26/04/2026
Odex Drilling
That’s a solid result! Hitting the 30-meter mark with ODEX (Overburden Drilling Excentric) in Southern African
ODEX system is that it lets you drill and case simultaneously, preventing the hole from collapsing in those tricky upper layers common in region
River sand is notoriously difficult because it collapses almost instantly, but ODEX is the perfect way to handle it. Since you are drilling and casing simultaneously, you’re effectively "locking" the sand out of the hole as you go.
In Southern African riverbeds or alluvial plains, here are a few things to keep in mind for this specific formation:
Preventing "Sand Lock": In loose river sand, keep your air pressure high enough to clear the cuttings quickly. If sand builds up around the eccentric reamer, it can get "locked," making it hard to retract the bit back through the casing.
Casing Shoe Placement: Once you hit the more stable layer beneath the sand (like bedrock or clay), ensure your casing shoe is firmly seated before you switch to a standard bit to continue deeper.
Common Standard ODEX Sizes
ODEX 165 (6.5 inch): Often used in technical specifications for government or industrial projects in South Africa, where 165mm finished diameter is required through the overburden.
Why This "Odex" Matters for River Sand
When drilling in river sand, the standard ODEX setup ensures:
Simultaneous Casing: The casing follows the bit immediately to prevent the sand from "washing out" or collapsing the hole.
Sealing the Overburden: Once you pass the 30-meter sand layer and hit competent rock, the "standard" practice is to seat the casing at least 3 meters into the bedrock to seal off the loose sand.
Equipment Compatibility: These standard sizes are designed to work with common 3”, 4”, or 5” DTH (Down-The-Hole) hammers widely available across Southern Africa.
How the ODEX System Works
The system uses a "Down-The-Hole" (DTH) hammer and a unique three-part bit assembly to handle both drilling and casing in one pass.
The Pilot Bit: This central bit leads the way, initiating the hole.
The Eccentric Reamer: This is a hinged "wing" on the side of the bit. When you start drilling (forward rotation), centrifugal force and impact cause it to swing out. This enlarges the hole so it is slightly wider than the steel casing following right behind it.
Simultaneous Casing: As the bit moves down, it pulls or hammers the casing into the hole at the same time. This provides immediate wall support, which is why it works so well in your river sand.
Retrieval: Once you hit stable rock, you reverse the rotation. This causes the eccentric wing to fold back in. The entire drill bit can then be pulled out through the inside of the casing, leaving a clean, protected hole behind.
Key Benefits
No Cave-ins: Essential for formations like sand or silt that fall back into the hole.
Speed: Since you drill and case at the same time, it’s much faster than traditional "temporary casing" methods.
Estimate water yield about 50 000 liter per hour. Using a 6 mm steel casings with welding shoe.
