Matrix acidizing impact on the geomechanical properties in carbonate rocks: an experimental approach using acetic acid at different contact times
摘要
This study aimed to evaluate the geomechanical changes in carbonates after matrix acidizing via acetic acid at different contact times (36/72/108 h). Synthetic carbonate rocks without fractures and with fractures were produced and subjected to matrix acidizing tests. X-ray microcomputed tomography, porosity and permeability tests were performed to identify the dissolution processes. Unconfined compressive strength tests (UCS) were performed on acidified and nonacidified samples to compare their stress–strain behavior, Young’s modulus and Poisson’s ratio before and after acidification. Petrophysical changes, such as increased porosity and permeability caused by the dissolution of the rock matrix with increasing injected acid, promote the formation of wormholes, affecting their structure. The samples exhibited a gradual decrease in mechanical strength with increasing contact time with acid; they were classified as moderately hard to hard (41.32 MPa to 50.80 MPa for nonacidified rocks) to soft (12.45 MPa to 24.18 MPa) after 36 h of testing; they also progressed from soft to very soft (4.61 MPa to 11.20 MPa and 4.12 MPa to 6.69 MPa) after 72 h and 108 h of acidification, respectively; and they exhibited a change in elastic behavior (brittle) to plastic (ductile) and a reduction in stiffness, as evidenced by a decrease in Young’s modulus, in addition to a reduction in Poisson’s ratio. Evaluating the impact of acid treatment on rock mechanics is essential for determining mechanical degradation after acid treatment to ensure that the stimulation technique does not compromise the integrity of the reservoir to the point at which its collapse.