Abstract: A conventional well bore drilling system includes a coiled tubing mounted on a reel and connected to a mud supply for supplying mud through the tubing to a downhole end of the tubing to which is attached the downhole drilling tool. The system is modified by the addition of an inner tubing attached to the reel shaft and extending through the outer tubing to the drilling tool. The drilling mud is supplied in the space between the inner and outer tubes and a gas is supplied through the inner tube, The gas is vented through a coupling at the drilling tool into the well bore so as to enter the well bore and reduce the hydrostatic head of the fluids within the well bore to an under balanced condition below the pressure of the producing zone.

Abstract: A conventional drilling system using continuous coiled tubing connected to a reel at its upper end and connected to a drilling tool at its lower end is steered by rotating the injector at the well head which drives the tubing into the well about an axis longitudinal of the well bore to effect twist in the tubing along the well bore and thus to rotate the drilling tool. This twist in the tubing between the injector and the reel is negated by rotating the reel about a vertical axis parallel to the well bore in a direction, viewed from above, which is opposite to the direction of the injector.

Abstract: A supplemental horizontal section is drilled from a lower end of an existing well bore by a drilling tool which provides a short radius of the order of 20 feet of a curved section interconnecting the vertical initial section and the horizontal section. This enables the drilling to take place without expensive monitoring equipment since the distances involved are relatively small. The drilling tool includes a mud motor to which is attached a drilling section including a drill bit at the outer end thereof. The drilling section is connected to the mud motor by a knuckle joint which allows pivotal action about an axis at right angles to the longitudinal axis of the drill bit. A counterbore of increased diameter is formed at the lower end of the existing well bore and the knuckle and drill bit located therein. The knuckle is biased toward one side of the counter bore by a leaf spring so that the longitudinal axis of the drill bit takes up an inclined position with a knuckle bent at a shallow angle.