The use of multiphase flowmeters (MPFM) for well test measurements is increasingly becoming a standard practice replacing conventional test separators. These MPFMs are usually tested and calibrated in laboratory controlled flow loops using idealized fluids in steady state conditions. However for high water-cut, high gas-volume-fraction and low pressure unstable flow these controlled conditions are far from reality which can lead to unforeseen errors in the field. Recent experience shows that in certain conditions, the various types of multiphase flowmeters react quite differently to the measurement challenges of transient flows in high water cut and high gas volume fractions (GVF). Some meters can be unreliable in measuring oil rates in certain conditions which leads to inaccurate estimation of the wells' potential and associated uncertainty in plans for production optimization. For example the inaccuracies in measured oil rates could be greater than the gain expected from a stimulation or restoration. An inaccurate measure of oil rate also leads to a poor reconciliation factor and poor estimation of reserves. By resolving these inaccuracies and allocating oil correctly to wells it is possible to invest in right opportunities thereby saving unnecessary expenditure. The factors that affect multiphase flowmeter measurement can range from excessive gas-volume-fraction, low line pressures, solids and unsteady flow.

In 2007 an in-situ comparison was made of two types of multiphase flow meters and two separators to determine the most appropriate well test device for X Field in the Sultanate of Oman. X Field wells are artificially lifted and have a high water cut of 80%. The reconciliation factor (also known as the back allocation factor) before this well test campaign was 0.54. The comparison was made on twelve wells producing to X Field station. Each well was tested for 12 hours in series using an existing inline MPFM, a low pressure production test separator, a second mobile MPFM, a 1440psi separator, and a multiphase tracer technique. The objective to determine the most reliable technique(s) of measuring oil production rates was accomplished, and now the reconciliation factor is 1.03. This paper describes the comparison, how the results were analyzed, and the comparative error associated with each technique.

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