Abstract

Understanding changes to geomechanical properties accompanying exposure of shale to supercritical carbon dioxide (sc-CO2) and the effects of the interaction of shale with sc-CO2 is essential to evaluate CO2 utilization for waterless fracturing and CO2 storage. There is limited understanding of the impact of sc-CO2 on time-dependent deformation of shale rocks. This study investigates the short-term creep behavior of Green River shale samples under vacuumed and sc-CO2 conditions. To avoid tertiary deformation, a high pressure high temperature triaxial cell was utilized to conduct creep tests under relatively small stresses. The power-law model describing creep demonstrated an excellent fit to experimental behavior. Power-law model parameters reflect significant ductility of Green River shale and very small time-dependent deformation. Short-term saturation with sc-CO2 (three days) significantly reduced static moduli by 19 to 38%. From a viscous creep perspective, exposing this shale to sc-CO2 caused a reduction in time-dependent deformation. Our observations, combined with findings in the literature, highlight the critical role of water saturation in enhancing creep response before and after exposure to sc-CO2.

Introduction

Characterizing rock transport and geomechanical parameters is essential for shale reservoir stimulation success, long-term productivity prediction, and understanding the effectiveness of carbon dioxide (CO2) storage formation shale cap rocks. Shale samples under constant applied stress demonstrate time-dependent deformation that is indicative of viscous creep. Understanding creep deformation is important for both short and long-term responses. For short-term response, studies report that creep increases hydraulic fracturing gradient by causing stress isotropy (Yang & Zoback, 2016). On the other hand, long term response influences transport and productivity by impacting matrix permeability and fracture closure (Villamor Lora, et al., 2016; Sone & Zoback, 2014). Furthermore, creep deformation may cause adverse issues such as wellbore stability and reservoir subsidence (Du, et al., 2018). ) storage formation shale cap rocks. Shale samples under constant applied stress demonstrate time-dependent deformation that is indicative of viscous creep. Understanding creep deformation is important for both short and long-term responses. For short-term response, studies report that creep increases hydraulic fracturing gradient by causing stress isotropy (Yang & Zoback, 2016). On the other hand, long term response influences transport and productivity by impacting matrix permeability and fracture closure (Villamor Lora, et al., 2016; Sone & Zoback, 2014). Furthermore, creep deformation may cause adverse issues such as wellbore stability and reservoir subsidence (Du, et al., 2018).

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