Acid-rock interaction investigation and the influence of fractures during matrix acidizing in carbonate rocks

This study aimed to evaluate the effects of chemical dissolution on the properties of reservoirs by matrix acidizing, using synthetic carbonate rocks with and without fractures, prepared with limestone powder, epoxy resin (chemically inert) and fractures represented by non-woven geotextile strips positioned perpendicular to the fluid flow direction, to check their influence on the dissolution process. A system was developed using an acid injection cell to carry out acidizing tests, applying a solution of acetic acid and distilled water at constant pressure, to observe the organic acid-rock interaction for contact times of 36, 72 and 108 h. Chemical and petrophysical tests, as well as image analyses using X-ray micro-computed tomography were conducted to characterize the acidizing effects. Changes in rock properties were observed as the contact time increased, particularly the increase in porosity and permeability. Was observed the formation of CO₂ and calcium acetate as reaction products between calcite and acid solution. Ramified wormhole and uniform dissolution patterns were noted; moreover, fractures influenced the dissolution in regions where they were inserted, increasing the branches present along their structure and deviating the fluid flow to a perpendicular direction to the injection direction, especially observed at 72 h, highlighting the use of geotextile as a material that reproduces the fractures' transmissivity in synthetic samples. The methodologies used contributed to presenting the effects of mineral dissolution on the properties of reservoir rocks post-stimulation, emphasizing the importance of chemical/petrophysical aspects and the contribution of fractures to better understand the matrix acidizing efficiency in field.