Enhanced Annular Pressure Drop Modeling Assists to Drill Extreme Shallow Ultra-ERD Wells

Abstract

Accurate wellbore hydraulics simulations have been effective in assisting engineers to budget well time and materials, design and execute safe, optimum drilling operations. In this context, "accurate" is commonly understood as 0.1 pound per gallon (ppg) delta, or less, between measured and predicted equivalent circulating density (ECD). Extended-reach-drilling (ERD) wells have been gaining recent adoption due to advancements in drilling technologies. This type of well, by its geometrical nature, poses a challenge to pressure management, hole cleaning and wellbore stability. This increases the relevance of simulation aids. Simultaneously, the industry has seen challenges in achieving the accuracy levels required to model and simulate these wells appropriately. This work closes this gap. Several factors affect the accuracy of ECD predicting algorithms, including but not limited to: the wellbore geometry, pumping schedule, formation and fluid's temperature profiles, physical properties and drilling parameters. Offset information from five different wells was used as basis of investigation and verification. While opportunities for better simulation set-ups were found, it was also identified that refinements to the modeling assumptions were required. The prediction for these wells was enhanced by taking an existing drilling simulator and (1) improving the accuracy of pipe positioning estimation; (2) augmenting the understanding of the eccentric annular flow-field; and (3) including the effects of pipe rotation. This led to a superior determination of the downhole flow-regimes, pressure drops, cuttings transport efficiencies and constrictions due to cuttings beds accumulation. The presented enhanced simulator has been validated against 10+ additional wells. The prediction accuracy significantly improved where it previously lacked. Simultaneously, accuracy was maintained (or slightly improved) in conditions where it originally performed. For ERD wells as shallow as 5,000ft TVD and MD's in excess of 40,000ft, the original ECD predictions diverged as much as 1.5ppg (~400psi) from pressure-while-drilling (PWD). The achieved superior predictions were never above 0.1ppg (~26psi) delta when compared to PWD. Using this advanced simulator, engineers were able to tailor the appropriate rheology profiles to drill ERD wells at optimum performance and determine the best fluid systems’ configuration to achieve it. Operations were completed as planned and budgeted, without unexpected changes in drilling parameters This work presents an enhanced methodology to accurately model annular pressure drops in ERD wells. In addition to accounting for the appropriate flow-regime transitions in a downhole eccentric annulus, this method provides a "true north" as far as "tolerable" cuttings bed accumulation to maintain pressures within formation limits. By using this simulator, engineers were able to customize drilling fluids rheology profiles for minimum pressure loss gradients at performant sag resistant levels, and safely drill challenging ERD wells.