$/hp for incremental motive power

[ivymike]

Quick check here, gents, if you have a chance. I'm not very familiar with the gas compression market, so it's conceivable that I'm way off base.

I was asked how much annual value a single incremental horsepower has to someone with a ~650hp gas compression rig, assuming we're moving gas with 900btu/cf worth $10/MBTU.

My answer was "anywhere from $10 to $10,000, depending on the application."

My reasoning for the bottom end of the scale was that someone might not be able to utilize that extra hp even if it was available, so while it wouldn't be worthless, it would have relatively little value.

My reasoning for the top end of the scale was that if you assume that the guy who owns the compressor gets a full $10/MBTU for the gas, and that he is working with an inlet pressure of 0psig and an outlet pressure of 1000psig, he can probably move another 3350CFD with a value of $10k/yr. (subtract a tiny bit for fuel)

So how far off does that seem from the truth (especially the second bit)?

 

[zdas04]

The problem with the analysis is that there is no such thing as an "average" gas well. They all have a personality and most of them are unpleasant.

Adding hp can either lower suction pressure or raise discharge pressure. If lowering suction pressure results in moving to a better place on a particular well's IPR curve then sales will increase and suction and discharge pressure will go up a tad, then rate will decrease, the pressures will go down, etc. until the well finds a new equilibrium at a lower suction pressure, higher discharge pressure, and higher flow rate (this is the best possible scenario).

If the additional hp is needed to overcome discharge pressure then the suction pressure has been creeping up to match the reduced flow caused by the hp being used to overcome discharge pressure increases and you'll be lucky to see anything.

The magnitude of any of these numbers is very much specific-well dependent. In San Juan Basin Fairway CBM wells, I've seen 2 psi reduction in wellhead pressure increase flow rate 2 MMCF/d. I've also seen a 10 psi reduction causing a 1 MMCF/d decrease (long story, but true).

In deep, pore-volume-storage (i.e., conventional) reservoirs I've seen a 2-5 psi decrease in wellhead pressure make zero improvement in immediate rate, but flatten decline a couple of points (a major win).

Man, I'm sorry, but there just isn't a simple answer to this question.

David

 

[ivymike]

...so if an engine dealer were trying to sell you an engine upgrade kit at overhaul, and the kit could deliver better altitude capability, higher torque turn-down, increased horsepower, improved engine monitoring, tighter emissions control (though not lower emissions necessarily), and perhaps a bit better reliability, how would you determine whether the asking price was a reasonable one?

 

[zdas04]

It really depends on your system. Will the wells respond to lower pressures? Is there enough pipe in the ground to really translate lower suction pressures into lower wellhead pressures (I see a lot of gathering systems that are simply full, you add a new well and it just pushes the check valves shut on the older wells, net gain is near zero)? Is there enough pipe away from the compressor to carry any extra gas without eating all your new hp in increased discharge?

I design compressors to run about 80% of derated hp at the design conditions. I rarely ever see any uplift from decreasing the suction pressures just to grab some of that extra hp (and consistently running over 90% has been shown to increase downtime). It sounds like the gains (if any) will be in reliability. That can often be enough to justify major expenditures, but if your machine is already running over 95% up time then the payout will be tough.

David

 

[dcasto]

My first reaction to a vendor making claims is "WARNING, SNAKE OIL APPROACHING". If the engine is really old, say 25+ years, you'd be better off upgrading to a 21 century engine. An engine between 20 and 10 years old may have have some factory and aftermarket modifications that improve the engines performance. If the engine is less than 10 years old, stick with OEM advice.

The ones that scare me the most are the guys with software fixes or increased monitoring or tighter emmission controls. They claim a few percentage points of improvement. Well, on a 600HP unit, naw. If you can get 2% on a fram 5, I'd listen. But on a 600HP field unit it would cost more to maintainthe new system.

Zadas04, I use to be an 80% load guy (Warren Petroleum Engineering Manual), now I'm a 95% load on the new stuff. The change is I do all the maintenance and inspections now because I get all the operating help and budget I need. I like this model versus overbuy and scrimp on maintenance model I use to have to live in.

 

[zdas04]

You work in plants and pipeline compressor stations. If I did that I would be in the 90-95% camp too. Suction pressure is set by contract, discharge pressure is set by your own maintenance activities, etc.

I'm a blood-guts-and-feathers wellsite kind of guy and well perfomance changes from minute to minute. I really hate when a compressor goes down on high manifold pressure or under speed because the well just decided to give me a bunch more gas too fast for the suction controller to operate. Also, no one (especially not me) ever gets the design flow rate "right" on a well just getting compression. Being content to have average fleet hp utilization in the 70-80% range and not being upset by 60% significantly improves up time.

David

 

[ivymike]

well, it's a dealer selling a kit of factory-spec parts, which involves external hardware only and brings a 5-10-year-old engine up to the current hardware spec, for both mechanicals and electronics. Includes software too. 6% more horsepower, 3% lower BSFC, modern engine electronics w/upgraded interfaces, a few thousand more feet altitude capability, etc. I trust the claims are legit, I just don't quite know how to answer the question about what it's worth. (The fuel economy part is easy enough to figure out, obviously)

To further show my ignorance, what's a Fram 5? (Frame 5 gas turbine with a missing e?)

 

[pmover]

consider this . . .

request references (corporation and contact person & number) for previous purchaser's of the kit.

consider a purchase agreement similar to an experiment - that is, install the system on 1-engine and if system works as specified, you buy it. if system does not perform as specified, then return to seller at no cost. the only cost incurred by user would be installation & minor material costs.

several years ago, a simmilar purchase agreement was made with an ignition system provider to be used on a CB GMV-10 naturally aspirated ICE. the offer by supplier of ignition system was that by simply installing the ignition system (including plugs), the emissions rate would be reduced by 30%, but fuel consumption would either remain the same or it will slightly increase (<2%). so, ignition system installed, test was done, and we bought the ignition system. surprised everyone. we ended up transferring the ignition system to a turbo-charged Clark TLA-10 where the benefits were greater.

yes, my guess is Frame 5 as 2% hp is a large value.

something to ponder . . .
good luck!
-pmover