Patent ID: 8453762

Claim:
A method for operating an earth-penetrating drill rig, comprising: operating a rotary drill bit at an end of a drill string in a borehole, to penetrate into the earth; wherein vertical travel of said drill string is controlled by at least one hydraulic actuator; and wherein said operating includes, at various times, actions of a) during drilling, progressively retracting said hydraulic actuator under load from the weight of said drill string during lowering the drill string into the borehole, to thereby permit the drill bit to keep drilling, while also routing pressurized discharge from said hydraulic actuator to an accumulator; and b) as additional elements need to be added to the drill string during said action (a), then temporarily detaching the drill string, and extending the hydraulic actuator under a load which is less than the weight of the drill string, while discharging pressurized fluid from said accumulator into said hydraulic actuator; wherein said action (a) scavenges and stores gravitational energy from descent of said drill string, and said action (b) recycles said energy to work against gravity.