气体钻井中泥页岩地层遇水时的井壁稳定性研究

EVALUATION FOR SHALE HYDRATION AND STABILITY IN GAS DRILLING

常规钻井液钻井中,水在正压差、毛管力和化学势等作用下进入泥页岩发生井壁失稳,而气体钻井除了自身的力学失稳外,主要在毛管力作用下吸收下部地层水造成泥页岩地层井壁失稳。因此,随着气体钻井技术的发展,在钻遇下部地层出水后,泥页岩地层的井壁失稳机理值得研究。从分析气体钻井条件下泥页岩吸水扩散系数、吸水膨胀系数和吸水后的力学参数变化入手,结合建立的力学化学耦合模型,紧紧抓住气体钻井和水基钻井液钻井的不同点,使得该模型能较好地运用到气体钻井泥页岩井壁稳定性的分析中,并通过DY1井气体钻井实践验证了文中的模型。

In conventional drilling fluid drilling, borehole is instability due to water transmitting in shale by the action of positive differential pressure, chemical potential, capillary force adsorption, shale hydration and instability in gas drilling mostly are caused by capillary force adsorption formation water, except for mechanics instability. Therefore, the theory of shale hydration and instability in gas drilling should be researched with the development of gas drilling technique.Based on coefficient of diffusion of shale, coefficient of expansion, rock mechanics parameters, a model coupling with mechanics and chemistry which is different from water based drilling, has been established in this paper. Finally a computer simulation works was finished and some simulated results were discussed according to a gas drilling case in DY1.