"Fossil fuels"
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I tried to reply 2x on my ipad and it froze. trying again from desktop. hope i encapsulate my previous. i want to make 3 points, namely, kerogen maturity, historical narrative, future outlook.
kerogen is much more than shit. you're being salty, i like it. studying kerogen, we can predict what hydrocarbons will be produced. more woody...gas. more algal...more oil. that being said, there is a temperature-pressure relationship. important for economic calculations. It has to do with elemental ratios of what is preserved through oxidation.
https://imgs.search.brave.com/_ESA76eKCeB9qe6hFW97g7HgZX8wew6Pz7OkXaYC5zs/rs:fit:430:225:1/g:ce/aHR0cHM6Ly90c2U0/Lm1tLmJpbmcubmV0/L3RoP2lkPU9JUC5w/cVRvTk9Zc0Q2ZzVV/S3owZXllVHNnSGFJ/SyZwaWQ9QXBp
https://en.wikipedia.org//wiki/Kerogen
with depth of burial and increased temperatures this creates an "oil window" and "gas window". with increased depth and increased temperature we can drill, in oil areas, for gas wells. alternatively, we can seek the temperature source (tectonic; see west texas delaware basin) and drill gas wells at the same depth but drill gas wells. I can point you towards literature that shows this. this affects LPG yields and economics.
https://www.researchgate.net/profile/Robert-Ross/publication/322641749/figure/fig4/AS:613903448936461@1523377396612/Diagram-showing-how-the-formation-of-oil-and-gas-depend-on-temperature-and-pressure.png
I can get into the details, but modern oil/gas leases only cover the deepest productive rock. older leases do not. pugh clause.
let's take a step back. 100 years ago we only drilled the best shit. now, we are forced in to drilling pretty crappy rock. crappy rock that the ppl from 100 years ago would not have imagined. all of their equations break down. this is the shale revolution. that does not mean it is unexhaustive. but a calculation is made on how deep to target for a lease. the deep rights may expire.
let's go back to kerogen. the old model was source rocks (rocks deposited during oxygen-starved times (think woodford formation)) produced oil, which migrated to petroleum traps. circa-2005-08 we migrated to a new model where we target the source rocks, under active hydrocarbon generation, that's the new target (accelerated ~2017 ((my involvement))). So now we drill the rocks actively generating hydrocarbons (think Wolfcamp).
What we monitor? Pressure relationships from nearby wells. Rinse-n-repeat the pressure depletion. How do we get an extra few % recoverable?
it's all about economics. a good recovery factor for a many reservoirs is 40%. and that's after waterflooding. waterflooding is a process of injecting water from surface to maintain the reservoir's pressure. not all reservoirs are good enough to economically do this.
so natural pressure depletion is called primary production. waterflooding is one method of secondary recovery.
now, what is tertiary recovery? let's stick to oil and forget gas for now. as you decrease the oil saturation (through production), the relative permeability to water (the wetting phase) increases. at some point you reach an economic limit, because it costs money to pump the fluids to surface, etc. that is when wells get shut in, plugged, etc. but there is still recoverable resource in the reservoir.
i once worked on a project (15 years ago) where we pumped soap into an underground reservoir. same as washing your hands, right? if oil stayed at a high enough price for long enough, this technology would unlock vast amounts of recoverable oil. we got local recovery factors exceeding 90% of OOIP on that pilot project.
resource vs reserves https://en.wikipedia.org/wiki/Mineral_resource_classification
Blasingame fanboi https://www.youtube.com/watch?v=GIORNcSUbD4
EOR https://en.wikipedia.org/wiki/Enhanced_oil_recovery
ASP flooding https://onepetro.org/SPEEURO/proceedings-abstract/17EURO/2-17EURO/D022S014R003/194812