New tools and technology for the offshore industry
Clear WELL Oilfield Solutions
Mineral scale deposition is a common yet
critical flow assurance challenge for onshore
and offshore oil and gas wells. Scale deposition is responsible for multiple production and
integrity challenges: wellbore and pipeline
restriction; blocking valves and pumps, reducing reliability, constricting the operational capability of plant and equipment, and impacting
integrity with under-scale corrosion.
Increased water produced rates along with
higher gas production are worsening current
scale problems and preventative action must be
taken. Common solutions include implementing mechanical intervention techniques, such
as milling, drilling, or jetting. These methods
can be successful ways to remove scale but
often prove costly and effectiveness is patchy.
A more cost-effective proven solution is using
chemicals to dissolve the scale; however, success is dependent on the type of scale and the
Scale remediation is costly; mobilization of
equipment, direct rental costs, manpower and
deferred production need to be considered.
Operators try to avoid remediation for as long
as possible and scale prevention strategies are
a proven way to do this.
Prevention of oilfield scaling has been
traditionally managed using specialty chemicals – scale inhibitors. Treatment on process
systems downstream of the christmas tree can
be efficient but because temperature, pressure,
and mineral content constantly fluctuate, establishing the amount of inhibitor required can be
tricky and constant monitoring is needed.
An alternate method of preventing scale below the tree without intervention would deliver
significant value to installation operators by
removing intervention cost, intervention risk,
and no longer deferring production.
Pulsed radio frequency
for scale control
Clear WELL has developed and deployed a
chemical-free scale control technology which
uses a radio frequency energy pulse to control
mineral deposition and consequent scale
The surface mounted device is connected to
the well and an electromagnetic pulsed current
is injected along metal pipework to the target
well tubulars. This signal induces homogenous
mineral crystallization within the well fluids
so that scale remains in the fluid stream and is
carried downstream with the produced fluids,
It is estimated that
some 70% of the scaling
ions form homogenous
crystals and cause no
problem in production.
It is the remaining 30%
of scaling ions which
crystals and attach to
the production system
that cause the problems.
The Clear WELL system
changes that balance to
give enough energy to
precipitate a far higher
proportion of homog-
Parts of the North Sea, such as the Danish
sector, present region-specific challenges such
as high produced water calcium concentration, which can lead to carbonate scaling. This
proved to be the case for a Danish operator’s
installation where production comes from a
fixed platform in 60 m (197 ft) water depth.
Production commenced in 1999 with water
injection starting in 2000. The operator had
a particular challenge with one well, where
increasing the pressure drop from reservoir
to wellhead in order to increase production
induced carbonate scaling in the well.
During a well intervention in 2011, a restriction was tagged and subsequently milled clean.
To prevent the formation of mineral scale,
the well was operated within a scale free
‘envelope’ derived from an analysis of the pressure, temperature, water composition, and well
architecture. The effectiveness of this envelope
was monitored using regular VLP analysis
modeling to identify increases in the calculated
friction coefficient to ensure scale build up was
identified before a resulting loss of production.
In 2012, an increase in the friction coefficient
and observations in the modeled gas lift orifice
size pointed to a scale build up in the upper
completion. An acid wash was carried out and
the friction coefficient was reduced.
Restricting production to prevent scale
deposition is an expensive mode of mitigation; production losses are estimated at 200
b/d. Committed to maximizing the value of its
assets, the operator decided to investigate alternative means of mitigating scale deposition.
To remove the need for intervention and
assure flow, Clear WELL
was introduced as a scale
control technology on a
wellhead to treat the pro-
duction tubing. To evalu-
ate performance, multi-
rate production tests were
performed to establish a
baseline before the new
unit was installed, with
additional tests running for a minimum of one a
month thereafter. The operator used vertical lift
performance (VLP) analysis software to track the
well’s performance and predict and plan when
an intervention treatment would be needed.
This same method was used for flow assurance
measurement with the new unit deployed.
The first set of well test data was generated
after 10 weeks and indicated no more than a
negligible increase in the friction term, well
within the range defined as successful. The
next test, four months later, again showed that
the friction terms had not changed significantly.
This led to the conclusion that there had been
no changes in eight months, and that the elec-
tromagnetic signal generating unit was success-
ful in mitigating against the build-up of mineral
scale. Well production continued at higher
drawdown without intervention required.
Upon completion of the nine-month test,
this method of preventing scale deposition was
deemed effective. The unit controlled scale depo-
sition protected the production system, increased
reliability of gas lift valves, ceased tubing acid
washes, and enhanced production. The unit al-
lowed production of an additional 200 b/d without
the requirement of well intervention. The previ-
ous cost of annual intervention on the installation
was around $4 million, which is equivalent to 10
times the cost of scale control chemicals. The unit
is still in use with only one intervention treatment
required in the four years since it deployed.
Setting clear success criteria and being able
to measure these was a critical part of demon-
strating the effectiveness of the unit. The instal-
lation now operates multiple Clear WELL units
to control mineral scale, with plans to increase in
the future. •
Electromagnetic signal generating unit improves scale prevention
Clear WELL is a surface
mounted device that is
connected to the well
and an electromagnetic
pulsed current is injected
along metal pipework to
the target well tubulars.
(Image courtesy Clear-WELL Oilfield Solutions)