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Gas Injection - JT Cooling Issue

Gas Injection - JT Cooling Issue

(OP)
Hello,

We have a producing field with a single gas injector. Right now we are injecting into a pool with a reservoir pressure of ~23MPa. We're considering adding an injector in an adjacent pool, but the reservoir pressure is ~13MPa. As the two gas injection wells will be sharing a single gas injection system and will be drilled out of the same drill center, the second injector will experience a significant dP across the injection choke at any rate due to the line pressure being maintained to inject into the first well.

This dP results in WHTs dropping to as low as -15°C. Our problem is that the downhole equipment is not rated for these temperatures (minimum geothermal warming occurs at the rates we are interested in). Our vendors are suggesting that we spend $100k's in order to qualify the equipment, but there must be a better solution. Any experience with such an issue out there? We can't be the first to inject into two different pressured pools.

Also, I realize that a DH choke could take the brunt of the dT within the reservoir and away from equipment, but if we're considering a dual zone well with active DH valves this may still be a problem. Any thoughts?

RE: Gas Injection - JT Cooling Issue

A heater will solve that issue.

Depends on the ambient temperature, flow rate and how high the temperature needs to get to to avoid any issues. You might get enough heat energy from the air or you might need extra heat.

Either that or run the joint system at ~13Mpa and then add another compressor to get up to your 23Mpa.

Lots of ways to skin this cat.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Gas Injection - JT Cooling Issue

(OP)
Ah yes, I should have mentioned that we are in an offshore setting and any additional equipment (although a viable solution) is going to be difficult and expensive to install especially another compressor.

Ambient temperature is one of the drivers of the problem. Sea floor is at -2C

RE: Gas Injection - JT Cooling Issue

I would look at driving an ejector with the 23 MPa stream (maybe sucking on your lower pressure wells?) and leave the exhaust at your 13 MPa target injection pressure with no J-T cooling. If you used the ejector to pull on the LP well then you'd only need about half the mass of 23 MPa gas as you are injecting. I designed a similar system for a project in the shallow part of the Gulf of Mexico and the exhaust temperature was only a couple of degrees below the mass-weighted average of the suction and power gases.

Another option would be to take the dP in 2-4 stages using progressively smaller choke nipples.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

RE: Gas Injection - JT Cooling Issue

1. Is -15 deg C the fluid temperature, or the metal temperature?

2. What temperature is the "downhole equipment" rated for?

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

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