Some more info on annual depletion rates of remaining URR.

Tariq Shafiq, a petroleum engineer who was Vice President and Executive Director of the Iraq National Oil Company (INOC) said:
http://www.mees.com/postedarticles/oped/a46n50d02.htm

Adopting a depletion rate for Iraq of 4-5%, which is well within good reservoir management practice for large fields, would permit increasing Iraq’s production rate to a peak of 10mn b/d, maintaining it for nine years and then allowing a natural decline. At the end of 25 years, the production rate would be 6.4mn b/d, but the reserves would have declined to 42bn barrels from its current level.

On the same basis of maintaining a depletion rate of 4-5%, Iraq can lift the 10mn b/d plateau to 12mn b/d, and maintain it for eight years provided that 60bn barrels of additional new discoveries are added. This represents only 28% of the likely potential reserves. The plateau could be maintained for eight years, as new reserves are ploughed in at the rate of 3bn barrels per year starting on the seventh year. By the end of the 25th year, production would have reached 11mn b/d and remaining 88bn barrels.

Shafiq thinks 4-5% depletion rate is good for large fields. Perhaps my forecast for Saudi Arabia is too optimistic since I am assuming a maximum of about 5.3%, which is greater than Shafiq's upper limit of 5%.

If Saudi Arabia produces its fields at a higher rate of say 6% the forecast curve in my Fig 9 will show a slower production decline rate in the next few years but then the decline rate will steepen even more. The North Sea is a good example. From 2000 to 2003, the annual depletion rate of remaining URR was just over 12%/yr. As the depletion rate drops due to maturing fields, the production decline rate has been around 10%/yr.

Colin Campbell's modelling assumes that for
http://www.feasta.org/documents/feastareview/campbell.htm

the post-midpoint group, production is assumed to decline at the current Depletion Rate, which is annual production as a percentage of the Yet-to-Produce. In the pre-midpoint countries, production is assumed to rise to midpoint on the current trend or as otherwise determined.

The midpoint is the date when 50% of the URR has been produced. As Saudi Arabia has passed midpoint some years ago, assuming 112 Gb produced out of an assumed total URR 175 Gb, maintaining an upper limit of about 5.3% annual depletion rate of remaining reserves seems appropriate. 5.3% was the depletion rate reached in Aug 2006 when it is believed that Saudi Arabia was producing at its maximum potential.

Here is a more detailed view of the first part of Fig 9 which shows the depletion rate of remaining URR exceeding Shafiq’s 5% limit starting in about Mar 2005 and returning back to just under 5% in Feb 2007.

I'm still waiting for an ex Aramco employee to post here and clarify Saudi Arabia's forecasts :)

No, I am aware of the difference between depletion and decline. But a constant depletion rate (as a percentage) against a shrinking reserve will result in declining production.

In other words, if I have 100 Gb of reserves this year and I deplete those reserves by 5% or 5 Gb (produce that much) then next year I have 95 Gb (not counting reserve growth for a moment, ok?). Now if I deplete 95 Gb by 5%, I only produce 4.75 Gb for the year.

Thus, if I maintain a constant depletion rate against a shrinking reserve resource my production must decline. That was how I understood Ace's comment and his further explanation below appears to go in the same direction though again he didn't directly answer that.

Anyway that is why I asked, because that is how I understood the comment and it was clear from your comment that you believe he meant something else so I was hoping for a bit more clarity.

"The greatest shortcoming of the human race is our inability to understand the exponential function." -- Dr. Albert Bartlett
Into the Grey Zone