DOWNHOLE VIBRATION MONITORING AND CONTROL SYSTEM

The project continues to advance approximately per the revised (14-month) schedule. Tasks 1-3 (Modeling, Specification and Design) are all essentially complete. Work has begun on designing the test equipment for the Test and Evaluation (Tasks 4 & 5.) One of the intents of this project is to not only dampen vibration above the damper, but to also dampen vibrations below the damper. This is accomplished by smoothing out the discontinuities as the bit drills ahead. The model has the capability to simulate the drilling looking at the depth of cut along the discontinuities. It can also look at the amount of time that the bit is in contact with the formation. It is found that under some conditions the vibrations increased the discontinuities due to resonant conditions. In the ideal situation, the damper reduces the discontinuities and smooths out the drilling. APS looked at a wide range of spring stiffness and damping properties to determine the optimum damper. Spring rates of 10,000 lb/in to 60,000 lbs/in were analyzed. The best compromise is at 30,000 lb/in for the 6 3/4 inch tool. Low spring rates would require large displacements for the damper, while stiff springs do not provide enough motion for the damper. Several damping concepts were analyzed: (1) The first thought was to have a damper providing high damping in the upward direction and low damping in the downward direction. It was found that this increased the vibration by wallowing out the troughs of the discontinuities leading to increased displacements at the bit. (2) Another method investigated was having increased damping at high acceleration levels and less damping at lower acceleration levels. This gave improved results. (3) Constant damping so far provides the damping situation. With the proper damping level the damper can smooth out the discontinuities and provide smooth drilling. However, the damping values are different for different drilling conditions. Different WOB and ROP require different damping coefficients and therefore must be constantly adjusted to provide optimum drilling conditions. The DVMCS system is designed to provide this adjustment (4) Other methods are still being investigated. One method is a constant force damper that might provide optimum damping over a wider range