Systems, apparatus and methods for measuring while drilling

Abstract

A method and apparatus for continuously logging while drilling a well bore with a rotary drilling rig comprising a drill string, a jet type drill bit, and mud pump means for circulating fluid under pressure. The apparatus generally includes means for sensing one or more downhole parameters near the drill bit, means for generating a sequence of electrical pulses representative of said parameter, and means for generating negative mud pressure pulses in the drilling fluid ('drilling mud') within the drill string in response to said electrical pulses. Receiving means at the earth's surface detect the negative mud pressure pulses and utilize the sequence of these pulses to produce signals representative of said parameter. The receiving means employ means to substantially eliminate the effects of the pressure pulsations generated by the mud pump and to extract the negative mud pressure pulses the sequence of which represent the downhole parameter. The means for generating the negative mud pressure pulses involves utilization of the existing energy on the high pressure side of the drill bit through a bypass to the low pressure side of the drill bit controlled by a valve mechanism and arrangement. The design of the valve mechanism and arrangement is such that the valve can be powered for actuation as necessary over a requisite time period by self-contained downhole power source, and is not subject to unacceptable wear.