Autostart Pump Application 1

[zdas04]

I've got what has turned out to be a much tougher pumping problem than it looked like when I started on it.

I'm in a remote location (think of the surface of the moon with 5 ft of snow, archaeological relics, elk, and environmentalists--it makes ANWAR look like a mall) at 7,000 ft elevation, and of course there is no electricity and the sun hits the location about 2 hours on a sunny day (we can't keep wellsite automation batteries charged let alone power rotating equipment).

To get water into a water-gathering system (this is a natural-gas field with 1.01 SG water) I have to go from a tank (call it 10 ft of NPSHa) over a 400 ft knob and back down 200 ft (there is a vacuum breaker at the top) and then into about 40 psig water-system pressure. Production varies from 0.5 gpm to 3 gpm so the well produces into a 17,000 gallon tank and the pump cycles between 20 ft and 10 ft. I wanted the pump to run about 1/4 of the time at the highest production rate so I spec'd a 12 gpm pump and 7 Hp natural-gas fired auto-start engine.

It all looked pretty straight forward with a Honda engine and a Hydroseal pump until we installed it. The engine just wouldn't run on our natural gas (12% CO2 content and considerable water vapor), so we installed a gasoline tank for people to steal from. Then the engine wouldn't start under load period.

An automated bypass we installed leaked so much that the pump wouldn't keep up.

We installed a check valve just over the knob with a drain line and needle valve to let the pump start unloaded, but the vacuum breaker froze shut and we siphoned the water system through the leaking check valve into the tank (luckily we caught it before we put water on the ground).

We don't have enough gas pressure to run a double-diaphram pump.

Does anyone have any suggestions for places to go to find a pump/engine combination that will work in this environment?

David

 

[d23]

David:

I would guess the best thing is use what you have, but put a second engine (Generator) in as a source of electric heat and control power. You will need to be inside a small well insulated building and have enough power to operate heat tapes for the valves.

Good Luck

 

[CB2]

Where is this gas tank, I paid $2.05 per Gal. this morning!

 

[zdas04]

CB2,
Drive to the end of the earth and take a right

 

[Kawartha]

zdas04,

As I understand your comments, you have a tank of sour water from which you will pump from. What pumps the water into the tank? If you are pumping from this tank, why is NPSHa only 10'? Is the pump located at a higher elevation than the tank? Is the water temperature high? I haven't checked, but is the V.P. at 7,000' el. > 20'?

Whatever your comments to the above, it appears that you don't have a pumping problem, you have an energy problem. You will have to identify the potential sources of energy and the motive power for the pump at your remote site? Electrical? Air or gas pressure? Energy from fuel?

Have you considered high pressure AOD's - this can provide a higher pressure discharge than available gas pressure. I have not looked at this type of pump for some time, but as I recall the pressure can be multiplied by a factor of about 3:1. What is the available gas pressure?

 

[d23]

zdas04

Kawartha makes some excellent points.

After answering your post I was wondering how you keep the water from freezing in the tank?

Another idea is why don't you just use a pressurized tank. I don't know the friction loss, but you are only talking about 175 PSI to make the 400 foot hill. Does you well have enough pressure for that? A higher pressure tank and a regulator may be a better mouse catcher. A pressure tank would eliminate pump problems with CO2.

 

[zdas04]

This is a natural-gas well application with associated produced water. The available wellhead pressure is 125 psig (atmospheric pressure is 11.5 psia).

The water is nearly potable (1.01 SG, 6,000 mg/l TDS, very little disolved or entrained gases). We produce the full well stream into a 2-phase (gas and liquid) production separator which sits in a heated glycol bath, the gas goes to the gas pipeline and the water goes into the tank (vented to atmosphere and with a tank-heater that runs off wellsite natural gas and a pilot light). There isn't enough pressure at the location to go directly into the water gathering system. The tank heater is set to maintian the water temperature at 60-80F. The VP in these conditions is way below the NPSHa (total NPSHr for the system we installed was under 3 ft)

The only energy source at this remote location (think surface of the moon) is wellsite natural gas. Hauling gasoline or other fuels to the location is only possible about 100 days a year. Electricity is about $10 million away.

High pressure diaphram pumps have not had much success here. Without dehydradation we have a real bad problem with the exhaust valve freezing shut. Dehydradation causes more problems than it solves (glycol dehy's at this pressure have to have a very large contact area and correspondingly large recirculation requirements and associated maintenance problems, delequiesent dryers don't last long enough for the inaccessible periods and have a hard time getting the gas to a low enough dew point to help, and mole seives require too much energy to regenerate). Also, the exhust stream on a diaphram pump is a huge green-house gas emmitter--my company (and my industry) is under a lot of heat right now to reduce these emmissions.

