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.

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