Mechanical response to dynamic compressive load applied to shale after thermal treatment

Abstract

In deep shale gas extraction, high temperature environment and dynamic loads are two important factors in affecting reservoir reconstruction and shale breaking. By employing the test techniques of Split Hopkinson pressure bar, dynamic compressive mechanical response of shale specimens with five different bedding dips after thermal treatment of 25–200 °C was investigated under the same impact energy. Results reveal that the increasing thermal treatment temperature weakens the post-peak behavior in stress-strain curves of specimens with bedding dips of 0°, 30° and 90°, and strengthens that of specimens with bedding dips of 45° and 60°. The dynamic compression strength variation of specimens versus increasing thermal treatment temperature shows two opposite trends bounded by the bedding dip of 30°. With increasing thermal treatment temperature, failure mode of specimens with bedding dips of 45° and 60° is affected evidently, but that of specimens with bedding dips of 0°, 30° and 90° has no fundamental change. The increasing thermal treatment temperature impacts the amount of absorbed energy in one of two ways depending on the bedding dip, and increases the dynamic fragmentation degree of all specimens, but that of specimens with bedding dips of 45° and 60° is much larger. Furthermore, the dynamic anisotropy of specimens after thermal treatment and its possible application in deep shale gas extraction are discussed. Results can be beneficial to the perforation design in hydraulic fracturing and the dynamic fracturing technology development in deep shale reservoirs.