Lots of questions and answers at The Oil Drum.
See in particular the post from Matt Savinar (AlphaMale Prophet of Doom) about a third of the way down, from which I extract this:
If the decline rate is 4%, that halves production in 17.5 years or so. On top of the usual decline rate, I think it reasonable to expect further/additional disruptions due to war/terrorism and weather. (More Katrina-type events) So that bumps it up to 6% let's say, halving the supply in 11.5 years. If the decline rate is 8% (as some have speculated) plus anohter 2-3% due to terrorism/war and weather plus then we're looking at a 50% cut in 7 years.The 'some have speculated' is Schlumberger.