Abouzar Mirzaei Paiaman - National Iranian South Oil Company, Department of Petroleum Engineering, Ahwaz, Iran,
Amir Salehi - Petroleum University of Technology, Faculty of Petroleum Engineering, Ahwaz, Iran

Chemical formation damage as a result of clay swelling in Asmari reservoir, SW Iran, was investigated. In the first part of the work, a relation between pH of water based mud (WBM) filtrate and cation exchange capacity (CEC) of clays was investigated. Clay samples were prepared from sample rocks. Grain-size analysis was performed followed by settling tube for the coarse-grained fraction. XRD method was applied for air dried, ethylene glycol solvated and heat treated clay samples. XRD results emphasized the main presence of kaolinite and illite in the clay samples. CEC values at various pH values were measured using methylene blue method. There was a non-linear relationship between pH of WBM filtrate and CEC. As pH of WBM filtrate increases, CEC decreases. In the second part of this work, permeability reduction due to the injection of WBM filtrate into core samples was measured. Filtrate with different pH values was injected into the core samples and percentage of permeability reduction was measured. As pH of injected filtrate increases, permeability reduction is less than where the pH was low. Therefore as pH of filtrate increases, CEC decreases that result in less clay swelling and less chemical formation damage.

Chemical formation damage, permeability, clay swelling, CEC and Ph