| CPC E21B 15/00 (2013.01) [E04H 12/345 (2013.01)] | 13 Claims |
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1. A drilling rig system comprising:
a mast, the mast comprising:
one or more front legs;
one or more rear legs positioned opposite the one or more front legs; and
a crown block at the top of the mast;
a raising line coupled to the crown block or the one or more rear legs and configured to apply a first force to the mast, the first force acting in a direction opposing a second force generated by the weight of the mast as the mast pivots between a substantially horizontal position and a substantially vertical position;
a drawworks assembly coupled to the raising line and configured to pull the raising line to generate the first force; and
a telescoping spring assembly coupled to the one or more front legs, the telescoping spring assembly comprising one or more compression springs selected to have lengths and spring constants such that:
the one or more compression springs are in an uncompressed, relaxed state and apply substantially no force to the one or more front legs when the mast raised to the substantially vertical position; and
if the raising line or drawworks fails, then the mast, as it falls due to the failure, pivots towards the substantially horizontal position and the one or more compression springs absorb at least a portion of a kinetic energy of the falling mast and applies to the mast a third force acting in the direction opposing the second force substantially equal to the second force upon the mast then arriving at the substantially horizontal position.
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