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UK oilfield in low-salt water injection first

BP is deploying a new technology that could significantly increase the oil yield from the UK’s largest hydrocarbon resource.

The Clair Ridge development, west of Shetland, is the first approved large-scale offshore application of enhanced oil recovery (EOR) using reduced salinity water injection (LoSal EOR).

Over the life of the field the scheme is expected to enable a higher proportion of oil to be extracted from the rocks deep below the seabed than has previously been possible.

The £4.5bn development at Clair Ridge includes around £80m for the desalination facilities to create low salinity water from sea water.

BP estimates this will enable the production of an additional 42 million barrels of oil compared to waterflooding with conventional seawater, making a significant contribution to the estimated 640 million barrels of recoverable oil from the development.

A low salinity waterflood is also planned for a second offshore scheme, Mad Dog Phase 2 in the Gulf of Mexico.

This facility will have an injection capacity of more than 250,000 barrels of water per day.

The technology has already been successfully tested in a field trial in the Endicott field, Alaska, between 2008 and 2009, where low salinity water was injected in one well and the incremental oil production observed in another.

Endicott proved up the laboratory trials at full scale.

Oil reservoirs are not underground caverns, but layers of sandstone with oil and gas held in the spaces between the grains that make up the rock.

Allowing an oil reservoir to produce oil through declining natural pressure results in relatively low recoveries, so many fields inject water into the oil-bearing rocks to increase the yield.

Waterflooding sweeps oil towards the producing wells, but even then, much is often left behind. Globally, only about 35 per cent of the oil in place is extracted, leaving huge resources untapped.

In conventional waterflooding, injected water flows through layers of porous reservoir rock displacing oil from the injection well to the production well.

The pore spaces often contain clays to which oil is bound. Using reduced salinity water releases a lot more of the bound oil and pushes it to the production wells.

“Oil industry wisdom says you shouldn’t inject anything too fresh or the clays within the oil-bearing sandstones can swell and reduce the ability of the oil to flow,” says Jackie Mutschler, head of upstream technology at BP.

“So we looked at the fundamental chemistry which makes the oil molecules stick to the rock surfaces in reservoirs. What we discovered is that by reducing the salinity, and hence the ionic concentration of the injected water, more molecules of oil could be released from the surface of the grains of the sandstone rock in which they’re held.”

LoSal EOR was developed by BP’s enhanced recovery technology team following a decade of laboratory tests on sandstone samples at the company’s UK research centre at Sunbury-on-Thames.

Then, near well-bore single-well tests were performed in several oilfields to prove the technology worked in practice, culminating in the Endicott field trial in Alaska.

BP now intends to deploy the technology in suitable oil field developments from now on, and is assessing whether retrofitting some existing fields is commercially viable and technically feasible.

Five new and retrofit projects are under active evaluation following on behind Clair Ridge.

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