David

 

[Kawartha]

zdas04,

Looks like you have considered everything. Have you thought about wind power? If you are at such a high elevation, isn't wind at a fairly steady velocity. I know wind turbines are expensive, but maybe worth investigating.

Regards,
Richard

 

[zdas04]

Richard,
This stupid well is at 7,000 ft, but the hills around it are at 7,400 ft and the peaks are over a mile away to the north with a shear cliff (up) to the south - the wind never blows and the sun rarely shines. I wouldn't be surprised if it would also resist tidal and geothermal energy sources!

David

 

[d23]

Mr. Kawartha sir:

Wind power may not be practical, but it is quite an example of “thinking outside the box.”

You impressed me!

 

[Kawartha]

Thanks a lot for compliment d23,

Wouldn't it be nice if zdas04 could buy a small nuclear reactor for this application?

 

[d23]

zdas04:

If you are 400 feet up, then 200 feet down does that mean that you have 600 feet (more or less) tubing from the well to the tank? Do you have power at the water tank? Is a small tubing very expensive to install on the moon?

Point I'm getting to:

I have never seen a jet or hydraulic system used in this configuration, but if you had power fluid (water) available and pipe (tubing) is economically practical you could set up a "jet lift system" to get the water over the hill.

 

[209larry]

Zdas04.
I would recommend a Capstone microturbine which can run on wet gas to power-up your pump motor. This is a newest technology now and has been found to work in thousand hours without breakdown. Available are 30 and 60 kw models and can be put in parallel if you want more power.

209larry

 

[zdas04]

Larry,
I'm familiar with Capstone (my company was on the proof-of-concept JIP and I saw some of the reports), but it turns a bit fast for most pumps I know about. Were you thinking about a genset and motor or is there some sort of pump/reduction gear that works with it?

D23,
I guess I wasn't clear. It is 100 ft (horizontal) from the wellhead to the separator, another 50 ft from the separator to the tank, and 3 miles (which includes the elevation change) from the tank to the 40 psig water gathering line. I looked at using an eductor to pull the water over the hill, but I wasn't sure I could sustain a siphon that far (with the tank 200 net ft lower than the jet pump). Do you have any experiance that would suggest that this might work?

David

 

[d23]

zdas04

When you find a problem you don’t mess around.

One thing that has been done on very limited bases in the US is to make a “dual completion” type well where you have both the production and disposal in the same well bore. I don’t know the well bore or availability, but your company may like this approach to eliminate handling water beyond location.

Permitting may not be possible (problem in US) and the zones(s) may not be available, but you may want to look.

 

[Scipio]

Zdas04, sounds like you're working on the far side of the same neck of the woods I'm in, with the exception the wells I work with are usually accessible enough to truck out water in situations like yours. Out of curiosity, is the liquid lift on the well plunger assisted or is the well flowing hard enough to carry up the water with the gas?

Unless you're gathering the produced water for a reason, it might be easier to get rid of it on site. Is it close enough to potable, and is your tank heater a high enough duty, to just boil off the tank? I've seen it done on some remote sites with 100-200 bbl tanks and 250000 BTU burners, the only place it caused any problems was when someone decided to do it on a tank with liquid hydrocarbon condensate in with the produced water - the tank turned into a flare stack. These were also manually ignited burners, judging by the sounds of your site you'd probably have to automate it by figuring out a way to combine level control and temperature control.

As far as pumping goes, we use pneumatic-driven plunger pumps like Texsteam, Arrow or Texas Carbide (don't know if those are still made though) in services like that, but never in anything with that high a flowrate, as they use a lot of pneumatic gas. As you say, emissions are a real problem, especially with that CO2 content, but you might be able to minimize the effect by using the vented drive gas as fuel gas for the tank heater (which I assume is a fired heater, not catalytic). I've also seen a few types of diaphragm pumps driven by rotary vane-type air motors, but the motors usually foul pretty quickly when powered with wet fuel gas.

By the way, if you're having problems keeping automation batteries charged, have you tried using a TEG unit instead of solar panels? You've got to chain them down so they don't wander off to someone's home, but they work 24 hrs a day, 365 days a year, and are nowhere near as attractive a bullseye for target practice for hunters as solar panels are.

 

[zdas04]

D23,
If the problem were easy, I wouldn't waste this group's time with it.

