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Geologist: Depletion of Oil Reservoir "Unlikely"
There are 4 alternative explanations
for the unexpectedly low oil pressure in the BP well: (1) A leak in the
pipe in the well bore; (2) flow under the well between sand layers; (3)
a blockage in the well; or (4) depletion of the oil reservoir.
This
essay focuses on the fourth possibility: depletion of the oil
reservoir. Specifically, BP claims that the oil well pressure is
perhaps 1,200 pounds per square inch less than expected because the oil
reservoir has been depleted.
The size of
the reservoir is crucial in testing BP's theory. While there are other
factors which determine oil pressure, the size of the reservoir is
probably the most important.
BP claims that there are only 50 million barrels worth of oil in the reservoir underneath the leaking spill site. Assuming a worst-case scenario of 100,000 barrels leaking a day, and given that the spill started 89 days ago, that would amount to around 8,900,000 barrels which have leaked to date.
Under this scenario - where 17.8% percent of the oil has leaked - the pressure of the well could, in fact, be declining.
But the Guardian noted on June 18th:
But
the 50m figure cited by Hayward took some industry insiders by
surprise. There have been reports the reservoir held up to 500m barrels
– the figure quoted by Hayward's questioner, Joe Barton, a Republican
from Texas.
"I would assume that 500m
barrels would be a more likely estimate," said Tadeusz Patzek, the
chairman of the department of petroleum and geosystems engineering at
the University of Texas at Austin. "I don't think you would be going
after a 50mbarrel reservoir so quickly. This is just simply not enough
oil to go after."
I spoke with the top geologist
at a major oil company today. He agreed that BP wouldn't have spent the
amounts needed to drill such a deep well unless BP thought that the
reservoir was a lot bigger than 50 million barrels of oil.
He
also said that it was unlikely that the well pressures have decreased
because of depletion of the oil in the reservoir unless BP's estimates
were way to high (in other words, if the well was as big as BP must
have thought to invest so much in the well, it couldn't have been
substantially depleted by now).
Indeed the Guardian article notes that even BP is not sure of the 50 million barrel estimate:
"We haven't made an assessment of the reserves as far as I know," said Toby Odone, a BP spokesman. "You start evaluating the reservoir once you complete the well. Obviously we didn't get to that point."
Wolf Blitzer noted on June 16th:
One
-- one expert said to me -- and I don't know if this is overblown or
not -- that they're still really concerned about the structural base of
this whole operation, if the rocks get moved, this thing could really
explode and they're sitting, what, on -- on a billion potential barrels of oil at the bottom of the Gulf of Mexico.
Similarly, Bloomberg reported on June 19th:
The ruptured well may hold as much as 1 billion barrels, the Times reported, citing Rick Mueller, an analyst at Energy Security Analysis in Massachusetts.
And Rob Kall claims that a source inside BP tells him:
Size of reservoir - estimated by BP and its partner, Andarko to be between 2.5B and 10B bbl. (that's 100,000,000,000 gallons and 400,000,000,000 gallons).Yes - all of those numbers are BILLIONS.
Given that BP's nearby Tiber and Kaskida wells each contain at least 3 billion barrels of oil (see this, this, this and this), estimates of more than a billion barrels for the leaking Macondo reservoir are not beyond the realm of possibility.
Recoverable Versus Total Oil Reserves
There's also the issue of whether 50 million is an estimate of recoverable oil or total oil in place. As the Guardian wrote:
BP
spokesmen said that Barton [with the 500 million barrel estimate] was
referring to recoverable oil rather than the total size of the
reservoir.
The Guardian clearly got this backward: the
total size of the reservoir is - by definition - larger than the amount
of recoverable oil. So what BP spokesmen must have said (and the
Guardian got backwards), is that 50 million was an estimate of
recoverable oil, while 500 million is one possible estimate for total
oil in the reservoir.
Early Estimates Are Usually Low
It is well known that:
In general, most early estimates of the reserves of an oil field are conservative and tend to grow with time. This phenomenon is called reserves growth.
Therefore,
50 million barrels might have been BP's early - and, hence, understated
- estimate of the amount of recoverable oil in the reservoir.
Seismic Tests are Imprecise
Is
it possible that BP drastically overestimated the size of the oil
reservoir, and that it really is only 50 million barrels or so?
Perhaps.
The
geologist I spoke with today told me that seismic readings so deep
under the ocean and so deep under the seabed can only pick up
impressions of things around the size of an olympic pool.
Similarly, oil industry expert Bob Cavner said seismic tests are generally used to find bigger scale things like geologic structures:
Cavner explained more about seismic testing yesterday.
