Abstract: An apparatus and accompanying method for monitoring and reporting downhole bit failure. Individual sensors are placed on a sub which is separate from the drill bit itself, and are powered by a vibration driven power system. The sensor readings are used to compute values which represent the ratios of sensor readings on one sensor in relation to the readings of one or more other sensors. This creates a self-calibrating sensor system that accounts for changes in downhole conditions which might cause sensor readings to fluctuate, but which do not indicate failure.

Abstract: An apparatus and method for monitoring and reporting downhole bit failure. Sensors are located on a sub assembly (which is removable from the drill bit) and send data to neural net or other adaptive filter. The neural net uses past sensor readings to predict future sensor readings. The value predicted for the sensors is subtracted from the actual value to produce a prediction error. Increases in prediction error are used to indicate bit failure. The results of this are transmitted to the operator by varying the pressure in the drilling mud flow.

Abstract: A method and apparatus is described for signalling the surface operator about downhole conditions. Sensors located downhole collect data while drilling and the data is processed to determine bit failure, for example. When the sensor data indicates a failure, the pressure of drilling mud is varied using a valve on the downhole unit, and this pressure variance is indicated by a pressure gauge visible to the operator. This pressure change tells the operator a failure has been indicated.

Abstract: An apparatus and method for monitoring and reporting downhole bit failure. Sensors are located on a sub assembly (which is separate from the drill bit itself but located above it on the drill string). Strain measurements are taken from the sensors to detect changes in induced bending and axial stresses which are related to a roller cone bearing failure. As a cone begins to fail, the average share of the total load on the bit that the failing cone can support changes, which causes a change in the bending strain induced by the eccentric loading of the cone.

Abstract: An apparatus and method for monitoring and reporting downhole bit failure. Sensors are located on a sub assembly (which is separate from the drill bit itself but located above it on the drill string). Data from the sensors (preferably accelerometers) are collected in blocks, then analyzed in the frequency domain. The frequency domain is divided into multiple bands, and the signal power in each band is compared to that of another band to produce a ratio of powers. When a bit is operating at normal condition, most of the spectral energy of the bit vibration is found in the lowest frequency band. As a bearing starts to fail, it produces a greater level of vibration in the higher frequency bands. This change in ratios is used to determine probable bit failure. Bit failure can be indicated by a given ratio surpassing a given threshold, or by monitoring the standard deviation of the frequency ratios. When the standard deviation exceeds a certain value, a failure is indicated.

Abstract: The rotary drilling jar includes inner and outer mandrels releaseably locked against relative longitudinal movement. The inner mandrel is connected to the drilling string and the outer mandrel is connected to the drill bit or other well tools suspended below the jar in the well bore. A detent mechanism releaseably connects the inner and outer mandrels and includes a stack of Belleville springs that is configured to determined the amount of force required to move the detent mechanism to unlock the mandrels to permit relative longitudinal movement. In one aspect, the jar also includes an upwardly facing shoulder on the inner mandrel and outwardly facing shoulder on the outer mandrel that are in engagement when the jar is being lowered into, suspended in, and pulled from the well bore to prevent the imposition of string weight on the detent mechanism.