Adopted Factorial and New In-Situ Micro Designs for Stimulation of Matrix Acidizing of Carbonate Reservoir Rocks

Matrix acidizing have been developed in petroleum industry for improving the petroleum well productivity and minimizing the near wellbore damage. Mud acid (HF:HCl) has gained attractiveness in improving the porosity and permeability of reservoir formation. However, there are several challenges facing the use of the mud acid comprising its corrosive nature, high pH value, formation of precipitates, high reaction rate and quick consumption. Therefore, different acids have been developed to solve these problems including the organic-HF or HCl acids. Some of these acid combinations proved its effectiveness in being alternative to mud acid in reservoir rock acidizing. The current research deals with new acid combination based on hydrochloric-oxalic acids for acidizing carbonate core samples recovered from Qamchuqa Formation in Kirkuk oilfield-Northern Iraq. A new in-situ micro-model adopted laboratory technique is utilized to study the microscale alteration and evolution of pore spaces, dissolved grains and identification of matrix acidizing characteristics. The in-situ micro-model is based on the injection of an identical dose of different concentration of the new acid combination into thin section samples under optical light microscope. The adopted procedure aims to provide unique and rapid information regarding the potential for texture and porosity modification that can be caused by the acidizing stimulation procedure. In connection, solubility tests for the untreated and treated reservoir core samples and density of the combined acids after treatment are conducted based on designed experiments using Response Surface Methodology (RSM). The effect of acid concentration [12% HCl: Oxalic acid (3.8-8.8%)], acidizing temperature (from ambient to 78.8 o C) on solubility percentage of the samples and percentage increase of the combined acid density after acidizing were optimized and modeled.