Abstract: A method and apparatus for automatically shutting in a producing well whenever the pressure in the well annulus drops below a defined pressure. A valve is positioned in the production tubing above an isolated production formation in the well and is maintained in an open position in response to the defined pressure in the well annulus. When the defined pressure is lost in the well annulus (e.g. due to intersection by a second well being drilled in the proximity of the producing well), the valve will close to shut in the producing well.

Abstract: In a well drilling system, a drill bit is raised or lowered through formations surrounding a borehole in response to the movement of a cable onto and off of a drawworks drum. Magnetic markings are affixed to the drum, and a pair of sensors detect rotational movement of the magnetic markings as the drum rotates to take in or pay out the cable. These sensors provide signals indicating both the direction and magnitude of drum rotation. These signals are digitized and selectively gated to operate a bidirectional counter whose count output is recorded as a function of time to provide a depth recording indicating penetration of the drill bit through the formations surrounding the borehole.

Abstract: In a well drilling system, a drill bit is raised or lowered through formations surrounding a borehole in a response to the movement of a cable onto and off the drawworks drum. Prior to drilling operations, the drilling system is calibrated by lowering the traveling block to its lowest position above the rig floor. At this position, the distance from a predetermined reference point to the traveling block is measured as is the rotational position of the drawworks drum. Cabling is then taken into the drum until one full layering of cable is wound onto the drum. At this time, the distance from the fixed reference point to the new position of the traveling block is measured as is the amount of rotation of the drum required to move the traveling block to this position.