Gas Contents - I dont like companies that report in an air dried basis. Bow are bad boys for this. Example - if you have high ash coals going 60-80% ash like Bow and Rog have. A correction back to ADB gives you far higher GC's than what you really have. The way it should be done is you report at seam ash and either a 15% or a 40% or a 80% ash depending on what your average seam ash is expected. The amateurs who report on ADB claim it gets them back to a base for comparison but the experts mostly agree it is misleading and can cause significant errors in reserving calcs.
The problem with the riflebird well is (after reading the Geo's litho log) which is a little better than I can make with my eye....Is that a lot of the seams are made up of large amounts of carb mud. This is very high ash carbonaceous material and will have no cleat. It can adsorb gas but does not give it up very easily unless you provide a big surface area (like coring or fracturing it) There are alot of small bands of coal that appeared cleated to the Geo but didn't show so well in the photos. I still stand by and say that 17m gross is overstating the Net coal in the well. But unfortunately that is the industry lingo and pretty common practice so no one could really call them out on it.
The other thing that struck me with their reports were the claims of gas saturation. Gas content at saturation should steadily increase with depth because there is more hydraulic pressure forcing gas to stay chemically held to the coal. The gas contents should be incresing from 600 to 800m where it should after that start to flatten off. So I found their comments a little confusing. There is only a couple of scenarios here - 1. The top seams are saturated and the bottom ones aren't. 2. the coal is so ashy it can't adsorb more than the figures they stated..... Its a bit hard to make a call on this because the seams really are so high ash. Generally you would say that those contents for those depths are not saturated but because of those contents. We do have similar coals in the Bowen Basin at shallower depths with higher gas contents - and they aren't saturated....so its a hard one. Only the isotherm testing will tell and I very much doubt you will get a look at the curves....just a stated figure or a superlative (like with the perm).
The other issue in the Clarence Moreton is that unlike many other coal basins there are clean sandstone units that can act as reservoirs. Higher levels of ethane and other hydrocarbons indicates the gas is of a thermogenic source i.e. has been generated by maturation of the coal. When basins are uplifted and disturbed late in their lifetime it lowers the reservoir temperature and lets some of this gas escape leading to undersaturation. This is oft times offset by micro-organisms that turn the coal, CO2 and nutrients into gas. These only make CH4 and not ethane. So the potential gas we are seeing in these wells may be free gas from sandstones. Hence the feeling of good perm and good saturation when really it is only a small amount of free gas in the system.
Argon flushing - coal on contact with air forms nitrogen. During Q3 the last phase of gas desorption a selected representative sample is selected and is crushed very fine in a sealed ring mill at 1 atmosphere. When you crush the coal you expose a large surface area to air. This air oxidises the coal and gives off nitrogen. By using an inert flush the coal does not oxidise. The figures I usually see are in the order of 6-8% N2 without an Argon flush. The ones in the report are in cases 60-80% so not sure what has gone on here. Even if you wanted to save a few bucks you would still run one argon flush per seam....or five or six just to validate the results...there looked to only be one or two in the report with high levels of N2.
Cheers, Gaz
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