Drilling challenges in the Hassi Messaoud (HMD) oilfield have proven to be equal to the magnitude of its production. Historically, wells drilled in this field were vertical, moderate borehole diameters having a long 12 ¼"section. In order to increase production and to gain a better understanding of the reservoir, Sonatrach Drilling engineering moved to moderately deviated large diameter boreholes, delivering 1000 meters of drain in the reservoir.

Instead of the conventional 12 1/4’’ vertical section, 1800 meters was drilled in 16’’ diameter. This section consists of abrasive sands, inter-bedded evaporate/carbonate and sand/claystone formations prone to instability and collapse. In addition, there is a 30 meter band of extremely hard dolomite. Rock strengths vary widely from 5 Kpsi to 30Kpsi.

Since early 2000, Sonatrach and National Oilwell Varco (NOV) have been working as a team to rise to the challenges presented by the larger hole size. Most significantly drilling vibrations, slow penetration rates, increased trips to TD, severe bit and BHA damage and NPT due to stuck pipe while pulling out-of-hole.

This article describes first, the process by which significant performance improvement was achieved as a result of combining innovative bit design techniques and technologies, BHA optimization, optimization of parameters through BHA dynamics modelling, and formation Rock Strength Analysis.

Secondly, the article discusses optimized techniques introduced to enhance performance for the 16’’ section on rigs that have been recently equipped with VFD - AC top drives and properly deal with torque limitation issues.

This enabled Sonatrach to repeatedly set ROP drilling records as well as consistently making section TD in a single run. The net result was a 37% improvement in rate of penetration1 .

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