ENERGY EVOLUTION LAWS AND BRITTLE PROPERTY OF SHALE LONGMAXI FORMATION UNDER DIFFERENT CONFINING PRESSURES

The mechanical property of shale gas reservoir is an important factor affecting the stability of shale wellbore. According to the results of shale uniaxial and triaxial compression tests under different confining pressures, energy evolution laws, damage evolution laws and brittle property are analyzed. The results show that before yielding stage, the total absorption energy of shales almost transforms into the elastic strain energy. During the period between yielding stage and peak strength stage, the ratio of the elastic strain energy to the total absorption energy gradually decreases, while the dissipation energy gradually increases. After the peak strength stage, the elastic strain energy sharply decreases and the dissipation energy rapidly increases. The dissipation of energy can lead to the damage of the rock. The damage evolution laws determined from energy perspective conform to the "S-shaped" curve. The brittleness index of shale becomes weaker with the increase of confining pressure. The study of improving the reservoir fracturing effect and evaluating the wellbore stability has important practical significance and application value.