I've been looking at deep-zone injection for a while now, and I just can't make it work without some sort of pump (CDI has a cool rod pump that discharges below a packer for example, Weatherford has a hydraulic stroking pump that can do it as well). Just using hydrostatic head to inject below the productive zone seems to require more cleverness than I've been able to muster yet. Underground Injection Control (UIC) permits generally take a year here, and where this well is would require depening it from 3,000 ft to 8,500 ft - I have to be able to find a cheeper answer than that.

Scipio,
It does sound like we're in the same universe. This is a coalbed methane well (i.e., just methane, CO2, and 6,000 mg/l TDS water) so light ends are not a problem. The well flows 2 MMCF/d and velocities are still high enough to free flow - we haven't had much success using plungers at these rates.

Boiling 100 bbl/d takes something on the order of 5 million BTUs or 20 250 MBTU burners (I don't know how to fit that many burners in a 400 bbl tank). The well is in a national forest (Craters of the Moon National Forest, right down from Mare Undrum) so even beneficial surface discharge is verboten (your tax dollars at work).

I've never considered exhausting a diaphram pump into tank and/or separator burner, but the idea has a lot of merit.

I looked at TEG units a few years ago, but they just weren't ready for prime time. Are they now? I just did a Google search for Thermo-Electric Generators and found a bunch of egghead references, but nothing practical and no vendors. Do you have a vendor reference?

David

 

[Scipio]

zDas04,

We've used TEG's successfully in a few remote sites where we need power for automation or callout (RTU or cell phone) systems to transmit data from the site to the central control room. I'm in northern Alberta, so during the winter we only see 6 or 7 hours of daylight, as a result solar panels aren't always capable of providing enough power, the TEG's have been filling the power gap between solar and gensets fairly well, from what I've been told. Ours come from a company here in Alberta called Global Thermoelectric Inc (they're actually sized and purchased by our electrical contractor, I've never done it myself), but I think they've got offices in the states as well. I doubt they're the only company out there, but it's a place to start - I'd expect a few more names would pop up in one of the electrical forums.

As far as your pumping goes, I'm not sure you're going to find a healthy way to run a combustion engine with that gas (I'd sure be interested if you do!) That said, the only thing I can think of is an air-operated double diaphragm. If I've followed the thread right, you need to move up to 3 USGPM of water (design rate 12 USGPM) against a pressure of 40 psig. Only source of energy is wellhead gas flowing at 125 psig. This is fairly easily hit by something like a Wilden or an ARO double-diaphragm pump - NPSHr might be a bit tight though. 125 psig is about the max you can hit those pumps with on the drive side anyway, and 40 psig discharge shouldn't pose a problem. Take the vented gas and use it for fuel gas to various burners, you'd need to have some sort of back pressure control on the vent side of the pump to vent excess gas if the pump is using more drive gas than the burners can use as fuel gas, or alternatively a small flare/VCU to combust the vented drive gas, but I've got no idea what the environmental regulations you contend with there are like, if they'd even allow flaring in a park.

 

[zdas04]

Scipio,
The discharge requirements are a bit tougher than that - I have to get into a 40 psig gathering system AFTER I climb a 400 ft hill (total discharge pressure to overcome hydrostatic, friction, and gathering pressure is close to 220 psig). I just looked at Global Thermoelectric's web page and I have several places where that size equipment would be a godsend. Thanks for pointing me that way.

We have no problem running big natural gas engines down to 0.750 BTU/SCF (28% CO2 and 100% relative humidity), I've talked to folks who run Cat 3412LE engines on 0.500 BTU/SCF gas with digester carbs on landfill gas (the guy says he's burning methane, keytones, baby dipers, and trash bags). The smallest engine we successfully run is a naturally aspirated Arrow 220 (call it 60 Hp at altitude). Below that the problems mount.

When I think of the conditions in Northern Alberta I feel like I'm whinning down here in sunny New Mexico. I did a peer assist on our Kirby and West Pem fields last year and was quite humbled by the hurdles that Mother Nature threw in those guy's path. Their best conditions were marginally worse than our worst conditions and I don't even want to think about accessing the wells on a quad or having to build pipelines and wellsites on the freeze.

David

 

[Scipio]

zdas04,
At least the TEG was useful advice then

The only other way I can think of to go pneumatic is going back to basics with something like a Texsteam 6100 gas-driven plunger pump, which are high (relatively speaking to other gas-driven models) capacity/high pressure pumps. Another manufacturer of similar pumps is Bruin, but I don't have any of their catalogue cutsheets. You might have to put two or three in parallel to get your 12 GPM, but the discharge pressure shouldn't be a problem. Put them in an insulated shack with a small catalytic heater and your exhaust valve freeze-ups won't be an issue. Only two drawbacks are the plunger packing adjustments, and the vented gas.