It is well documented carbonate formations cause a multitude of drilling problems. Because the majority of reservoirs in Kuwait are carbonates, the operator is consistently searching for technology to improve drilling efficiency. To reach the hard Jurassic carbonate reservoir, the operator must drill through a series of demanding Tertiary and Cretaceous formations. The fractured Dammam and Tayarat formations are notorious thief zones and can aggravate drilling problems.

The strategy to get maximum hole size to the deep HPHT Jurassic reservoir starts by constructing a 28" borehole through Dammam to TD in Mutriba. The section is interbedded with anhydrite/shale and has compressive strengths between 4- 30Kpsi. At TD, 24" casing is run to isolate the problematic formations. The hole section is approximately 5000ft long but varies depending on the field. These interbedded formations and thief zones create a major challenge for rollercone bits including, impact damage from hard stringers, high WOB and on-bottom time in excess of 250 hours can reduce average ROP to an unacceptable level. Additionally, heat-induced bearing stress caused by low circulation rate in loss-prone formations adds to the applications complexity.

To solve the challenge, the drilling team produced an optimized 28" TCI rollercone bit with custom insert geometry and updated carbide grades to increase cutting structure longevity. Over the last several years the new-style bit, along with optimized operating parameters has consistently drilled the entire section in one run and set a multitude of new footage and ROP records. The authors will discuss the application challenges and TCI bit development. They will present an in-depth engineering analysis that documents footage increases and several new ROP benchmarks in Kuwait. The improved performance has resulted in an average per application cost savings of 3.5 rig days/$175,000 for the operator.

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