The exact chemistry of Natural Gas as it comes out of the ground is data that is not always easily available – and industry watchers always seem to charge a lot just to access rudimentary information that was hastily published in trade journals.
But the exact chemistry of Natural Gas as it comes out of the ground is very important to know, especially as, over time, naturally-occurring gases collected from the sub-surface of the Earth are expected to change in their composition. This is due to a number of factors, including the depletion of major oil fields – where much Natural Gas comes from.
Changing Natural Gas chemistry will also arise because of changes in the choice of resources. Here’s a note from Lallemand et al. from PTQ magazine for Q4 2013, starting at page 81, “For decades to come, gas will be an energy source of choice to meet increasing energy demands. Oil and gas operators have always preferentially produced the gas from those reservoirs that are technically the easiest and the cheapest to develop, but they will have to develop fields with a higher acid gas content in the future. Effectively, over 40% of the world’s conventional gas resources currently identified as remaining reserves to be produced, representing over 2600 trillion cubic feet (tcf), are sour, with both [hydrogen sulfide] H2S and [carbon dioxide] CO2 present most of the time. Among these sour reserves, more than 350 tcf contain H2S in excess of 10%, and almost 700 tcf contain over 10% CO2. The Middle East, the Caspian Sea area and China have gas reserves with a high H2S content, while large amounts of gases with a high CO2 content are encountered in South East Asia and, to some extent, in South America and North Africa.”
Another Natural Gas contaminant to look out for is nitrogen, which can be present in very high percentages.
What’s astonishing to me is that there is not more discussion of the issues surrounding the attentuation or lessening of value of Natural Gas owing to this chemistry.
Not that I’m going to attend, but there is a conference up soon on this matter, “Sour Oil & Gas Advanced Technology 2016”, or SOGAT, being held in Abu Dhabi, and the blurb makes for interesting reading : “…The technologies involved in sour field management and production are always progressing and the latest developments across the whole management spectrum including observations on capturing CO2 from sour gas processing facilities for use in [Enhanced Oil Recovery] EOR will be included in the SOGAT Conference Programme…”
Now, admittedly, Enhanced Oil Recovery is a valid use for unwanted carbon dioxide in Natural Gas, and is widely in use to achieve this aim. Carbon dioxide and other inert gases are pumped into an oil field to create extra “lift” pressure, to increase the production of crude petroleum oil liquids. It’s a technique that can be fairly effective over some length of time.
It’s not always certain if the re-injected carbon dioxide stays put – so it’s not necessarily a recipe for permanent “sequestration” of that CO2 back underground. However, this was the original CCS – Carbon Capture and Sequestration, or Carbon Capture and Storage, method proposed by the oil and gas companies when the United Nations Framework Convention on Climate Change (UNFCCC) wanted to hear on carbon mitigation technologies.
But is there another way to deal with the carbon dioxide emerging in Natural Gas, rather than using it to pump up more oil ? After all, even if the re-injected CO2 stays re-buried, it assists in the liberation of more carbon dioxide overall, when the oil gets burned.
The answer is “yes”. The carbon dioxide that emerges with Natural Gas could be used to increase the overall volume of sweetened gas supplied to market. How is that possible ? Well, if the sour gas countries of the Middle East took to deploying desert plains full of solar panels, and then made Renewable Hydrogen from seawater using this solar electricity, then they could methanate the carbon dioxide from Natural Gas into high-methane gas that could be added back to the Natural Gas, increasing its volume.
This would make a better asset out of the carbon dioxide than using it for EOR.
None of this technology or chemistry is new. It just needs applying. And it’s important because a lot of the world’s remaining Natural Gas has a high level of carbon dioxide in it – and that can’t all be used for Enhanced Oil Recovery.