Date of Award

January 2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Petroleum Engineering

First Advisor

Vamegh Rasouli

Abstract

Efficient hole cleaning in drilling operation is essential to ensure optimum rate of penetration. This complex problem involves simultaneous analysis of multiple parameters, including cuttings characteristics, fluid rheology and the geometry of the annulus space. For instance, accurate calculations of the equivalent circulation density (ECD) requires the effect of the mud density increase due to the cuttings’ concentration to be considered, which itself is a function of the settling velocity and the rate of penetration (ROP). Analytical models, lab experiments and numerical simulations have been used to determine the optimum flow rate for efficient hole cleaning. Most of these models are based on the drag coefficient-Reynolds number relationship, where both parameters are velocity dependent, making the calculation workflow to be implicit, tedious and time consuming. While several attempts have been made to present explicit correlations, precise equations covering a wide range of Reynolds numbers are not available.Terminal settling velocity was used in this research to determine the minimum required transportation velocity of drilling cuttings in the annulus space to ensure an optimal cleaning. The ROP also affects the hole cleaning as it defines the volume of the cuttings produced. We first used analytical models to investigate the effect of the cuttings size, density, and fluid properties as a function of wellbore deviation and circulation rate on hole cleaning efficiency. The results were compared with lab experiments using a slurry loop. The analytical models predict the critical velocities for lifting and rolling the cuttings particles based on the equilibrium cuttings bed height model and forces acting on a cuttings bed. For vertical sections of the wellbore, the critical transportation velocity showed to be proportional to the terminal settling velocity of the drill cuttings. Hence, we developed two new methods to predict the hindered terminal settling velocity due to the presence of wellbore and pipe walls and particle shape. We then used the Artificial Neural Network (ANN) algorithm and generated two models to predict the terminal velocity of drill cuttings and proppants considering the particles shape and the wall effect. The results of both analytical models and ANN were applied to estimate ECD. In addition, the drilling Mechanical Specific Energy (MSE) was calculated to determine the effect of different drilling parameters on hole cleaning and ECD. A new model was proposed for predicting the ECD in vertical and deviated wellbores that considers fluid and formation properties as well as wellbore and drill string geometry and drilling operational parameters. The developed model was used to study the effect of different drilling parameters on ECD and help engineers to optimize their operational parameters. The final step of this study was to investigate the effect of stabilizers geometry on hole cleaning. A total of more than 30 different designs of straight, straight with offset and helical blades geometries were built numerically and the results were compared. The reliability of the numerical simulation was confirmed against experimental and field data from the literature. The effect of size and shape of the stabilizer blades on the motion of the particles was investigated. Numerical simulation results showed that the straight blade geometry causes less disturbance to the cuttings transportation as compared to the straight with offset and helical blades, respectively.

Download

Share

COinS