Improved Hydraulic Modeling Through the Addition of a Transient Cuttings Transport Algorithm
Authors: Fallah AmirHossein , Goyal Gaurav , James Chris , Sankaran Sathish , Adams Craig , Hinshaw Chris , Borjas Ricardo 
Published: May 2023

Hydraulic models are widely used in the drilling industry to simulate downhole conditions, estimate pressures and velocities in the wellbore, and ensure sufficient flow rates are maintained. While wellbore hydraulics are hugely dependent on cuttings transport and deposition, most of the models in the industry either completely ignore cuttings transport, or use overly simplified methods (e.g., correction factors) to include its effects. This leads to inaccurate pressure estimations, especially during transient drilling conditions.

A robust cuttings transport algorithm is developed and integrated with a real-time hydraulics model. The algorithm discretizes the annulus and estimates the cuttings bed blockage, volume fraction of suspended cuttings and cuttings and mud velocities both at steady-state and transient conditions for each discretized cell. Solid-liquid slip velocity, cuttings bed generation and erosion, and mixture viscosity and density are accounted for using experimental models. The effect of the cuttings bed and suspended cuttings on friction factors, hydrostatic pressure, and mud rheology are included in the hydraulics model, providing accurate estimates of the transient pressure and velocity profiles. Moreover, a dynamic discretization algorithm is implemented to account for extended, real-world drilling operations.

The hole cleaning algorithm provides an estimation of the real-time cuttings bed and suspended cuttings concentrations, as well as important parameters such as the weight of cuttings in the wellbore, maximum cuttings bed blockage, and clean-up cycles required to clean the wellbore. Through the integration with the hydraulics model, pressure and velocity profiles are accurately estimated, including minimum cuttings velocity in the wellbore, standpipe pressure, and bottomhole pressure. Results show that while pure hydraulics modeling underestimates the standpipe pressures, integrating hole cleaning effects into hydraulics modeling accounts for pressure drops that are otherwise ignored (such as increased hydrostatic pressure from suspended cuttings, cuttings bed blockage effect on annular velocities and friction factors, and effect of cuttings on fluid viscosity). Additionally, the integrated model predicts the transient standpipe pressure behavior, which results from cuttings accumulation and removal during different drilling operations. Finally, the model can be used to simulate clean-up cycles and determine required flow rates and clean-up times to remove the cuttings from the wellbore.

The integrated model simulates transient wellbore conditions using sophisticated physics-based and experimental algorithms, while not requiring advanced domain expertise from the users on the rig. Model results provide the drilling crew with accurate and valuable information on the cuttings bed, transient standpipe behavior, and clean-up cycles that are often missing from the models used in the industry today.