Compressible Carbon: Particle Behavior in Drilling Fluids and Field-Scale Deployment

Abstract

Abstract Annular pressure buildup (APB) can occur due to an increase in fluid temperature during the production of hot reservoir fluids, geomechanical loading from the surrounding rock formation, and hydraulic connectivity to pressurized reservoirs. In this study, a novel, compressible, carbonaceous fluids additive was deployed and tested for APB mitigation in a well-scale field trial. The additive is shown to appreciably reduce pressure changes in trapped, downhole volumes by increasing the fluid mixture's compressibility and reducing its thermal expansivity. The proposed additive, referred to as compressible carbon, is a granular spongy carbon with an internal porosity that remains closed to fluid ingress. Lab-scale results demonstrate the durability of compressible carbon in high temperature and high pressure environments when immersed in typical drilling fluids. At a loading of 20% by volume, the use of carbon reduced pressure buildup by 30%-50% relative to reference measurements performed in fluids without carbon. Moreover, the particles showed no long-term relaxation while being held at 10,000 psi and 220°F for up to three months, and exhibited only a marginal loss in reversible compressibility over 100s of pressure cycles between 500psi and 13,500psi. Following the material's characterization in the lab, field trial results were collected during the deployment and testing of carbon in two unconventional land wells above the cemented section of the production-by-intermediate annulus. Wireline logging on both wells confirmed minimal fluid losses to the formation and an adequate cement barrier that reached above the outer-lying casing shoes. Field-scale performance of compressible carbon was confirmed by pressuring up on the annuli at surface and comparing the injection volumes to those collected on an offset well without carbon. Although alternate methods of reducing pressure buildup in wells exist, compressible carbon is a versatile new material that provides repeated APB relief across the pressure ranges that are relevant to deepwater wells. To minimize the risk of first application in deepwater wells, successful deployment and expected performance were demonstrated in two unconventional land wells, paving the way for subsequent applications offshore.