Evolution of rotary steerable BHA designs in Mexico offshore: Solution to stop multiple drillstring failures in high-vibration environment

Pemex, the local oil producer in Mexico, has identified young fields as potential alternatives to compensate for the production decline experienced in recent years. However, those with the largest reserves and the lightest oil offer the most difficult drilling conditions. Just such an example is a target field in the Marine Southwest region where production objectives have been compromised by significant delays in drilling operation. The complexity of the 17 1/2-in borehole section, made so by high lateral and torsional bottomhole assembly (BHA) vibration, resulted in costly drilling incidents, such as, drillstring twist off, physical damages, and failures of downhole tools. These incidents resulted in fishing and side track operations that averaged 15 days of nonproductive time per 17 1/2-in section per well. This paper will explain how rotary steerable BHA designs developed out of a need to achieve drilling stability and ultimately resulted in an enhancement on average ROP. This discovery, termed Powered Rotary Steerable System (RSS), combines, within the same BHA, a mud motor power section with a push-the-bit RSS tool. This system decouples surface RPM from downhole RPM allowing for the low revolution rotation of the drill string, thus preventing vibration but not sacrificing the rotation and hydraulic power needed by the bit to generate good rate of penetration (ROP). The design was capable of drilling the 17 1/2-in section of the field in one run and reduced drilling time from 36 days to 8 days; nonproductive time due to BHA vibration was completely eliminated in additional wells.