Kuwait Oil Company Sets Drilling Record Completing the Zubair Section in One Run

摘要

Drilling deep exploratory wells in Kuwait presents a numberof distinctive challenges. The 16" hole section is particularlydemanding because it must be drilled through hardinterbedded formations including the Zubair sandstone,Ratawi shale, Ratawi limestone, Minagish limestone/dolomiticlimestone, Makhul limestone/shale and Hith anhydrite.1Historically, 16" roller cone bits were used to drill the floatequipment and several hundred feet of Zubair in order to getthe stabilizers out of the casing. Several such wells have beendrilled in North Kuwait with the best case requiring three PDCbits to complete the section subsequent to the roller cone run.The main challenge has been the highly abrasive Zubairformation with UCS in the 12,000-15,000 psi range.Traditionally, drilling abrasive formations with PDC has beenchallenging even in smaller hole sizes (8-1/2" etc).2 However,as hole size increases torque response is magnified increasingvibration issues. In this application, vibration is furtheramplified by variations in formation hardness. These factorsmake efficiently drilling the Zubair with PDC a seriouschallenge. The operator required new PDC bit and cuttertechnology.A team was assembled that analyzed PDC technology usingnumerical models, laboratory and field tests. Engineersfocused on the bit frame/cutting structure, and cutter design.Cutters diamond table properties were evaluated in an effort toincrease durability and wear resistance. The result is atougher, more abrasion-resistant cutter capable of maintainingan efficient edge in the hard/abrasive Zubair sand.Patented depth-of-cut control (DOCC) technology providedsmoother, more stable drilling through the interbedded formations. By limiting the unnecessary depth-of-cut of PDCcutters, the amount of torque generated can be effectivelycontrolled. Penetration is managed by adjusting cutterexposure from the bit body and providing a load-bearingsurface. Laboratory testing proved how DOCC technologymaintains bit aggressiveness needed and limits reactive torqueas more weight is applied or as softer formations areencountered. The threshold for bearing engagement isprecisely adjusted for each application. This minimizedvibration when transitioning between formations whileoptimizing the ROP advantage of a PDC bit.Utilizing the new bit design, the operator drilled the entireZubair 16" interval in a single run for the first time and wasable to cut drilling costs by eliminating several trips for newbits and the up-front expense of the extra downhole tools. Theauthors will discuss how the new technology cut costs andincreased drilling efficiencies.