Thermal Conductivity Variations in Frozen Hydrate-Bearing Sand upon Heating and Dissociation of Pore Gas Hydrate

IF 2.4 Q2 GEOSCIENCES, MULTIDISCIPLINARY
Evgeny Chuvilin, Dinara Davletshina, Boris Bukhanov, Sergey Grebenkin, Elena Pankratova
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Abstract

High-latitude permafrost, including hydrate-bearing frozen ground, changes its properties in response to natural climate change and to impacts from petroleum production. Of special interest is the behavior of thermal conductivity, one of the key parameters that control the thermal processes in permafrost containing gas hydrate accumulations. Thermal conductivity variations under pressure and temperature changes were studied in the laboratory through physical modeling using sand sampled from gas-bearing permafrost of the Yamal Peninsula (northern West Siberia, Russia). When gas pressure drops to below equilibrium at a constant negative temperature (about −6 °C), the thermal conductivity of the samples first becomes a few percent to 10% lower as a result of cracking and then increases as pore gas hydrate dissociates and converts to water and then to ice. The range of thermal conductivity variations has several controls: pore gas pressure, hydrate saturation, rate of hydrate dissociation, and amount of additionally formed pore ice. In general, hydrate dissociation can cause up to 20% thermal conductivity decrease in frozen hydrate-bearing sand. As the samples are heated to positive temperatures, their thermal conductivity decreases by a magnitude depending on residual contents of pore gas hydrate and ice: the decrease reaches ~30% at 20–40% hydrate saturation. The thermal conductivity decrease in hydrate-free saline frozen sand is proportional to the salinity and can become ~40% lower at a salinity of 0.14%. The behavior of thermal conductivity in frozen hydrate-bearing sediments under a pressure drop below the equilibrium and a temperature increase to above 0 °C is explained in a model of pore space changes based on the experimental results.
孔隙气体水合物加热解离过程中含水冻结砂导热系数的变化
高纬度永久冻土,包括含水冻土,会随着自然气候变化和石油生产的影响而改变其性质。特别令人感兴趣的是热导率的行为,这是控制含天然气水合物聚集的永久冻土热过程的关键参数之一。利用从亚马尔半岛(俄罗斯西西伯利亚北部)含气永久冻土带取样的沙子,在实验室通过物理建模研究了压力和温度变化下的导热系数变化。当气体压力在恒定的负温度(约- 6℃)下降至平衡以下时,样品的导热系数首先由于开裂而降低了百分之几到10%,然后随着孔隙气体水合物解离并转化为水,然后转化为冰而增加。热导率变化的范围有几个控制因素:孔隙气体压力、水合物饱和度、水合物解离率和额外形成的孔隙冰的数量。一般来说,水合物解离会导致含水合物冻结砂的导热系数降低20%。当样品被加热到正温度时,其导热系数会根据孔隙气体水合物和冰的残余含量下降一个量级:在水合物饱和度为20-40%时,其导热系数下降约30%。无水盐冻砂的导热系数降低与矿化度成正比,当矿化度为0.14%时,导热系数降低约40%。基于实验结果,用孔隙空间变化模型解释了含水合物冻结沉积物在压力降低于平衡、温度升高至0℃以上时的导热行为。
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来源期刊
Geosciences (Switzerland)
Geosciences (Switzerland) Earth and Planetary Sciences-Earth and Planetary Sciences (all)
CiteScore
5.30
自引率
7.40%
发文量
395
审稿时长
11 weeks
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