RE: Rns11 Aug 2021 09:39
Porosity refers to the spaces between the individual sediment grains that make up the sandstone reservoir in the Karoo (for example), you need a decent porosity in sandstones, typically 5 - 20% is a good sweet spot. Anything above 35% and you start to risk poor consolidation in your rock formation and therefore undermining problems with strata and, in the case of oil, sediment being extracted along with any oil. The other side of the coin is permeability, which essentially refers to the plumbing capabilities of the rock, so are there fractures or other mechanical properties allowing the oil/gas/helium to 'migrate'. The two go hand in hand as if you have great porosity but low permeability (such as with shale) you can't extract anything, hence the need for fracking in shale gas situations to stimulate flow from the pores... Hope this helps!