温度影响天然气水合物地层井壁稳定的有限元模拟

由于天然气水合物特殊的理化性质，水合物地层要比常规地层的井壁稳定问题更加复杂，钻井液温度对天然气水合物地层的稳定性影响将是一个不容忽视的因素。为此，考虑热传导、对流、水合物分解、地层力学性质变化等诸多因素及其相互耦合作用，建立了温度影响天然气水合物地层井壁稳定的数学模型，并进行有限元求解。最后以国外某深水天然气水合物地层实际取得的地质资料为例，计算分析了钻井液温度对地层水合物分解、地层力学性质变化及井壁稳定的影响规律。结果表明：地层水合物因受热分解会导致地层力学性质急剧变差，进而极易导致地层屈服失稳，选择低温体系钻井液并控制其温度低于水合物相平衡温度，有助于维持井壁稳定，实现安全钻进。

Finite element simulation of temperature impact on wellbore stability of gas-hydrate-bearing sediments

Due to the special physical and chemical properties of gas hydrate,the issues associated with wellbore stability of gas-hydrate-bearing sediments(HBS) are far more complex than those of normal sediments,among which the impact of drilling fluid temperature will never be neglected.Given this,a mathematical model is established considering the interactions of multiple factors such as heat conduction,convection,hydrate decomposition,formation mechanical property changes,etc.Additionally,finite element solutions were calculated.Taking the geologic data obtained from a foreign deep-water hydrate formation as an example,this paper studies and analyzes the influence law of drilling fluid temperature on hydrate decomposition,formation mechanical property changes and wellbore stability.According to the result,the thermal decomposition of hydrates in the formation deteriorates the mechanical properties sharply,easily resulting in the instability of formation yielding.For that reason,the low-temperature drilling fluid will be beneficial to maintaining wellbore stability and ensuring safe drilling with its temperature controlled lower than the phase equilibrium temperature of hydrates.