforts have been made to introduce non-indigenous microbes into the reservoir, or feeding the microbes with an external carbon source like molasses. These methods, however, did not take hold. Though from those experiments, current technology has improved to focus on the factors that worked in those experiments and avoiding those that did not.
The focus of contemporary technology is now centered on two factors: bio-surfactants, and induced bio-plugging. The idea behind these two factors are simple; bio-surfactants will allow oil to become more mobile, while bio-plugging facilitates greater access to oil by encouraging the flow path to deviate to underutilized or isolated pathways.
Glori Energy and DuPont are two companies that put these ideas to use by utilizing the tenacious nature of microbes.
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Glori Energy’s AERO System becomes part of an oil field’s existing waterflood infrastructure. |
Found in the reservoirs are indigenous microorganisms that are inactive or dormant and deprived of nutrients. These hearty microbes have already adapted to the extreme living conditions in the reservoir and thus serve as an affective medium for MEOR technology. Once supplied with the proper nutrients, the microbes become active and multiply. However, not all of the microbes are useful, so a sample of the organisms found in the reservoir must be taken back to the lab where the useful organism can be isolated. From the lab, a nutrient package can be developed to positively select for the useful organism, however, a carbon source is left out that will require the organism to use the oil in the reservoir as the carbon source. When the nutrient is injected into the reservoir, the useful organism can outcompete the other reservoir flora. Though both companies have their own proprietary nutrient treatment packages, they have similarly focused on nitrate formulas and have stayed away from sulfate formulas.
“Addition of sulfate could encourage oil well souring by sulfate reducing organisms. Therefore, we have restricted ourselves to a limited set of electron acceptors, concentrating mostly on nitrate,” says DuPont in a paper, SPE-146483 [1].
Glori
The Glori AERO System, only involves adding a nutrient package to the existing waterflooding of a candidate well. As a result, there is minimal production disruption and initial results can be seen in 6-12 weeks, Pavia says.
The process begins with the selection of a candidate field: must be a sandstone reservoir undergoing a waterflood, and generally permeability of 100mD or better, pH range between 6-9, temperatures below 200°F, salinity up to 14%, and good conductivity between the injector and producer well.
After selection, a sample of live water is taken so that the reservoir flora can be examined and brought back to the lab where the nutrient package will be developed to enable the growth of the beneficial microbe(s). This package may then be taken to the field where it will be introduced into the existing waterflood, a process that can be repeated as long as the operator desires.
The AERO System is hypothesized to affect two factors within the well to improve recovery:
“Primarily the disruption of interfacial tension and secondary the dynamic growth and death of microbes that change the water flow patterns,” Pavia says.
One mechanism, surfactant activity, is hypothesized to affect the oil-water interfacial tension. In order for the organism to access the oil as a carbon source, it must traverse the oil-water interface and bring the oil droplet into the water, releasing the unconsumed oil.
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Phase contrast microscopy is used to visualize microbes and oil in Glori Energy’s Houston laboratory. |
“What we believe happens is that these microbes behave as surfactants themselves, and they change the interfacial tension of the oil-water interface,” Pavia says. “The interfacial tension is disrupted and the water pressure squeezes the oil out into the producing well. If the microbes produce the surfactant, than other microbes will eat that surfactant. That’s the reason some of the older techniques failed.”
The other mechanism of recovery, bio-plugging, is simple and results in improved sweep efficiency. As the nutrients package is added, dormant bio-plugging microbes are activated and replicate.
“The microbes grow on the oil as a carbon source, and as the microbes collect in the pore, the water flow patterns will change. Once that oil is produced, the microbes will go find a new source in another pore and repeat the process, so it’s kind of a dynamic,” Pavia says.
DuPont
DuPont field candidates must also be sandstone reservoirs undergoing a waterflood with additional minimum reservoir characteristics: permeability greater than 50mD, pH from 5-9, temperature below about 150°F, salinity less than 9%, oil viscosity greater than 16°API, and well pressure less than 3000psi.
After the candidate field is selected, a sample of live oil is similarly collected and a nutrient package is designed to enable the desired microbe(s) to grow and outcompete the other microorganisms. However, unlike the AERO System, the desired microorganism is cultured in a separate broth that will be used to inoculate the reservoir in the initial phase of the injection process.
The key component to the DuPont MATRx system is the inoculation of the well with the bio-plugging microorganism prior to the addition of the nutrients package.
