Effect of Chlorite Clay-Mineral Dissolution on the Improved Oil Recovery From Sandstone Rocks During Diethylenetriaminepentaacetic Acid Chelating-Agent Flooding

Abstract

Summary Sandstone oil reservoirs consist of different clay minerals, such as kaolinite, illite, and chlorite. While these clay minerals can highly affect oil recovery from sandstone oil reservoirs, no attention has been given to investigating the effects of clay minerals during such oil recovery, and no solution has been introduced to alleviate the effects. In this study, and for the first time, the effect of chlorite clay-mineral content on the improved oil recovery (IOR) from different sandstone rock samples was investigated. A new solution was proposed to eliminate the effect of chlorite on the oil recovery from sandstone rocks. Different sandstone cores were used, such as Berea (BSS), Bandera (BND), Kentucky (KSS), and Scioto (SCS) sandstone rocks with different clay minerals. ζ-potential measurements were used to investigate the surface charge of the different clays and different sandstone rocks with different fluids. Fluids such as seawater (SW), low-salinity water (LSW), fresh water, and chelating agents were used. Diethylenetriaminepentaacetic acid (DTPA) chelating agent was introduced to mitigate the chlorite effect on oil recovery from sandstone rocks. The wettability was evaluated using contact-angle measurements and the Amott test for different solutions and different rocks in the presence of actual crude oil. Coreflooding experiments were conducted using these fluids with different sandstone rocks to identify the effect of chlorite on the oil recovery. Coreflooding experiments showed that sandstone cores with high chlorite content yielded the lowest oil recovery when SW and LSW were used. The effect of chlorite on the oil recovery from the two sandstone rocks was minimized with 3 wt% DTPA chelating agent. More oil was recovered in the case of DTPA because of the iron chelation from chlorite. ζ-potential showed that sandstone with high chlorite content has a surface charge close to zero in the case of SW and fresh water. In addition, contact-angle measurements showed that samples with high chlorite content have less water-wetness, which will reduce oil recovery. Contact-angle measurements on chlorite sheets showed that chlorite is oil-wet compared with mica at the same conditions. The addition of high-pH DTPA chelating agent sequestered the iron from the chlorite clay minerals and changed the surface charge to very high negative value, and the contact angle confirmed that the rock changed to water-wet after adding the chelating agent. The Amott index showed that adding DTPA increased the water-wetness for SCS that contains 4 wt% chlorite.