Means for varying MWD tool operating modes from the surface

摘要

A method and apparatus for establishing a remote communications link from the rig floor to the downhole MWD system is presented. In accordance with the present invention, the state of a physical condition downhole is changed in a predetermined timed sequence. This state change is controlled on the surface at the drilling platform and detected downhole by the MWD system. The desired operating mode of the MWD system is then determined based on the detected time sequence of the state changes. Preferred embodiments of the present invention utilize two different state changes which are detectable downhole and which can be controlled at the surface. In a first embodiment, the state changes comprise a preselected timed sequence of powering the MWD system up or down. This power cycling is accomplished by operating the mud pump in an ON/OFF sequence which will cause the MWD turbine to similarly be powered up or down. In a second embodiment of the present invention, the state changes are accomplished by modulating the mud flow in a timed sequence which will result in modulations to the MWD turbine. Preselected modulations in the turbine will result in a pattern of power modulations in the MWD systems which will trigger a different operating mode.