Nature's little helpers
An extra 600 billion barrels of oil could be extracted from existing oilfields by using microbes according to oil giant BP. E&T investigates.
Proposed since the 1920s, the use of microbes to enhance oil recovery has remained practically unseen. However, the advances of modern biotechnology and the recent discovery and characterisation of indigenous microbes living in the oil reservoirs has now brought this technology to the attention of oil companies.
The process is called microbially enhanced hydrocarbon recovery (MEHR), and it is being studied in a BP-funded programme at the Energy Biosciences Institute (EBI) at the University of California at Berkeley.
The most basic method of oil recovery, called primary oil recovery, uses the natural pressure in the well to capture the oil. To increase the recovery rate, secondary recovery methods are used in which the oil wells are flooded with a medium - water, gas or vapour - allowing the modification of the physicochemical properties of the reservoirs.
But the average recovery rate obtained by using both these classical methods is only around 20 per cent.
Enhanced oil recovery
In order to increase this the oil companies have developed more complex tertiary techniques such as enhanced oil recovery (EOR), but their use is not always practical because of their high cost. These methods consist, for example, of injecting surfactants and polymers in the reservoirs to modify the viscosity and permeability of oil.
Terry Hazen, principal investigator and senior scientist in earth sciences at Berkeley Laboratory, says the programme is designed to understand all biological, environmental and geological aspects of oil resources, including microbial community structure, function, and distribution, linked to the physical and chemical nature of the sedimentary rock reservoir in which they are housed.
"From this basic information we hope to develop predictive models of MEHR applicability in various environments, as well as novel technologies to enhance hydrocarbon recovery for fuels," he adds.
Eventually, Hazen says, the use of microbes might even result in "oil sweetening", or converting its chemical structure to a more environmentally friendly and useful form, like methane.
It is estimated that less than 20 per cent of the oil reserves in a typical subsurface reservoir is extracted using primary recovery techniques. An effective MEHR programme could recover another 5 to 10 per cent, or more. The microbes used in this bio-recovery process produce harmless by-products such as slippery low-viscosity substances or gases, which in turn help mobilise the oil and facilitate oil flow and extraction.
Micro-organisms grow as biofilms lining the surfaces of sedimentary rock grains, as well as 'bacterioplankton' floating in the fluids that fill the rock pore space. These microbial communities can enhance oil recovery in a variety of ways, which include breaking down the molecular structure of crude oil and making it more fluid, producing carbon dioxide gas or biomass that displace the oil, and by creating biosurfactants that behave like slippery detergents in moving the oil.
As MEHR reduces or eliminates the need to use harsh chemicals during oil drilling, it is an environmentally compatible method of carrying out tertiary oil recovery.
Among the programme's 'natural subsurface laboratories' will be a demonstration injection well and two monitoring wells at Decatur, Illinois, which are being drilled as part of research on carbon sequestration being funded by the US Department of Energy.
University of Illinois associate professor of geology and microbiology Bruce Fouke says the goals include "developing quantitative models that identify these underground biology networks, predicting reservoir porosity and permeability changes that occur during resource extraction, and establishing universal approaches to using MEHR to recover oil".
The Decatur injection well and monitoring wells are located at Archer Daniels Midland in Decatur whose ethanol plant will provide the carbon dioxide for the storage and capture tests - injection of CO2 is scheduled to begin next October.
The wells will descend more than 6,500ft, where the gas will be trapped between sandstone and shale in a natural saline reservoir.
The EBI teams will analyse the environmental and geological conditions of shallower Paleozoic hydrocarbon reservoirs as well as the deeper Cambrian CO2 sequestration saline reservoir target. This includes water and rock geochemistry and hydrocarbon composition and will chart the geologic thermal burial history of each sample.
They will then determine the genetic spread and profiles of the subsurface microbes, including bacterial and viral communities, under various conditions. Their results will be gathered into a model framework that future EBI research can use for MEHR microbial engineering, on-site biology manipulation, and treatment and monitoring strategies.
"We hope to develop conceptual models of microbial community structure and function that may enable control of these environments toward maximising energy recovery, energy quality and carbon sequestration, as well as understanding the fundamental mechanisms of petroleum maturation and migration," says Hazen.
According to BP officials, the prize in enhancing recovery rates is enormous. A 1 per cent improvement in recovery on BP's original hydrocarbons equates to two billion barrels of additional reserves. Worldwide, a 5 per cent increase in recovery - a conservative increase thought to be achievable - would yield an additional 300-600 billion barrels, which could be critical to meeting the growing global energy demand.