Elastic behavior of partially saturated gas shales during unloading - reloading cycles in uniaxial compression

Elastic properties of gas shales are of utmost importance for the exploitation of shale gas reservoirs. Static elastic properties are usually measured by performing unloading-reloading cycles in uniaxial or triaxial compressive tests. The response of gas shales typically observed during a stress cycle is characterized by nonlinearity and hysteresis due to the presence of cracks and their sliding during the stress change. However, this response is significantly affected when gas shales are tested in partially saturated conditions. The presented work shows evidence of this aspect obtained through a uniaxial compressive test performed on a gas shale with control of total suction to impose different water saturation conditions. Several stress cycles carried out at different total suction values were performed to analyze the elastic response of the material. A decrease of nonlinearity during unloading and opening of the loop was observed when stress cycles are per-formed after a wetting process. The reason for feature is attributed to sliding of cracks, which is influenced by the response of the material during the total suction variations applied to the tested material before performing the stress cycles. A misleading evaluation of the elastic properties might occur if these mechanisms are not properly considered.