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47 comments on An oilfield in Arabia

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memmel on August 16, 2006 - 2:53am Permalink | Subthread | Comments top
I hate to keep harping on a topic but
barrels a year, sustainable through 2010. (At 8% depletion, although Aramco are claiming that they are holding depletion below that - by continuing in-field drilling). However if the OIP is 31 billion and they are only able to recover 11.5
This is where I have a big problem with KSA I'm assuming that the way there keeping decline rates low is via horizontal branch wells or bottle brush wells. These seem to serve to only deplete a field faster. So what is the production profile for wells drilled in old fields. It seems to me that there trading keeping high flow rates for a very steep final decline.

For peak oil the most important factor is the decline rate post peak if the decline rates at the well level are dramatic a bottom up analysis indicates the final overall decline rate will accelerate rapidly post peak.

The one piece of information that I'm missing is what is the production profiles generally for these secondary wells ?

I found this

http://www.bbean.com/Business-Mall/bbus203.htm

The important part is that the paper claims that a well is only drawing oil from about 120 feet from the borehole. This seems very low to me I'd expect a well to draw oil in from several kilometers at least.

Sure the will be bypassed zones and infield drilling to recover these actually add to the overall recovery. However drilling more wells to keep production rates up only result in a increasingly steep decline profile.

This discusses depletion problems with gas but oil suffers the same problem.

http://www.daystaroilandgas.com/Articles/oil-production-wells.html

Finally in reading some of the material on recovery in advanced fields I found a lot of it sounded like a used car salesman when I see this type of marketing I get a bit concerned about the real benefits of aggressive infield drilling. It just seems to me that except for recovering bypassed oil your simply increasing the depletion rate.

Again sorry to keep harping on the topic but I can't seem to find enough information to alleviate my concerns and a bottom up analysis indicated very steep decline rates.

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copelch on August 16, 2006 - 6:01am Permalink | Subthread | Parent | Comments top
Memmel, you write:

"I'm assuming that the way they're keeping decline rates low is via horizontal branch wells or bottle brush wells. These seem to serve to only deplete a field faster."

The idea that technological progress in oil extraction basically means getting the stuff out faster rather than getting out more of the stuff seems to be one of the Hubbertians' core articles of faith.

Isn't horizontal extraction also used to extract a greater percentage of the original oil in place (OOIP)?

Oh TOD experts, I am perplexed about this.

Hope I'm not being too heretical ....

   

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oilmanbob on August 16, 2006 - 10:58am Permalink | Subthread | Parent | Comments top
Memmel, the horizontal wells make many formations that are "tight" economicially productive as well. The Austin Chalk is a good example of this, or the Barnett-Woodford shale fields. Although fields with good permiability are very possibly depleted faster, in tight formations recovery is increased because the oil can flow in to a well bore quickly enough to be a good investment return, so wells get drilled that would not be drilled by traditional vertical well methods.
 The problem is that demand is increasing a hec k of a lot quicker than supply, and these new extraction methods are a lot more expensive on a per barrel basis. I doubt that horizontal drilling can do more than slightly slow the decline rate in production. But, the techniques ought to make a lot of producers rich.
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copelch on August 16, 2006 - 11:55am Permalink | Subthread | Parent | Comments top
Oilmanbob writes:

"I doubt that horizontal drilling can do more than slightly slow the decline rate in production.

Now I'm even more perplexed than before (at least pending HO's upcoming contribution, which I'm looking forward to).

So does horizontal drilling slow down or speed up the depletion rate? It can't to both at once. Or does it all depend on the characteristics of the field in question? Or does HD speed up the depletion rate but at the same time convert a certain percentage of the technically recoverable oil into economically recoverable oil?

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Dave Cohen on August 16, 2006 - 12:56pm Permalink | Subthread | Parent | Comments top
Deviated drilling speeds up the extraction rate and thus pushes the envelope on current production at the expense of longet term yields. The depletion rate may be very sharp after the extraction starts declining. In HO's original example, once the water encroachment reaches the drilling contact points, that's pretty much all she wrote.

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frontierenergy on August 17, 2006 - 1:43am Permalink | Subthread | Parent | Comments top
That is absolutely right Dave once the water hits it-its all done.  There are essentially two types of horizontal wells-

"Grass Roots" where wells are drilled from the surface and then go horizontal.  These are new field development wells where as Oilmanbob noted they wouldnt produce anything otherwise.  These are drilled horizontal or they are not drilled at all.

