Influence of Rock Firing on the Wettability of Clay-Rich Sandstones

Rock firing is a conventional technique of core preparationtoprevent clay swelling and fines migration in clay-rich rock; however,the influence of rock firing on the wetting behaviors and alterationsof mineralogical compositions of clay-rich sandstones is not yet explicit.Thus, we assessed and compared the impacts of rock burning at twodifferent temperatures (700 and 1100 & DEG;C) on the changes in wettingstates of Bentheimer (BN) and clay-rich Bandera Gray (BG) sandstonesthrough contact angle measurement, Amott wettability index determination,and thermogravimetric analysis (TGA). Results showed that rock firingmakes the rocks more water-wet, but the clay-rich BG sandstone becomessignificantly more water-wet than the quartz-dominated BN rock withincreasing temperature. There was no change in rock porosity due tofiring, but some clay remained, whereas some clays were transformedinto other minerals after rock firing. Particularly, there were thermaltransformations of clay to quartz and the disappearance of dolomite,chlorite, and clinochlore. Such transformation of these minerals intoalkali metal oxide silicates dispersed on the rock matrix makes thesurface more polar and enhances the interactions with water molecules,resulting in more water wettability for the BG sandstone. The studysuggests that rock firing could change the clay-rich rock-wettingstate into a more water-wet condition than the clay-poor or zero-claysandstone samples; thus, the influence of rock burning on rock-wettingbehavior should be considered to ensure an accurate prediction ofthe rock-wetting state due to rock burning. Moreover, burning at 1100 & DEG;C is recommended to achieve effective clay transformation andremoval in clay-rich rock to prevent swelling, fines migration, andclay-fluid interactions.

Automated summary

Rock firing is a conventional technique used to prevent clay swelling and fines migration in clay-rich rock. However, the influence of rock firing on the wetting behaviors and alterations of mineralogical compositions in clay-rich sandstones is still unclear. This study assessed the impacts of rock burning at different temperatures on the wetting states and mineral compositions of Bentheimer (BN) and clay-rich Bandera Gray (BG) sandstones. The results showed that rock firing made the rocks more water-wet, with the BG sandstone becoming significantly more water-wet than the BN rock as the temperature increased. The study also revealed thermal transformations of clay to quartz and the disappearance of other minerals, leading to enhanced water wettability for the BG sandstone.