Produced brine could aid CO2 injection in North Sea fields, institutes claim

Offshore staff

LOUGHBOROUGH, UK – Britain’s Energy Technologies Institute (ETI) has initiated a nine-month project to investigate the impact of removing brine from undersea stores that could in the future be used to store captured carbon dioxide (CO2).

Heriot-Watt University, a founder member of the Scottish Carbon Capture & Storage (SCCS) research partnership, will manage the “Impact of Brine Production on Aquifer Storage” study, with support from Element Energy, T2 Petroleum Technology, and Durham University in northeast England.

The program is designed to build on earlier CCS research work and help develop understanding of the potential CO2 stores beneath the UK’s waters, such as depleted oil and gas reservoirs or saline aquifers.

It should also help build confidence among future operators and investors, ETI hopes.

An earlier ETI CCS project led to development of the UK’s principal storage screening database, CO2Stored, which estimates the capacity and injectivity for each 550 potential stores identified off the UK’s coasts.

One of the assumptions was that brine was not produced from the reservoir store before, during or after CO2 injection. However, if pressure builds within a store as a result of CO2 injection, brine can potentially be removed from the store through a purpose-built well or wells (to depressurize it), while still retaining the store’s operation and integrity.

ETI says brine management is a recognized approach in the oil and gas industry for controlling reservoir pressure and fluid flow, and brine production is a feature of every oil and gas development. Removed brine could be exported to another aquifer or displaced to the sea.

Recent work by Heriot-Watt University suggests producing brine on the UK continental shelf may be beneficial to CO2 injection rates and storage.

Paul Winstanley, ETI CCS project manager, said: “Although the UK government is no longer pursuing its CCS demonstration competition, ETI’s view remains that CCS offers long term the lowest cost solution to meeting the UK’s legally binding 2050 climate change targets.

“The project will produce a cost-benefit analysis of brine production, using the CO2Stored database and numerical models developed in the ETI’s previous UK Storage Appraisal Project as a starting point. The analysis undertaken will cover both saline aquifers and oil and gas reservoirs.

“The first stage of the project will examine any changes in injectivity and storage capacity as a result of producing brine, the additional cost of using brine wells as part of storage site operations and the potential for any savings. If the first stage shows there are potential benefits, these will then be refined and the operational implications examined further.”

Professor Eric Mackay from Heriot-Watt University added: “More brine than oil has been produced from North Sea oil reservoirs. This brine is cleaned to conform to environmental regulations and then either displaced to sea or reinjected into subsurface rock formations.

“Seawater is also injected into oil reservoirs to maintain the pressure while the oil is being produced and also maximize oil recovery. This project will investigate the potential to do the reverse – produce brine to prevent the pressure increasing during CO2 injection. This will reduce the risk of leakage, increase the amount of CO2 that individual wells can inject and increase the storage capacity of the whole system – potentially by a factor of three to four times.

“As a result, fewer wells overall will be required, and fewer sites may be required to store the same amount of CO2 – with clear benefits in terms of reduced cost of appraisal, drilling, operation, and monitoring. Provided existing regulations on water quality are adhered to, the environmental footprint of CO2 injection will also be reduced.”


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