An experimental investigation analyzing effects of injection pressure on efficiency of matrix acidizing stimulation on marcellus shale core samples

Matrix acidizing is applied to oil and gas reservoirs to remove or bypass near-wellbore damage resulting in an increase in the formation permeability yielding higher production rates. Effects of matrix acidizing injection pressure on the rock properties including porosity, permeability, solubility, and acid penetration rate were investigated in this research. The results of the X-ray diffraction (XRD) and the solubility tests were used to select the optimum acid type and concentration, 15% hydrochloric acid (HCl). Three core samples contained continuous carbonate layers, from Marcellus shale gas formation, were used in this research. Matrix acidizing treatments were conducted at the reservoir temperature (66°C) and three injection pressures (1.72, 3.45, and 5.17 MPa). The results of the aforementioned rock properties were used to evaluate the efficacy of the acid treatments and determine the optimum acid injection pressure. The results demonstrated that performing matrix acid stimulation resulted in creating highly permeable channels (wormholes) with a permeability of 2.3 Darcy inside the core samples. Moreover, the results demonstrated that the increase in the acid injection pressure increased the porosity and permeability of the samples. However, increasing the injection pressure above 3.45 MPa resulted in insignificant enhancements in the properties.