Horizontal wells are drilled in Hassi Messaoud oilfield with 6" drains of +/−800m into the Cambrian reservoir using both PDM and Turbine. The multi layered reservoir is +/-3400m deep, mainly quartzite, sandstone and silt. Looking at the rock strength, the confined compressive strength can reach 60 kpsi. Therefore enhancing ROP and durability, when drilling the very hard and very abrasive Cambrian reservoir in Hassi Messaoud, remains one of the major drilling challenges.

This paper describes the iterative approach by which SONATRACH and NOV Downhole Tools Algeria are developing and improving impregnated bits for the very hard and very abrasive formations; for both applications: PDM and Turbine as well. The main objectives are to:

  • Enhance ROP.

  • Increase durability.

  • Maintain inclination and reasonable dogleg severity.

  • Be able to drill out float equipments and shoe.

  • Fit for both PDM and Turbine application

  • Suit both OBD and UBD application

As all new bit types, a complete field study was carried out, including logs and rock strength analysis, offset wells comparison in order to bring into the light the first version of the design. Four versions of the impregnated bit were tested, so far.

The first version drilled 120m. A second version was tested, with an improvement related to the anti-coring cutters, replacing them by a new generation more wear resistant. The subsequent improvement consisted in increasing blade volume, enabling one of the best ROP achieved in Hassi Messaoud 5.27 m/h. To improve durability, blade volume was increased more. The bit achieved 365 m in one run, with an average ROP of 3.49 m/h.

In the last version developed and tested, an increase in the grit mix was made. The bit drilled an interval of 399 m with an average ROP of 3.89 m/h.

Furthermore, several design considerations have been taken into consideration in order to improve impregnated bits in relation to different types of lithology drilled. The newest design has the same blade volume and the same grit mix as the last bit design recently used in Hassi Messaoud field. However the blades are thicker and the hydraulics / water ways are optimized.

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