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Choke modeling and flow splitting in a gas-condensate offshore platform
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Well production rate is a major factor for simulation of commingled gas wells. It is the base of computations of well flowing pressure, pressure drop, well performance, flow regime, liquid holdup, reservoir performance, material balance and average reservoir pressure. Typically, well flow rate is measured using flow meters like orifice, but in some wells flow rates remain unknown due to shortage of flow meters and commingled production. In this paper, well flow splitting of a gas-condensate field with two platforms is studied. Each platform consists of ten wells and wellhead pressure is controlled by a choke valve. Total flow rate of platforms mixed production is measured after sending their production to refinery. The proposed methodology for dividing total flow between wells consists of choke modeling using test separator data and flow modeling in the wells. Choke models include mechanistic and Ashford and Pierce as theoretical models and Gilbert, Ros and Pilehvari as empirical models. In most investigations choke size is represented with length unit such as inches but in this work, flow is calculated on the base of choke opening percent and choke size as a function of choke opening percent is obtained. Chokes are modeled with upstream temperature, upstream pressure and downstream pressure. Rich gas flow calculations with the proposed method were compared with reported total flow of platforms and showed mean absolute percentage error of 3.2% for mechanistic model as the best of studied models. This error can cause 0.5% error in calculated well flowing pressure. Sensitivity analysis on operation parameters showed that since the gas-condensate field is lean, gas flow rate is the major phase for modeling and uncertainty of gas-condensate ratio and changing specific gravity and molecular weight of condensate with time do not have considerable effect on well flow rate calculations.
Researchers Reza Azin (Second researcher) , Shahriar Osfouri (Third researcher) ,