Rotating off bottom
Sinusoidal buckling (All operations)
Helical buckling (rotating)
Helical buckling (non-rotating)
Effective tension (kip)
800.0 1,200.0 1,600.0
Mean sea level
Previous casing shoe
Effective tension by measured depth
to evaluate buckling risk during deployment.
potential areas of improvement, increasing the zonal density can help
sustain high production levels for longer periods and also minimize
water or gas breakthrough by shutting in trouble zones. Another
possibility is using multilateral technologies. Multilateral technology
has evolved and can be combined with sand control systems, such as
gravel packs and frac packs, and can be integrated with a multibranch
control coupled with multizone ( 3+) intelligent completions.
Additionally, the industr y is adopting reliability language and analy-
sis methods for completions hardware. Many efforts are in progress
among operators and service companies to determine a baseline for
reliability metrics, and also normalize the reliability language and
concepts among stakeholders. For this effort, collaboration with other
industries that are more advanced in this field is crucial. This is a step
that must be taken and the prize for the industry is high. With fewer
wells and higher production from each well, the economic impact of
failure can exceed hundreds of millions of dollars in production losses.
The control system used for this campaign was direct hydraulics.
This can be considered the simplest method to control the intelligent
completion because of its flexibility, ease of understanding, reliability,
and extensive track record. For the applications in the presalt case,
transient pressures due to control system actuation play a significant
role in the time necessary to manipulate the intelligent completions.
The pressure source is normally supplied at the wellhead with accumulators. Even in this scenario, the pressure has to travel through
more than 3,000 m of 0.152-in. internal diameter line. This slows the
response time of the ICV significantly.
Additionally, no downhole sensors that allow for tool face pressure
measurements or direct position reporting for the ICV were installed.
This lack of instrumentation has hindered the troubleshooting and
root cause determination in some isolated instances, making it very
difficult to develop and apply corrective measures. Considering also
that only two intervals were accommodated during the planning phase,
the number of control lines was not a restriction. Producer wells also
require chemical injection systems with dedicated lines to be deployed
alongside the intelligent completion equipment, adding
a significant number of lines. However, some presalt
reservoirs may require additional compartmentalization
to better manage water or gas breakthrough throughout
the life of the well. Because of some wellhead design
considerations, increasing the number of available
penetrations is very difficult. To date, this has been
limited to injectors where the chemical injection system
is not required. Nonetheless, if new presalt wells require
additional compartmentalization, then a new control
system should be considered. Implementing a multiplexed system using downhole electronics to control
the ICV movement is the best solution. In addition to
improved control and faster response time, bringing the
electronics downhole allows for improved monitoring
of the completion and can be used to facilitate deployment of new reservoir monitoring technologies. The
system can evolve to be a single control scheme for all
the remotely actuated valves in a well, meaning that
chemical injection valves and even downhole safety
valves could be controlled safely by the same system.
To effectively implement this vision, reliability becomes
a significant concern and the qualification process of
such a control system must be robust to quantify the
controller for the expected life of the system.
Multiplexed control systems are normally divided into
two categories: the hybrid, which uses electric cables for
communication and powering electronics and sensors
downhole, but uses hydraulic fluid as a motive force for
the ICVs. This system provides a simple, but elegant
solution for the downhole power system. The second system, often
referred to as an all-electric system, is in fact either electro-mechanic or
electro-hydraulic, with a single electrical interface at the wellhead. The
electric system uses the electric power for communication, and actua-
tions downhole. The main difference resides on the wellhead interface.
For hybrid systems, the wellhead needs to provide both hydraulic
lines and an electric line. A downhole electro-hydraulic system has
a built-in hydraulic power supply downhole to move hydraulic ICVs.
The electro-mechanical system converts electric power to mechanic
movement to actuate downhole valves directly. Evaluating existing
technologies, hybrid systems and electro-hydraulic systems tend to
provide more force to the ICVs, allowing them to more easily overcome
eventual inorganic deposition when compared to electro-mechanic
systems. Also, bringing more equipment downhole leads to a reduc-
tion in reliability if the system architecture does not incorporate
redundancy. Nevertheless, eliminating the need for such hydraulic
systems in the wellhead can significantly affect the economics of a
field when compared on a system level because a purely electrical
wellhead interface can significantly reduce the capex necessar y when
compared to an electro-hydraulic multiplexed wellhead.
This also follows the trend to increase the activity level at the seabed,
including boosting, separation, reinjection, etc. Those technologies, when
applied, will require a more refined control of the well and can require
additional downhole control of the flow behavior. These concepts and
trends will be most easily adopted when electric downhole control systems
are developed and meet a well establish system level reliability target.
Also, scaling and organic deposition pose a significant risk for the electric
wellhead because there is not an available technology that is as effective
as continuous injection of scaling inhibitor by means of hydraulic capillary
tubing from the wellhead. If chemical injection means are necessary, this
might modify the economic balance of the preferred solution.
Lastly, all the benefits associated with the usage of intelligent comple-
tions: reduction of unwanted fluid production, increased ultimate recovery from fields, avoidance of intervention, etc. requires actual decisions