Experimental investigation of the acidizing effects on the mechanical properties of carbonated rocks

One of the useful techniques for increasing well productivity by improving permeability in carbonate formations is matrix acidizing. Acidizing leads to the dissolution of minerals and forming of ''wormholes", which act as flow channels for oil production. On the other hand, this mineral dissolution and forming the wormholes can increase the risk of collapsing. As a result, the mechanical stability of rock should be predicted before acidizing treatment. Hence, rock mechanical evaluations are required to prevent undesirable results. In this study, A study of rock strength was conducted for two scenarios. The first one refers to the injection of HCl 15% at different injection rates, while the second one focuses on the injection of HCl 15% and 28% by weight at different number of pore volumes for another type of rock. Results show that the rock strength is subject to the change significantly in face dissolution patterns rather than other dissolution patterns. The dominant wormhole has a lower reduction in rock strength than the other dissolution patterns. In addition, the accuracy of two semi -empirical wormhole models were examined by calculation of core length through prediction of wormhole growth rate and comparing with the initial length. The average error of each model was calculated, and Furui's model showed better results. Based on this observation, prediction of wormhole penetration depth was determined by Furui model. Finally, the Young's modulus and Uniaxial Compression Strength (UCS) of acidized cores at various pore volumes injected were determined using uniaxial tests. Then, wormhole penetration depth was simulated by Furui's model as a function of the number of pore volumes injected, and combining the rock strength data obtained by laboratory experiments with the wormhole penetration depth simulation, provided the strength of the formation in the region where it is penetrated to acid.