Sub-salt26 Apr 2025 00:15
Re. the salt layer and helium. Although PRD has found salt above the Jurassic, that is not where it is from originally. Salt is much lower density than other rock, and acts like a very viscous liquid, so flows very slowly under the surrounding pressure. The salt PRD has encountered was originally a coherent layer of Triassic age, immediately under the Jurassic. It has flowed upwards through the surrounding rock layers to produce domes - diapirs - and at MOU-5 the diapir seen on seismic line 03-ML-06 has unexpectedly turned over to the west and flowed sideways, associated with faulting. The helium detected has probably seeped along the salt intrusion-related fault.
Much of the Guercif basin will still have that Triassic salt layer in place, which will act as a very effective seal for both helium and methane (and oil). I expect there to be substantial amounts of hydrocarbons beneath the salt around Guercif, deeper than any wells drilled to date. Any helium released from the underlying Hercynian (aka Variscan) basement rocks should also be trapped, potentially seen at higher concentrations than at MOU-5 - the helium there is just a minor leak associated with horizontal faulting from the salt diapir to the east.
The next Guercif licence stage, in addition to the much-discussed 3D seismic, requires a 2750m drill into the Jurassic (see p.14, ITR Jan 24) before November 2026. Such a depth would extend beyond the Jurassic, and penetrate a large section of the Triassic, below the salt cap. If, and only if, something of interest had already been found in MOU-5, it would make sense to return at a later stage and deepen the well, which has conveniently been completed for future re-entry. Of course, if nothing of interest had been found, it would make sense to plug & abandon - which hasn't happened.
Salt layers have formed at various stages of geological history, and have proven highly successful targets for exploration - all the Australian helium targets are pre-Cambrian sub-salt, the Cretaceous sub-salt oil reserves in Brazil are estimated at 50-100 billion bbl oil, and the sub-salt reserves of the US section of the Late Jurassic Gulf of Mexico are estimated at 64 billion bbl of oil & 272 TCF of gas.
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