English Edition (6 MB pdf) - Saudi Aramco

Fig. 8. Powered rotary steerable system.
BIT DESIGN TOOLS
To obtain the maximum potential from the PRSS, it was
necessary to design a 12” PDC bit to match the system to get
the proper gauge pad geometry (thickness, wrap and reinforce -
ment), and to provide adequate cleaning and sufficient wellbore
contact to limit over engagement and undercutting of the
formation. In addition to the gauge configuration, which must
match the PRSS for maximum tool steerability, the process of
designing a bit to drill directionally through this tough interval
provided a series of challenges that were addressed during the
bit optimization process. The ultimate goal was to create a bit
with the right profile and optimum cutting structure, and that
provided efficient cleaning and adequate protection; it must also
be steerable, stable, and durable, with a neutral walk tendency.
To meet these challenges, several bit design analytical tools,
including IBitS, Direction by Design (DxD), and computa -
tional fluid dynamics (CFD) software, were used emphasizing
bit steerability and stability.
IBitS
IBitS software is the bit designing tool platform that enables
the bit designer to generate the cutter layout and to simulate
the forces to which the bit will be exposed under specific
drilling parameters. Depending on the cutter geometry and
space position on the bit face, this tool can be used to
calculate the torsional, axial, and lateral forces of each cutting
element showing the total bit force imbalance as output. Force
imbalance provides a good measure of the bit stability
through homogenous intervals. The IBitS tool can also be used
to calculate the bit force. It obtains low values by manipu -
lating the cutter layout and enables increased bit energy levels
by evenly distributing cutter forces. It also includes the
transition drilling model, which helps to identify possible
areas of impact damage when the bit moves from soft to more
competent formations.
Direction by Design
Direction by Design software is a high-technology analytical
tool that provides advanced bit design engineering to optimize
directional performance. It provides a powerful means of
optimizing the matched bit design for the specific directional
application and drive system. The software eliminates lengthy
and expensive trial-and-error bit design, making it possible to
define the relationship between specific bit design changes and
their full effect on the directional deliverables. This tool
enables the bit designer to compare the performance of
various bit designs before they are run. It was a key factor in
reducing the learning curve during this optimization process
of the 12” PDC bit used with the PRSS in the Ghawar field.
The new DxD tool is based on a mathematical model 3 .
Computational Fluid Dynamics
This type of analyses was also performed during the bit
optimization process to ensure that the new bits had the
correct hydraulic configuration. Proper bit face cleaning is
critical through the Sudair formation because of the reactive
shale that can cause bit balling situations.
CUTTER TECHNOLOGY
During the last decade, the development of new PDC cutter
technologies was based on improving the abrasion and impact
resistance by using various components and interfaces with PDC
table substrate geometries. In many applications, including the
12” directional section in the Ghawar deep gas wells, the dull
grade analyses showed what was believed to be impact damage
because the PDC cutters were broken or chipped when they
SAUDI ARAMCO JOURNAL OF TECHNOLOGY SUMMER 2010 49