Auto-Correction Algorithm of Multiphase Flowmeter Water Cut Measurements in Undersaturated Oil Wells

Abstract

Abstract Dual energy gamma ray attenuation in multiphase flow meters (MPFMs) are commonly used in the oil and gas industry to measure the flow rate of hydrocarbon producing wells. The low energy gamma ray attenuation is highly dependent on water salinity, making this type of MPFM very sensitive to water salinity. This challenge is evident in oil fields where lower salinity water is injected into the reservoir to maintain pressure for oil producing wells, imposing changes in water salinity with time. Hence, frequent fluid sampling and calibration is required to ensure high reliability measurements from such meters. In this paper, a new methodology is proposed to automatically correct the deviation in MPFM water cut measurements due to water salinity changes without the need to collect fluid samples. The methodology proposed in this paper is a gas-oil ratio (GOR) based method that corrects the deviation in MPFM measurements due to the change in water salinity without the need to collect any fluid sample. In addition, the method does not require any additional information to be acquired from any other sources, other than the normal parameters acquired by the MPFM. The method is applicable to oil wells producing from undersaturated reservoirs. Furthermore, for the method to be reliable, the operating condition at the MPFM has to have adequate amount of free gas because the methodology is GOR based methodology. The results from the proposed method were cross checked against data collected from multiphase separator tests and showed excellent agreement. It was also tested across multiple undersaturated oil reservoirs against a wide range of oil properties and water salinities. The method will help identify the MPFM that require calibration and will eventually make MPFM measurements more reliable without the need for frequent fluid sampling for meter calibration. This method will also lead to reducing the need for rigless multiphase separator testing requirements resulting in substantial cost reduction.