天然气水合物藏井眼蠕变缩径研究

天然气水合物作为储量丰富的清洁能源备受世界各国的关注,但水合物储层的不稳定性使得其钻井和开采都存在困难.当井眼钻开后,水合物储层的蠕变特性会造成井眼缩径,进而影响水合物井的钻井安全.对冻土水合物地层在井眼钻开后的井眼缩径进行分析.结果表明:缩径发生时井眼不同方位地层将以不同速率进行缩径,但随着时间的增加,不同方位处的缩径速率趋于相同;随着水合物层埋深的增加,井眼的蠕变量将呈近线性增加;井眼的蠕变缩径速率将随着地应力非均匀性的增大而增大;随着水合物饱和度的增加,井眼的缩径速率降低.研究结果可为水合物地层钻井液密度的选取提供理论依据.

Wellbore Shrinkage during Drilling in Methane Hydrate Reservoirs

Methane hydrates as a clean and abundant energy source, have attracted the attention of the world. However, the instability of hydrate reservoirs makes it difficult to drill production wells. After drilling, the creep properties of hydrate reservoir would cause wellbore shrinkage, which will affect the drilling safety. The law of wellbore shrinkage after a hydrate well drilled is analyzed. The results show that in different orientation around the well, the wellbore shrinkage rates are different. But the shrinkage rate tends to be the same at different orientation with increasing time. The wellbore shrinkage will increase as the burial depth of the hydrate increases. With the increases of the in-situ stress non-uniformity, the shrinkage rate would increase. With the increases of the hydrate saturation, the shrinkage rate would decrease. The research results can provide a theoretical basis for the selection of drilling fluid density while drilling in hydrate formations.