Study Of Wet Gas Metering Technology Based On Slotted Orifice And Swirlmeter

With the advancing of exploitation of oil and natural gas field into offshore, desert and remote areas, it extremely desirable to have a wet gas metering system that is capable of providing cost effective, compact in size, and on-line measurement of wet gas with sufficient accuracy to replace a bulky and costly test separator, in terms of cost savings, production optimization, field monitoring and reservoir management. The method employing mature gas flowmeters to meter wet gas had been and still is a highly focused subject for many researchers around the world. In this dissertation, two mature gas flowmeter, namely a sloted orifice and a swirlmeter, are employed to meter wet gas. The main contributions can be enumerated as follows:First, a novel noninvasive approach, based on flow-induced vibration, to the online flow regime identification for wet gas flow in a horizontal pipeline is proposed. The flow-induced vibration signals were measured by a transducer installed on outside wall of pipe, and then the normalized energy features from different frequency bands in the vibration signals were extracted through wavelet package transform. The three classifies, namely the RBF neural network, the probabilistic neural network, and support vector machine classifiers, are respectively constructed to identify wet gas regimes. The results show that the three classifiers can identify flow regimes effectively.Second, researches into the wet gas flow performance of the horizontally installed slotted orifice meter were performed. After studying of the relationship between the over-reading and Lockhart-Martinelli parameter X_LM, gas Froude Number, the gas to liquid density ratio and beta ratio, two new metering correlations for low-pressure wet gas flow are proposed. The results show that the calculate accuracy of the correlations are higher than all of the previous ones, and therefore they can be used to meter the gas flow rate for wet gas flow.Third, the wet gas flow performance of a swirlmeter based on vortex precession frequency was uniquely investigated. When X_LM> 0.12, the flowmeter failed to meter the gas flow rate due to disappearance of vortex precession. WhenX_LM≤0.12, the entrained liquid in a gas stream tends to induce a negative bias in the gas flow rate reading of the swirlmeter, and therefore a metering correlation is proposed by using the surface-fitting technology. The results show the correlation improves the gas flow rate prediction errors of the wet gas flow to within±5%at a confidence level 95.4%, and therefore it can be used to meter the gas flow rate for wet gas flow at X_LM≤0.12. Fourth, the wet gas flow performance of a swirlmeter based on differential pressure was uniquely investigated. It shows that the differential pressure of swirlmeter has similar metering characteristics to that of Venturi tube, and and a metering correlation is proposed by using the surface-fitting technology. The results show the correlation improves the gas flow rate prediction errors of the wet gas flow to within±5%at a confidence level 96.4%, and therefore it can be used to meter the gas flow rate for wet gas flow.Fifth, a novel approach to meter individual flow rates for wet gas by using two dissimilar flow sensors, i.e. a sloted orifice and a swirlmeter, is proposed. The steps of iterative solution of obtaining individual flow rates are also given. The results show that the proposed approach predicts the gas mass flow rate within±6%at a confidence level 89.2%, and the gas mass flow rate within±20%at a confidence level 100%, and therefore It can be used to meter individual flow rates for wet gas flow at X_LM≤0.12.Sixth, a novel approach to meter individual flow rates for wet gas by using two dissimilar output signals of a swirlmeter, i.e. vortex precession frequency and differential pressure, is proposed. The steps of iterative solution of obtaining individual flow rates are also given. The results show that the proposed approach predicts the gas mass flow rate within±8%at a confidence level 91.3%, and the gas mass flow rate within±20%at a confidence level 89.2%, and therefore it can be used to meter individual flow rates for wet gas flow at X_LM≤0.12. In view of installation, maintenance and cost, the proposed approach is cost-effective due to using only a flow sensor.