Overburden Drill Bit overburden drilling system 70mm - 400mm OD
The Stratex Drill System
The Stratex Drill System (SDS) is an overburden drilling system
designed for conditions where a cased hole is required. Collapsing
holes tend to make overburden drilling expensive, with lost
drilling equipment and down time.
In cooperation with drillers and drilling contractors, the SDS was
developed to overcome these problems. The patented eccentric design
and the Drop Off Ring (DOR) drill bits enable the drill string and
casing to be lowered in the hole simultaneously with a conventional
hammer drilling system.
The SDS eccentric designed bit rotates outward and drills a larger
diameter hole than the casing, avoiding cave-ins, wash-outs, and
other problems common in normal drilling operations in soft and
gravel-type strata or loose rock. Since 90% of the world's
overburden drilling is in loose strata, potential utilization of
the SDS is enormous.
After reaching the designated depth, the SDS reamer-bit is
retracted by reversing the direction of the rotation and by
applying tension on the reamer-bit, which has a taper and will
retract into the casing for easy removal of the entire
drill-string. This leaves the casing in place for other
applications or for removal at a later date. The SDS method is
designed for use with flush joint threaded pipe or welded-type
casing and provides a bit size for a wide variety of different
casing wall thicknesses.
Advantages of SDS:
Low capital investment
High drilling performance
No rotation of the casing
Compatible with most drilling rigs
Virtually no casing stress
Casing is simultaneously lowered by the guide device and to deeper
depths than other methods allow
Cost and on-site time reduced due to better penetration rates,
easier bit changes, and stable hole conditions
Smaller pilot bit for faster and better penetration
Water supply wells
Bridge and building foundations
Standard slant or horizontal drilling
Mining air holes
Environmental monitoring wells
Seismic shot holes
Soil sample and geotechnical applications
Ground anomaly and tiebacks
Storage caverns and dam
Accessories Available with SDS:
Drop Off Ring (DOR)
Drill pipe and subs
Casing drive shoes
Hydraulic casing pullers
Overburden Drill System
Assembly of the Stratex System
The Stratex Drilling Method is used with air rotary drilling rigs
and most manufacturers' downhole hammers. The drill rod is
connected to the rig top drive using a changeover sub or swivel
sub. The drill rod is then connected to the down-hole hammer by the
same method. The chuck nut and split rings are removed to insert
the guide device shank and secured by replacing the split rings and
The reamer bit, in the closed position, is now inserted into the
casing shoe. Since the percussion hammer is at the bottom of the
hole, working directly above the drill bit, the force to pull down
the casing tube is transferred by way of the casing shoe. The
exhaust air from the drill redirects the loose cuttings up through
the groves on the guide device, forcing them up between the drill
rod and the casing wall out through the discharge head, which is
attached to the casing tube. By using a discharge head, drilling is
not only safer but also environmentally cleaner. Stratex can be
used with foam or water to aid in cutting removal.
Good Flushing is essential with any successful drilling operation
or in using an overburden drilling system. The Stratex System
provides air jets above and below the guide device, creating a
vacuum across the face of the reamer bit, removing the cuttings
with greater annular velocity. The gauge carbides along the side of
the pilot and reamer bit act to crush the cuttings into finer
particles, the majority of which are removed from the hole. The
remaining cuttings are forced back into the walls of the cavity,
leaving less material to be extracted from the hole.
- Efficient removal of cuttings from above the guide device, which
prevents the hammer from jamming and torque problems
- Removal of fine cuttings from around the bit system and casing
creates less friction and achieves deeper depths and easier casing
- Reduction in losses due to circulation problems by increased vacuum
in cutting removal
- For unique applications, the annular velocity can be increased by
changing the airflow in the reamer pilot system
- One-piece reamer and pilot bit
- One-piece guide device and shank
- Casing with shoe sleeve
- Wing-nut centralizing system
- Drill rod
- Casing adapter
- Discharge head
- Swivel sub
Air velocity is important for efficient hole cleaning. A minimum
return air velocity of 4000 feet per minute is desirable. Annular
space between drill pipe and the drilled hole as well as compressor
capacity determines the air velocity. The annular air velocity in
foot per minute can be calculated with the following formula if air
consumption and annular area are known:
annular air velocity (fpm) =
free air consumed (cfm) x 144
annular area (sq. in.)*
*annular area = .7854 x (hole diameter - drill pipe OD)
The following flushing mediums are also useful:
- Air with water injection
- Air with foam injection
NOTE: Foam has the ability to lift cuttings and stabilizes the wall
of the hole and provides lubrication for easier casing penetration.
