MEOR: Making the Case

More research and good PR are needed if the oil industry is to reap the rewards to be had from microbial enhanced oil recovery

BASED upon the recent ill-informed hysteria surrounding the safety of fracking, the above vision of press coverage of the highly-promising microbial enhanced oil recovery (MEOR) technique is not beyond the realms of possibility. In 2014, the UK witnessed the farcical situation where Dame Vivienne Westwood, a fashion designer, suddenly became an expert in drilling and well completion practices in the US states of Wyoming and Delaware, and seemingly knew more about lithology than the British Geological Society. If the same anti-fracking mindset persists, using bacteria for oil recovery could result in similar ill-informed public and press outrage. The MEOR technique in question involves using bacteria to convert irrecoverable oil into methane (natural gas) and subsequently producing the bio-synthesised gas. 

Oilfield waterflooding

Waterflooding is a technique that greatly enhances production from oil fields. It’s a common practice and involves injecting seawater into the oil-bearing rock at a volume rate equivalent to the volume rate of removal of oil from the producing oil wells. This serves two main purposes: it prevents the pressure in the oilfield from dropping and, as the water travels through the oil-containing rock, it sweeps oil towards the production wells. Without waterflood, oil recovery levels would be around 10–20% of the oil in place. Waterflooding increases this to 60–70%. However, the water cannot sweep out oil contained within some parts of the rock, so when oilfields are decommissioned the oil company is leaving around one third of the oil behind.

Figure 1 illustrates the pre-waterflood situation with oil contained within the pores of the rock (left) and the situation at end-of-field-life where oil is trapped in locations the waterflood fails to reach and remains unrecovered (right).

Enhanced oil recovery

Because of the large amount of oil left behind post-waterflood, oil companies have for many years researched a range of enhanced oil recovery techniques. This work includes polymers which help the water find the oil trapped in the hard-to-reach areas, low salinity waterflood which reduces the oil-rock adhering forces, surfactants which act much like soap cleaning oil from the rocks, adding heat to help the oil flow, and injecting high pressure gas which swells the residual trapped oil and makes it easier to move. These techniques are expensive and, apart from the thermal methods, their use has been limited.

Microbial enhanced oil recovery – MEOR

There are a range of MEOR options under development with one in particular showing much promise: using methanogens.
Methanogens are present in the guts of ruminants and in wetlands; they are responsible for the methane emitted in cow farts and for marsh gas (methane). For methanogens to thrive they require a biomass (eg grass in cow gut) or oil remaining in rock post-waterflood. The MEOR methanogen option is to inoculate the waterflood with methanogens and nutrients prior to ceasing oil production. The methanogens subsequently colonise the oilfield and metabolise the trapped oil, converting it to methane (Figure 2). The bio-produced methane gas is much more mobile than the trapped oil and migrates upwards, accumulating as a large gas cap. The gas cap is then produced through the existing oilfield wells and processing facility. This sounds like a low cost, highly effective hydrocarbon EOR recovery option for a mature province like the UK. So what’s the catch?

Whilst methanogens function at cow gut temperature and pressure (38.6⁰C and atmospheric pressure), developing a methanogen capable of metabolising trapped oil at the subsurface conditions of 80–120⁰C and at many hundreds of atmospheres will be difficult. It will require straining and probably genetic modification of the existing methanogen community – a ‘Frankenstein Bug’ perhaps?

For those understandably concerned about any process which produces more fossil fuel, the synthesised methane need not be used as a fuel source. It could be reformed into syngas – hydrogen and carbon monoxide – with the hydrogen used as carbon-free fuel and the carbon monoxide used as a feedstock for the manufacture of carbonyls, methanol and formaldehyde.

Methanogen EOR research

Whilst there is EOR methanogen research activity in some parts of the world, such as China, the UK appears to have no active groupings. This is surprising since the technology sits extremely well with the Oil and Gas Authority’s (OGA’s) primary remit of maximising economic recovery from the UK’s remaining hydrocarbon reserves. Indeed the OGA’s EOR Strategy Document makes no mention of microbial EOR. Low salinity waterflood is highlighted as a preferred technique – but this is somewhat baffling as it is a high-cost option not suited to mature provinces. MEOR would also prolong field life, defer decommissioning and further preserve the UK’s oil and gas infrastructure – key objectives of the OGA. If you consider the UK’s renowned expertise in biotechnology, this makes the lack of UK MEOR activity even stranger. UK MEOR – where are you?

The message though to any MEOR researcher and developer is to note the public reaction to fracking and ensure that public engagement is not hijacked by ill-informed scaremongers.