Setting Time Effects on Bentonite Water‐Well Annulus Seals

Abstract

Shear strength tests are conducted in a model of a water, well on four, commercially available, granular bentonite well sealing products. The time dependency of annulus seal shear strength and resistance to piping is examined. Dry bentonite samples are placed through water in the annular space between the casing and borehole and allowed to set for a specified time. Pressure is applied at a constant rate to one end of the clay seal until shear or piping failure occurs. Pressure and seal displacement data are recorded on a digital data acquisition system. Annulus seal strength and resistance to piping increase with setting time. Ultimate shear strength is reached in 72 to 120 hours after placement. Differences between this laboratory scale study and field scale applications are discussed.