Drilling in the Middle East is challenging and when it comes to drill string selection and design, the drilling engineer has to consider all the parameters that will influence the lifetime of the drill string, among which drilling environment, well geometry, need for drilling deeper wells in an always more economical manner.

As an example, on the environmental side, the presence of H2S in most fields doesn't allow using standard grades of material and could also require adding geometrical features to the string that allows regaining an acceptable lifetime, in conjunction with a control of the drilling fluid characteristics.

The well geometry and the necessity to tap oil in areas that could not be reached easily and are remote from the drilling site will require that the string has the ability to carry substantially higher loads and in particular allows transmitting high torques through the connection. This could be even more challenging when the operation requires that the tool joint diameter be limited to allow fishability.

Larger hole drilling dictates optimization of hydraulic in order to remove the cuttings efficiently and once again the geometry of the drill pipe is to be considered thoroughly. In this case, streamline connections with enlarged internal diameter can be provided without compromising on the torsional and tensile capacity of the drill string.

This paper aims at answering some of the drillers most commonly asked questions when designing drill strings, since it is essential to understand which parameter to play with in order to optimize the string design. We will expand, in particular, on the raw material selection, stress relief features, geometries and connections that allow increasing drilling performances, thus reducing the overall cost of the drilling operation.

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