冷钻过程中气体从孔隙水向钻井液扩散引起的井壁水合物分解

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冷钻过程中气体从孔隙水向钻井液扩散引起的井壁水合物分解

Ager,2018, 2(4): 410-417

原文网址: http://www.astp-agr.com/index.php/Index/Index/detail?id=85

  在水合物地层钻进过程中，钻井液较高的温度会引起地层气体水合物的分解，这一结论已经取得广泛的共识。本文研究表明，即使钻井液的温度和压力能得到很好的控制，维持含水合物沉积层的温压条件在气体水合物的相平衡条件之上，井壁水合物仍会发生缓慢分解，这种分解是由于气体从孔隙水向钻井液的扩散引起的，本文基于Fick第一定律建立了水合物分解模型，根据模型分析，发现水合物分解速率主要取决于沉积层的温度，得到了井壁上甲烷水合物和二氧化碳水合物分解前缘位置与时间的函数关系，分析了井壁水合物缓慢分解对沉积物稳定性和电阻率测井的影响。

Hydrate dissociation induced by gas diffusion from pore water to drilling fluid in a cold wellbore

Youhong Sun, Hongfeng Lu, Cheng Lu, Shengli Li, Xiaoshu Lv

(Published: 2018-08-24)

CorrespondingAuthor and Email: Shengli Li, lishengli@jlu.edu.cn

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Citation: Sun, Y., Lu, H., Lu, C., Li, S., Lv, X. Hydrate dissociation induced by gas diffusion from pore water to drilling fluid in a cold wellbore. Advances in Geo-Energy Research, 2018, 2(4): 410-417, doi: 10.26804/ager.2018.04.06.

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ArticleType: Original article

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Abstract：

    It is a common view that the high temperature of the drilling fluid can lead to the dissociation of gas hydrate during drilling through hydrate-bearing sediments. This study indicates that the hydrate dissociation in wellbore can also be induced by gas diffusion from pore water to drilling fluid even if the temperature (and the pressure if necessary) of the drilling fluid is well controlled to keep the conditions of hydrate-bearing sediments along the hydrate equilibrium boundary. The dissociation of gas hydrate was modelled based on Fick's first law. It was found that the dissociation rate mainly depended on the temperature of the sediments. The locations of dissociation front of CH4 hydrate and CO2 hydrate in wellbore were calculated as a function of time. The impacts of the hydrate dissociation on the wellbore stability and the resistivity well logging in sediments were evaluated.

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Keywords: Gas hydrate dissociation, model, gas diffusion, pore water, wellbore stability.