Utilization of Mobile Multiphase Flow Meter in an Uncertain H2S Media: Precautions and Benefits

Abstract

The deployment of Multi-Phase Flow Meter (MPFM) from commissioning to execution campaign in harsh offshore/H2S uncertainty conditions is presented. The case study was performed in Lam and Zhdanov fields operated by Dragon Oil, Offshore Caspian-Turkmenistan. The objective was to enhance the quality of well testing and allocation factor by comparing test separators (TS) measurements against multiphase flow meter (MPFM) readings and, in a bigger scope to converge the difference versus onshore plant measurements of oil and water. Commissioning stage of MPFM was started off by comparing its results with TS. Comparison program was made and followed by considering the operating envelope of both technologies: MFPM and TS, input PVT parameters, measurement conditions and success criteria. Water-liquid ratio (WLR) and water rate from MPFM was compared against wellhead samples utilizing automatic centrifuge and total water at plant. MPFM was subjected to measure flow during both: well clean-up stage and production logging of a slugging well. High gas volume fraction and scale/wax precipitation have required methodology development to maintain the accuracy of MPFM. 14 wells were subjected to comparison test showing differences in gas and liquid rates between MPFM and TS are within acceptable criteria while difference in water rate was high due to slugging nature of flow. High-frequency measurements of WLR from MPFM showed water rates accompanying slugging were consistent with wellhead sampling and total onshore water production. Two-phase test separator was underestimating the water due to few sampling and improper separation at manual centrifuge. In high gas volume fraction equal to 98.5% and above MPFM accuracy in liquid rate becomes very sensitive to reference point of gas. To maintain the liquid accuracy, the in-line measurement of gas point was done so that accuracy of liquid measurements improved. MPFM has identified wells with scale and wax precipitation, which can be observed from photon counts deviation at two energy levels of gamma-ray spectrum. By adding 3rd energy level, it was possible to estimate the thickness of scale and wax on the wall of meter venturi throat and hence maintaining the MPFM flowing rate accuracy. MPFM campaign showed accurate measurement of water for Cheleken in addition to adding efficient well testing frequency while providing reliable high data frequency. This case study shows the first mobile MPFM application in Caspian offshore for producing wells’ testing. Results in comparison with TS signifies better and faster ways to calibrate the surface TS. MPFM testing campaign has led to the early identification of possible flow assurance issues and consequently, development of methodologies and recommendations to ensure reliability of MPFM and permanent test separators.