Innovative Hybrid Bit Mitigates Geological Uncertainties, Improves Drilling Performance in Brazilian Pre-Salt Formations

Abstract

An innovative hybrid bit design has been successfully applied offshore Brazil to mitigate geological/formation uncertainties in pre-salt formations and eliminate several trips for new bits. In the application, PDC bits can drill these carbonates effectively until the cutters are damaged by problematic chert inclusions. The hybrid bit is capable of similar ROP and run lengths as standard PDC and allows the operator to achieve a long run at high ROP when no silicate inclusions are present. However, the hybrid bit also provides the added benefit of continued drilling at reasonable ROP when a nodule is encountered with its secondary and tertiary cutting elements. The unique hybrid design utilizes grit hot-pressed inserts combined with alternating PDC shearing elements and wedge shaped TSPs all set in an impregnated post-on-blade design. Extended bit life is achieved when the cutting mechanism changes from shearing to grinding as the PDC/TSP elements are worn away. When the PDC cutting structure is worn down to 50%, the bit still has 75% of life remaining. The paper will focus on case studies where pre-salt carbonate lithology is non-uniform with a high occurrence of silicate inclusions. The authors will discuss drive system and drilling parameters selection that were critical to achieving the desired performance. When used with the appropriate BHA and drilling parameters, the hybrid bit displayed good ROP performance and total footage capabilities. Lower cost/meter was achieved because the hybrid bit had faster initial ROP compared to PDC and stayed on bottom drilling longer due to improved durability with TSP then impregnated cutting structures. Cuttings size and resulting lithology analysis will also be discussed. Engineers are currently working on a real-time surface/downhole data processing system to detect when the impregnated cutting structure engages formation in order to make changes in operating parameters to maximize drilling efficiency and penetration rates.