Total System Optimization Delivered Significant Performance Improvement and Cost Savings in GoM Challenging Salt Section

Abstract

It is well known in the oil industry that there are many drilling challenges associated with salt drilling in the Gulf of Mexico continental shelf. Although many wells have already been drilled through salt, hazard prediction is still not very accurate, which makes extensive planning a critical requirement. While drilling a prior well through a thick salt body in the shallow waters of the Gulf of Mexico Ship Shoal area, the operator experienced many drilling-related problems, including numerous downhole tool failures, leading to considerable non-productive time (NPT) and additional costs. This paper will focus on the planning and execution of a sidetrack to this problematic well, again drilled through and exiting the salt. This paper highlights the problems encountered and the substantial cost savings realized by the operator.During the planning phase, a thorough offset analysis was conducted using an engineered optimization process, which allowed the identification of the root causes for the downhole tool failures and mapping of the main drilling hazards. The main drilling challenge in this project was to drill and underream efficiently through anhydrite layers imbedded in the thick salt body. In the offset well, most of the drilling problems were associated with these anhydrite layers, which induced significant vibration and premature cutting structure damage. Location and thickness of the anhydrite layers were difficult to predict, therefore pre-established drilling procedures and best practices were key to help identify the anhydrite layer promptly and successfully overcome it.The implementation of a multi-discipline total system approach to select the ideal combination of an application-specific rotary steerable system, real-time downhole drilling dynamics tool, drill bit and underreamer, in combination with appropriate planning, recommendations, drilling procedures, and best practices was crucial to deliver significant performance improvement by drilling the sidetrack salt section six days ahead of AFE, which represented US $2.1 million in savings for the operator.