Making Use of Associated Gas
In the early days of oil exploration, natural gas was considered an unwelcome byproduct. As reservoirs were tapped in the drilling process, workers were forced to stop drilling to let the gas vent freely into the air CO2 and all. Now, natural gas is considered an important source of energy, accounting for nearly 21% of total global energy supply. Because it is also relatively clean burning producing about half as much carbon dioxide as burning an equivalent amount of coal there is increased interest in utilizing natural gas as an energy source. It is estimated that globally around 150 billion m3 of gas are flared or burned every year, causing some 400 million tons of CO2 in annual emissions, which is equivalent to one-third of the entire EU’s gas consumption.
The World Bank’s Global Gas Flaring Reduction (GGFR) is a public private partnership launched at the World Summit on Sustainable Development in 2002. GGFR supports the efforts of oil producing countries and companies to increase the use of associated natural gas and thus reduce flaring and venting. The partnership facilitates and supports efforts to use currently flared gas by promoting effective regulatory frameworks and tackling the constraints on gas utilization, such as insufficient infrastructure and poor access to local and international energy markets, particularly in developing countries.
There are several options for the handling and utilization of associated gas providing power and heat for the field facility and/or to adjacent premises and possible power and heat grids. Other options include re-injecting the gas to enhance oil production or storing the gas for future utilization. Eventually processing to liquefied natural gas (LNG) would be another way to use the light fractions of associated gas and the heavier components into liquefied petroleum gas (LPG).
Wärtsilä is one of the companies participating in the GGFR. The company explained that its gas-diesel (GD) technology can be used for power production and, in fact, called it a “perfect fit.” Introduced in 1987, the Wärtsilä 32GD engine became the first gas engine in its portfolio. “The GD technology makes it possible to run the engine on either gas or oil associated gases of almost any quality and liquid fuels from diesel oil to heavy fuel oils, even crude oils,” said Pekka Laine, application manager, Wärtsilä Power Plants. “In 2002 we introduced what we called fuel sharing, meaning that the engine can run on gas and liquid fuel in different proportions.”
The engine operator can easily set the fuel type and its relevant percentage and, in a case when the available gas fuel is not enough for a required output, compensate with the required amount of liquid fuel oil. “We have an 11 MW power plant in Ecuador which has been in operation since 2003. Two Wärtsilä 16V32GD are fueled by associated gas and crude oil from the processing facility,” said Laine. “These units are utilizing our fuel-sharing system.”
The storage of gas for future use or for reinjection requires large amounts of energy. Wärtsilä received a contract in July 2007 to deliver gas engine mechanical drives and auxiliaries for a compressor plant from MOL Hungarian Oil & Gas Plc for an underground gas storage plant for utility gas at Szöreg, in the Csongrád region in Southern ungary.
The plant, equipped with five Wärtsilä 9L34SG gas engines driving gas reciprocal compressors supplied by U.S.-based Cameron, was inaugurated in October 2009. The five engine-driven compressors and two electric motor driven compressors will compress natural gas into underground storage caverns having a total capacity of 1.9 billion m3. The emergency backup storage of 1.2 billion m3 will secure the public gas consumption in Hungary for 45 days.
“The idea is to push gas down into the old gas reservoir at a pressure of 200 to 300 bar,” said Harry Lindroos, director, oil and gas industry, power plants at Wärtsilä. “The 2 billion m3 that MOL intends to store in Szöreg is about half the annual consumption of gas in, for example, Finland.” Mindful of the current financial crisis affecting oil and gas producers in general, the World Bank-led GGFR is focusing on efforts that help partner countries and companies deliver on their gas flaring reduction projects and prepare for potential opportunities to increase the utilization of associated gas.According to the GGFR partnership, total global flaring has remained stable, but is not yet in decline. The partnership continues to highlight best practices and share case studies of operations that have been able to overcome the barriers to gas utilization. The group is also providing opportunities to look at emerging technology for flare gas utilization. After all, flare reduction remains one of the most cost-effective ways to reduce greenhouse gas (GHG) emissions.