52 comments on Five Easy Leases: Ghawar's Discovery Wells
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52 comments on Five Easy Leases: Ghawar's Discovery Wells
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Joules,
Did you try deconvolving those cumulative graphs to yearly production histories? The rates should show the story of why North Ghawar is so important, and by eye the gradients of the cumulative plots paints an interesting story if correlated to Aramco spare capacity and price.
I unstacked them, if that's what you mean by deconvolving (really just subtracting). To get the production rate from the cumulative, you take the derivative. However, the starting graphic wasn't that good, and the errors expand after awhile. I did note slopes where it was fairly clear.
Excellent Joules-
When do the cumulatives end??
One of the great mysteries is starting to be answered as it is apparent from the family of cumulative curves that they have begun pulling Hawiyah hard to make the market.
Thanks
FF
If he does mean deconvolving, then it would be a deconvolution of the yearly production with an exponential decline function. The result would give us an incremental yearly reserve growth function.
I argue that we should be doing more of these convolution based analyses otherwise we can never separate the decline from the growth factors.
Reserve growth is typically a hyperbolic 1/(1+1/t) factor while exponential decline goes as e-t. The combination of these two is not something easily expressable in closed form.
Yep, something like that. Since these are single wells, we have a good idea how they will naturally behave.
However the thing I'm interested in is where the slow downs/cuts in production hit. If Aramco decide to produce a million less barrels to force prices up - where are those cuts felt?
If they've been cutting back on North Ghawar then those high quality fields might have a long life left. However if they don't then they have to basically be empty - and with them much of the production capacity.
However as Joules says, reversing out that much from cumulative numbers tends to push the noise through the roof.
In one of the SPE papers on water management in north Uthmaniyah, Saudi Aramco listed one of the remedies as rotating a well out of production. I know they also do that for wells in Safaniyah. This might have been going on for some of the wells here, but it's hard to tell. ANDR-1 seems to have been shut off in the 90s, but it didn't correlate with an overall decrease from 'Ain Dar/Shedgum. That's why I think it was a water issue there.
I'm skeptical of depletion modeling for Ghawar as a whole, and certainly for individual wells. There are too many other things going on. Different bottom-hole pressures, valves possible closed up top, and increasing water cuts.
My usual take is that you acquire a distribution of responses, statistically aggregate these, and then use a probability model to come up with a macro behavior.
This is referred to a stochastic model. This approach works in many other engineering and science domains but for some reason, is historically not done here.
Dunno why this is, but Steve_Piper yesterday said [regarding most geologists] "They are by training data-oriented empiricists who rely very little on models."
http://www.theoildrum.com/node/5460#comment-507710
I agree that concentrating on any one field is deadly inaccurate, yet the aggregate stochastic model tells us what we want to know.
Stochastic approaches work when you have a statistically useful set. If you average enough fields, you might come up with a model that you can apply to similar large sets. It is possible that the random "above ground factors" cancel out, and the remaining behavior is related to geology and normal production logistics. But this behavior hardly be useful for predicting a single field (or well).
Stochastic approaches are being used to come up with better estimates for porosity and permeability in heterogeneous reservoirs such as the Arab-D carbonate. Kringing (interpolating) between widely spaced wells and 3D seismic still leaves much to be desired. You still can't predict what an individual well will do, but it might help in deciding where to put it (i.e. place your bets). You can search around and find a few examples such as:
http://www.spe.org/elibrary/servlet/spepreview?id=SPE-104496-MS&speCommo...
Stochastic both in the geospatial and the temporal domains.
Web -- I suppose I'm not one of those empiricist geologists. I've been pretty much a development/reservoir geologist my whole career. Virtually all my work has focused on stochastic analysis. I suppose this is the distinction between those of us who work production histories vs. those without hard data speculating of on the "what if" possibilities out there. If anything I tend to ignore what the "book" says about theoretical production models. But when you have hard data refuting those models it's easy to do.
And thus we are back to the primary problem with the KSA numbers. IMO even if we just had the change in water cut over time for each well we could make much more reliable estimate of future production levels then any theoretical reservoir model. Of course, there's much more data then water cut to be mined but at least it would give a glimpse into the current state of the system.
I just don't see anyone talk about this stuff with the same terminology as many of the other applied mathematicians in other discipline.
Further, I see a real distinction between using models to try to empirically fit and thus make projections on availability or viability (i.e. via kriging) AND that of just basic understanding. Of the latter, no one is making any fundamental kind of effort. I have explored about ten different spatial and temporal behaviors that could use a basic explanation that otherwise get completely glossed over in every oil text that I have come across. This seems to me to be an incredible oversight -- coming from a basic physics background, the fundamental understanding was always the first priority. I just don't get why this occurs in this field.