[v6g]

Hi - occasional reader first time caller...

I've been playing with the numbers in the BP statistical review and found that over the time period for which data is available (1965+) oil is getting lighter. I did this by taking annual oil production in tonnes and dividing it by the annual production in barrels. This shows a constant decrease in the average weight of a barrel of oil - why?

I could accept if it was just a one-off annual change - but it's a constant trend.

Any clues / suggestions?

[zoidberg]

Maybe they keep adding barrels of oil equivalent like natural gas liquids, biofuel so thats why the barrels number gets higher, while actual oil production isnt rising as fast.

[Bas]

Would you care to illustrate your findings?

[Schmuto]

They're using thinner and thinner barrels.

[efarmer]

Could it be that catalytic cracking and refining are more
efficient? They do end up with more than a barrel
of net liquids from a barrel of crude after refining
because things like gasoline are far more volume
and less density than what they are derived from.

Stay tuned, the deep talent pool of this forum
has petroleum scientists and geologists and they
will put us in the know with the numbers to back it up.

[v6g]

Ok - here goes (not too good with attaching pictures ... first try).

Graph (large)

This shows the weight of a barrel of oil in tonnes according to the 2007 Statistical Review of world energy. (ie: in 1965 a barrel of oil weighed about 0.135 tonnes).

I made this chart by taking the world data from the statistical review worksheet for "Oil Production - tonnes" and dividing it by the data on "Oil Production - barrels". The barrels data is in thousand barrels daily - so I corrected it for leap years (interestingly otherwise it showed a noticable "bump" every 4 years).

It's a very small change - but there's a definite trend - it's that that arouses my curiosity. This shows world totals - it would be interesting to compare specific regions/countries.

[v6g]

Maybe they keep adding barrels of oil equivalent like natural gas liquids, biofuel so thats why the barrels number gets higher, while actual oil production isnt rising as fast.

I don't think so - BP's spreadsheet has separate worksheets for Natural Gas and I get the feeling that they don't consider things like biofuels in their data. But maybe you know more about it than me - I'm just a "casual" observer.

Could it be that catalytic cracking and refining are more efficient? They do end up with more than a barrel of net liquids from a barrel of crude after refining because things like gasoline are far more volume and less density than what they are derived from.

Again, I don't think so, AIUI the data is for raw production, not refined end-product.

[efarmer]

Since a tonne of oil is 1000 kilograms mass and a barrel is 42 U.S. gallons
of volume the only guess I have is we have been averaging progessively
lighter crude supplies or measuring in warmer temperatures, or both.

I know they use BOE and TOE (barrel of oil equiv. and tonne of oil equiv.)
to adjust for varying energy content of crude by weight or volume.

I assume the money goes down for TOE and BOE and that the
weight versus volume trends and variances are adjusted out.
Either that or money is dumber than I believe it to be.

Over 4 kilos per barrel on an almost straight line trend does
seem strange.

[v6g]

Damnit - you've got me wondering now...!!
Here's the graph for a number of countries - they all show the same thing (I wonder what happened in the UK in the early 70's).
Chart (huge)

Remember, these are AVERAGES not production TOTALS.

Note how Canada starts increasing once the oil sands came online around the turn of the century.

[v6g]

Since a tonne of oil is 1000 kilograms mass and a barrel is 42 U.S. gallons
of volume the only guess I have is we have been averaging progessively
lighter crude supplies or measuring in colder temperatures, or both.

I know they use BOE and TOE (barrel of oil equiv. and tonne of oil equiv.)
to adjust for varying energy content of crude by weight or volume.

I assume the money goes down for TOE and BOE and that the
weight versus volume trends and variances are adjusted out.
Either that or money is dumber than I believe it to be.

Or, in other words, this could be an inverse measure of global warming ... now there's an idea!!??

[efarmer]

I have seen weights per barrel vary from about 127 to almost 155 kilos depending on source so
it does seem that 130 to 135 range you are showing is on the lighter end and well within the
norms. I will be interested to learn why it is such a constant slope down for this period
once someone who knows chimes in.

Do you have global data instead of BP company specific?

[Pops]

Wow! A real live oil question, how novel.

I have no clue but notice on the country chart each plot starts at a certain level, drops some, then recovers before a continual decline.

I know nothing about the science but it is nice to see a thread about something other than politics.

[v6g]

Bump!

Nobody knows - seriously??

[dinopello]

I would look for some other fundamental trend that would point to a correlation. For example - most likely the specific gravity of oil (on average) is getting smaller. Do "heavy" crudes or "light" crudes have (in general) the lower specific gravity ? What about "sweet" and "sours" ? I know specific gravity and viscosity are generally not correlated.

[Pops]

Bump.

[Grautr]

I would look for some other fundamental trend that would point to a correlation. For example - most likely the specific gravity of oil (on average) is getting smaller. Do "heavy" crudes or "light" crudes have (in general) the lower specific gravity ? What about "sweet" and "sours" ? I know specific gravity and viscosity are generally not correlated.

It must be something to do with the quality of the oil. Over time they are pumping out less quality stuff.

What happened in Britain in the 70s? Thats when North Sea oil came online big time.

[Grautr]

If what I said above is true then I can only think that as heavier oils are pumped up then the distilation process is lowering the gravity. Maybe because the distilation process is improving over time and they are constantly refining a better grade of fuel?

[HumbleScribe]

The trouble is that most crudes are actually heavier now than they used to be, as sourer crudes are used.

My only contribution is to add that tonnes of oil equivalent is a unit of energy, not volume. Is it possible that the energy content of the oil is falling, not the mass? Higher proportions of sulphur might account for that. The change looks to be the same order of magnitude as graphs of sulphur content I have seen.

Has anyone asked BP? Maybe I'll give them a call.

[TheDude]

When I divide annual tonnes/annual barrels I get numbers in a range from 0.04928 to 0.04802, not the figures you have. But I see the same weird downward trend. I'm using the 2009 Stat Review. The notion of lighter hydrocarbons sneaking into volumetric measurements makes sense to me, good catch. But this is affecting only one side of the equation...how does that work? Presumably the equations themselves haven't changed over time. Apply a linear trend over the data I get a .96 correlation.

You might want to play with numbers from the EIA's International database. These only go back to 1980 but you can select C+C, NGLs, or "Other Liquids," as well as Total oil supply. They also have Heat Content data for oil from various nations, but these are almost wholly unchanging, except in the early 80s for a few nations like Indonesia, Australia, and Thailand, near as I can tell by skimming over the list.

Stat Review also has Oil Consumption figures in both metrics, there might be something of interest there as well.

[Pops]

My only contribution is to add that tonnes of oil equivalent is a unit of energy, not volume.

I think the new guy is the winner.

The tonne of oil equivalent (toe) is a unit of energy: the amount of energy released by burning one tonne of crude oil, approximately 42 GJ (as different crude oils have different calorific values, the exact value of the toe is defined by convention

http://en.wikipedia.org/wiki/Tonne_of_oil_equivalent

Seems logical the energy embodied in less desirable oils would be, less.