ABSTRACT
In this paper we address the problem of selecting a specific type of equipment based on testing of the equipment. The product of interest is a drilling jar for use in offshore drilling operations. This is a combined hydraulic and mechanical impact device utilized downhole as a part of the drill string (Kylllingstad & Halsey, 1990). Drilling jars are designed and used to reduce drilling downtime caused by stuck-pipe, i.e. stuck drill string. Such downtime is expensive as it causes pause in the drilling, and consequently increased use of time and cost. The traditional way to handle stuck-pipe incidents is by using drilling jars – the process of using this device is called jarring. In such operation the drill string is pulled or pushed from the rig floor with a controlled force (overpull) and this triggers the drilling jar to transform strain energy in the drill sting to kinetic energy and produce an impact to the stuck point. Depending on which drilling jar is used, there are substantial differences in how much force the jarring impact produce, and thus also considerable variation in effective time to free the drill string. The number of impacts needed may vary from as few as 10 to as many as 1000 (Kalsi et al., 1987). In some cases the jar impacts will not all be able produce sufficient impulse to exceed the stick force required to free the drill string.
