Abstract

Directional drilling in the Highlands of Papua New Guinea is extremely challenging, especially in the intermediate 12!" hole section. 12!" drilling is through medium strength claystones, where severe tectonic breakout occurs. This results in an extremely poor quality, ledged, ovoid, over gauge wellbore. Traditionally positive displacement motor (PDM) bottom hole assemblies (BHAs) were used to directionally drill in these difficult hole conditions. Drilling performance was far from ideal. Steering penetration rates were typically 50–80% less than those obtained when rotating, even at low inclination, with weight stacking, hang up and motor stalls becoming progressively worse with depth. Additionally, the motor pressure drop placed a hydraulic limitation on flow rates. This limitation handicapped hole cleaning optimisation, which was critical if the abundant large 1–3" cavings generated by wellbore breakout were to be removed from the hole.

An initial attempt to introduce a rotary steerable system to improve penetration rates and hole cleaning had been unsuccessful. It was only with the innovative introduction of a rotary steerable system originally designed for soft formations that success was obtained. Modifications to the original system specific for this new environment brought further performance improvements. Performances will be analysed from a series of wells in Papua New Guinea to demonstrate the improvement obtained by the introduction of this new directional drilling technology. ROP improvement, dogleg capability and improved drilling hydraulics will be presented.

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