Prospects for Deep Water Oil

ltplayer · Coal Joined: Jul 10, 2008 Posts: 2

What are the prospects for deep water oil finds? I read somewhere (and I've been trying to find the book all day) that deeper than a certain level oil basically cooked or could not form or something like that. The depth seemed pretty shallow but I can't remember the exact number.

So I'm wondering if I was mislead by the book, or if I'm missing something.

heroineworshipper · Posted: Thu Jul 10, 2008 2:13 pm Post subject: Re: Prospects for Deep Water Oil

Nothing in the deep water but deep water. The amount of energy needed to lift oil a certain distance exceeds the energy in the oil. That is until we rediscover slavery.
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obixman · Posted: Thu Jul 10, 2008 2:51 pm Post subject: Re: Prospects for Deep Water Oil

Two things about deep water....

1) In order for there to be Oil, first there needs to be (or have been) a fairly thick layer(s) of sediment. With the exception of a few places, deep water simply doesn't have thick enough sediments to be a major oil source.

2) Also for the most part, oil containing sediments have to be old (or the oil has to to come from old sediments) - and for the most part deep water sediments are new .. and not really connected via a migration path to older sediments. Again, as in point one, there are some exceptions, but they are VERY few.

You are right in that below a certain depth (about 20,000 feet [7,000 meters]) the sediment has for the most part had the oil cooked out into gas. There are few oil resevoirs below that depth (which does change somewhat depending on the history and geothermal history of the basin you look at.)

I was with Gulf Oil in the mid 70's when it became obvious that there was a depth below which Oil will not be found, the revision in thinking was great, and a fair number of people in the industry became quietly aware that peak oil was going to come about much quicker than they thought....

ltplayer · Coal Joined: Jul 10, 2008 Posts: 2

The book was called "Hubbert's Peak".

entropyfails · Moderator Joined: Jun 30, 2004 Posts: 607

Read

http://en.wikipedia.org/wiki/Cracking_(chemistry)

and
http://en.wikipedia.org/wiki/Geothermal_gradient

and probably
http://www.theoildrum.com/tag/deepwater

You were not mislead. The earth gets warmer the deeper you go. Oil breaks down at those temperatures. There are only a few special spots in the world where deepwater wells work, we may find more, but they are likely to be very small reserves.
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ROCKMAN · Posted: Wed Jul 16, 2008 8:25 am Post subject: Re: Prospects for Deep Water Oil

Everyone is right and wrong. To be exact it's not so much a depth limitation but a temperature limit. Yep..temp breaks oil down. A lot of the natural gas resource plays you've been reading about have followed that very history: big oil accumulations turned into big NG accumulations. And yes, there aren't too many spots where you can drill to far without hitting the thermal barrier. The Gulf of Mexico is one spot. Last fall I drilled the 3rd deepest well in the western hemisphere (34,000'). A $148 million dry hole. Not too hot for oil to survive though. There just wasn't an accumulation in that spot.

Other deep but cool enough spots are off the w coast of Africa, off the w coast of the US, off Alaska. The big DW play everyone talks about now is offshore Brazil. Though the water depths are significant (3000'+) the formations are actually relatively shallow (above 15,000')

dorlomin · Light Sweet Crude Joined: Aug 05, 2007 Posts: 1062

Would I be wrong in thinking that the abysall plain would tend to be lacking in cap rock type formations to trap any oil? Also the Atlantic would mostly be too young for the Mid-Cretatious and Upper-Jurassic times when most of the oil formed. would it not?

Another question the oceanic crust is much thinner than the continents would this mean that the thermal gradient is much thinner so is the so called 'oil window' inherently thinner on the ocean floor\ abysal plain?

rockdoc123 · Light Sweet Crude Joined: May 16, 2005 Posts: 1685

ROCKMAN temperature is most important but time also comes into the equation. Long periods at lower temperatures is as effective converting source to oil as higher temps over shorter periods. The Arrehenius function determines the response. That being said a lot of the major oil and gas discovered in deep to ultra deep water is in Tertiary sediments which means that temperature does take a greater role. However when we look at potential Cretaceous or older reservoirs in places like West Africa time and an understanding of burial and uplift history is pretty crucial. If you are speaking of phase change...(i.e liquid oil to condensate or gas) then temperature is of course the main player with time being somewhat inconsequential.
And that segways to Dorlomin's question. Yes the oceanic crust is thinner and because of the rock type is also a better thermal conductor. Rule of thumb used to be that for cratonic areas (continental crust) the geothermal gradient is somewhere in the order of 10 - 20 C/km, which moves to about 40 C/km for transitional crust and up in the 60 and higher range (depending on how old it is) for oceanic crust (the highest heat flow would be at modern rifts where it is well over 100 C/km an example being the east africa rift system). The interesting part of this is that for Tertiary deltaic or turbidite fan deposits the thickest deposition is at some point from shoreline which might be shallow to deep water. In cases such as offshore Namibia and the Nile Delta the thickness of sediments is so great that the older source rocks generate gas. As you move into deeper and deeper water the reservoir section thins depositionally which in turn results in the source rock at some point being in the oil kitchen. Offshore South Africa that is demonstrated by the Ocean Drilling Program wells which intersected Cretaceous source rocks which are immature out board of a major gas field that has the source rocks in the gas window. So somewhere there should be an oil rim to major gas plays like the Nile Delta. Shell paid a huge amount of money looking for it many years ago with no success. It's a complex modeling problem that the industry has struggled with for a long time.

ROCKMAN · Posted: Thu Jul 17, 2008 11:39 am Post subject: Re: Prospects for Deep Water Oil

So true rockdoc,

I'm working E Tx and the basin centered gas plays there have had 60 million years to cook.

ROCKMAN · Posted: Thu Jul 17, 2008 11:46 am Post subject: Re: Prospects for Deep Water Oil

dorlomin,

There's a lot of younger oil then you might think. Rockdoc talks about it in detail. As far as the Atlantic goes are you refering to the lack of potential in the center of the basin? If not, check out the near shore discoveries off the Canadian Atlantic coast. Not nearly as many fields as the Gulf of Mexico but they have found some big oil and gas accumulations.