May 2016 /// Vol 237 No. 5

Columns

Energy issues

Bugs!

William J. Pike, World Oil

My wife doesn’t like bugs. While I don’t find them particularly welcoming myself—I am uncomfortable with the thought that my body is a feeding ground for multitudes of single cell creatures—I am more accommodating of them. The oil and gas industry, it would seem, is feeling the same way.

For a number of years, microbial enhanced oil production (MEOR) has been a topic of conversation, and development, in our industry. Early discussions and R&D centered on the injection of microbes into oil formations. The microbes would, it was proposed, ingest oil and expel gas, creating an ersatz gas drive. While tentative results were promising, widespread adoption was not.

Then, along came another bug-based technology for improved MEOR. Based on initial research by Statoil, the new technology makes use of microbes that already exist in water, in oil and gas reservoirs. As originally found, the microbes are comatose, due to near-starvation. But feeding them can awaken them, and send them on a feeding spree, with good results.

The technology applies, primarily, to mature, water-flooded formations, although it may be applied to some non-water-flooded mature formations. It works on the strand theory. The theory is best described by Sunde, et. al., in “Towards a new theory for improved oil recovery from sandstone reservoirs” (SPE paper 154138). It notes, “when oil is displaced by water, in a two-dimensional system, which can be studied in transparent models under a microscope, the oil body will ‘snap off’ and form discrete oil droplets in the pores, due to the different water velocities in the pore network. However, there is common agreement that the system (rock, oil, water) will organize itself to produce the smallest possible resistance to the flowing water.

“In a three-dimensional system,” the paper continues, “the oil will self-organize, according to the sum of pressures acting on it and the available pore network, thereby also redistributing some of its surrounding film of water. This, and the fact that oil and water will seek the greatest possible separation to minimize friction, will leave the residual oil in continuous oil strands occupying pore spaces in all three dimensions. However, the general orientation of the oil strands will be parallel to the direction of flow, due to the acting shear forces.” But these strands will not have been produced to the wellbore, because they are trapped by capillary-bound water in the pore throat, in regions close to the production well.” It is microbes in these waters that can be fed for enhanced MEOR.

MEOR can provide a number of benefits over traditional EOR, including:

  • Increased oil production
  • Decreased decline curves
  • Increased recoverable reserves
  • Lower Capex/Opex
  • Ease of installation

Working in collaboration with Statoil, Glori Energy has developed the AREO system that injects microbial nutrients into the formation with the waterflood process, in carefully screened candidate fields. To classify as a candidate, a field must meet a set of criteria, including:

  • Permeability of 100 MD or more
  • A pH range of 6-9
  • A reservoir temperature less than 200°F
  • Salinity of up to 14%
  • Conductivity between injectors and producers

The process is fairly simple. The MEOR process begins with analysis of reservoir fluids, especially the water. From these analyses, which identify the specific microbes to be fed in the water, a nutrient formula is developed for the specific application. However, the nutrient formula does not meet all the microbes’ dietary demands. Carbon is omitted.

When the nutrient mix is determined, Glori moves portable injection equipment to the location and ties it into the waterflood system. Once nutrient injection begins, a strange phenomenon occurs. The now-active microbes become hungry. Since they are being fed a dietary supplement minus essential carbon, they begin to search for that material. This leads them to pop through the oil-water interface to seize droplets of oil (in the strands), which they drag into the water phase to consume. Unconsumed portions of the oil seized by the microbes float back to the interface.

The combination of continual disruption of the oil/gas interface, combined with the release of the unconsumed oil to the interface, results in the creation of, essentially, a surfactant boundary or biofilm between the oil phase/strand and the water phase. This breaks the interfacial tension between the two and allows the oil/strand to move, due to waterflooded reservoir pressure. According to Sunde, et. al., this can be compared to “stepping on a tube of toothpaste. The water does not push the strand from the end, but squeezes it from all sides.”

A second benefit of MEOR technology is that of bio-plugging. Eventually, as the bio-population grows in a flow path, the biofilm produced will begin to build up in the pore throats, to the point that it blocks the flow path, causing the fluid to divert to another flow path with additional unrecovered oil strands.

While Statoil’s version has been deployed for testing in Norway’s Norne field, Glori has introduced the system in a number of regions globally, including fields in which they have acquired an interest specifically for further testing and refinement of the technology. Results of initial tests of the AERO system have been positive. In one test at an unidentified field in Alberta during 2014, continuous MEOR injection resulted in 13,591 bbl of additional oil production in nine months, representing a major increase over projected production, for the period of 8,284 bbl. The value of MEOR comes not just in incremental production, but also in decreased costs. At an estimated cost of $10/bbl, MEOR handily outscores more traditional EOR methods, which may reach into the $60/bbl price range.wo-box_blue.gif 

The Authors ///

William J. Pike has 47 years’ experience in the upstream oil and gas industry, and serves as Chairman of the World Oil Editorial Advisory Board.

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