Shale inhibition by low-molecular-weight cationic polymer in water-based mud

Abstract

The presence of oligomers possessing amine or ammonium functionality in drilling fluid plays an important role in stabilizing the shale formations during drilling with water-based mud. In this study, we have compared the activity of neutral to charged amine polymers towards shale stabilization. Low-molecular-weight polymer possessing charged moieties provided superior inhibitive capacity compared to that of the neutral amine functionality-based polymer. The polymer with cationic functionality (polyAETMAC) exhibited higher shale recovery, lesser shale swelling and lower capillary suction time compared to that of the neutral amine-based system (polyDMAPMA) supporting the above. Shale recovery in shale disintegration test improved from 92.3 to 98.7% for polyAETMAC concentration of 0.625 w/v% in water-based mud. The prodigious shale recovery is attributed to the strong interaction between the cationic sites of the polymer with the minerals present in the shale. The overall rheological properties of drilling fluids also improved in the presence of charged amine polymer before and after hot rolling. Apparent viscosity of mud increased by ~ 29% for polyAETMAC as compared to ~ 25% for polyDMAPMA at a concentration of 0.625 w/v%. Plastic viscosity and yield point of base mud were also improved by ~ 43% and ~ 15% at 0.0625 w/v% concentration of polyAETMAC and to a similar extent by polyDMAPMA for the same concentration. The decrease in API fluid loss after hot rolling of drilling fluid at 100 °C for 16 h was ~ 20% for polyDMAPMA and ~ 13% for polyAETMAC compared to base mud for the same concentration of the polymers. These polymers can be used as a potential shale stabilizer for water-based drilling fluids.