State-of-the-Art Modeling Eliminates Drilling Dysfunctions in a Challenging Wildcat Ultradeepwater Wildcat Well

Abstract Operators have expanded their search for new oil and gas reserves to more complex and challenging environments such as the ultradeepwater, presalt carbonate plays offshore Brazil. The major challenge these wells have faced historically is the well cost overrun from low rate of penetration (ROP) and downhole tool nonproductive time (NPT) related to drilling dysfunctions. To avoid costly trial and error, advanced software was combined with service provider and operator experience to get it right the first time: improving ROP while minimizing damage to the bottomhole assemblies (BHAs), drilling each section on time and on budget. An advanced 4D (spatial 3D + time) finite element transient drillstring dynamics modeling package is used to design the cutting structures, predict the drilling dynamics, evaluate different BHAs and drilling configurations, and optimize drilling parameters. BHAs for riserless, post-salt, salt, and silicified carbonate sections of the well are analyzed and optimized. Simulations are run to determine proposed BHA configurations and the potential for axial, lateral/torsional, and stick-slip vibration for different rock strengths. The BHAs are then optimized by adjusting cutting structure, stabilizer placement, hole enlargement ratio, and drillstring configuration. Once an optimum BHA is selected for each section, a sensitivity analysis is conducted on RPM, weight on bit, and torque to maximize ROP for each BHA. Three criteria are used to evaluate BHA performance: stability, robustness/reliability, and measurement quality. The performance of each optimized BHA is compared to the performance of the base case BHA from offset wells. The accuracy of the model's simulations and the optimum recommended parameters is also examined against field results. Overall, the optimized BHAs delivered up to 50% higher ROP compared to the base case from offset wells drilling similar formations. In most cases, the optimum parameters recommended by the model were also the optimum parameters in the field test. The increased confidence in the model from the field tests enabled its use to optimize the BHA further for future wells. This work presents a digital bit and drillstring design workflow, used to virtually run and analyze different BHA designs prior to running in the field. The work, tested in the field, resulted in multiple learnings shared in this paper, specifically in the realm of drilling mechanics.