 | The National Energy Essay Competition | The Oil Drum: Australia/New Zealand | The Bullroarer - Friday 18th July 2008 |  |
67 comments on How Technology Increases Oil Production
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67 comments on How Technology Increases Oil Production
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you fail to mention, as a significant drive mechanism, good old mother nature. i.e. gravity drainage. what is the typical reservoir dip angle on this field ?
i agree that eor has limited benifit in this case, because of the relatively high (gravity aided) secondary recovery. too few people grasp the concept of material balance, which in it's simplist form simply states that the amount of oil remaining is equal to the original amount minus the amount produced.
this sounds like a very complex reservoir, without some additional data, i find it hard to believe that secondary recovery could be in the 70% range without a significant gravity drainage contribution.
i know of examples where similar recoveries were obtained by waterflood, but guess what - steeply diping reservoirs. and not that good of reservoir properties, with the exception that the oil being of high gravity thus low viscosity.
memmel keeps banging on the theme that smaller fields can't replace bigger fields (which i agree with) and i keep banging on the theme of gravity drainage.
the percentage production figures are proportions of the total oil produced up to 2002, not percentage recovery of oil initially in place. you are right - recovery of oil in place in this field will not be anywhere near 70%.
gravity drainage will also not be significant for this field!
sorry, i guess i missed that part. what is the recovery % of ooip ?
sorry to disappoint, but recovery factors are not available in the JPT article. you'd have to ask somebody working for TOTAL in Indonesia..
Gravity drainage fields can really confuse the villagers. I have one such fld that has produced for 50 years (20 mmbo so far) and will produce for another 100 years (maybe another 20 mmbo). When the angry villagers hear such tales they begin to think there really is help out there for them. The wells in this field make about 1 bb/ per day. It obvious has no bearing on PO. But the little ma and pa operators are slowly becoming millionaires.
But what compounds the confusion are the public claims by oil companies regarding the great profitability of EOR these days. Those optimistic statements are valid with regards to the company's financial future but have a minimal impact on PO. The villagers will see many press releases from the public oils rightfully touting the profits of additional exploration and EOR. And we should count on these angry villagers to take those press releases as a sign that there really isn't a big problem with PO.
BUT: EOR and more exploration will delay PO. That's a point of logic that cannot be denied. But whether it delays it 5 years or 5 months is the question we can bounce around just for the fun of it. My guess would be NOT 5 years.
What are the rate laws that affect gravity drainage? Is it a first-order diffusional law, something akin to Fick's law? In that case, you will see a fractional power-law growth in cumulative reserve (specifically a square-root law if you work out the math) and the reciprocal of this for extraction. This kind of behavior does show the long tails you would see.
I suppose you can provide a more detailed analysis, but this kind of first-order look can provide a lot of context for those of us that come from different areas of expertise.
the basic's of gravity drainage are contained in d'arcy's law which stated mathmatecally is:
v = c(k/u)(dp/ds)
with a substitution v=q/A then c becomes 1.127 (usually presented with a minus sign, because dp/ds is negative)
where q is in bbls/day
and A is the x-sectional area of flow, sf
k, permeability, is in darcies
u, viscosity is in centipoise
dp/ds is pressure drop, psi/ft
for the case of gravity drainage dp/ds can be taken as (dp/dh)*(dh/ds)
dp/dh is the bouyancy of the oil or difference between the fluid gradient for oil and water, psi/ft.
= 0.433 (rhowater-rhooil), at reservoir conditions.
and finally dh/ds is the change in elevation over a distance. or simply sin dipangle.
and strictly speaking d'arcy's law only applies to single phase isothermal flow under steady state conditions. and for cases where the capilary pressure is zero(well above the oil/water contact)petroleum engineering usually makes lots of assumptions, so these restrictions are usually just ignored.
So this is actually Fick's Law of diffusion!
This in fact is very simple to solve. I have done a post on this behavior before (http://mobjectivist.blogspot.com/2006/01/grove-like-growth.html) and in actuality diffusion and dispersion are the same sides of a coin so it follows the same trending of the Dispersive Discovery curve.
Take the equation for d'arcy's law
v = c(k/u)(dp/ds)
and then substituting (dp/dh)*(dh/ds)
The key is the dh/ds term, the dipangle. The ds is essentially a displacement in volume as the gravity drainage starts to move material from one volume to the other. So whatever goes from one side of "s" goes to the other side, the "v" side. This means that the length of the partially drained volume gets bigger and bigger with time.
Look at the width in the following figure where x is the s term:
So x or s gets bigger and bigger with a cumulative increase proportional to the integral of v. With the small sin approximation for sin (dipangle) you get dh/ds = h/s
so rewriting this, replacing U with s to denote cumulative volume
dU/dt = k / U
this solves simply as U(t) = k * sqrt(t), which is Fick's Law. The bottom-line is that you get progressively diminishing returns over time.