Carbon dioxide thickener could improve crude-oil extraction
Crude-oil extraction could be improved and accessible oil reserves expanded with an economical carbon dioxide (CO2) thickener being developed by engineers at Pittsburgh University.
Current oil-extraction methods across the US involve oil being pushed from underground layers of porous sandstone or limestone reservoirs using a first-water-then-CO2 technique known as the water-alternating-gas (WAG) method.
CO2, obtained from natural CO2 reservoirs and pipelined to oil reservoirs, is claimed to be an ideal candidate for oil extraction given its ability to push and dissolve oil from underground layers of porous rock.
However, its viscosity is said to be too low to efficiently extract oil. Consequently, it tends to ‘finger’ through the oil rather than sweep oil forward towards the production well. This process, ‘viscous fingering’, results in oil production companies recovering only a small fraction of the oil that is in a field.
During the late 1990s, a team at the university was the first to demonstrate that it was possible to design additives that could enhance CO2’s viscosity at low concentrations, although the compounds were costly and environmentally problematic.
‘The thickeners we developed years ago were too expensive for wide use,’ said principal co-investigator Eric Beckman, the George M Bevier Professor of Engineering in Pittsburgh’s Swanson School of Engineering. ‘So, in this proposal, we’re looking at designing candidates that can do the job at a reasonable cost.’
Beckman and Robert Enick, principal co-investigator and the Bayer Professor and vice-chair for research in the university’s Department of Chemical and Petroleum Engineering, intend to build upon earlier Pittsburgh models of CO2 thickeners, but this time with a more affordable design that could cost only several dollars per pound.
Ideally, their small molecule thickener would be able to increase the viscosity of pure CO2 by 100 times.
‘An affordable CO2 thickener would represent a transformational advance in enhanced oil recovery,’ said Enick in a statement. ‘More than 90 per cent of CO2 injection projects in the US employ the WAG method to hinder the fingering of the CO2. However, if a thickener could be identified that could increase the viscosity of the CO2 to a value comparable to that of the oil in the underground layers of rock, then the fingering would be inhibited, the need to inject water would be eliminated and more oil would be recovered more quickly using less CO2.’
‘It’s clear there exists a very wide market for this type of CO2 thickener,’ said Beckman. ‘It’s long been recognised as a game-changing transformative technology because it has the potential to increase oil recovery while eliminating water injection altogether.’