Avoiding Losses in Depleted and Weak Zones by Constantly Strengthening Wellbores

Abstract

Summary Drilling depleted or weak zones has always been a challenge, but with the aging of fields and the desire to drill to deeper in-field plays, the situation is becoming more exacerbated. The typical problems associated with drilling these types of intervals are lost circulation, stuck pipe, and wellbore instability, resulting in significant and expensive nonproductive time (NPT) and costly remediation operations. Conventional lost-circulation remedies (e.g., pumping lost-circulation pills and squeezing) have given way to popular wellbore-strengthening solutions. Our approach to strengthening, based on beneficial manipulation of fracture- propagation pressure and continuous application of specialized wellbore-strengthening additives, has had tremendous success in reducing downhole mud losses by more than 80% in Gulf of Mexico (GOM) deepwater operations and dropping the cost of these incidents out of the top 10 contributors to NPT. This paper focuses on the various theories and approaches to wellbore strengthening and what the available field and literature data actually support. Building upon this, the approach of gaining wellbore fortification through fracture-propagation-resistance (FPR) enhancement is introduced, for which experimental results, field data, and case histories are shared. Central to our application of FPR to drill-challenging deepwater production wells is the notion of providing continuous wellbore protection through a novel and unique solids-recovery and reintroduction method that allows for drilling with high concentrations of wellbore-strengthening materials (WSMs) in the drilling fluid.