The only gas leak is from someone's rear end.13 Aug 2025 03:39
Yesterday there was a repeat of the suggestion that due to two inversions, the gas in the Guercif region has all leaked away, and all that is left is 'residual gas' of no economic value. This is plainly incorrect for a number of obvious reasons, leading me to the conclusion that this assertion is made by someone woefully ignorant of the geology of the Taza-Guercif Basin (hence TGB Sands), or is a deliberate falsehood.
There were indeed two significant inversions – uplift of strata due to tectonic compression.
The first occurred in the Cretaceous, resulting in the uplift of the underlying Jurassic, giving rise to a series of half-grabens that influenced later sediment deposition. At that time, the Jurassic had not been buried sufficiently deeply for there to be enough temperature and pressure to convert the organic content to oil and gas. Since at that time there was no oil and gas, how could the inversion cause it to leak away?
The as-yet unproven deeper Triassic and Ordovician strata may possibly have been in the temperature and pressure window for hydrocarbon formation at that time, but would remain sealed by a very substantial thickness of upper Triassic salt.
The second, lesser, inversion occurred in Neogene times, ending 6.4 million years ago with the Messinian salinity crisis. This was mostly a minor reactivation of the existing structures, together with the formation of ideal structures for hydrocarbon trapping, such as salt-cored anticlines and synsedimentary faulting (flower structures). The thick layers of carbon-containing sediment deposited in the Rifian corridor, linking the Mediterranean and Atlantic along the path of the Guercif graben, became the source of the biogenic gas found in the upper levels of the Guercif boreholes. Biogenic gas is formed in-situ by the action of methanogenic bacteria on the contained carbon material. This occurred after the second inversion, and is possibly still ongoing. Since at the time of the second inversion much of the sediment had not been deposited and the gas had not yet formed, how could this inversion cause it to leak away?
Overpressured gas has been measured throughout MOU-1, and at top and bottom of MOU-3. How on earth can 'residual' gas be overpressured?
Gas clouds and gas chimneys are different phenomena. A gas chimney is a narrow column (around 100-200m across) from reservoir to surface, imaged by chaotic lines on seismic. It usually originates from the crest of a structure and is caused by faulting allowing gas escape. A gas cloud, as seen to the east of MOU-2, is wider in extent, and originates from the bottom of the structure. This indicates a full structure overflowing (underflowing?) from the base. I specifically asked Paul Griffiths if the cloud at MOU-2 indicated a fill-to-spill situation; in his opinion this is the case, and was part of his highly positive opinion of the structure's commerciality.