What should be done to the annular space while driving permanent casing into an aquifer in unconsolidated formations?

Filling the annular space with bentonite slurry while driving permanent casing into an aquifer in unconsolidated formations is essential for several reasons. Bentonite, a clay material, is used because of its water-retaining properties and ability to swell, thus effectively sealing the space between the casing and the borehole wall.

When driving the casing into unconsolidated formations, keeping the annular space at least half full with bentonite slurry helps to prevent the collapse of the surrounding formation into the borehole during installation. This is particularly important in unconsolidated materials that lack structural integrity. Additionally, the bentonite slurry serves to create a barrier against surface contaminants, safeguarding the quality of the groundwater within the aquifer.

This practice also aids in maintaining hydrostatic pressure within the borehole, preventing water from flowing into the borehole from surrounding areas. Consequently, using bentonite slurry increases the stability of the well structure and ensures the reliability of the water supply.