High Performance Water-Based Fluid Replaces Oil-Based Mud on the Execution of a Complex 3D Well Trajectory in Aguarague National Park, Bolivia

Abstract

Abstract The South Sub-Andean Bolivian Basin hosts Aguarague National Park, which prohibits the use of oil-based mud due to its high environmental sensitivity. In response, the drilling team selected a high-performance water-based fluid as the mud system for the 16-inch hole section. The objective was to manage engineering and operational issues related to reactive shales and hole inclination. Lessons learned from an appraisal well drilled in a complex 3D trajectory are presented in this article. The drilling team designed an appraisal well with two main objectives: to drain hydrocarbons from the main structure and limit reservoir extension. To accomplish these goals, they designed a high-angle S-shaped 3D well, including a 16-inch hole section with an inclination of up to 50 degrees and a slight turn to align geological targets. The section consisted mainly of 1000 m of challenging shale formation at an unfavorable target angle. Moreover, the team used high-performance water-based mud due to environmental constraints in the area. The drilling team drilled 1250 m of the 16-inch section through high reactive shales without any wellbore stability issues, thanks to accurate density control and suitable mud additive concentrations, such as biopolymers or synthetic polymers. The mud met lubricity requirements and reduced drilling torques. The synergy of the key drilling fluid components produced stable rheology and low fluid loss, proving to be a cost-effective alternative to oil-based mud in environmentally sensitive areas. The team achieved the planned trajectory without major problems, meeting the estimated schedule. The well was completed on time and within budget, and wireline logs were able to survey the open hole without issues. Finally, the 13,375-inch surface casing reached the bottom and was cemented in place successfully. The drilling team successfully used a high-performance water-based mud system to drill complex 3D well trajectories in the South Sub-Andean Bolivian Basin, despite environmental constraints. The operation's success in achieving well objectives depended on appropriate mud formulation and maintaining the right concentration of shale inhibitors.