考虑盐度影响的深水水合物地层钻井井筒流动规律

Wellbore Flow in Drilling of Deepwater Hydrate Formation Considering the Influence of Salinity

水合物分解的气-液-固多相流动问题是深水水合物地层钻井面临的一个新问题。考虑钻进过程中井筒内的多相流动、传热和水合物分解三者之间相互耦合关系,建立了考虑海水盐度影响的含水合物相变气-液-固多相非等温瞬态流动模型。采用室内试验数据与现场实测数据验证了模型的准确性。案例井计算结果表明:随着海水盐度的增加,井筒内水合物分解区域和分解速率逐渐增大。同时,海水盐度越高,钻井过程中井底压力降低的幅度越大,井口气体含量也越高。井口回压和注入流体温度可以有效控制井筒内水合物的分解量。为了保证井口安全,降低水合物分解速率,井口回压应大于4.5 MPa。当入口流体温度在15~30℃范围内时,海水盐度应控制在0.8%~1.9%之间,这将保证井口最大气相体积分数小于10%。研究结果可为深水水合物的开采提供理论支撑。

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-bearing 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 decomposition 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 wellhead 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.