Temporal Evolution of the Reaction-Altered Zone Thickness in Tight Silica-Rich Rocks during Post-Fracturing Shut-in Period

Summary In this work, we aim to understand the geochemical changes occurring in the near-fracture region during the long shut-in periods, including the rate of progression of the dissolution front inside the rock. In this effect, we take a coupled experimental/simulation approach. A series of batch reactions is conducted by exposing seven identical silica-rich marlstone samples (coated on five sides) to an acidic brine for 1 day, 4 days, 7 days, 14 days, 28 days, 56 days, and 100 days. The withdrawn samples are cut horizontally, and the freshly exposed surface is scanned using micro-X-ray fluoroscopy (μXRF) and scanning electron microscopy to track the dissolution front and the chemical evolution of the exposed surface. Separately, the fluid time series is determined using gas chromatography-mass spectrometry. A reactive transport simulation is also set up to mimic the experiment to better explain the changes occurring inside the rock. Results show that the carbonate minerals are quickly dissolved due to the rock/fluid interaction. The dissolution front, exhibiting an increased porosity of roughly 8%, is observed to stabilize at ~1 mm from the interface. Evidence of fluid imbibition is present in zones deeper than the dissolution front. The results show that water blocks occur very near to the fracture surface.