Interface level measurement in an oil/water emulsion?

Hello Brad,

A couple of decades ago, I wrote a paper about water in crude oil measurements. A device was tested that was referred to as a 'ration tube' which used the specific gravity measurements of the crude oil and water from a particular well. When a give well was diverted to the test separator, we used very specific values for the crude and the water from that particular well. It measure the difference in weight between 2 taps in a vertical section of pipe. The device was manufactured by ITT Barton (don't know if they still exist). Bottom line, it worked well in a test separator at prudhoe bay, as long as the pressures were low (less than 200 psi. Above 200 psi, the water and oil formed a 'tight emulsion' and the accuracy of the measurements was much less reliable. This would not be a problem for a reservior deep into secondary or tertiary recovery, unless the pressures were quite high.

The typical pressures of the field separators was over 700psi (that was when prudhoe was making close to 2M barrels of oil a day!). At that time capacitance probes were know not to be accurate above a few percent. This 'specific gravity' ratio tube measurement system did require that we measure the specific gravity of the crude, on a frequent basis to ensure it had not changed. Various wells produce oil at different S.G. within larger oil fields. S.G. also varies quite a lot over the life of a given well, depending on how the reservior was managed. In those days, early 1980s, the gas was reinjected and not many of the 'light-ends' were removed, so the S.G. variations were managable.

At the time I presented the paper to the SPE, in 1981, as a student paper contest entrant. During the conference, I met a fellow ARCO engineer that had been studying the same issue for years, and had tested all sorts of devices. I not certain where ARCO's R&D results are published. Maybe the SPE has some articles, as it is a fundamental problem for oilfield operations.....

Surely the equipment has changed significantly.

One thing I learned was to 'verify' the measurements against traditional analysis of samples.

James

Magneto-strictive works for interface as well, as long as there is enough SG difference between the two liquids and nothing to stick the float(s). MTS,

etal.

It depends on the SG of the oil. If it is low enough (the API high enough) density based devices will work. The kind of crude oil I work with has an SG very close to 1., sometimes even more. In those cases capacitance or u wave absorption are the only way to go. Drexelbrooke and Agar are the two commonly used brands.

Now here is a weird trick for detecting the rag layer (emulsion) which gets stuck between the oil overflow and the water underflow: These is a grid of

1/2 dozen thermometers spanning the interface. There will be an abrupt temperature change when there is a well defined interface. The gradient is blurry when there is an accumulation or emulsion.

Oh, you might ask, how does one use a separator when the API < 10 (SG > 1)? Everything is upside down. Weird but it works.

Walter.