Then there are "re-entry" wells in existing fields where a whipstock is set in an existing vertical well, a window is cut in the casing and a slimhole tool is used to drill out at a very high build rate.  These in my experience are only somewhat successful in increasing production and are high risk and expensive.    It requires highly skilled people and most hands decline to work these jobs simply because of the stress involved.  The better people can pretty much pick and choose where they want to work now anyway.

I can't speak for what is going on in Texas but in my part of the country...the Rockies,  re-entry work is very limited.      Most of the work going on in the older fields is simply workover.  As far as increasing depletion I don't think anyone knows at present on horizontal re-entry on old fields.  

Maybe this doesnt clear this up, but to people in my business it is considered apples and oranges between these types of horizontal wells.

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alistairC on August 16, 2006 - 12:57pm Permalink | Subthread | Parent | Comments top
You're confusing "decline" and "depletion" I think.

Smart extraction slows the decline in production by accelerating the depletion rate. (I think)

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Dave Cohen on August 16, 2006 - 1:20pm Permalink | Subthread | Parent | Comments top
OK, let's try this again. I said:
Deviated drilling speeds up the extraction rate and thus pushes the envelope on current production at the expense of longet term yields. The depletion rate may be very sharp after the extraction starts declining. In HO's original example, once the water encroachment reaches the drilling contact points, that's pretty much all she wrote.
Decline refers to production drops. Thus the decline rate is the year-on-year percentage drop in a producing field (basin, country).

Depletion refers to the exhaustion over time of URR which is itself some percentage of OOIP.

In my text, the extraction rate is the daily flow (barrels per day) as a percentage of URR.

So, here's what I should have said.

Deviated drilling increases the extraction rate and thus pushes the envelope on current production at the expense of longer term yields. The decline rate may be very sharp once production has peaked after such drilling was inaugurated. In HO's original example, once the water encroachment reaches the drilling contact points, that's pretty much all she wrote.

That's better. Now all our terms are defined and there is even the possibility that we can all understand what we are talking about.

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memmel on August 16, 2006 - 1:29pm Permalink | Subthread | Parent | Comments top

Good post and to agian plaster the same message.

In field drilling esp with advanced recovery maintains production rates but ...

Once the wells start watering out the decline rate increases over time before finally decreasing with production at a low level. The basic cause is once a region waters out it waters out several wells at once the old producers plus the new ones drilled to keep up the production rates then net effect is production rates plumment and your left with stripper wells.

The unknown is what is the general production profile of these new wells how long do they last on average with a high production rate years decades ??? Assuming that the orginal drilling gave decent field coverage. My gut feeling is in field drilling only helps production rates for a few years at most esp with lateral wells since the depletion rate is doubled.

That is my thesis.

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phxbanks on August 16, 2006 - 11:03pm Permalink | Subthread | Parent | Comments top
http://www.foreignpolicy.com/story/cms.php?story_id=3567
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GreyZone on August 16, 2006 - 12:29pm Permalink | Subthread | Parent | Comments top
Claims are made that it will increase recovery but for a reference case, I refer you to Yibal. EOR did not increase total oil by much (though it may have increased it very slightly) but what it did do was crash production through the floor when decline set in. Another case is the North Sea, both UK and Norwegian production. EOR there appears to have increased recovered oil by some amount but the North Sea peaked in 1998 or 1999 (can't recall which offhand) versus a predicted peak in 2010 by the EOR advocates. The North Sea has been in steady decline since its peak and is down significantly from there. I am not aware of any examples where EOR has really proven to increase recovered reserves by a significant percentage of original estimates of total oil though there ought to at least be a few if the technology actually does what is claimed rather than just draining the field faster.
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memmel on August 16, 2006 - 1:04pm Permalink | Subthread | Parent | Comments top

As mentioned before it does allow tight formation to be produced so it opens up new production.

Next it works well for extracting bypassed oil but the original estimates that I have seen seem to assume that bypassed oil is not a factored into the overall recovery.

But agian these methods in general seem to trade increased production rates for massive decline rates later since they basically increase the rate of depletion.

Wich in a bottom up anaylisis leads to a increasing rate of decline in production rates once depletion finally catches up.

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Heading Out on August 16, 2006 - 10:35am Permalink | Subthread | Parent | Comments top
I think I am going to write one more post to try and clear up, to the extent that I can, some of the questions raised in the last two.
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memmel on August 16, 2006 - 11:17am Permalink | Subthread | Parent | Comments top

Thanks !

I think a good explanation of the technical details of depletion and modern recovery methods at the well and field level would be fantastic.

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