CO2 INDUCED ALTERATIONS OF MICROSTRUCTURE AND MECHANICAL PROPERTIES IN TIGHT RESERVOIR

With the high demand for carbon capture utilization and storage (CCUS) worldwide, more studies conducted to improve knowledge of reservoir dynamics for characterization, safe use, and storage. Samples from the Middle Bakken Formation were analyzed to understand the effect CO₂ has on the microstructural and geomechanical properties of pre−CO₂ and post−CO₂saturation. X−Ray Diffraction was used to study the mineral composition, and FESEM was used to characterize the pore structure at micro and nanoscale pre and post CO2 saturation. The pore structure and pore size distribution (PSD) of the sample at the nanoscale were quantified using image analysis. The geomechanical behavior of the rock sample, including Young's modulus and hardness, was investigated using nanoindentation testing. The volume fraction of quartz, k-feldspar, and dolomite increased while calcite, pyrite, and halite decreased in different degrees suggesting dissolution and precipitation of minerals. The pore size distribution pre−CO₂ is up to 300 nm and 200 nm post−CO₂. The pore size from the pore size distribution analysis showed a reduction in the pore size of the sample post−CO₂saturation, which suggests scaling from mineral precipitation. The Young’s modulus and hardness result of the sample reduced and showed a non−monotonic trend post−CO₂ saturation. In comparing the FESEM images of the rock sample, fractures are present in the post−CO₂ images indicating CO₂ saturation might be responsible for the fracture propagation and growth in the rock sample.