页岩水化对岩石应力分布关系的影响

页岩气钻井井壁不稳定是钻井过程中的一个重要难题,含水量的多少直接影响岩石应力分布.根据现场数据得到含水量随时间和距井眼轴线距离的变化规律.通过力学与化学耦合的总吸附水量模型表征含水量和应力分布关系,并且考虑地层的各向异性.将假设地层为各向同性时的水化应力和地层为各向异性时的应力耦合.通过计算机编程分别得到径向应力、切向应力和垂向应力随井周角和距井眼轴线距离之间的三维关系图.结果表明,页岩径向应力,切向应力和垂向应力随距井眼轴线距离的增加而减小,说明在井壁处水化膨胀造成应力值很高,随距离井眼轴线距离的增加钻井液入侵减小,从而水化膨胀应力逐渐减小.切向应力和垂向应力随井周角变化明显,是由于地应力非均匀性造成的,页岩的水化增加了地层的不稳定性.

The influence between shale hydration and rockstress distribution relationship

:Borehole instability of shale gas is an important matter juring drilling.Water content has direct relationship with rock strain distribution.This paper get the variation rule of water content and distance fromSthe borehole axis based on field data.The relationship between water content and strain distribution is also get by the model of the totalSamount of the adsorbed water.The anisotropy of formation is also considered.The total stress is caused by the uniform distribution of stress caused by shale hydration and the unevenSdistribution of stress caused by the heterogeneity of formation.The three dimensional relationship figure of radial stress, tangential stress, vertical stress with well angle and distance fromSthe borehole axis has been got by Computer programming.The results show that radial stress, tangential stress, vertical stress decrease with the increase of distance fromSthe borehole axis.It could say that the stress of borehole is high because of hydration and swelling. With the distance of the borehole axis grows, hydration stress decrease because fewer drilling mud invade into the formation. Tangential stress and vertical stress vary significantly with the variation of well angle,which is caused by the inhomogeneity of stress.The hydration and swelling of shale increase the instability of formation