Downhole Drilling

One of the special drilling techniques Seaboard Foundations utilizes is the use of the "Downhole Hammer", also known as the "Downhole Drill". This tool grants the capabilities to remove rock from 18" to 96" diameter. The unique characteristics and design of this air-powered percussion tool allow for the removal of the hardest type of rock found anywhere in the United States. Seaboard Foundations, a pioneer in this procedure, is currently one of the few organizations that utilizes large diameter hammers. This procedure is extremely economical and time-effective. A quicker procedure does not exist. Please review the information below. Feel free to contact us with any questions you may have regarding Downhole Drilling.

Downhole Drilling (DHD)

The DHD hammer is located on the end of the drill string. The hammer piston directly contacts the bit. Because the piston discharges energy directly to the bit, energy does not dissipate through the drill string as the hole deepens. This means that given adequate air, DHD performance will not decrease as depth increases.

A hydraulic or air rotary head or kelly-bar drive outside of the hole provides rotation. Drilling pipes conduct compressed air to the DHD hammer. After cycling the hammer, the air passes through the bit and flushes cuttings out of the hole.

Although no energy is lost as drilling depth increases, friction between the drill pipe and hole wall reduces drill speed slightly. Increasing the air pressure increases piston energy and provides faster penetration.

DHD hammers drill straight holes because their drilling power comes from high frequency percussion rather than from high rotation and pulldown and because the piston impacts directly on the bit rather than through a drill string, which can bend over long hole depths. This makes DHD drilling especially suitable in broken ground conditions where hole deviation may be a problem.

Advantages of Downhole Drills

• Quieter operation

• Straighter holes

• Less torque and pulldown required

• Drill exhaust flushes hole

• Effective in broken ground

Originally, DHD percussion drills were used primarily for improved penetration where formations were medium hard to very hard rock. More recently, numerous other advantages of DHD drilling are expanding its popularity throughout the range of consolidated formations: wherever air and air foam circulation systems can be used.

1. Minimum weight on bit required

   The moderate pulldown force on bit of 500 lbs/inch (9 kg/mm) of bit diameter required by a DHD compared to 3000—7000 lbs/inch (53.7—125.3 kg/mm) for rotary drilling, eliminates the need for heavy drill collars and high hydraulic loads in the rig's pullback system. You can drill deeper holes with a smaller rig using a downhole drill.

2. Straighter hole

   The short rapid blows of the DHD minimize the effect of broken or unconsolidated formations, assuring a straighter hole.

3. Lower rotation torque & speed

   Drillstring torque loads are much lower than with straight rotary drilling. Rotation speeds are also much lower than with rotary drilling. Normal operating RPM ranges are from 10 to 60 RPM.

4. Effective hole cleaning

   Drill exhaust air passes through the bit to clean the bit face and carry cuttings to the surface up the annular space around the drill pipe. Using exhaust air to clean the hole makes DHD drilling more efficient.