Downhole two-phase flow measurement

[egillj]

Hi all

I am working on a method to measure downhole enthalpy in geothermal wells. This means that I am dealing with two phase flow inside the wellbore at up to 2000 m depth, pressures up to 100 bar and temperatures up to 350 °C. There are also other complications like pH in the range 3-9 and very variable conductivity (10-100000 microsimens/cm). To determine the entalpy I will need to measure the temperature (and/or pressure), the void fraction and steam and water flow rates/velocities.
Measuring temperature and pressure is not a problem but I have found the rest to be quite challenging. As far as I can tell the closest thing to give me the void fraction and perhaps the steam flow velocity is the EFP probe developed by Mohr and Associates <

http://www.mohr-engineering.com>.

I still have doubts that this device will work for all flow regimes. I have also had a hard time figuring out how to measure the downhole liquid flow-rates (the only thing I know of is using spinners but I think they don't yield very accurate results in two phase flow).

So if anyone has any helpful suggestions I would greatly appreciate it.

Thanks

Egill Juliusson

 

[Cockroach]

Interesting. Yes, you can get temperature measurement from thermocouples and pressure from a transducer. Depending on your thermal energy content, probably quartz or vibrating wire would be the transducer of choice.

I think you have more of a chemistry question here than thermodynamic. In order to use the thermo tables accurately, this presupposes knowledge of the chemical nature hence, the elements of the flow. Being in the oil business, I have never ran across thermodynamic tables for the various combinations of working fluids encountered in the well. This is probably because of the large variation in chemistry from one formation to another.

I suppose a guy could use the methane tables for simple hydrocarbon flows like propane, but this would most likely give you only ballpark answers.

Ultimately, you may need to determine enthalpy as a result of isentropic throttling between uphole and downhole states. In any case, rather an interesting problem. Good luck with it.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[egillj]

Thanks for that Cockroach,

I think I could get a fairly good estimate of the enthalpy by assuming that I have a pure steam/water system. The challenge is to get the flow rates/velocities of steam and liquid and the void fraction.

As an answer to your las comment, I don´t know it the isentropic assumption would work because geothermal wells usually have open fractures feeding the well at various depths. One of the advantages of having a downhole enthalpy meter is to be able to quantify the entalpy being fed into the well by each fracture.

-Egill

Egill