Modeling Wellbore Dynamics during Oil Well Blowout
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Blowout or uncontrolled flow of an oil well involves complex flow phenomenon involving transient multiphase flow and heat transfer in the wellbore. Various wellbore and reservoir parameters govern the maximum velocity attained in a given well. The maximum velocity may be either critical (sonic) or subcritical. This work adapts a transient model to capture the events leading to the onset of maximum velocity of a fluid mixture. The model uses a numeric method to solve the mass, momentum, and energy equations for the wellbore, and an analytic approach for fluid flow in the reservoir. The theoretical sonic velocity computed by assuming isentropic expansion turns out to be higher than the actual maximum velocity attainable in the well. Computational results also show that the assumption of isentropic expansion becomes progressively worse with increases in gas/oil ratio, because of increased frictional loss. Among various parameters, the blowout rate increases with increased well-productivity index, flow-string diameter, reservoir pressure, and gas-oil ratio (GOR). The probabilistic reservoir-simulation approach is used to answer the reservoir-fluid-loss question.