While
BP talks confidently about seismic tests for leaks beneath the
seafloor, I am not so sure that a leak could be detected using seismic
given the low-resolution of seismic tests.
BP Stonewalls
The
biggest problem is that BP is keeping the information it has about the
size of the reservoir to itself, and refusing to disclose to the public
or even Congress what it knows.
Congressman Markey - chair of the Select Committee on Energy Independence and Global Warming - wrote to BP on June 23rd demanding more information:
Please
provide all documents related to the geologic formation in which the
Macondo well is located. Are there significant deposits of oil and gas
in formations above the target reservoir? Please provide an estimate of
the total amount of oil and gas that is contained in i) the Macondo
well target formation and ii) each formation above the target formation
that could leak hydrocarbons into the annulus as a result of poor
cementing, damage caused by the initial explosion(s), or the failed Top
Kill effort.***
a. In order to understand the geological
complexity of the well, please provide all geological logs, including
the mud log, and all geophysical logs, including resistivity and
porosity logs.b. A May 23, 2010 article entitled “Documents
show BP chose a less- expensive, less–reliable method for completing
well in Gulf oil spill” in the Orlando Sentinel stated that well
records indicate that in late February, there was a loss in drilling
mud pressure. According to the article, this could mean that the mud
fractured layers of sand or shale in the formation and vanished. The
article goes on to state that in early March, the pressure of the oil
and gas encountered overwhelmed the pressure of the drilling mud. In
mid-April, a loss of drilling mud was reportedly again experienced. Do
any or all of these events indicate that oil and gas could be flowing
from somewhere other than the target reservoir? If so, please explain
fully, and if not, why not?
On July 15th, Congressman Markey told CNN that there has been no response from BP.
- advertisements -
THE GULF WELL IS STILL LEAKING
http://whatreallyhappened.com/WRHARTICLES/gulfwellstillleaking.php
Official: Seep found near BP's blown out oil well
http://www.google.com/hostednews/ap/article/ALeqM5gIXWYBTpLtSayJtg41LKXpxSxVPAD9H1N4B05
There's a thread over at godlikeproductions.com you may be interested in. "Eddy" says that Jesus told him the well is still leaking.
brilliant idea from over at oil drum
http://www.theoildrum.com/node/6745#comment-680410
uhhh... welcome to last month when BP already decided to do this?
http://www.bp.com/genericarticle.do?categoryId=2012968&contentId=7063047uhhh , no need to post the entire press release (a link normally will suffice), particularly when it has nothing to do with what I had posted.
the comment you linked to was talking about producing the well and donating the revenue from it to restore the gulf area. That's exactly what BP announced in June. How does it have nothing to do with it?
Is it possible to redirect the relief wells if a kill is successful? I mean could they make producing wells from the relief well work? If so, use the production from the "new" well to fund a clean-up and restoration fund. Oh boy, more money for politicians to spend.
latest from Thad
(now we know where Obama was getting his talking points from)
http://www.deepwaterhorizonresponse.com/go/doc/2931/790959/
(also note that in earlier statements Thad said the resevoir had a considerable amount of pressure)
Augustus, gasmminder and Rockford: one of you has mentioned a "75 foot pay zone". Can you kindly provide the exact quote and exact link so we can assess that info? Thanks!
GW - found em'
http://energycommerce.house.gov/documents/20100614/BP-Production.Casing....
GW - the well logs have been posted here at ZH several times. I don't have them here at home but the main pay sand was 60' thick above that there was about 20' of shale then a second pay sand ~15' thick. The numbers people are quoting on reserves are not reasonable - these have been out there for some time and they are absurd - now we're back to people making shit up and others believing it.
Some basic parameters - the sand has about 30% porosity - that means that about 30% of the rock is open space that can contain oil & water. An acre is 43,560 sq ft. So one acre-foot is 43,560 cu ft. Every cu ft is 0.178 barrels of oil. Now 43560 cu ft = 7,758 barrels of oil. So if 30% of the rock volume is available for oil then one acre-foot is 2,327 barrels of oil. This is an oversimplification as the amount of dissolved gas and temperature and pressure change things - but it gets you in the right range because oil is relatively incompressible (situation is much different in gas reservoirs).
