Drilling deep 16-in. hole sections in Saudi Arabia's gas wells is particularly challenging due to complex stratigraphy consisting of carbonates with interbedded hard stringers, abrasive sandstone, and dense dolomite. These hard/abrasive formations can cause high-axial and lateral vibrations, which have led to premature PDC bit damage. To combat these drilling performance problems, a holistic approach was undertaken to optimize bit design and the drilling system. This included a thorough analysis: Rock samples that matched the challenging formations were collected and laboratory tested to quantify the forces between the cutters and rocks in order to formulate relative rock removal rates. This information and that gathered from a test BHA—after operating for 24 continuous hours during which drilling parameters were monitored—was evaluated using an advanced dynamics model. This enabled improvements that resulted in an optimized bit design and drilling system. This highly beneficial modeling technology is a comprehensive, 4-D, and finite element model, which accurately predicts the drilling system's performance from bit to surface and simulates the transient response of the entire system in time domain. Applicable for any drillstring configuration, the modeling technology is capable of providing performance information on specific BHA components: RSS, PDM, PDC/roller-cone bits, stabilizers, reamers, MWD/LWD, and other downhole tools. Such information includes: acceleration, velocity, forces, bending moment and displacement at any node along the drillstring. Using an advanced dynamics model enabled engineers, working in a virtual drilling environment, to make an extensive effort toward bit design improvements. The resulting bit design, BHA, drilling parameters, and their effect on instantaneous ROP, drillstring vibrations, and directional tendency were quantified and optimized. This holistic approach significantly improved drilling performance in Saudi Arabia's problematic formations. The newly designed bit drilled an entire 16-in. section 5,219 ft from mid-Thamama to base Jilh Dolomite formation at an average ROP of 29.2 ft/hr and achieved the longest 16-in. PDC run in "deep casing design" wells. ROP was 18% faster than the previous best run in a similar application. The authors will outline the analysis, resulting cost reduction, and how applying advanced modeling technology improved drilling performance through the bit, BHA, and drilling parameter optimization.

The abrasive Pre-Khuff sandstones combined with high downhole temperatures and the propensity for BHA and bit sticking present a uniquely hostile drilling environment. These limit run durations and the ability to optimize ROP with the use of conventional rotary assemblies, PDMs/conventional turbodrills and/or rotary steerable systems. Catastrophic damage or loss of drill strings, poor hole quality and logging problems are common even with the advancements in PDC bit technologies. Of the systems listed above, historically, turbodrilling systems have best addressed the high temperatures and the abrasive nature of the Pre-Khuff formations and held the potential for drilling economics optimization but have been unsuccessful in addressing bit sticking challenges. The resultant development of best practices produced only marginal results because they require surface intervention and thus did not fully address sticking problems (in particular bit sticking). The engineering challenge was to develop a downhole device that automatically engages and imparts sufficient drill string torque to maintain bit rotation. The turbodrill device disengages when conditions return to normal and returns the operation to high productivity drilling without surface intervention. The turbodrill device coupled with advancements in BHA design, stabilizer and jar placement along with formation characterization and drill bit technology, is the solution to bit sticking incidents. Presented with this advancement in turbodrilling technology, the Operator/Service Company team has completed trials using this technology and presents data that supports the use and benefits of anti-sticking technologies. With this success, the team has regained focus on drilling optimization and reset the goal for single run-casing point to casing point. Introduction Saudi Aramco continually seeks ways to improve drilling efficiencies through the difficult Pre-Khuff Formations. This paper is about a fortuitous trial of last resort that has delivered favorable results. In Saudi Arabia, Pre-Khuff Formations (Unayzah, Jauf; Tawil, Sharawra, Qusaiba, Sarah, Qasim; and Saq) are encountered at depths between 13,000 and 17,000 feet. These strata primarily comprise sandstones interbedded with shales, limestone, dolomite, anhydrite and siltstones. Sandstones with some siltstone predominate in the top Unayzah strata downward through the Qusaiba. At the bottom, the Sarah can also include some interbedded shale. The Unayzah and Jauf are generally characterized by hard, abrasive sandstones interbedded with shale and siltstone. Unconfined compressive strengths can reach 40,000 psi with internal angles of friction ranging from 25° to 75°. Hardness, abrasiveness, toughness, irregularity in size and orientation of rock constituents, and problems with sticking all contribute to a significant challenge and expense associated with drilling in the Pre-Khuff Formations. High wear rates on bits and BHA components cause a significant potential for premature equipment failures, limit on bottom rotating time, and necessitate long and frequent trips. The Upper Pre-Khuff (Unayzah to Jauf) strata are the most difficult of the Pre-Khuff formations to drill. These strata typically consist of very irregular, fine to coarse grained pebbles and conglomerates that can vary significantly in their dimensions and hardnesses (both in adjacent wells and at different depths in a particular well) and the Jauf formation may also contain Pyrite.