RE: Jimmy 23. Question about subsurface risks20 Oct 2022 13:18
Hi fernan
Yes I have considered those risks, particularly as the anchois basin went through two geological periods of basin inversion which increases the risk of compartmentalisation.
Firstly, we have 3D seismic which most fields now have and most importantly the reservoirs can be imaged directly on the seismic hence intra reservoir faulting is easier to see.
Faulting within a reservoir acts as a flow barrier, think of a kink in garden hosepipe as an analogy.
Importantly, chariot have used both Avo and successfully used spectral decomposition of the seismic signature to predict both reservoir and gas composition and confirmed this by the drilling of anchois 2.
Now it’s important when doing post well analysis to see what was predicted and why and compare this to the actual drill results.
So the pre drill analysis and spectral decomposition correctly predicted the C & M sands however the O sands were confirmed as being a thick reservoir and had minor gas thickness. When I look back at the seismic analysis page 16 of the January presentation, and earlier presentations, it’s obvious that the anchois 2 well was to be drilled into a compartmentalised section of the O sand with a week spectral decomposition gas signal. Because that was the top of the O sand structure, it was the logical place to drill the o sand, but the importance of the well is that it validated that spectral decomposition and 3D seismic identified the O sand reservoir compartment and that the gas seismic signal was week. It’s equally important to predict where gas and reservoirs are and where they are not and chariot have done this.
The other factor to consider when evaluating compartmentalisation risk is the thickness of the reservoirs, so if the reservoir is 50 meters thick and the throw on a fault is 10 meters the fault will act as a flow barrier but not stop the flow of gas across the barrier.
From a gas production point of view, these factors are taken into account in a 3D petroleum reservoir model which is used to optimally locate the production wells, which in turn reviewed by the CPR audit of recoverable gas volumes.
As the throw on faults are relatively small at anchois this should not be a problem
The evidence used to confirm the audited gas volumes, has also identified the continuation of the gas volumes across the anchois west and north faults, but this additional gas is not included in the audited 2C gas volumes, instead it’s included as derisked prospective resources with a chance of success of 49 to 64% .
I days of old these 735 bcf of additional gas volumes would have been classified as “probable gas reserves” but modern reserve classifications don’t allow that anymore.
That’s a long winded way of saying that the audited Cpr 2c gas volumes have taken compartmentalisation risk into account, and confirmed the huge potential of the nearby low risk gas filled reservoir potential.
Jimmy
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