Optimization of jars
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- Master's theses (TN-IPT) 
Stuck pipe is a major problem for the oil industry, and getting bigger as more complex horizontal and deviated wells are drilled. What causes this problem and the ways to avoid it are presented. The main tool to unstuck pipe is the accelerator and jar system, generating a strong shock that travels down the drill pipe. One of the main issues is to ensure that sufficient hammer weight is placed above the jar for high impact. This is usually done by mounting heavy weight drill pipe between the accelerator and the jar. A hydraulic jar-accelerator system is specified and simulated by a fast numerical method, and the main output, the shock transmitted down the BHA, is shown as material stress in the BHA as function of time. The most critical parameters affecting the maximum stress were found to be the lengths of the heavy weight drill pipe and hammer. After several simulations with different lengths and ODs, the stress is much higher when hammer length is short. On the other hand the length of HW drill pipe does not affect stress so much, even if its length increases several times. However, HW drill pipe length affects the time duration when stress is larger than 1000 bar. The longer HW, the longer time will the stress act on the string. The time is important to a successful jarring operation, since the stress shock acts on the stuck pipe only a short time. The longer the shock last, the longer the stuck pipe moves for each shock delivered.
Master's thesis in Petroleum engineering