222 (2023) 211447 Available online 7 January 2023 2949-8910/© 2023 Published by Elsevier B.V. Experimental investigation of the acidizing effects on the mechanical properties of carbonated rocks Mojtaba Parandeh, Hamid Zafari Dehkohneh, Bahram Soltani Soulgani * Petroleum Engineering Department, Faculty of Petroleum Engineering, Petroleum University of Technology, Ahvaz, Iran A R T I C L E INFO Keywords: Carbonate formation Acidizing Rock strength Wormhole penetration depth Chemical reaction Modeling ABSTRACT 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 fow 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 frst 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 signifcantly 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. 1. Introduction Rock mechanical properties, which mainly consist of elastic modulus, Poisson’s ratio, and rock strength parameters (Peng and Zhang, 2007), have a signifcant impact on estimating the in-situ stresses in subsurface formations. An understanding of these properties can lead to optimization in the drilling process and casing design and develop- ment of geomechanically models for addressing the minimum required mud weight to drill a stable well (Alsubaih et al., 2017). Laboratory tests are the most reliable and direct way to determine rock mechanical properties. However, they are usually accompanied by some limitations, such as the signifcant expense of these methods and the small size of laboratory-tested cores in comparison to the entire reservoir. (Abbas et al., 2018). The second method for obtaining these properties is using log surveys. If there are insuffcient core samples or log data, the last option is to predict rock mechanical properties using the dynamic Mohr-Coulomb cycle, which usually yields reasonable results. (Al-Dri- weesh et al., 2016). Furthermore, it should be noted that mechanical properties cannot be determined directly from wireline logs, and several correlations have been introduced to conduct these calculations. (Sharma et al., 2010). Acidizing is one of the oldest practical techniques for increasing well productivity by improving near wellbore permeability that has been widely used in the petroleum industry. There are other ways to increase production rates like using EOR methods, such as injecting optimum fuids into the reservoir. From surfactant point of view hamidreza yar- veisi and ali haghtab 2017 investigated the effects of surfactants on increasing oil recovery in reservoir and showed that Cocamido propyl betaine is good for high salinity systems and amphoteric surfactant is suitable for EOR process (Yarveicy and Haghtalab, 2018). Later hami- dreza yerveisi and ali javahery investigated the effect of lauryl betaine on EOR progress and compared it with water, solvent and emulsion * Corresponding author. E-mail address: Soltani.b@put.ac.ir (B.S. Soulgani). Contents lists available at ScienceDirect Geoenergy Science and Engineering journal homepage: www.sciencedirect.com/journal/geoenergy-science-and-engineering https://doi.org/10.1016/j.geoen.2023.211447 Received 13 July 2022; Received in revised form 30 November 2022; Accepted 10 December 2022