Editorial
Authors
Abstract
Numerous parameters influence bit selection process, which considering all them is not normally feasible. Existing methods use limited number of these parameters to choose a suitable bit for a specific drilling condition. One of the widely used methods is cost per foot. Specific energy and drilling strength are another methods currently used for bit selection. Different methods of bit selection and bit lifetime estimation were tested on a gas field, in southern Iran. Although cost per foot method is most widely used, present study showed that similar bits may have different cost per foot in different wells, rock formations or drilling conditions. Therefore, where geological and geothechnical conditions widely vary in a single formation, this method cannot be used alone for bit selection. The specific energy method was also found to have some deficiencies as it is highly dependent on drilling parameters. The outcome of using existing formula for predicting unconfined compressive strength from petrophysical data of oil and gas wells is in fact drilling resistance, which is a very rough estimate of unconfined compressive strength. On the other hand, the drilling strength method, using Young's Modulus and clay content, showed to have rewarding results on the studied field. This method, if used together with cost per foot method, will give better results. The present study also showed that the results derived from the drilling strength method should be modified according to drilling parameters.
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