Data on all offshore wells drilled by Dubai Petroleum Company were analyzed for comparison of the Petroleum Company were analyzed for comparison of the effectiveness of different bit types, weights on the bit, and rotary speeds in penetration of the various formations and depth intervals common to this Middle East area. This program was initiated in an attempt to improve penetration rates and reduce per well drilling times. Based on this study, an optimum bit selection, bit weight and rotary speed program was incorporated into drilling plans for subsequent wells drilled in the area. Initiation of this program resulted in a significant improvement in penetration rates, in spite of the fact that some adverse conditions existed, such as formations which have been pressure depleted by production, and drilling pressure depleted by production, and drilling angle holes.


An in-depth study of readily available drilling records was used by Dubai Petroleum Company engineers to improve all facets of development drilling. The areas of drilling technology that were critically examined were:

  • Bit Selection

  • Mud Practices

  • Completion Techniques

  • Bit Energy Levels

  • Cementing Practices

  • Directional Techniques

While each of these studies contributed to the improvement of drilling efficiency, this paper will concern itself with the bit selection and bit energy studies. This restriction was made for the following reasons:

  • Application of the findings of the bit selection and energy studies had the most dramatic effect on efficiency.

  • Effects of mud properties on drilling efficiency are too subjective to have universal application.

  • Directional techniques must be studied on afield by field basis. These findings are valid only for the DPC area of operation.

  • Completion practices are so varied that the present time and motion studies apply only to the DPC situation.

The findings of this study effort were successfully applied in the field. The bit selection energy study was mainly responsible for cutting average drilling time below 20" casing from 26.85 to 21.26 days per well. Application of the entire study reduced overall average drilling and completion time from 54.9 to 46.9 days per well. Average total cost per foot was cut by 5.6% despite a 11.5% increase in per foot was cut by 5.6% despite a 11.5% increase in daily costs and a slightly increased average well depth.

Methods used in the bit selection - energy studies will be detailed at some length. This is not done to advocate that the method used by DPC is the only or even the best one, but rather to show at least one means to attack the problem. Results are shown for the same reason, to demonstrate one way to display the effects of bit selection and bit energy on drilling efficiency.

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