深水钻井天然气水合物地层井壁稳定流固耦合数值模拟

Fluid-solid coupling numerical simulation on wellbore stability in gas-hydrate-bearing sediments during deep water drilling

考虑钻井液与地层的热交换和水合物的分解,建立了水合物地层井壁稳定流固耦合数学模型,并开发了有限元程序。实例分析了钻井液压力和温度、原始地层水合物饱和度及施工作业时间等因素对水合物地层井壁稳定的影响,结果表明:随着钻井液温度、施工作业时间的增加,井眼周围地层水合物分解区域、地层最大屈服区域增大,不利于井壁稳定;随着钻井液压力、原始地层水合物饱和度增加,井眼周围地层水合物分解区域、地层最大屈服区域减小,有利于井壁稳定,因此深水钻井中应选择造壁性能好的低温钻井液并适当增加液柱压力。

Considering the dissociation of gas hydrates and thermal transport between drilling fluid and formation,a fluid-solid coupling mathematical model was established for wellbore stability in gas-hydrate-bearing sediments（HBS）,and a corresponding finite element program was developed.Taking a specific hydrate formation as an example,this paper analyzes the effects of influential factors on wellbore stability in HBS,such as drilling fluid pressure and temperature,initial hydrate saturation and working time.The results show that： both the hydrate dissociation zone and the maximum yield region around borehole enlarge with the increasing of drilling fluid temperature and working time,which is disadvantageous to wellbore stability;but they reduce with the increasing of drilling fluid pressure and initial hydrate saturation,which benefits the wellbore stability in HBS.So the low temperature drilling fluid with good plastering property should be chosen and the drilling fluid pressure can be increased appropriately in deep water drilling in order to maintain the wellbore stability in HBS.