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Oil fields: heavy crude or light crude?

General discussions of the systemic, societal and civilisational effects of depletion.
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Re: Oil fields: heavy crude or light crude?

Unread postby Tanada » Fri 30 Nov 2012, 09:10:21

$this->bbcode_second_pass_quote('rockdoc123', '')$this->bbcode_second_pass_quote('', 'o') the recently drilled sub salt deposits off of Brazil that were in the news so much in 2010 and 2011, what age are those source rocks?


I believe that they are mainly the mid-Cretaceous source rock that is so prolific as a source along both Atlantic margins but there is a possibility that Late Jurassic sources come into play. I haven't run across a paper that talks about oil typing of the sub-salt (not something I've followed too closely due to the high cost of the wells and tight control by Petrobras), I'm pretty sure it is out there and I'll just have to look.

I found sources stating it is early Cretaceous, thanks!
$this->bbcode_second_pass_quote('Rockdoc123', '
')
$this->bbcode_second_pass_quote('', 'A')lso I have seen several places speculate on major deposits in the deep Arctic basin's from the Azola event just as the PETM was declining, do you think those are realistic expectations?


Very rich organic material but it would have had to have been buried quite deep under elevated heat flow conditions given it's age. Areas where there has been strong outflow of post Eocene sediments (deltas) would be the most likely spots for this to work. I haven't come across any geochem modeling in my normal meanderings through the literature but will have a look see as to what I can find.


So that sounds like the Mackenzie Delta in Canada and the Ob, Lena and Enisei in Siberia. Does the river have to be one of the big four to make the kind of delta you are referring too or will smaller rivers do the same thing just at a slower rate of deposition?
$this->bbcode_second_pass_quote('Alfred Tennyson', 'W')e are not now that strength which in old days
Moved earth and heaven, that which we are, we are;
One equal temper of heroic hearts,
Made weak by time and fate, but strong in will
To strive, to seek, to find, and not to yield.
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Re: Oil fields: heavy crude or light crude?

Unread postby rockdoc123 » Fri 30 Nov 2012, 11:11:54

$this->bbcode_second_pass_quote('', 'S')o that sounds like the Mackenzie Delta in Canada and the Ob, Lena and Enisei in Siberia. Does the river have to be one of the big four to make the kind of delta you are referring too or will smaller rivers do the same thing just at a slower rate of deposition?


the main components in the equation that describes source rock maturation and expulsion is temperature and time and type of source rock. The activation energy associated without different kerogen types governs the rate at which a particular source rock expels hydrocarbons. As a consequence Type I kerogens might have to be buried deeper to get the same maturity as their Type II conterparts. Temperature is by far the more important to the extent that some authors have argued that it is strictly a temperature relationship although that isn't mainstream thinking. Temperature has several components that are important, firstly the crustal type governs largely what heat flow recognized in the sedimentary column will be. Continental crust is thick and heat flows are much lower than oceanic crust which is thin, transitional crust being in the middle. As well the type of sediment deposited has some influence as different rock types have different thermal characteristics. Time refers to how long a particular source rock remains buried at elevated temperatures. In deltas the deposition is quite quick so there is a chance to get younger source rocks mature quicker. Unfortunately there is no rule of thumb as to burial depth. My guess (and I qualify that as being a wild ass guess) without having any data is that you probably need burial depths of 2.5 to 4.0 km before you would see much in the way of oil generation unless, of course, the heat flow is higher than I am assuming (I am guessing it is somewhere around 40 - 60 mW/m2).
You might want to check the USGS website. As I remember about 3 or 4 years ago they did an Arctic Ocean analysis of future hydrocarbon potential and put together a map that highlighted the areas with greatest potential. As I recall it seemed to be mainly gas prone but can't remember exactly.
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