Giant Fields (or Complexes) and Massive Depletion Rates

mekrob · Expert Joined: Dec 09, 2005 Posts: 2663

I am about to email a friend of my energy professor who works for Shell as a exploration geologist, but I thought I'd run this by you guys first.

I was thinking about how we get so much of our oil from so few places: Ghawar (5mpd), Burghan (2mpd), Cantarell (2mpd), North Sea (not sure, >3 mpd), Chinese Major (1 mpd), etc. Few fields that are just gigantic and make up a pretty significant portion of the world's supply. But 3 of the Majors (of past and present) have been in, are in, or will be in depletion and of those, we know the (expected) depletion rates. The North Slope as a whole was 15% according to one report in another thread but was reduced to 6%, and Prudhoe Bay had a massive dropoff as well. Cantarell is expected to have double digit depletion rates and maybe as high as 14%. North Sea production has been waning for several years now, and the depletion rates have actually been acclerating and are now, in some areas, in double digits.

Is this all just a coincidence that massive fields have massive (compared to most fields) depletion rates? Does it have something to do with the geology that allows such giant fields? Or is simply the management (as in the case of Cantarell) that has fallen on its face?
Thanks

I am mising any other high depletion rates from majors?

Bnjmn · Coal Joined: Mar 27, 2006 Posts: 2

I'm not an authority...but from what I've read the depletion rates are directly proportional with the amount of technology used to increase extraction rates.
More water injection and horizontal drilling allow higher flow rates, but also a steeper post-peak decline.

The bigger fields may be the ones that get the most advanced techniques used on them - perhaps the thinking is that they are giants and the increased flow is worth the cost/labor of employing the more advanced techniques.

(again...this is general...someone in the know, feel free to step in with details).

Ben

Ancien_Opus · Heavy Crude Joined: Jul 21, 2005 Posts: 148

There is no simple answer to a complex problem. Here's a simple example but it does not do justice to all the geological and engineering issues involved.

I drain the water from my cabin every year in preparation for winter. Think of the water as an oil reserve. I've got a number of options.

1. Open one drain and let gravity flow the water "natural pressure" but this takes a lot of time and there is always some water left in the plumbing.

2. Open several drains (horizontal drilling) and let gravity flow the water, this takes less time.

3. Combine options 1 or 2 with air pressure (water or gas injection) to push the water out faster, this takes the least amount of time.

The total amount of water never changes, only the rate at which it is removed.

Hope this helps.

mekrob · Expert Joined: Dec 09, 2005 Posts: 2663

So then it would be an appropriate question for a geologist working at Shell? I'd like to see his response, I just don't want to sound like an idiot even though I'll never meet him ever.