Well of the Future: A New Approach to Real-Time Wellbore Stability Monitoring in the Colombian Foothills

Abstract

With operations reaching a performance plateau, an operator and service company embarked on an ambitious project called "Well of the Future" (WoF Project) to increase well delivery performance, utilizing current technology, knowledge and experience. The main goal was to reduce overall well construction and completion cost and time up to 30%. In the past, wells typically took up to 300 days and USD 65 million to drill. Twenty years of drilling performance history in the Colombian Foothills were analyzed, and global 'best practices' reviewed to determine what innovative and sustainable solutions can be applied to future wells in the hydrocarbon-rich foothill license area and beyond. Many of the identified cost/time issues related to borehole instability occurred in the Carbonera Formation, a series of intercalated formations that include argillaceous and sandy-silty coal beds. The classical approach to evaluating borehole stability was not effective, and was expanded using additional formation evaluation data, fluids properties and historical operational data to gain a better understanding of the problem. Parameters that affect the Equivalent Circulation Density (ECD) were also evaluated, including: mud density, mud rheology, Rate of Penetration (ROP), gas, mud flow, restrictions and contaminants. In addition, caving volume measurements from offset wells were included in the pre-well study. During the execution of the first well, the caving rate data was fed into the real-time data management/visualization system and plotted together with all other factors that affect the ECD, enabling a more coherent analysis. Percentage of Caving shape was also plotted during drilling and tripping operations, enabling a deeper understanding of wellbore instability that included: Fragility of rocks associated with micro-fractures, sensitivity to the amount of mechanical energy applied to the weakest formations while drilling or tripping, time dependency, attack angle with respect to shale bedding plane and well trajectory, coal bed displacement and sealing strategy. All the information combined with Logging While Drilling (LWD) data and on bottomhole Measured While Drilling (MWD) enabled not only the detection of the events, but the understanding of the root causes. Results indicated that the mud weight and sealing management aren't enough to solve the wellbore instability in the Carbonera Formation. The solution involves other factors such as correct casing seat, BHA designs, trips frequency, pills record, identifying the stronger intervals to circulate, caving monitoring as a borehole quality indicator, and the handling of drilling assembly. As a result of this workflow, a new record for the field was achieved: 216 days of drilling for the total well (65 days faster than the original plan), where real time wellbore stability monitoring contributed to reduce the days of drilling of one of the most difficult sections and establishing lessons learned for further drilling campaigns.