“Methane is essentially INSOLUBLE in salt water...”
Thank you for your post here of reasoned observation. Seems one of the things in this discussion that has been missing has to do with the nature of the product that was actually released into the Gulf. There was some discussion of disappearing ‘plumes’ of oil, but very little as to the nature of these methyl hydrates that were so critical, at first, to the challenge to cap the discharge at the sea floor. Ultimately, under less pressure, these compounds would progressively volatilize. None of this was very clearly reported during the event.
I'm sorry, but this is simply not true. The solubility of methane in both fresh and salt waters is far from negligible.
"At atmospheric pressures, the methane solubility in water ranges from 26 to 32 mg/L."
The above is for fresh water. The higher salinity of seawater probably dictates a somewhat lower value at atmosphteric pressure, but that is offset by the higher pressures sub-sea, which should mean the solubility is significantly higher, but the above number is sufficient to make my point. I haven't located a value for seawater yet.
When my wife wakes up, I'll ask her. She is a retired petroleum engineer, and methane solubility is brines is a BIG part of reservoir characterization.