Continuous bit positioning system

Abstract

A method for determining the precise position of the drill bit, in three dimensions, in the earth during a drilling operation, with a minimum of effort and interruption to the drilling process. It provides placing a motion sensor on the drilling apparatus and a plurality of vibration sensors or geophones, positioned in a two-dimension array on the surface of the earth, above the expected position of the drill bit. To make a measurement from which can be determined the position of the bit, the drill stem is raised a selected distance and suddenly released, so that it will fall in the borehole, and the bit will strike the bottom of the hole. This impact will cause an elastic wave to be generated at the bottom of the borehole. The elastic wave will be transmitted through the earth and will be detected by the geophones. The sensor provides information from which can be determined the time when the bit strikes the bottom of the drill hole. This determines the initiation time of the elastic wave. The arrival times at the geophones of the elastic wave can be measured and the position at which the elastic wave originated can be determined. Alternative embodiments involve the use of jars in the drill string which generate secondary elastic waves. Also when the pipe is lifted and the bit is lifted off bottom, an expansion elastic wave will be initiated.