American Oil and Gas Reporter - July 2015 - 63

they limit the flexibility of CT designs
and available reach. High pressures necessitate larger wall thickness to prevent
CT collapse, require higher circulating
pressures that significantly reduce CT
fatigue life, and increase diametrical
growth on thin wall sections. If the base
case well application assumed very low
pressures, the minimum wall thickness
could have been reduced from 0.156 to
0.134 inches to increase the lateral reach
by more than 1,000 feet. Unfortunately,
this is at odds with most CT operations,
where well production and pressures increase as the job progresses.
The weight a CT string can deliver to
the bit is a significant consideration in
calculating reach. The injector head and
buoyant weight of the CT above the
lateral section apply the force to the bit.
In extended-reach wells, much of the
force applied at the surface and available
tubing weight is lost to tubing buckling
and drag friction on the borehole wall,
especially along the curve section. Consequently, the loss of torque means the
bit likely will not have enough weight to
drill optimally. Bit selection depends on
the application, available WOB, and
motor rpm. Generally, 500 pounds has
been suggested as a working minimum
WOB at total depth.
Tortuosity was analyzed to consider
how continuous minor trajectory changes
in the lateral could impact reach (Figure
6). Tortuosity was assumed to apply to
cased holes, although the values were
generated from a set of open-hole measurements. Because of the limited availability of cased-hole logging data, most
CT force analysis is based on measurement-while-drilling or open-hole logging
runs. This effectively applies open-hole
macro-tortuosity to CT force models.
For this study, continuous lateral
macro-tortuosity had a dramatic impact
on lateral reach. Adding 0.7 degrees of
tortuosity per 100 feet to the base case
reduced reach by 1,123 feet. Increasing
tortuosity to 1.44 degrees/100 feet resulted
in the loss of more than 1,538 feet of
lateral reach. This effect is similar to that
of turns in the lateral. The effective
number of degrees turned at 0.7 degrees/100 feet over the lateral reach of
7,292 feet is nearly 54 degrees more,
while 1.44 degrees/100 feet of tortuosity
over 6,877 feet creates an equivalent turn
of more than 99 degrees.
As the Marcellus case study illustrates,
custom CT string designs that reduce friction in the lateral, increase weight in the
heel, and increase stiffness in the vertical
sections can reduce or eliminate helical
buckling in the lateral to extend the effective
reach of coiled tubing. Using these designs

places the vast majority of force transfer
losses in the vertical section of the horizontal
well instead of the lateral section.
r

Editor's Note: For detailed information
on the methodology and results of the
Marcellus case study of CT reach capabilities referenced in this article, see SPE
173666, a technical paper the authors pre-

pared for presentation at the 2015 SPE/ICoTA Coiled Tubing & Well Intervention
Conference & Exhibition, held March 2425 in The Woodlands, Tx.

Coming In August
COGA Convention Section

engineering from Hartford Community
College, a B.S. in mechanical engineering from the University of Maryland,
and an M.S. in mechanical engineering
from the Massachusetts Institute of
Technology.

PATRICK
KELLEHER

Patrick Kelleher is senior engineer
at Athena Engineering Services in New
Waverly, Tx., where he works with operators, service companies and manufacturers to produce well intervention
and stimulation engineering tools to
model and mitigate issues related to
work string stresses, extended-reach
designs, and material fatigue. Before
joining the company in 2013, Kelleher
served for 11 years in various positions
at NOV CTES, including senior technical
adviser of engineering, project engineer,
and software engineer. He holds a B.S.
in electrical engineering from Texas
A&M University.

IRMA
GALVAN

Irma Galvan is an engineering specialist in coiled tubing string design
optimization at Global Tubing LLC in
Dayton, Tx. Her custom-made CT designs are being used worldwide to improve operational capabilities, service
life and horizontal reach in unconventional CT operations. Before joining
the company in 2012, she was a CT engineer in oil field services at Archer,
and an automation and control systems
project engineer at AMI GE. Galvan
holds a B.S. in electronics and automation engineering and an M.S. in manufacturing engineering from the Universidad Autónoma de Nuevo León.

KEN
NEWMAN

Ken Newman is founder of Athena
Engineering Services, which provides
consulting and software development
for well intervention and drilling. He
is also founder of Cormorant Engineering. In 1993, Newman founded
CTES LLC and served as its president
until it was sold to NOV in 2007. After
beginning his career at as a scientific
programmer at NASA, Newman served
as a turbine and compressor design
engineer at GE and at Schlumberger,
where he managed the company's worldwide CT business. He holds an A.S. in

STEVE
OPEL

Steve Opel is software manager at
NOV CTES in Conroe, Tx. With 20 years
of experience at the company, he previously served as a senior software engineer.
Opel holds a bachelor's in computer
science from the University of Houston.
JULY 2015 63

American Oil and Gas Reporter - July 2015

Table of Contents for the Digital Edition of American Oil and Gas Reporter - July 2015