Foam also has good drilling performance in most types of clay.
The Stratex Drill System
Blank Casing End
The Stratex System utilizes a one-piece reamer and pilot bit that
moves outward to full open position on an eccentric shaft by
rotating a half turn to the right.
This reamer pilot bit system opens a larger diameter hole than the
diameter of the casing. The casing is simultaneously lowered into
the hole as the reamer pilot bit drills. The pilot bit is rotated
at 10 to 40 rpm while drilling with the hammer.
When the designated drilling depth is reached, the reamer pilot bit
system is retracted into the casing by applying slight tension and
reversing the direction of the drilling rotation. The design of the
reamer pilot bit system incorporates a closed bearing method that
makes the loss of the pilot bit virtually impossible. This bit
system, in the closed position, is easily removed through the
casing shoe and casing.
Using a telescoping drilling method can achieve deeper depths.
Some string samples are as follows:
Casing depths with Stratex can reach 500 feet or more with the
down-hole hammer versions depending on the type of formation,
drilling equipment, and drilling personnel experience.
Stratex System (mm)
Normal Max - Hole Depth (ft)
The Stratex Drilling Method
The Ultimate Drilling Method
The Overburden Drilling Method that was designed by drillers for
drillers. Overburden material strikes when least expected. Be
prepared. Use Stratex!
The PATENTED Stratex Drill System:
1. One-piece shank and guide device manufactured from the highest
quality material with stringent quality control.
2. Air jets are used to prevent any malfunction of the opening and
retraction of the reamer pilot bit operation and the clearing of
cuttings above the reamer pilot bit system.
3. Sealed bearing system for ease in rotating the eccentric bit
outward or retracting it into the casing.
4. Casing with shoe: Casing may be supplied with plain or threaded
5. Grooved bypass directly above the lock system to clear cuttings
and ensure complete drilling face contact.
6. Tapered shoulder on the reamer bit eliminates casing binding and
assists in the retracting of the reamer bit into the casing.
7. One-piece reamer and pilot bit manufactured from the highest
quality material, with stringent quality control.
8. Gauge protection carbides on heavy duty, one-piece pilot and
9. Dome carbides on heavy duty pilot and reamer bit.
DROP-OFF RING UNDER REAMER
Used when concentric drilling is a requirement:
- High performance drilling
- One-piece reamer
- One-piece guide device
- Made from tough heat-treated alloy steel
- Studded with an aggressive array of tungsten carbide inserts
- Lower drilling costs per foot
- Guaranteed performance*
- Guaranteed service
- Large range of accessories
- Manufactured under strict quality-controlled conditions
*When used in conjunction with manufacturer's recommendations and
Drop-Off Ring Under Reamer
TOOLS OF EXCELLENCE AND DURABILITY FOR OVER 30 YEARS
Recommended Maximum Air Pressure for Stratex Drill Systems
The maximum recommended air pressure for Stratex drilling with
down-hole hammers is 12 bar, which equals 210 psi.
Rotation speed depends on the size of the Stratex bit and the
formation being drilled. The rotation speed may have to be varied
as the formation changes. The table shows recommended rotation
speeds for the various Stratex sizes.
Recommended Rotation Speeds
Stratex System (mm)
20 - 40
10 - 25
Drill rigs must have sufficient torque for drilling with Stratex.
The table shows recommended rotation speeds for the various Stratex
Stratex System (mm)
Minimum Torque (ft/lb)
"ROSCHEN provides the widest range of flexibility when it comes to
casing wall size
thickness, which makes it a high demand by users. All systems
complete and ready for
resale within a week or two, a time frame that cannot be met by
Stratex Over Burden Drilling Tool: Size and Technical Chart
Drive Shoe I.D.
Drive Shoe Length
Guide to Casing Distance
Guide to Casing Distance