Fracture and Strain Field Evolution in Faulted Brine-Saturated Sandstone

Abstract

Abstract Geological carbon dioxide (CO2) sequestration has received significant attention over the past two decades as an effective method to reduce the emission of greenhouse gases to the atmosphere through deep underground injection of CO2. However, fractures or faults commonly exist in the rock mass, which provides the potential for CO2 leakage. To better understand the reactivation of preexisting fractures, it is essential to investigate fracture development and its effect on the stability of the rock. In this study, uniaxial compression tests were carried out on sandstone specimens by using a SANS rock mechanics servocontrolled testing system (MTS Systems Corporation, Eden Prairie, MN). Three kinds of Zunyi quartz-rich sandstone cylindrical specimens were tested, i.e., dry intact specimens, and both dry and brine-saturated specimens containing two preexisting faults. Based on the experimental results, the stress-strain curves and mechanical properties were analyzed and were closely related to the fault angle under both dry and saturated conditions. The macrofailure patterns can be classified into three modes: tensile coalescence failure, shear coalescence failure, and no coalescence failure. During the testing, a three-dimensional digital image correlation method was applied to the sandstone cylinders that contained two preexisting faults. Furthermore, acoustic emission (AE) sensors and strain gauges were bonded on the specimens to measure the AE signal and local strain in real time. The evolution characteristics of strain field, AE counts, and measured local strain were investigated. These findings can be regarded as a reference for future studies of fracture mechanisms in brine-saturated sandstones to better inform parameterization of constitutive geomechanical models in the study of CO2 injection in deep saline aquifers.