Abstract Drilling fluid invasion into hydrate-bearing sediments could induce hydrate dissociation and complicate heat and mass transfer around wellbore, and further affect mechanical strength of hydrate-bearing sediments and accurateness of wellbore logging interpretations. In this study, a cylindrical numerical model was established to study the characteristics of drilling fluid invasion into hydrate-bearing sediments and the effects of permeability on this process. The distributions of temperature, pressure, saturation, and salinity of pore water around wellbore at different time were obtained. The pressure and temperature around wellbore gradually increase, and the hydrate around wellbore dissociates with the high-temperature drilling fluid invasion. Meantime, water and gas generated from hydrate dissociation gradually migrate outward and then form ‘secondary hydrate’ in some areas outside wellbore. Dissociation and formation of hydrate can sharply change the salinity of pore water around wellbore. The drilling fluid invasion and hydrate dissociation ranges become larger when the intrinsic permeability is higher. The salinity in sediments decreases sharply while the dilution range is narrow when drilling fluid invasion into hydrate-bearing sediments with low permeability. In addition, the permeability decline exponent of the Masuda model has a significant influence on drilling fluid invasion. However, the Corey exponents of the relative permeability model only have a limited influence on drilling fluid invasion into hydrate-bearing sediments with low intrinsic permeability (e.g., 5.5 mD), while they have a noticeable influence on hydrate-bearing sediments with high intrinsic permeability (e.g., 75 mD).

中文翻译：

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钻井液侵入含水合物沉积物的数值模拟及渗透率影响

摘要 钻井液侵入含水合物沉积物会引起水合物分解，使井筒周围传热传质复杂化，进而影响含水合物沉积物的机械强度和测井解释的准确性。本研究建立圆柱数值模型，研究钻井液侵入含水合物沉积物的特征以及渗透率对该过程的影响。获得了不同时间井筒周围孔隙水的温度、压力、饱和度和盐度分布。井筒周围压力和温度逐渐升高，井筒周围水合物随着高温钻井液的侵入而解离。与此同时，水合物解离产生的水和气逐渐向外运移，在井筒外的部分区域形成“二次水合物”。水合物的解离和形成会急剧改变井筒周围孔隙水的矿化度。固有渗透率越高，钻井液侵入和水合物分解范围越大。钻井液侵入低渗透水合物沉积物时，沉积物矿化度急剧下降，稀释范围变窄。此外，增田模型的渗透率下降指数对钻井液侵入有显着影响。然而，相对渗透率模型的 Corey 指数对钻井液侵入具有低固有渗透率（例如 5.5 mD）的含水合物沉积物的影响有限，