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Prediction of flaring CO2 emissions during pressure depletion in oil field

Flaring emissions related to upstream activities in oil and gas industry were analyzed. CO2 produced by flaring at natural gas processing facilities has proved to be negligible. Largest flaring CO2 emissions are present at small oil fields that are not connected to gas transportation system. Production from oil fields can be represented as set of vapor-liquid equilibrium conditions due to pressure decrease in an oil reservoir. It was assumed that at each pressure decrease, due to gas liberation in reservoir, oil composition changes. Laboratory differential liberation analysis of bottom-hole oil sample was used in order to adjust the parameters of cubic equation of state. With adjusted equation of state, separation of gas (flash separation) at surface was simulated. These results gave compositions of gas that will be separated at the surface and burned at flare. Despite vapor-liquid equilibria and phase compositions cannot be correlated (they are calculated by iterative procedures defined by Rachford and Rice and by solving cubic equation of state for each phase), resulting amounts of CO2 from flaring at different periods of production from an oil field (i.e. from different pressures in an oil reservoir) can be linearly correlated. By comparing estimated emissions from gas liberated directly from a reservoir to atmospheric conditions (and then flared) and emissions from gas separated at 7 bar, it is obvious that significant reduction of CO2 can be achieved (more than 100 %) by incorporating a separator. Feasibility of such process with smaller amounts of emitted CO2 should be analyzed by including estimates of oil production, reservoir pressure change and producing gas to oil ratio. General conclusion was emphasized – CO2 from flaring at small oil fields will decrease naturally with pressure depletion in reservoir.

CO2 emission, vapor-liquid equilibria, cubic equation of state, gas flaring, oil reservoir, pressure depletion

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