Why Do Boreholes Collapse? - Borehole Drilling In Zimbabwe!

To keep loose sand and gravel from collapsing into the borehole, it is necessary to use Borehole Casing. 


Borehole Casing supports the Borehole walls while allowing water to enter. This means that the casing must be strong enough to withstand underground pressures. This is why as Nakiso Borehole Drilling, our preferred Borehole Casing is Class 9 and Class 10.

This is because Class 9 and Class 10 Casings are more collapse resistant. The strength of a Casing is often described as collapse resistance.

Formation Stress:

The Borehole Casing can be deformed by external pressures arising from changes in the rock and soils outside the borehole. The drilling of a borehole alters pressures underground and also exposes rocks or formations that expand when hydrated. For example, some clays and shales can swell when exposed to water. It depends upon the chemistry of the clay or shale, and the chemistry of the water. 
Why Do Boreholes Collapse? - Borehole Drilling In Zimbabwe!
Why Do Boreholes Collapse? - Borehole Drilling In Zimbabwe!
The annular space around the Borehole Casing is often very small. Therefore the swelling does not need to be large before the clay or shale touches and begins to exert pressure on the Borehole Casing. The swelling can deform the casing, particularly if the pressure from the clay or shale is confined, by a sealed annulus above and below the formation. In other words, the shale or clay can only expand laterally. 

The Borehole Casing can be deformed even if there is a gravel pack between the shale or clay and the casing. The pressure is exerted against the gravel pack, which, in turn, transfers the pressure onto the casing.
Borehole Casing In Zimbabwe - Why Do Boreholes Collapse?
Borehole Casing In Zimbabwe - Why Do Boreholes Collapse?

With this in minds, it is important to consider the integrity of the Borehole Casing. This is why we encourage you to always choose to have your borehole Cased with Class 9 and Class 10 Casings since they are more collapse resistant. 

The strength of a Casing is often described as collapse resistance.

As Nakiso Borehole Drilling - Our Prefered Borehole Casing Is Class 9 and Class 10 (Pressure Classes.)

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