Flow metering using conventional separation-based technologies in low-pressure high gas rate environments typical of gas-lifted wells is a very difficult operation. Owing to low retention times of the gas, the quality of separation and existing instrumentation is often doubtful leading to an under-estimate of liquid rates. An aggravating factor is that such wells are often producing at high water-cuts, thus leading to significant uncertainty on oil rates.
To solve such metering challenges with a large majority of their wells operating above 95% gas fraction under metering conditions and water cuts often higher than 90 %, TOTAL ABK has evaluated different well testing & monitoring strategies based on multiphase metering use.
A compact dual-energy gamma-ray Venturi multiphase flow meter (MPFM) was selected and placed under field trial to assess whether this technology could reduce the uncertainty on oil production by removing any impact of imperfect separation. 20 tests were performed considering 15 wells over a period of 10 days to assess MPFM performance and repeatability in a wide range of conditions.
In most cases, it was found that the meter's performance compares favorably with that of the test separator located in line. Furthermore, the high-frequency high-resolution output of the meter allowed the operator to assess well efficiency and stability and to understand the behavior of the gas lift system. It was shown that such wells have a tendency to behave erratically at very high frequency, leading to fast and significant variations of the well productivity that could not be captured by conventional means and could potentially lead to erroneous results as well as sub-optimal well performance.
The field test proves that the multiphase metering solution used in this trial can be used successfully and is presenting a reliable alternative or complement to conventional test separators for flow metering in low-pressure high water cut wells under gas lift, providing operational flexibility and additional information of interest to optimize well productivity.