Abstract
The present work investigates the effect of adding polymer as a retarding agent to acid solutions to slow and control the reaction in matrix acidizing treatment of carbonate rocks. Two different polymers, Polyacrylamide (PAA) and Polysaccharide (Xanthan) and three different acids, hydrochloric acid; acetic acid and formic acid were used through this study. Polymer-acid solutions were prepared and their viscosity was measured to identify the compatibility of the acid with the polymer. The measurement was conducted as a function of shear rate, salinity, temperature and acid concentrations. The results revealed that the presence of PAA did not change the viscosity of the acid solution significantly, while the viscosity of Xanthan-acid solutions was decreased with increasing the acid concentration. Additionally, the reaction of polymer-acid solutions with the rock material was monitored under microscope. Original rock samples obtained from Saudi reservoirs containing mainly carbonate were used in the reaction. The PAA-acid solution did not show any decrease in the reaction rate compared to that of acid solution. Thus, the PAA solution applied in this study is not recommended as a retarder.
However, Xanthan-acid solutions showed a significant decrease in the reaction time. Therefore, Xanthan was selected to perform further investigations in Rotating Disk Reactor (RDR) at different pressures. The results showed clearly that the presence of Xanthan leads to an increase in the acid spending time by decreasing the reaction rate with the rock samples. This indicates that Xanthan can be added to the acid solution as a retarder to achieve an extended matrix acidizing. Moreover, scanning electronic microscopy (SEM) was conducted on pre-treated and post treated rock samples. This provides the opportunity to perform a detailed description of the rock surface and facilitates the identification of the changes occurring due to polymer-acid treatment.
