American Oil and Gas Reporter - June 2014 - 109

SpecialReport: Artificial Lift Technology

Rod Lift Successful In Horizontal Wells
By Ryan Orr

Design Delivers Benefits
Eliminating threaded connections provides several well-known advantages over
conventional sucker rod strings. Each connection in a traditional sucker rod string
introduces a point of possible failure. Under- or overtightening joints with tongs
may promote fatigue failure, for example,
and manual joint tightening can yield
poorer control of proper makeup torque.
In addition, a conventional rod introduces
greater safety risks because two dedicated
rig personnel are required on the floor at
all times during makeup and breakout.
Continuous rod strings, by contrast,
require only two threaded connections:
one at the top and one at the bottom of
the string. This significantly reduces rig
time for personnel and speeds the overall
deployment of the string.
Another key feature of a continuous
rod string is its uniform body design,
which yields three major benefits. First,
the uniform design helps reduce contact
loads between the tubing and the rod as
it moves up and down during pumping.
The couplings in a conventional rod
string set up concentrated contact loads
with the tubing, which increases the rate
of wear at the contact site. The continuous
rod, by contrast, does not create these
concentrated wear sites, but instead distributes the contact load evenly across

the entire tubing. This dramatically reduces
wear rates and extends the run life of the
entire system, resulting in fewer costly
interventions and a longer life span for
the assembly (Figure 1).
The uniform body design also creates
a larger annular clearance between the
rod string and production tubing, thus
reducing pressure losses and leading to
potentially increased production with the
same surface equipment. A larger and
more uniform annular space also helps
ensure that the flow of the fluid is laminar,
compared with the turbulent flow that
arises in traditional sucker rod strings
with couplings. Eliminating couplings,
centralizers and rod guides also acts to
increase overall system efficiency while
reducing lifting costs.
Finally, the uniform body design delivers a continuous string that is up to 8
percent lighter than a sucker rod string
of equivalent length. This ensures less
loading on the surface unit, and enables
the rod to be deployed farther into the
well for improved pumping efficiency.
Continuous rods offer an additional
benefit over conventional sucker rods in
terms of rod stress and fatigue. Bending
stresses typically are magnified near rodcoupling connections, thanks to the greater
stiffness of the coupling relative to the
rod body. The curvature experienced at
the connections in conventional sucker
rods is magnified up to 10 times, while
the uniform diameter of a continuous rod
ensures that rod curvature equals the curvature of the wellbore.
This has the effect of distributing the
contact load more uniformly at a bend in

FIGURE 1
Tubing

Tubing

t
ac
nt ing
Co ac
Sp

Guide
t
ac
nt ing
Co ac
Sp

EDMONTON-The vast majority of
artificial lift deployments have been in
vertical wells that produce oil and gas
from conventional (i.e., nonshale) reservoirs. The last decade, however, has seen
a dramatic shift to unconventional oil
and gas production from horizontal wells
that stretch a lateral distance of one mile
or more from the wellhead.
These long-distance laterals create
unique production problems, such as
liquid loading in the horizontal section
of the wellbore. Horizontal wells typically
are not truly horizontal, but rather possess
undulating trajectories that create low
spots where water and other fluids can
accumulate.
Removing these fluids is a major driver
for artificial lift in lateral wells, and operators have been deploying various options,
including rod pumps, electric submersible
pumps, and gas lift. While these methods
have all been proven to boost production
in vertical and deviated wells, there is less
practical industry experience in deploying
them effectively for horizontal wells.
Service providers hope to change that
by tailoring lift solutions to meet the specific challenges of horizontal wells so as
to optimize production and extend operating life. One lift method receiving particular attention for unconventional wells
is reciprocating rod lift (RRL) to bring
fluid to the surface through the reciprocating pumping action of a surface pump
attached to the rod string and downhole
rod pump assembly.
Conventional rod lift systems deploy
a sucker rod string consisting of individual
sections that are joined by threaded connections at each end. A conventional
sucker rod string requires a coupling
every 25-30 feet to connect two sections
of rod together. This amounts to hundreds
of connections in many wells.
Continuous sucker rod, which deploys
a continuous rod with no couplings, has
replaced conventional sucker rods in
RRL and progressing cavity pumping
systems in many applications. Continuous
rods are a superior alternative to conventional sucker rods in many production
scenarios.
Among the latest applications of continuous sucker rod lift systems are horizontal wells in the Permian Basin, where

rod pumps are used for artificial lift in
the vast majority of producing wells, and
where the emergence of multiple unconventional oil resource plays continues to
drive a dramatic increase in horizontal
drilling activity.

Sucker
Rod

Concentrated
Contact Load
Concentrated
Contact Load

Concentrated
Contact Load

Uniformly
Distributed
Contact Load
Hole Angle

Continuous
Sucker Rod

The comparison above shows how the contact load is distributed in a conventional
sucker rod system with couplings (left), a conventional system with guides (middle) and
a continuous sucker rod system (right). The uniform distribution of load afforded by the
continuous system extends run life and system reliability.

JUNE 2014 109

American Oil and Gas Reporter - June 2014

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