Efficient and Reliable Vertical Drilling of Top Holes with RSS in Deepwater GOM

Abstract

The requirement for a reliable technology to efficiently drill vertical large tophole sections has increased substantially along with the number of deepwater wells. Inefficient salt drilling with mud motors and high rig spread rates were some good reasons for operators to prefer rotary steerable tools (RSS) in large-hole sections since they became available to the Gulf of Mexico (GOM) in October 2004. As the use of RSS in 26-in. and 24-in. sections is becoming more popular and deeper wells require minimum dogleg severities in top holes, the use and requirements for RSS have taken higher importance.Deepwater wells are drilled through ultrasoft formations in the first 800 ft; additionally, surface conductors are normally set with an inclination at the shoe of 0.5° to 2°. The unconsolidated sediments and inclination at the beginning of the 26-in. section present a challenge to either hold vertical or drill directionally with mud motors and RSS. The combination of the issues resulted in difficulty to verticalize a few wells below the surface conductor.While from 2004 to 2009 84% of the runs were successful, a major study was conducted during the drilling moratorium in the GOM to understand the environmental conditions that were the root cause of the issues described above. The investigation of 58 bit runs with 26-in. RSS performed from 2004 to 2010 in deep water were studied using advanced drilling software to understand and solve the issue of inability to drop inclination and, in a few cases, of unwanted inclination buildup. The advanced drilling software included time-and-depth based replay of the drilling operation, bottomhole assembly (BHA) tendency, BHA vibration models, unconfined compressive strength (UCS), and e-Caliper computations.The study helped in understanding that conductor inclination and instantaneous borehole washout, in the first 800 ft below mudline (BML) due to UCS values as low as 350 psi, hinders the RSS push-the-bit pads from contacting the borehole, preventing a drop in inclination and, in some cases, allowing further inclination buildup. As this study was concluded during the moratorium shutdown, the lessons learned and best practices gathered helped to optimize BHAs, drilling parameters, and drilling practices. Implementation of these allowed all 26-in. RSS runs made post-moratorium to deliver vertical well intervals.