隔热套管抑制水合物地层分解规律研究

针对深水钻井中水合物地层易受高温钻井液影响而分解,影响井筒完整性的问题,提出了采用隔热套管降低水合物分解的工程措施,并对隔热套管的隔热效果进行室内试验分析。采用牛顿迭代法计算其视导热系数,建立了钻井液与地层之间的传热模型,对隔热套管的传热情况进行数值模拟。研究结果表明:隔热套管的中间段外壁温度很接近环境温度,且其外壁温度基本不随流体温度的变化而变化;隔热套管内流体温度升高会提升接箍位置温度,但并不影响中间套管段温度;使用隔热套管可以有效降低水合物地层温度,特别是水合物地层与水泥环相交边界温度,使得整个地层短期内都处于相平衡温度以下,从而减弱水合物分解程度。研究结果对保护水合物地层井筒完整性具有借鉴意义。

Research on Insulation Casing Inhibiting the Decomposition of Hydrate Formation

Aiming at the problem that the hydrate formation in deep water drilling is easily decomposed by the influence of high temperature drilling fluid and affects the integrity of the wellbore,the engineering solution to reduce the decomposition of hydrate by the thermal insulation casing is proposed.The thermal insulation performance of the insulation casing is analyzed by laboratory test.The apparent thermal conductivity is calculated by the Newton iteration method,and the heat transfer model between the drilling fluid and the formation is established to numerically simulate the heat transfer of the insulation casing.The results showed that:the temperature of the outer wall of the middle insulation casing section is very close to the ambient temperature,and is basically unchanged with the change of the fluid temperature.The increase of the fluid temperature in the insulation casing will increase the temperature at the coupling position,but does not affect the temperature of the middle insulation casing section.The insulation casing can effectively reduce the temperature of the hydrate formation,especially the boundary temperature at the intersection of the hydrate formation and the cement sheath,so that the entire formation is below the phase equilibrium temperature in a short time,thereby reducing the degree of hydrate decomposition.