Wellbore Flow in Drilling of Deepwater Hydrate Formation Considering the Influence of Salinity
The gas-liquid-solid multiphase flow problem considering hydrate decomposition is a new problem faced by drilling in deepwater hydrate formations.After having taken into account the coupling relationship among multiphase flow,heat transfer and hydrate decomposition in the wellbore in the course of drilling,a hydrate-bear-ing facies change gas-liquid-solid multiphase nonisothermal transient flow model considering the influence of salinity of sea water was built.Then,the laboratory test data and field measured data were used to verify the accuracy of the model.The calculation results of the case well show that as the salinity of seawater increases,the decomposi-tion area and rate of hydrates in the wellbore gradually increase;meanwhile,the higher the salinity of seawater,the greater the decrease in bottomhole pressure during drilling,and the higher the gas content at the wellhead;the wellhead backpressure and injection fluid temperature can effectively control the decomposition amount of hydrates in the wellbore;in order to ensure the safety of wellhead and reduce the rate of hydrate decomposition,the well-head backpressure should be greater than 4.5 MPa;when the inlet fluid temperature is within the range of 15～30℃,the salinity of seawater should be controlled between 0.8%and 1.9%,which can ensure the maximum gas phase volume fraction at the wellhead to be less than 10%.The research results provide theoretical support for the exploitation of deepwater hydrates.
hydrate formationgas-liquid-solid three-phase flowsalinity of sea waterhydrate decomposition
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