Keeping a cap on carbon: part two

Read part one of this article here.

Not just a waste product

Far from being simply a problem to deal with, CO₂ can also be a solution to the challenge of extracting further deposits from gradually depleting oil and gas reservoirs. Known collectively as enhanced hydrocarbon recovery, the methods include enhanced oil recovery (EOR), enhanced gas recovery (EGR) and enhanced coalbed methane recovery (ECBM).

EOR acts as the third stage of oil recovery, after the primary stage of relying on the natural pressure within the oil and the secondary stage where pressure is created by injecting water into the oil reservoir. EOR uses two main methods: one using CO2 alone and the other employing alternate injections of CO₂ and water. The latter method is expected to be more popular due to its generally shorter payback time.

It has been estimated that, using CO₂ obtained through CCS and using it for enhanced oil recovery, £150 billion worth of otherwise unrecoverable oil could be extracted from UK North Sea oilfields. A study undertaken for the Government of Alberta in 2010 discovered that using EOR could extract a further 1.08 billion bbls of oil, from reservoirs originally holding nearly 11.6 billion bbls. Extracting this oil would require the purchase of 253 million t of CO₂, all of which would eventually be stored in the studied reservoirs.

EGR makes use of the fact that CO₂ is denser than the natural gas to be extracted. Injected into a target well, it pools in the depleted reservoir, forcing any gas to float on top. The K12b project, initiated by GDF Suez in the North Sea, is investigating the injection of CO₂ back into the gas reservoir once it has been scrubbed from the extracted natural gas. The project involves extensive storage testing including tracer injection and examining potential for enhanced gas recovery. However, the potential uses for EGR are small, since the majority of the natural gas in many gas fields can be recovered without the use of enhanced techniques.

In coal seams, coal bed methane (CBM) can be found adsorbed onto the surface of coal in the many cracks and fissures. CO₂ has a greater adsorption affinity for coal than methane. This means that injecting CO₂ into a coal seam just prior to the end of a coal bed methane production project, any remaining methane will be displaced. The result is extra recovery of methane at the same time as storing CO₂.

There are a number of drawbacks with this method. Due to the low permeability of coal seams, a large number of wells will be needed to inject enough CO₂ to extract the methane. Methane also represents a low fraction of the energy value of coal and the remaining deposits could not subsequently be mined without releasing the sequestered CO₂ to the atmosphere. Preventing methane reaching the atmosphere is also an important goal as methane is a far more potent greenhouse gas even than CO₂.

Cutting the cost of power

CCS has a major role to play in reducing the carbon emissions involved in the production of electric power using fossil fuels.

A major project in this area is the White Rose CCS project. Announced by project partners Alstom, Drax and BOC, this aims to build a 448 MW coal powered power plant at the Drax Power Station site near Selby. Using the oxy fuel process, the plant is intended to demonstrate CCS technology at a commercial scale and will also have the potential to cofire biomass. The potential for biomass is significant, since the use of biomass combined with CCS will lead to negative carbon emissions.

Capturing approximately 2 million t of CO₂/y some 90% of all emissions from the plant, the proposal also includes the development of a large capacity pipeline, the Yorkshire Humber CCS Trunkline, which will have capacity to serve additional carbon capture projects in the area.

Building the carbon free future

With its experience in coal fired power generation and petrochemicals, its legacy of North Sea hydrocarbon extraction, its strong skill base and world renowned academic facilities, the UK is well placed to be a world leader in CCS. The government has recognised this and is investing in several of the projects outlined above, as well as financing fundamental research into new technologies and putting in place a licensing scheme for offshore carbon storage.

Private initiatives (academia and industrial sponsorship) include the joint ABB/Imperial College London Carbon Capture Pilot Plant, which will train the UK’s next generation of chemical engineers on this vital technology. The 12 m tall, £9 million facility is a fully operational carbon capture pilot plant.

Using a combination of ABB’s control, instrumentation, drives, motors and extensive process automation equipment, the plant provides students with hands on experience of pilot scale industrial plant operations and is the only facility of its kind in an academic institution in the world. The pilot plant is used in undergraduate teaching, with the aim of equipping students with the practical skills needed for a career in industry. Working on the plant, students become increasingly familiar with a technology that is set to form an ever more important part of the UK’s industrial landscape.

Written by Will Leonard, Chemical, Oil and Gas UK, ABB Limited. This is an abridged version of an article taken from the June 2015 issue of Hydrocarbon Engineering.

Read the article online at: https://www.hydrocarbonengineering.com/special-reports/05062015/keeping-a-cap-on-carbon-part-two-888/