Transient Cuttings Transport for Real-Time Systems

Abstract Control of cuttings in well drilling results in higher operation performance and mitigation of critical pipe stuck events. Nowadays, digital twins for rig operations drive drilling automation services, where hole cleaning is a continuous and essential process. For efficient automation, models should enable real-time evaluation of cuttings transport. This work presents a pragmatic transient one-dimensional model of cuttings transport in the annular section. The model is based on a coupling of the drift-flux model with a two-layer approach. The one-dimensional implementation presented here solves the momentum and mass conservation equations of drilling fluid with cuttings, and mass conservation equation for suspended cuttings. The latter is coupled with the mass conservation equation of stationary cuttings through erosion and deposition fluxes. The direction of the fluxes is determined according to the maximal cuttings bed heights evaluated with mechanistic models. Moreover, the rates of the fluxes are functions of operating parameters. We make use of diverse closure relations available in the literature for cuttings bed heights, slip velocities and pressure losses and combine them with new closures derived from CFD simulations of wellbore segments. The CFD-based closure relations consider drill string eccentricity and rotation. The model can supply equivalent circulating densities (ECD), equivalent static densities (ESD) and cuttings volume returns. We validate the model with field data from the North Sea, where all the necessary data to set up the case was available: (1) wellbore survey points, (2) wellbore and drill string geometry, (3) drilling mud rheological properties, (4) cuttings properties, (5) mud composition, (6) temperature points and (7) operating parameters recorded with a frequency of 1 Hz. We compare simulation and measurement of ECD values and cuttings returns. The combination of the transient cuttings transport model with appropriate preprocessing of the input drilling fluid density and rate of penetration results in ECD predictions with errors below 0.02 specific gravity.