Instructional

Introduction

Sealing (grouting) a casing involves filling the annular space between the casing and the drilled hole with suitable slurry of cement or bentonite. Boreholes are sealed to:

• seal the annular space between the casing and the borehole
• prevent surface water run-off or shallow subsoil
• maintain aquifer pressures and prevent the transfer of water between zones, contamination or pollution from reaching the aquifers
• seal off aquifers containing poor-quality water
• prevent uncontrolled flow at the surface in artesian wells
• protect the integrity of the casing from corrosive soils and waters
• isolate the targeted production zone from other formations

Research has shown that the absence of a borehole seal results in contamination of the well from surface contaminants. In addition, the unsealed well can result in the contamination of a sealed nearby well, as the contaminants move with the water from all directions toward the well intake (Fig 1). The same applies to decommissioned or abandoned wells that are not sealed and become contamination pathways into aquifers...