Carbon conundrum

Minimising the environmental impact of fossil fuels and enhancing oil recovery are front running issues for oil companies world wide.

The oil and gas industry is embroiled in the challenge of worldwide climate change more than most, with fossil fuels contributing much of the harmful carbon dioxide (CO₂) released into the atmosphere.

The greenhouse effect - CO₂ and other greenhouse gases absorbing infrared radiation from the sun, resulting in global warming - has been recognised by all but the most ardent industrialists as a real phenomenon, and in turn governments and companies have begun pushing development of technologies to address the situation.

One such technology is carbon capture and storage (CCS), which involves reducing carbon in the atmosphere by capturing it. What is then done with the captured carbon has been an obvious stumbling point for the development of the technology, but now there is a viable solution provided by the oil and gas industry - enhanced oil recovery (EOR) injection of CO₂ into reserves that are depleting.

CCS comes in three main types: pre-combustion capture, post-combustion capture and oxy-fuel combustion. Pre-combustion capture is the decarbonisation of fossil fuels, at the moment possible with coal and natural gas through coal gasification or reforming. The fuel is converted to hydrogen and CO₂, with the CO₂ then either used for EOR or stored, and the hydrogen used for electricity production and potentially for cars and heating appliances.

Post-combustion capture involves capturing CO₂ from exhaust, done by absorption in a suitable solvent or using high-pressure membrane filtration. Oxy-fuel combustion is essentially post-combustion, but by burning the fossil fuel in pure oxygen it results in a much more concentrated stream for easier purification.

CO₂ has been used in EOR programmes to coax more oil from the reservoirs. But it is only now that companies, including the likes of majors Shell, BP and ExxonMobil, are seriously looking at the development of CCS from power stations and refineries to be injected into fields around the world.

The main concern with the technology has been the costs and the increased energy needed. It has often resulted in many empty promises made by governments and companies alike, who claim to be delivering CCS soon yet fail to deliver.

"CCS in power plants makes sense economically only for large, highly efficient plants. At present, the increased use of fossil fuels resulting from CCS could be as high as 35%-40%. It is expected to decline to 10%-30% in next-generation plants, and could be as low as 6% for more speculative designs," a report from the IEA (International Energy Association) says.

IEA are adamant however of how important the technology could be to the world, stating that fossil fuels provide the world currently with 80% of its energy with little to suggest much will change for decades to come.

"Global energy related CO₂ emissions increase 55% between 2004 and 2030 in a business-as-usual outlook. It is increasingly clear that this development path is not sustainable, and that CO₂ capture and storage is a critical technology to significantly reduce CO₂ emissions," says the report.

Shell is one company that is looking to develop the technology by working with industry and government to find the most cost-effective solutions to the technical challenge involved. The storage of the gas would be done either through injection into old oil and gas reservoirs, or in saline aquifers deep beneath the surface.

Shell has been looking at the possibility of developing the technology in Oman, and in particular in conjunction with Petroleum Development Oman (PDO), which has maturing oil fields which require EOR to keep them productive.

"The main change in PDO's strategy towards EOR is due to the maturity of the company's producing oil fields. All fields, anywhere in the world, have limited recovery from primary mechanisms and Oman is not an exception," says Xu Dong Jing, manager of Shell Technology, Oman. "We have now reached a point when we need to embark on tertiary recovery mechanisms."

While the supply of natural gas for EOR was the only realistic option to most producers, with CO₂ there is now an attractive alternative which would free up the natural gas for domestic use or exportation.

"The gas injection projects are dictated by geography and demand, and ultimately, which solution you pick becomes an economic question. Where there is a market demand for that gas it may be preferable to exploit that, so usually hydrocarbon gas injection is done where there is a surplus of that gas. In the future the Middle East will see a move towards using CO₂ so that the hydrocarbon products streams can be more efficiently used," says explains Val Brock, business development manager for EOR, Shell.

"Greenhouse gases or man-made CO₂ capture will play a huge part in our future. We are working on developing capturing techniques for CO2 that would otherwise be emitted, such as industrial flue exhausts," adds Brock.

In 2007 BP and Rio Tinto - the largest coal mining company in the world - formed a 50:50 joint venture company named Hydrogen Energy International (HEI). Headquartered in London, UK, the company has more than 100 staff working around the world and two offices where their two major projects are to be based: California and Abu Dhabi.

HEI intends to be a "low carbon fuel supplier", with focus on the conversion of fossil fuels into low-carbon hydrogen fuel, which will be used in power generation, industry and ultimately the transport sector. The CO₂ produced during the separation will be then stored in deep saline aquifers or used in EOR injection, as proposed for the Abu Dhabi project.

"Our pre-combustion technology allows us to take a range of fossil fuel feedstocks (natural gas, petroleum coke and coal) and convert them into low-carbon hydrogen using proven technologies coupled with geological storage of CO₂," says Paul Bryant, regional director Eastern Hemisphere, HEI.

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