ABSTRACT
During drilling operations, special attention must be given to
wellbore hydraulics to ensure functional, safe, economic, and
environmentally responsible delivery of the well. The Hydraulics system
shares common purposes with the drilling fluid, it helps to control
subsurface pressures, remove cuttings from the well, clean the bit, size
the pump, increase the rate of penetration, and minimize surge and swab
pressures. Hydraulics optimization is an attempt to maximize the
pressure drop across the bit by minimizing the parasitic pressure
losses. A properly designed hydraulic system will help to improve
drilling efficiency and lower drilling time and cost.
This thesis examines hydraulics optimization using conventional
drilling fluids and nano-based drilling fluids. Nanofluids are
specialized fluids obtained by careful combination of nanoparticles and a
base fluid. The nanoparticles are particles with an average diameter of
less than 100nm. They possess unique characteristics that differentiate
them from microparticles, and make them adaptable to a wide range of
applications. The impacts of rheological models and equivalent annular
diameter definitions on annular pressure loss and ECD were examined for
the conventional drilling fluids while aluminium oxide nanoparticles
were used to examine the influence of nanofluids on the annular pressure
gradient and ECD. A user-friendly computer program was written to
facilitate repeated analyses using any combination of rheological model
and equivalent annular diameter definitions for the conventional
drilling fluids for all ranges of inclination using the Rudi
Rubiandini’s cuttings transport model.
The conclusions drawn are:
1. The Hydraulic Radius Concept, Slot
Approximation, and Lamb’s Method give almost the same pressure gradients
for various rheological models.
2. The Crittendon correlation overestimates the
values of the annular pressure gradient and ECD for various rheological
models. This phenomenon is compounded when the fluid is not in the
laminar flow regime.
3. The increase in density and viscosity of the
nanofluid compared to the base fluid leads to the need for a higher
capacity pump to flow the system. However, using a low density and low
viscosity base fluid, with lower density and concentration of
nanoparticles would reduce the effect of increase in the density and
viscosity of the mixture.
Hole related problems associated with conventional drilling
fluids can be eliminated by the use of nano-engineered fluids.
Nanoparticles can be deplored in high pressure, high temperature (HPHT)
locations. The user-friendly program can be used for a quick evaluation
of the optimization process.
CHAPTER 1
FORMULATION OF THE PROBLEM
1.1 Introduction
Hydraulics system plays an important role during rotary drilling
operations. Proper design and maintenance of this system increases
drilling efficiency (high rate of penetration) and lowers the overall
drilling cost. The hydraulic system is the drilling fluid system in the
wellbore when the fluid is in static or dynamic state. The dynamic state
deals with the fluid movement, pipe movement, and cutting transport.
Drilling is the art and science of making boreholes for hydrocarbon
production, in a manner that is safe, economic, and environmentally
responsible. An efficient hydraulics system is a prerequisite to the
success of any drilling and completions operation. It affects mud
circulation, hole-cleaning efficiency, cementing, rate of penetration
(ROP), and hence total drilling time and cost. Rotary drilling
hydraulics is concerned with proper utilization of the drilling fluid
pump horsepower. It is affected by the drilling fluid properties and
geometry (configuration) of the circulating system.
Rotary drilling involves the circulation of formulated drilling
fluids (called mud), to perform certain functions. The functions of the
drilling fluid include:
1. To maintain well control by counteracting and suppressing the formation pressure
2. To clean the surface of the bit and transport cuttings to the surface
3. To lubricate and cool the drill bits.
4. To hold the cuttings in suspension when fluid circulation is stopped
5. To transmit hydraulic force from the surface through the drill string to the bottom hole assembly (BHA)
6. To enhance wellbore stability
7. To serve as a means of logging and formation evaluation