Research Shale Hydration Effects On Wellbore Stability

Shale is a kind of water sensitive clay minerals, in the drilling process, the drilling fluid circulating in the process will be in contact with it, and interact to produce a hydration expansion, leads to the decrease of the intensity of shale, and change the wellbore pressure distribution near the wall, causing the instability of the wall, making the wall collapsed.This article is mainly through the shale hydration of the experimental study and theoretical analysis and calculation to study shale wellbore stability.The main research contents of this thesis and the corresponding conclusions are as follows:(1) Analysis of the shale mineral composition, physical characteristics and hydration mechanism to study the internal and external factors affecting the shale hydration, obtained the shale hydration of wells affect the stability of the wall.(2) Through the indoor triaxial stress test results:after shale hydration, its strength is reduced, reducing the elastic modulus, Poisson’s ratio increases, the shale of the cohesion and internal friction angle decreases with the increase of water content;(3) Analysis by NMR experiments drawn:shale samples and atural water quality overallthere is a growing tendency rate before and after immersion; at different times after soaking, shale Ta spectrum distribution mainly for two peak map, part of the three peaks map, with the extension of immersion time, all the peaks are increasing amplitude, T2spectral area gradually increased.(4) Through the study of the mechanical wellbore stability model to analyze the stress distribution before and after the shale formation wellbore hydration, given the appropriate calculation methods.(5) Use the strength criterion of rock failure,,given shale formations borehole collapse pressure, burst pressure calculation methods.