Drilling and Enlarging Surface Pilot Holes in Hard Formations Utilizing Drill Bits, Save Time, Enhance Performance and Reduce HSE Risks

Abstract

Abstract In some oilfields, drilling surface big-size wellbores through hard formations yields low drilling performance. Moreover, in these environments, high Shock and Vibration (S&V) are generated causing premature failures of the drilling rig equipment and the drillstrings, increasing rig maintenance costs, Non-Productive Time (NPT), and the risk of loosen drilling rig equipment that could result in dropped (falling) objects and consequent potential injuries to the drilling crews. In these cases, it is envisaged to use the Kelly system for drilling to prevent damage to the Top Drive System (TDS) that however, leads to non-efficient operations and to an increase of Health Safety and Environmental (HSE) hazards in handling more connections (singles). To improve efficiency, a pilot hole is drilled with a smaller drill bit to the section total depth using a performance downhole motor as the driving mechanism to deliver the required power, torque, and revolutions. The pilot hole is then enlarged to the required bigger-size borehole using a drill bit and, again, a downhole motor. The Bottom Hole Assemblies (BHAs) for both the pilot hole and the enlarged borehole, are designed and optimized to minimize BHAs' components handling, minimize S&V and to improve overall operational efficiency. To date, this technique has been successfully implemented in many wells in different drilling environments, improving the section drilling performance by 40-50%, and reducing both well time and drilling costs. Also, S&V diminished, with a consequent reduction of the HSE risks. This paper highlights the engineering aspects of the pilot hole and hole-enlarging design and implementation, together with the results obtained.