Study of meso-damage characteristics of shale hydration based on CT scanning technology

In view of the shale hydration problem in wellbore stability analysis during drilling in shale formation, a quantitative evaluation method based on CT scanning technology was proposed to research the meso-damage characteristics of shale hydration, and the CT scanning tests for shale samples in stages of shale hydration were conducted. The analysis results of CT images and their gray-level histograms show that the early period of soaking is the main period of meso-damage in shale samples, and as the soaking time increases, the meso-damage propagates slowly; the mark of meso-damage increasing dramatically is that the gray-level histogram of the CT image changes from unimodal style to bimodal style. The visual resolutions of CT images can be improved by the pseudocolor enhancement technique, and the integrity and damage degrees of CT images provide a convenient way for quantitative analysis. The relationship between damage variable and soaking time was obtained based on the segmentations of CT images, which shows that the meso-damage of shale hydration mainly occurs in the early stage of soaking, which is the initial stage and rapid evolution stage of meso-damage, from then on, as the damage variable increases continuously and slowly, the macro-damage of shale sample occurs.