Abstract: A method of drilling under barriers (rivers, highways and the like) is set out. The horizontal drilling system mounts a guidance tool on the end of the drill string just behind the drill bit. The guidance tool includes a pair of right angle accelero meters and a 3-axis mounted gyro. The gyro furnishes data in a plane at right angles to the z-axis. This defines four data streams to the CPU enabling determination of drill bit location and pathway.

Abstract: A method of drilling under barriers (rivers, highways and the like) is set out. The horizontal drilling system mounts a guidance tool on the end of the drill string just behind the drill bit. The guidance tool includes a pair of right angle accelero meters and a 3-axis mounted gyro. The gyro furnishes data in a plane at right angles to the z-axis. This defines four data streams to the CPU enabling determination of drill bit location and pathway.

Abstract: This disclosure describes a blended buoyancy oil well survey instrument capable of performing MWD measurements (measuring while drilling), where the well survey instrument is mounted. An oil well survey instrument in a closed cylindrical housing having a specific gravity greater than the drilling mud in which it is used is modified in buoyancy by attaching one of several identical elongate cylindrical hollow containers or cylinders to it. They are filled with light material. They are made sufficiently strong that they do not collapse at working pressures. The cylinders are provided with upper end and lower end threaded stub shafts and mating receptacles to thread together thereby providing a modified buoyant system. The method is concerned with adjustment of the buoyancy so that the rate of fall is modified; in conjunction with mud flow velocity in the drill string, the buoyant descent of the instrument is controlled to about 100 or 200 feet per minute.