Alain Besson

How Bit Profile and Gauges Affect Well Trajectory

The importance of wellbore deviation is well recognized by the drilling industry. An analysis of a drilling systems directional behavior must include the directional characteristics of the drill bit. This paper presentsa comprehensive analysis of the directional behavior of polycrystalline diamond compact (PDC) bits, including the effect of bit profile, gauge cutters, and gauge length. Numerical simulations as well as laboratory tests have been carried out to better understand the mechanisms of PDC bit deviation and to evaluate the most important parameters affecting the directional behavior of PDC bits. The analysis presented in this paper shows that each part of the PDC bit (profile and active and passive gauges) plays a major role in its walking tendency and steerability. A quantitative evaluation of how these factors contribute to well trajectory (inclination and azimuth) is given. For the first time, a full-scale directional-drilling bench was built to measure the walking tendency and steerability of PDC bits. The results obtained demonstrate that the bit profile, gauge cutters, and gauge length have a significant effect. A 3D theoretical rock-bit interaction model was developed to reproduce the drilling test results.

How to Design Rock BitsTo Drill Ultraabrasive Quartzitic Sandstone in Horizontal Wells, Algeria.

Drilling a long horizontal section within an ultra abrasive fonnation means short bit runs and high drilling costs. Despite many trials with standard technology bits in this gas reservoir in Algeria, the drilling performances were so poor that the profitability of the development project was greatly reduced. This paper describes the process to achieve the development of a specific bit design which eventually greatly improved the drilling performance in ultra abrasive sandstone formation and reduced the number of bits used. The problem analysis was based upon the evaluation of the bit performance history in combination with a full description ofthe physical characteristics of the rock. The abrasiveness of the sandstone was clearly the main factor which reduced the bit life, particularly in horizontal drilling. In order to increase the run length, the first objective was to reduce as much as possible the frictions of the bit cutting structure against the fonnation as well as to protect the bit gauge and heel. The analysis of the rock structure allowed to determine that despite its high abrasiveness, the sandstone presented a hardness weaker than expected. Therefore the penetration rate could be improved with a hit design aimed at favoring the crushing action. After developping two different bit designs and drilling three wells the rate of penetration and the footage were more than tripled. This is the result of a team work between the bit manufacturers and the operator.