Atlas Copco Secoroc has patented a method for directional pneumatic drilling. The new method increases penetration rates, reduces vibrations, decreases equipment damage, and enhances bit performance. With the new method, excess flow is released through one or more jet subs above the bottomhole assembly. This manages airflow through the motor when the hammer is in operation and allows the bit to turn at the correct speed. Without the use of a jet sub, the flow required to clean the hole effectively had to pass through the hammer/motor assembly, which caused the motor to overrotate, resulting in inefficient drilling with excessive wear and damage to the bit. Modifications incorporated into the company’s Model TD 90 DT, QL120 DT, and QL60 HF HC hammers keep the hammers’ flow/pressure profiles the same on bottom as off-bottom, to maintain constant rotation speeds. Constant rotation speed prevents whipping of the bottomhole assembly caused by a sudden increase in motor rotation resulting from high airflow rates while off-bottom, which can lead to motor damage. Vibration levels caused by whipping can destroy tools such as those in an electromagnetic measurement-while-drilling system.
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