Drilling the deep vertical 16" hole (starting at 9,300ft) in northern Kuwait is challenging due to the complex stratigraphic section that contains abrasive Zubair sand (with pyrite), reactive Ratawi shale, hard Ratawi, Minagish, Makhul limestones and Hith anhydrite (UCS 10-30kpsi). Completing the 16" section typically requires around 45 days of rig-time and four polycrystalline diamond compact (PDC) bits on a positive displace motor (PDM) driven bottom hole assembly (BHA). However, inconsistent PDC bit performance/durability and lack of downhole stability was causing premature bit/motor failure. The operator required new PDC technology that could efficiently drill the abrasive, Zubair and continue as far as possible into the Ratawi without premature cutter failure at acceptable rates of penetration (ROP). The PDC bit would also need to possess improved stability characteristics to reduce PDM failures/trip hours.An engineering team was assembled to analyze the latest drilling/PDC technologies, optimize BHA design, and determine the best practices to enable reaching section TD with two PDC bits/runs. A finite element analysis (FEA) based engineering system was utilized to predict the dynamic behavior of each BHA component. The resulting information led to greater bit stability when drilling in lithologies comparable to the specific field application. The development of a new abrasion resistant cutter was considered important to improving durability and maintaining cutting efficiency.The in-depth study and PDC design changes/advanced cutter technology produced a new nine-bladed PDC bit. The new bit was run on a performance motor in Raudhatain field and set new PDC footage and ROP records for drilling through Zubair (1,200ft) in northern Kuwait (Figure 1). Historically, the Zubair alone required three/four TCIs or two/three PDCs to complete the formation interval. Next an eight-bladed PDC, fitted with the new cutter technology, drilled 2,508ft from Ratawi to section TD for the first time in Kuwait. The improved performance reduced rig hours by an average of 13 days for a total savings of approximately $390,000USD compared to the closest two PDC offset runs. SPE 139873Conclusions KOC's Deep Drilling Team 1, working in conjunction with the service provider, set a new performance benchmark drilling the deep 16" vertical hole section utilizing teamwork and new PDC bit/cutter technology. The new HPHT PDC cutters have reduced accelerated cutter wear and diamond table loss enhancing penetration rates and bit durability. Using the advanced dynamic FEA engineering software systems helped prevent BHA and formation induced vibrations, associated failures and trips by providing dynamically stable BHA and PDC bit combinations. The application specific bit design was tested and certified according to the operator's requirements through the use of dynamic simulations and rock laboratory tests. The result saved the operator rig time and reduced drilling costs by eliminating the traditional trial and error improvement/optimization...

fax 01-972-952-9435. AbstractSabriya 72 (SA-72

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.