Evolution of normal deformability of acidized rock fractures
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ORIGINAL PAPER
Evolution of normal deformability of acidized rock fractures E. Asadollahpour 1 & A. Baghbanan 1 & H. Hashemolhosseini 2 Received: 8 November 2017 / Accepted: 10 October 2018 / Published online: 27 October 2018 # Saudi Society for Geosciences 2018
Abstract Fracture conductivity, created by acid fracturing, is a key parameter in the process of acid fracturing stimulation. As normal stress increases, fracture closure increases, and, as a result, the conductivity decreases with increasing fracture contact. Mechanical behavior under normal stress depends on the distribution, geometry, and mechanical properties of roughness. These properties change because of acid injection in the fracture in the acid fracturing technique. Therefore, the study of the fracture closure mechanism after acid fracturing is crucial. In this study, an acidizing cell has been developed to simulate the process of fracture surface etching in acid fracturing and study closure of acidizing fractures under normal stresses. The results showed that the amount of maximum normal deformation increased as a result of acidizing. Samples exhibit non-linear behavior in experiments, and the nonlinear behavior and permanent deformation increased by acid injection and, in unloading, all samples exhibit hysteresis behavior. The calculated fracture normal stiffness of specimens without acid injection are greater than the acidized samples with 10 and 20 min up to 300 and 600%, respectively. Reductions in the fracture normal stiffness due to acidizing can be caused by increasing the initial aperture and reducing the rock strength properties. At a high applied normal stress, fractures without acid injection show a relatively high normal stiffness and low hydraulic conductivity. When a low normal stress is applied, the rate of fracture stiffness-conductivity follow the same trend in both acidizing times while following a steep trend in long time acidized cases at high stress levels. Keywords Acid fracturing . Normal deformation . Normal stiffness . Fracture conductivity
Introduction The behavior of fractures under stress should be studied in order to determine the mechanical and hydraulic behaviors of a rock mass. Therefore, understanding of fracture closure in different rock engineering projects, such as the construction of underground and surface rock structures, and hydrothermal and hydrocarbon reservoirs, is necessary. Acid fracturing is a stimulation technique of hydrocarbon reservoirs that is used to increase the productivity of wells, particularly when hydrocarbon reservoirs have low permeability or oil wells are damaged. Intentional fracture acidizing treatment have been most-
* E. Asadollahpour [email protected] 1
Department of Mining Engineering, Isfahan University of Technology, Isfahan, Iran
2
Department of Civil Engineering, Isfahan University of Technology, Isfahan, Iran
ly confined to carbonate formations (Kalfayan 2007). It is a complicated phenomenon of injecting acid into created fractures under a certain pressure,
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