Non-Newtonian annular flow and cuttings transport through drilling annuli at various angles
Abstract
This thesis presents the results of the investigations in two areas,
i.e. non-Newtonian annular flow and cuttings transport in drilling
annuli at various angles.
In the first part of the thesis, a review of the fundamentals and
the previous studies on laminar concentric annular flow of non-Newtonian
fluids is given at first. Then two parallel theoretical studies are
performed, respectively, on:
a. Laminar eccentric annular flow of power-law and Bingham plastic
fluids. In this analysis, a new method is used which treats an
eccentric annulus as infinite number of concentric annuli with variable
outer radius. The analytical solutions of the shear stress, shear rate,
velocity and the volumetric flowrate/pressure gradient are obtained over
the entire eccentric annulus. This analysis is useful in design of any
engineering operations related to eccentric annular flow such as oil
drilling operations.
b. Laminar helical flow of power-law fluids through concentric
annuli. A group of dimensionless equations are derived in this analysis
for the profiles of the apparent viscosity, angular and .axial
velocities, and for the volumetric flowrate. These equations are
essential when one needs to simulate the helical flow conditions in
various engineering operations. In addition, another group of
dimensionless equations are also derived for pressure gradient
calculations which can be used directly by drilling engineers to predict
the reduction of the annular friction pressure drop caused by drillpipe
rotation during drilling operations. The second part of the thesis is dedicated to the investigations
into the problems directly related to cuttings transport through
drilling annuli at various angles. First, both theoretical and
experimental studies on settling velocities of drilled cuttings in
drilling fluids are conducted using new approaches to account for the
non-Newtonian nature of drilling fluids and for the shape irregularity
of drilled cuttings. Based on experimental results, a generalised model
is developed for calculating settling velocities of variously shaped
particles in power-law fluids. Then, the effects of various parameters
on cuttings transport during drilling operations are analysed based on
the previous and the present studies. After that, an extensive
theoretical analysis for the previous studies on the minimum transport
velocity (MTV) in solid-liquid mixture flow through pipelines, on
initiation of sediment transport in open channels and on MTV for
cuttings transport in deviated wells is presented. At last, theoretical
studies on the minimum transport velocity for cuttings transport in
drilling annuli at various angles are conducted and two parallel general
correlations are developed. When these correlations are experimentally
verified and numerically established in the future, they can be served
as general criteria for evaluating and correlating the effects of
various parameters on cuttings transport, and as a guideline for
cuttings transport programme design during directional drilling.