“Research has shown inoculation to be a critical step necessary to the overall success of MEOR technologies,” says DuPont’s website. The event follows an injection protocol downhole to help propagate the nutrients and microbe further from the injector, and periodic injection of nutrients to sustain the population. Also, according to DuPont’s paper SPE-169549 [2], to maintain the desired microbe’s dominance in the reservoir, inoculation is also repeated during the year.
“The increase in injection pressure happened within a few months and was sustained for the duration of the MEOR test. This clearly demonstrates that we have been able to develop significant and sustainable bio-plugging in this reservoir,” says DuPont in a paper, SPE-146483 [1], referencing a field test of the MEOR technology. “Oil production has increased in the field by 15-20% with a corresponding reduction in water cut.”
Key differences in the proposed mechanisms for improved recovery resulted in significantly different designs in the two technologies.
For the bio-plugging activity, DuPont selects for a microbe that is able to perform a specific EOR function. “That function is the production of an exopolymer as part of a biofilm that reduces the pore throat size and the apparent permeability in watered out channels in the reservoir,” says SPE paper 169549 [2].
As the microbe population grows, the production of the biofilm will build up along the pathway and obstruct the pore throats, resulting in the increase of resistance along that path to a point when another pathway will be less energy intensive, and the flow will naturally divert to that path. Thus, the oil found along the new pathway is more readily accessible. This process can also be continually repeated resulting in more of the reservoir’s oil being accessed and released. Though both hypotheses have ground, neither can be definitively proved at this time due to the nature of reservoir analysis.
Regarding the interfacial tension between oil and water, DuPont hypothesizes that the organism produces a bio-surfactant that would lower the interfacial tension between oil and water and cause spontaneous emulsification. While a reduction was observed, DuPont research showed that the change in interfacial tension was not great enough to cause spontaneous emulsification. Thus, DuPont’s MATRx system focuses on to taking advantage of the bio-plugging activities of the indigenous reservoir microbial organisms.
Future
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Glori Energy scientists perform core flooding experiments in the company’s Houston laboratory to study the effects of the AERO mechanism. |
Past ventures in MEOR technology did not instill much confidence in the industry; poor baseline data to compare results and poor follow-up impeded the success of some projects, while others failed due to unexpected behavior in the reservoir or did not produce the expected results. However, from those past ventures, the current players in MEOR technology have learned and improved upon the technology making this technique a commercially viable alternative in EOR technologies.
Statoil is currently applying MEOR technology offshore in the Norne field in the Norwegian Sea. Known as activated microbial enhanced oil recovery, the technology has been primarily for offshore use. Glori’s AERO System is the result of collaboration between Glori and Statoil. Results from the field are currently being evaluated.
With the fall in oil prices and the cost effectiveness following successful application of MEOR technology, will this technology catch on? Glori’s Pavia remains optimistic.
“If you go to someone and propose an EOR project that’s going to cost them $60/bbl, they’re going to say ‘No,’ but if you go to them with a technology that can be done at $10/bbl, they may say ‘here’s a reasonably priced technology that works in this environment,’ and when oil rebounds, which we’ve seen over and over again that it does, this will be a great technology then as well. I think we’re still in a reactive stage where everyone is worried about the prices and their budgets for EOR, but I’m optimistic that it will be fine,” Pavia says.
Academia shares a similar stance. Saif Al-Bahry, a professor at Sultan Qaboos University in Sultanate of Oman, says that due to aging oil fields, new and inexpensive technologies for EOR are a necessity.
“More research and knowledge on MEOR techniques are needed since understanding MEOR mechanisms in depleted oil wells can be used in wellbore clean up, oil-spill, bioremediation, heavy oil recovery and drilling fluid,” Al-Bahry says. “In the next 5-10 years, more research institutions will be involved in MEOR technology, evident by the increase in the number of publications in MEOR and international conferences.
“However, more international conferences related to MEOR are urgently needed to discuss various issues and means to make this technology cheaper and applicable.”
Works Cited
1. Jackson, S. and Fisher, J. and Alsop, A. and Fallon, R. 2011. Considerations for Field Implementation of Microbial Enhanced Oil Recovery. SPE Annual Technical Conference and Exhibition, Denver, CO. USA, 30 October- 2 November 2011. SPE-146483. http://dx.doi.org/10.2118/146483-MS.
2. Jackson, S. and Fisher, F. and Fallon, R. and Norvell, J. and Hendrickson, E. and Luckring, A. and D’achille, B. 2014. Increased Oil Recovery by Permeability Modification in Hwwigh Permeability Contrast Slim Tubes. SPE Western North American and Rocky Mountain Joint Regional Meeting, Denver, CO. USA, 16-18 April 2014. SPE-169549. http://dx.doi.org/10.2118/169549-MS.
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