海洋天然气水合物固态流化多相混合浆液水平段运移规律

Horizontal pipe migration law of multiphase mixed slurry in offshore gas hydrate mining

为了揭示天然气水合物多相混合浆液在固态流化开采工艺水平管段的运移规律,基于固液两相流模型,采用计算流体力学软件建立了相应的仿真分析模型,对比了在相同工况下,双层管双梯度钻井水合物固态流化钻采工艺与常规钻采方式水平段内水合物混合浆液运移效率,分析了水合物丰度、固相颗粒粒径、钻井液流量和举升泵扬程对水合物多相混合浆液运移效率的影响。研究结果表明:在同等条件下,双层管双梯度钻井水合物固态流化工艺水平段水合物混合浆液的运移效率比常规开采方法的高;随着水合物丰度提高,钻井液流量增大,举升泵扬程较大时,水合物多相混合浆体主要以悬移的方式运移,固相颗粒在水平管段中沉积率降低;双层管双梯度钻井水合物钻采工艺更适用于固态流化开采形成的含砂体积分数高、固相颗粒尺寸大的混合浆液运移;在长水平井段分节增设多级举升泵可实现水合物混合浆液二次破碎、减小固相颗粒直径,提高水平段固相颗粒运移效率;适当提高钻井液流量能有效提高水合物混合浆液在水平段中的运移效率。

In order to reveal the migration law of gas hydrate multiphase mixed slurry in the horizontal pipe section during the solid fluidized mining process,the solid-liquid two-phase flow model was employed and the computational fluid dynamics software was used to establish the simulation analysis model.The migration efficiency of hydrate mixed slurry in horizontal section of double-pipe double gradient drilling and conventional drilling was compared under the same working condition.The effects of hydrate abundance,solid particle size,fluid flow rate and lifting pump head on the migration efficiency of hydrate-sand multiphase mixed slurry were analyzed.The results show that under the same working conditions,the migration efficiency of hydrate mixed slurry in the horizontal section during the solid fluidization of hydrate in double-layer pipe double gradient drilling technology is better than that of traditional mining method.Hydrate multiphase mixed slurry migrates mainly in the form of suspension and the deposition rate of solid particles in horizontal pipe decreases with the increase of hydrate abundance,drilling fluid flow and lift pump head.Hydrate drilling technology of double layer pipe double gradient drilling is more suitable for the migration of solid particles with high sand volume fraction and large size particles formed by solid fluidized mining.Besides,multi-stage lift pumps should be added in segments of long horizontal wells to achieve secondary crushing of hydrate mixed slurry,reduce the diameter of solid particles and improve the migration efficiency of solid particles in horizontal segments.Appropriately increasing drilling fluid flow is an effective method to improve the migration efficiency of hydrate mixed slurry in horizontal section.