The number of active rotary drilling rigs in the United States has risen only 20 percent in the last year, to 146, according to Baker Hughes, a Houston oil services concern, and is still far below its highs for the decade.
12.
This design represented a significant improvement in drilling performance over the so-called fish tail scraper type bits commonly used in rotary drilling at the time, and over the next two decades, rotary drilling with rolling cutter bits largely replaced all other drilling methods in the oilfield.
13.
This design represented a significant improvement in drilling performance over the so-called fish tail scraper type bits commonly used in rotary drilling at the time, and over the next two decades, rotary drilling with rolling cutter bits largely replaced all other drilling methods in the oilfield.
14.
Prior experience with rotary drilling had established several principles for the configuration of drilling equipment down hole ( " Bottom Hole Assembly " or " BHA " ) that would be prone to " drilling crooked hole " ( i . e ., initial accidental deviations from the vertical would be increased ).
