隔热套管下入深度对天然气水合物的抑制分析

Analysis on the Inhibition Effect of the Setting Depth of Insulation Casing on Natural Gas Hydrate

针对井筒天然气水合物堵塞难题,采用隔热套管到深水气井中可减少海水以及地层与井筒的传热,也能实现井筒流体保温,降低天然气水合物生成风险。国内隔热油管一般适用于稠油热采中提升稠油温度,因隔热套管价格昂贵且过多层位隔热套管会引起强度不足,导致测试失败。因此精准确定隔热套管的下入深度可以极大地减少开采成本,最大化地实现井筒保温。在套管微元体迭代求解数值方法下,得到套管最佳下入深度的离散解,保证了最佳下入深度的收敛性。以我国南海Y气井建立的深水气井为研究对象,对天然气水合物的形成井段以及温压临界条件进行了模型预测,确定了在固定的井产量下隔热套管最佳的下入深度。研究结果表明:设计优选出的E级隔热套管外径127 mm,导热系数0.006 W/(m·℃),抗拉载荷615 kN;该隔热套管下入井筒1500 m处,可提升井筒流体温度15℃,满足井筒多产量采气要求,可以有效抑制井筒生成天然气水合物。研究内容和所得结论对于深水气井抑制天然气水合物的形成以及有效地控制开采投资具有一定的参考作用。

In order to solve the blocking problem of natural gas hydrate in the wellbore,insulation casing is applied in deepwater gas wells to realize wellbore fluid insulation and reduce the risk of natural gas hydrate formation.In China,insulation tubing is generally used to increase the temperature of heavy oil in its thermal recovery.Insulation casing is expensive and has too many layers which can cause insufficient strength,leading to test failure.And determining the setting depth of thermal casing accurately can greatly reduce the production cost and maximize the wellbore insulation.In this paper,the discrete solution of the optimal casing setting depth is obtained by means of the numerical method of casing micro element iteration,which ensures the convergence of the optimal setting depth.And the hole interval where natural gas hydrate is formed and the critical temperature and pressure conditions are predicted in the model and the optimal setting depth of insulation casing under the fixed well production rate is determined by taking Gas Well Y in the South China Sea as the research object.The results show that the selected E-grade insulation casing has outer diameter of 127 mm,thermal conductivity of 0.006 W(m·℃)and tensile load of 615 kN.When this insulation casing is set at the depth of 1,500 m,wellbore fluid temperature can be raised by 15℃so as to meet the requirements of multi-yield gas production in the wellbore and effectively inhibit the formation of natural gas hydrate in the wellbore.The research contents and conclusions can be used as the reference to inhibit the formation of natural gas hydrate in deepwater gas wells and effectively control the production investment.