| dc.description.abstract | In this study, we conducted laboratory experiments of acid fracturing using San Andres dolomite downhole sample cores and regular HCl acid 15%. These samples have variation of anhydrite content from 1% to 43% based on XRPD analysis and three different types of anhydrite’s distribution. In the experiments, we used treatment conditions that represented field and reservoir condition. Besides, acid etched volume and acid fracture conductivity at different closure stress were measured and calculated using surface scan profilometer and conductivity measurement apparatus consisting of modified API conductivity cell and loading frame, respectively. Acid fracture conductivity decline was evaluated and compared to the three different type of anhydrite distribution. Also, acid fracture conductivity at closure stress 0 psi and 3,000 psi were evaluated to see the correlations of acid fracture conductivity to the percentage of mineralogy of anhydrite and dolomite. In addition to that, acid fracture conductivity was compared to other carbonate rocks such as limestone and chalk.
Therefore, this study aims to study the effect of anhydrite distribution on the fracture surfaces of a dolomite reservoir to acid fracture conductivity. Based on experimental results, acid fracture conductivity decline and initial acid fracture conductivity at 0 closure stress showed that there were three different acid fracture conductivity decline and initial conductivity at 0 closure stress which could be grouped based on three different types of anhydrite distribution. Patchy distribution showed high initial conductivity and high conductivity decline rate, pore-filled distribution showed moderate initial conductivity and moderate conductivity decline rate, and bedded distribution showed low initial conductivity and low conductivity decline rate because the direction of bedded distribution is perpendicular to the fluid flow considering the way coring was carried out. Based on graphical plots of acid etched volume and acid fracture conductivity, these plots showed poor correlation of acid etched volume and acid fracture conductivity to the percentage of mineralogy, which is anhydrite and dolomite. However, removing outlier and samples that have non-anhydrite greater than 2%, these plots showed good correlations that acid etched volume and acid fracture conductivity are proportional to the percentage of dolomite but both parameters are inversely proportional to the percentage of anhydrite. The conclusion of the study is that anhydrite presence in the dolomite reservoir is affecting to the value of acid fracture conductivity at the initial and at the selected closure stress and also affecting to the declining rate of acid fracture conductivity. | en |
