They call them Service Lighters or SL's for short.  In reality they are pretty ugly vessels, looking like a cross between a coastal tanker and a barge.  The mate meets you at the top of the gangplank and leads you to the captain's quarters, where the air conditioning hits you like a plunge into the swimming pool.
This is Belém, a seaport in northern Brazil, right next to the equator; it is the operational base for the SL's which service the Amazon delta.
After greeting you, the captain issues curt instructions for the boat to depart and then enquires "How much do you know about the Methane Mining Operation?"

Just start from scratch, if you don't mind

"Well, it all stems from Global Warming, and a couple of discoveries made back in 2000:
The first was that the Amazon was a CO2 sink, as opposed to the wisdom of the day which held that mature forests were carbon neutral.  Well, as we all know now, the missing carbon was being 'exported' down the rivers and deposited, along with a good bit of silt, as debris in the outer Amazon delta and beyond.  Here is decomposed anaerobically to methane and CO2.
The second discovery was that, in deeper water still, much older methane had been stored in the seabed as Methane Hydrate… this is a crystal which forms when the pressure is high and the water is cold.  Unfortunately, when the temperature rises, it becomes unstable and dissociates to become methane gas and water once more.  The methane of course, re-enters the atmosphere as a powerful greenhouse gas; a scenario which the scientists call 'positive feedback', and stood to amplify the effect of Global Warming by a large factor.

Well, if you put these scientific factors together with a couple of economic ones, ie that Brazil was desperately short of energy and that the World Carbon Trading Bank was offering a substantial bounty for methane mining, and you don't need a crystal ball to see the outcome.  Our company BMR (Brazil Methane Reclamation) was founded within 6 months.

So we have two mining teams, the first, called 'Low-Pressure or LP Methane Miners', work in the relatively shallow waters of the delta; they harvest wood debris and low-pressure methane.  The second, called 'High-Pressure or HP Methane Miners', work in the deeper offshore waters and harvest high-pressure methane locked up in hydrate.  We Service Lighters are just runners for the LP Miners, but it's quite exciting enough for me", he finishes with a grin.

By now we're skimming across the light brown water of a river mouth: What speed are we doing?

"55 knots.  This boat, although it looks slow, is designed to plane on the relatively calm coastal waters, and of course, we're empty now.  We have to slow down a bit with TIRs behind."

You let that one pass.  Are we at the sea already?

"No way!" the captain laughs "this is the Point where the Pará River joins the Amazon.  In fact, if you look off the bow quarter, you can see the opposite bank", he hands you some binoculars.
There is a smudge of vegetation just visible on the horizon ahead through the heat haze.

And how far away is that?

"Oh, the river is only about 20km wide at this point, although this is only one of the branches.  The entire Amazon delta is about 300km across"
He sounds casual, but you think you can detect a certain pride in his voice

So how far is it to the sea then?  "From here, about 100km" 

Good Lord!  The scale of the place is amazing!

"So", he continues, driving the point home, "our shallow water concession extends some 250km from the coast and totals just under 95,000 square kilometres, or to put it in perspective, about three times the area of all the oilfields in the world combined"