Gippsland is currently drawing gas from 10 reservoirs spread across eight Bass Strait fields. The composition of the gas coming out of these reservoirs varies in terms of the chemicals they contain which ultimately influences the resultant heating value of the hydrocarbons (also known as Wobbe index rating).
The dominant chemical is methane – natural gas. However, most reservoirs also contain varying degrees of natural gas liquids (ethane, propane and butane), as well as heavier hydrocarbons, called condensates. The raw gas also contains varying degrees of chemical impurities. In Bass Strait, the most common impurity is carbon dioxide (CO2). Bass Strait gas containing a lot of CO2 – typically greater than four percent CO2 in Bass Strait – we call ‘sour’ gas. Gas containing little CO2 – less than four percent – we call ‘sweet’ gas.
Our objective is to run the ‘chemistry set’ in a way that maximises the amount of sales gas (gas with the correct chemical and heating value specifications) and natural gas liquids available for our customers.
We have installed a Gas Conditioning plant to process our sour gas to meet the required specification. Plant operators and engineers are constantly considering new ideas to improve the processes and lift productivity.
“One of the processes we use is gas blending,” explained Production Engineer Emmanuel Adeyinfa. “By mixing sour gas with sweet gas at various stages of the process we can accelerate production of the sour gas streams.
“Gas from our traditional fields – like Snapper and Barracouta – contain sweet gas with CO2 in range of two to four percent. While our new deeper fields – like Kipper, Turrum and the Tuna M-1 reservoir – contain eight to 15 percent CO2.”
Right now Bass Strait is a hive of activity during extended shutdowns on the West Tuna and Marlin platforms. One of the major projects of these shutdowns is the Turrum gas tie-in to the Marlin 450 pipeline to Snapper.
“This means we will be able to blend Turrum sour gas with remaining sweet Snapper and Barracouta gas,” said Emmanuel.
“This significantly improves our blending capability and helps us to maximise flow of Gippsland gas as we head into winter and beyond.”