Double Head Rotary/Rotary
Double head Rotary-Rotary systems are a preferred method for drilling straight, deep holes. These systems offer the driller a high level of flexibility and control to deal with varying ground conditions. In combination with a DTH system on the inner drill string, a Rotary-Rotary system is able to achieve deeper depths compared to drifter (top hammer) based systems.
- Utilizes two independent rotary heads to separately drive the outer casing and the inner drill string
- Uses a lower drill head to turn rotary casing equipped with a carbide casing crown. An upper rotary drill head turns the inner drill rod equipped with a down the hole hammer (DTH), drag bit, tri-cone, or an auger drill string.
- The two rotary heads are typically mounted on separate sleds which can be adjusted independently to control the position of the inner string in relation to the casing bit.
- The inner bit can be advanced in front of the casing bit to act as a pilot bit for the casing string or it can be retracted inside the casing crown to better contain flushing inside the casing.
- Shock absorber (important when drilling with DTH hammers on the inner string) is mounted below the upper rotary head for the inner string and protects this rotary head from the percussive energy of the DTH hammer.
- Elastometric elements in the shock absorber dampen the DTH vibrations protecting the internal gearing of the rotary head.