Now - you also have to understand that the pore space is not entirely filled with oil, some of the space is water. We refer to these percentages as "water saturation" and "oil saturation" - together they must equal 1. An 80% oil saturation would be an EXTREMELY good oil reservoir. So now the amount of oil in one acre-foot is 1861 barrels. Next - how much can you get out (recoverable)? Most oil reservoirs on primary production (which is all that will occur here) are very good if they recover 30% of the oil in place. Now you are at the point that matters - whats the recoverable oil per acre-foot? Lets be conservative and say they recover 40% then you can get 744 barrels. Lets make it a round 750 just for grins.
IF anyone wants to quibble with those numbers feel free. They are reasonable "back of the envelope numbers". That means that for the 75' of pay seen in the well to recover 50 million barrels the reservoir must exist and be continous over a total of 890 acres. That is quite reasonable and common. For it to produce 500 million barrels it would have to exist and be continous over 8900 acres approximately 14 sq miles- a much rarer and unlikely situation (this comment would get much too long if I go into slope depositional processes in salt withdrawal minibasins but I'm telling you it would be very unlikely - as in impossible).
Now - there are uncertainties, the reservoir could be tied into thicker sand downdip etc. I don't know what the real number is but I'm telling you as an experienced Gulf of Mexico geologist that the sands in that log in the geologic trends being tested 50-100 million barrels is a very realistic number. More than that is hard to believe and a billion is a joke - I don't know who your geologic source is but I'd encourage him to LOOK at the LOGS.
Finally - think about what happened here. BP was pinching pennies left and right and couldn't WAIT to get this damn well TA'd. A billion barrels recoverable means 64 BILLION in net revenue to the owners. No expense would have been spared and no care would have been to much to take to make DAMN sure this reservoir and development was done right.
Also - Tiber & Kaskadia are not analogs for this area. Those discoveries are in a trend we refer to as the Perdido/Mississippi Fold Belt which is composed of GIANT structures (literally mountain range sizes) that are squeezed up by all the material shedding off the continent and sliding down that direction on the salt & shale in the Gulf. The reservoirs are very thick pay zones composed of sands deposited in very deep water from turbidity currents - a setting that allows much better continuity. There is no connection to the setting here and the size of those is meaningless in relation to this.
^^^ There is so much amazing FACTUAL information in this post but my guess is that it will fly right over most peoples heads here. After all, it's more fun to think of conspiracies
Thank you gasmiinder for putting this together.
gasminder - which formation do you think people are theorizing is taking the oil and gas that might be reducing the reservoir pressures?
Thx
I don't know what those might be. I have not been able to find any technical information being discussed in the community (I left the company that worked that area recently so no longer have access to their data). I have heard the pay sand is Tex W (middle Miocene) but I cannot validate that. That would put a lot of upper Miocene and Plio-Pleistocene lowstand sands above in this general area - but again I have no data to support that rumor.
The pay zone is shown in the logs. here:
http://i90.photobucket.com/albums/k247/dhm1353/MacondoLog.png
http://energycommerce.house.gov/documents/20100614/BP-Production.Casing....
A pay zone of 75 feet, although large, is not jaw dropping. I've been on wells in the Norht Sea that had over 350 feet of almost continuous sand in an oil reservoir. The actual size of the payzone is not really that important. What's important is the Pressure of the reservoir - The mobility of the fluid within it - The pressure of water below, and gas above - The permeability of the formation. You can have the highest pressure ever recorded, but if it's in solid rock with no permeability there won't be any production.
Also, depending on HOW the well is produced, this will determine the life of a particular well. If you you open 'er up so to speak you are actually doing damage to the reservoir and can stunt further production later.
'The reservoir' as is so often quoted here could stretch on for miles. Poking one single hole in one place in the reservoir is not going to deplete the entire reservoir!! You have to drill many holes and inject water and C02, and all sorts of stuff to produce all of the oil. It's ludicrus to think all of the oil will escape out of one uncompleted borehole.
Finally - They relaly have NO IDEA how much oil is actually down there (not that it matters based on all above comments). All of these numbers are just estimates based on seismic and other things. The only way to really know is to drill more holes and test production - They still need to drill 10 more del wells before they'll really have an idea of whats down there.
GW:
Go ask a reservoir engineer (not a geologist) about the pressure drop and production numbers...
Well you sound like you know the business. I would tell you though that the porosity in this sand is ~30% and perms will be quite high. It's not an onshore blanket sand. It is a slope channel or fan (log character looks channeled but you really can't tell from just the log) in a salt-withdrawal minibasin - a setting that does not produce widespread blanket sands, nor does it produce reservoirs that stretch on from miles. I'd bet you can produce 50 MMBOE from 4-6 wells properly placed in this reservoir pretty easily. There will not be secondary/tertiary recovery here because of the cost (see my comments below)