The Wassana field is challenging in terms of formation. Past experiences with offset wells in the field confirmed that drilling below 5,000-ft [1,524-m] true vertical depth (TVD) is challenging due to the formation becoming harder and more interbedded, resulting in premature failure of conventional polycrystalline diamond compact (PDC) bit designs. Several bit designs were tested, but most of the cutting structures were damaged when drilling below 5,000-ft [1,524-m] TVD. The best strategy to optimize drilling performance in the Wassana field is to identify a suitable bit design with a durable cutting structure, which can drill beyond 5,000 ft [1,524 m].
To meet the operator's goals, the service company proposed drilling the section with a new-technology bit that uses conical diamond elements (CDEs) on the bit blade with a rotary steerable system. The goals were to achieve the directional objectives in the shallow interval and successfully drill beyond the harder interval [8,000 ft TVD] down to TD. The rock strength of the formation ranges from 12,000 to 15,000 psi.
The PDC bit has CDEs with an ultrathick synthetic diamond layer, which provides extra durability for drilling at higher rate of penetration (ROP). This bit can withstand more weight on bit compared with conventional PDC bits of the same size, resulting in additional mechanical energy to penetrate the formation more efficiently. The CDEs protect the PDC bit by making it more stable, resulting in better tool face control. The 8 1/2-in. directional section was successfully drilled to 11,200-ft 3414-m MD, which was the longest interval in the field. The strategically placed CDEs on the bit blades in conjunction with conventional PDC cutters not only increased the point loading but also enabled smoother torque control, leading to better steerability and durability. None of the offset wells achieved the feat of drilling more than 7,500 ft [2,286 m]. The bit achieved the operator's goal of drilling 9,690 ft [2,954-m] and 10,043-ft [3,061-m] MD. This result not only saved a trip but enabled the operator to gain confidence in redesigning the well profile with a greater measured depth. The operator accepted the fact that the bits with CDEs are more durable and also able to achieve the directional profiles better than conventional PDC bits. As a result, the operator changed the drilling strategy to drill longer intervals in the 8 1/2-in. section. This strategy will increase drilling efficiency and lower the drilling risk of planning for more trips. The subsequent wells were planned using the same bit with CDEs to minimize the number of runs.