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BP technology boosts oil recovery adding to potential energy supplies

ABERDEEN -- BP and its coventurers are deploying for the first time a new technology that could significantly increase the amount of oil that can be recovered from the UK’s largest hydrocarbon resource. The Clair Ridge development, west of Shetland, UK, is the first sanctioned large-scale offshore enhanced oil recovery (EOR) scheme using reduced salinity water injection (LoSal EOR). The intention is to extract a higher proportion of oil over the life of the field from the rocks deep below the seabed than has previously been possible.

The GBP£4.5 billion development at Clair Ridge includes around $120 million for the desalination facilities to create low salinity water for ‘waterflooding’ from sea water. BP estimates this will enable the production of around 42 million bbl of additional oil compared to waterflooding with conventional seawater, making a significant contribution to the estimated 640 million barrels of recoverable oil from the development.

The Mad Dog Phase 2 project in the Gulf of Mexico is the second offshore project that plans to include a low salinity waterflood to support increased oil recovery from the field. The facility will have a low salinity waterflood injection capacity of more than 250,000 bbl 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 (‘waterflooding’) into the oil-bearing rocks to increase the amount of oil that can be produced. Waterflooding sweeps oil towards the producing wells, but even then, much is often left behind. Globally, only about 35% of the oil in place is extracted, leaving huge natural resources – and energy supplies – untapped. LoSal EOR could significantly improve the recovery from waterfloods.

Around 60% of BP’s oil is produced using traditional waterflooding to help extract oil from reservoirs. Full implementation of potential low salinity projects across BP' s portfolio could increase net recovery by up to 700 MMboe.

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. LoSal EOR, 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 BP 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.”

The chemical studies showed that the oil molecules are bound to clay particles by ‘bridges’ of divalent cations such as calcium or magnesium and, in high salinity water – ie, with high ionic concentration – they are compressed to the clay surface by electrical forces. By reducing the salinity, this force is reduced and the ‘bridges’ are able to expand allowing the divalent cations to be swapped for non-bridging monovalent ions such as sodium. The oil molecules are then freed to be swept towards the producing wells.

LoSal EOR was developed by BP’s enhanced recovery technology team, known as Pushing Reservoir Limits, following a decade of laboratory tests at BP’s UK research centre at Sunbury-on-Thames, using sandstone samples from across BP’s global operations. Then, near well-bore single-well tests in several oilfields were performed to prove the technology worked in practice. This culminated in the successful field trial in the Endicott field, Alaska.

BP has decided to deploy LoSal EOR technology in all appropriate oil field developments from now on, and is assessing whether retrofitting some existing fields is commercially viable and technically feasible. As a result BP has at least five new and retrofit projects under active evaluation following on behind Clair Ridge .

BP operates a number of EOR projects around the world such as at Magnus in the UK northern North Sea where around 30% of the current oil production rate is due to EOR and Ula in the Norwegian North Sea where around 70% of the current oil production is from EOR.



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