Case Study: Reducing Risk and Cost in Presalt Wells through Planning, Selection, and Application of Technology, Process, and Real-time Optimization

摘要

The successful completion of a well in the Brazilian presalt depends largely on how effectively one drills through the salt section. Drilling through salt means dealing with time-dependent borehole stability as well as tough and constantly varying drilling conditions. Drilling through and casing off the salt section before it becomes unstable helps reduce overall risk and drilling costs and is key to a successful operation in such conditions. Careful analysis and planning, coupled with the selection and application of the most suitable drill bits and drilling tools, adherence to a best practices drilling process, and making use of real-time drilling dynamics data acquisition to apply to real-time drilling optimization has led to a significant reduction in drilling time, risk, and cost in this environment. This paper presents a case study showing the analysis used, the planning process and results, drill bits and drilling tools modified and selected, best practices, and the drilling process and real-time optimization used to achieve impressive early results, which are continually being improved as more of these wells are drilled. On the first two wells, the total time to drill through the salt was reduced by 50% from the historical average and is being improved with each new well drilled. Drilling through the salt zone in the 17 1/2-in. section is challenging because of the long interval, approximately 1700 m. In the final third of this section sticking problems are commonly encountered, making it necessary to constantly ream to avoid becoming stuck. The service company proposed using an a new bottomhole assembly (BHA) based on a point-the-bit rotary steerable system (RSS) configuration using a special bit stabilization capable of reaming the bottom section while drilling, saving reaming time and helping prevent sticking problems. The special stabilization reduced vibration levels compared to regular bit stabilizers offered the benefit of lower vibration and rate of penetration (ROP) increase. The optimized BHA and tool configuration combined with the planning and execution employed set a record for drilling through the salt section, resulting in significant cost savings.