Improving Multiphase Flowmeter Accuracy for Hydrocarbon Allocation and Wet Gas Production of Unconventional Oil-Gas Wells

Abstract

Unconventional resource development has become the most widespread form of energy production in the US and has gained increased interest in the Kingdom of Saudi Arabia (KSA). Reliable and robust multiphase flowmeters (MPFMs) using a combination of Venturi and multi-energy gamma-ray absorption represent a solution that can replace bulky and costly separators while providing accurate flow rate monitoring for high gas production. A high accuracy is required, particularly the US where, for the exploitation of mineral resources, landowners receive royalties calculated from the declared hydrocarbon production under their property. Although MPFMs using multi-energy γ-ray absorption cover the full range of gas-volume fraction (GVF) and water-liquid ratio (WLR), production from gas-lift and wet-gas unconventional wells typically features a GVF > 95% and high WLR, which are challenging conditions for achieving the oil flow-rate accuracy required for fiscal allocation. By advantageously modifying the MPFM radioactive source, the X-ray fluorescence (XRF) phenomenon generates a lower-energy X-ray emission in addition to those naturally emitted by the source radionuclide. The enhanced sensitivity to differentiating the oil-water droplets in a large gas volume reduces more than twice the WLR measurement uncertainty at high GVFs, thus significantly improving the gas and oil flow-rate accuracies. Proper extraction of fluorescence X-ray emissions is achieved with a full energy spectrum analysis by a dedicated proprietary data-processing algorithm. The new X-ray mode starts from a GVF ∼ 85% due to the large absorption by oil-water liquids. For lower GVFs, the higher-activity XRF source also leads to a small accuracy improvement. Extensive validation by flow-loop tests demonstrates the WLR uncertainty reduction over the entire GVF range, with more than twice reduction at GVF > 95% when compared to the MPFM with an existing source. The update of the nuclear interpretation model leads to a large accuracy improvement of the flow rates. The field exposure of the MPFMs equipped with the new XRF source demonstrates the simple retrofit of the existing deployed flowmeters and the significant improvement of WLR and flow rates, even under gas-lift slug-flow conditions. The high-accuracy XRF-source MPFM can lead to an increased new technology adoption in the US by replacing traditional bulky test separators equipped with natural gas-driven valves. The emission reduction of greenhouse gas will help US oil companies towards achieving their sustainability goals. In KSA, the high-accuracy MPFM can help the energy transition through natural gas, employed in blue hydrogen production. This paper describes the details of the new XRF radioactive source and the XRF energy spectrum interpretation that attain high flow rate accuracy even for high GVFs during production from gas-lift and wet-gas unconventional wells. Successful cases in both the laboratory and field conditions validate the technology.