Increasing Drilling Efficiency in Saudi Arabia Gas Development Project: Consistent Incremental Gains Significantly Improve Project Economics

Abstract

Because of high formation pressure in certain formations, there are three different casing designs available, including slim-bore wells and big-bore wells. The slim-bore wells are 12-in hole section applications, and big-bore wells drilled as 16-in hole sections. In 12-in slim-bore wells, a major challenge is to drill through different carbonate formations with unconfined compressive strength (UCS) between 10,000 and 30,000 psi with hard streaks peaking at 40,000 psi toward section end. Another challenge in the lower section is high formation abrasiveness, which increases PDC cutter wear rate and slows ROP to an unacceptable rate of less than 10 ft/h before reaching TD. The challenges of this extensively drilled application are well known, and the most efficient bit design to date is a seven-bladed PDC with 16-mm cutters. The existing PDC delivers an acceptable ROP, but its dull condition suggests that a more efficient cutting structure would improve project economics in areas of slim-bore wells where the operator expected poor performance. An R&D project to improve PDC bit performance produced a Conical Diamond Element (CDE) with twice the diamond thickness of a conventional PDC cutter. The CDE provides superior resistance to abrasive wear and impact load damage. To extract the maximum benefit from the CDE's enhanced durability, design engineers used a finite element analysis- based modeling system to position the element at bit center on the baseline design by reducing cutter volume. The new design would increase drilling efficiency at the center of the borehole, leading to higher ROP. This new type of PDC has also proven to reduce damage from torsional vibration for improved stability and borehole quality. The modeling system was also used to identify rpm and WOB combinations most likely to improve ROP and dynamic stability drilling through the difficult carbonate formations. Two new 12-in bits were run in the satellite field wells and set new back-to-back benchmarks for the fastest ROP on their first run. In the X field, this bit achieved an 18% improvement in ROP (73.1 ft/h) compared with four offsets drilled with conventional PDC, resulting in a 10% reduction in cost per foot. In the Y field, the central CDE-type bit achieved a 9% improvement in ROP (72.8 ft/h) compared with a direct offset resulting in an 8% reduction in cost per foot. The authors will discuss operational challenges and the technical justification for running the CDE equipped PDC bit. The paper concludes with a discussion of economic benefits for the operator by utilizing this new technology.