Hydrocarbon Dew Point - Measure instead of estimate
Hydrocarbon Dew Point - Measure instead of estimate
(OP)
thread135-253698: chilled mirror or software : this is...
The discussion of the proper use of EOS based on GC data is often one that overlooks the obvious - why calculate it using theoretical methods when it can be measured. There are many papers that describe the deficiencies of using EOS for determining this parameter and you can find a good one at:
htt p://www.ce esi.com/do cs_library /events/is hm2008/Doc s/5110.pdf
But in any case please review ISO23874 and a GE publication GER-3942. Accuracy in this measurement is critical to profitability and getting shut-in because the calculation is based on insufficient data is very expensive.
The discussion of the proper use of EOS based on GC data is often one that overlooks the obvious - why calculate it using theoretical methods when it can be measured. There are many papers that describe the deficiencies of using EOS for determining this parameter and you can find a good one at:
htt
But in any case please review ISO23874 and a GE publication GER-3942. Accuracy in this measurement is critical to profitability and getting shut-in because the calculation is based on insufficient data is very expensive.





RE: Hydrocarbon Dew Point - Measure instead of estimate
RE: Hydrocarbon Dew Point - Measure instead of estimate
In an article "The Need For Accurate Hydrocarbon Dew Point Determination", D. George, Ph.D. et al., Southwest Research Institute, published in Pipeline & Gas Journal, September 2005, he states "Based on comparisons to date, however, the C9+ characterization most often appears to predict measured dew points to within ±25°F."
I just am concerned that the information I have heard at some of the gas schools indicating the ability to get within 2° is highly doubtful at best data has been presentad that suggest the calculations may be even more inaccurate than the 25°. That could get suppliers shut in quickly.
RE: Hydrocarbon Dew Point - Measure instead of estimate
I had a pipeline try to shut me in when their $49 EOS package was predicting HC dew point. I asked the pipeline dispatcher to read the flowing temperature and pressure to me. It was 48F and 650 psia. I said your transmitters are off. He said they were exact and they are the gospel. I said, good, now get your engineer in and explain how a gas at 48F can have a measured (calculated from their cheapy BWR EOS) dew point of 55F and the spec is 50F.
Needless to say, the gas stayed online.
RE: Hydrocarbon Dew Point - Measure instead of estimate
RE: Hydrocarbon Dew Point - Measure instead of estimate
Daniel
RE: Hydrocarbon Dew Point - Measure instead of estimate
Thank you for your contribution.
You are very fortunate in that you have a supply of gas that has been processed very well. A common characterization practice is often based on a laboratory analysis on a properly extracted sample (per API 14.1) to a sensitivity of 0.1 ppm or at least 1.0 ppm to C14. Once a history of the field is established with multiple analysis reports over time, you can get to a reasonable set of actual characterization values for that field/supplier. Why analyze to C14? I have seen conditions where even a change of 1 ppmv of C10 in a natural gas system produces a 10°F change in dew point. One thing that I have seen is that if I take real analysis data and plug it into the EOS and then play with the values just outside the actual analyzed values, the impact of missing them is revealing.
When I assume that there is total efficiency in the processors facility to remove all of these heavies beyond C6 can get me into trouble. Also, characterizing the C7, C8, ... is fine until the source changes as in an upset condition at the processing facility.
The other wrinkle is having a well trained operator using the chilled mirror properly per ASTM D1142. Not just anyone can properly interpret the image on the mirror. I know with my older eyes, you would not want me to take this measurement and make decisions on my readings. The ASTM procedure recommends a procedure that typically takes a full hour to get right even for the experienced technician.
RE: Hydrocarbon Dew Point - Measure instead of estimate
It is important to filter values to get results comparable with those of chilled mirrors.
RE: Hydrocarbon Dew Point - Measure instead of estimate
RE: Hydrocarbon Dew Point - Measure instead of estimate
Daniel
RE: Hydrocarbon Dew Point - Measure instead of estimate
http
RE: Hydrocarbon Dew Point - Measure instead of estimate
there are many papers comparing results of chilled mirrors and VLE packages, both solutions have been extensively tested....