The ability to manage each producing zone in a multizone completion pays big dividends. Intelligent well systems (IWS) are needed to thoroughly analyze production dynamics, then act to optimize them.

Not too many years ago, operators with multiple producing horizons had about three completion choices, none of them good. They could complete each zone in sequence, starting from the bottom and working toward the surface in a series of plug-back workovers. They could complete two or more zones below the packer and commingle the production through a single tubing string. Or, they could attempt multiple completions, each produced through its own tubing string, and isolated by increasingly elaborate packers. One such well actually had a quintuple-string completion. Getting all that hardware into the well without incident required a PhD. in plumbing and an unusual amount of luck. Each option had several disadvantages.

Intelligent well systems, as the name implies, provide downhole production monitoring using reliable permanent sensors. Depending on the complexity of the production scheme, varying degrees of information may be required to manage the reservoir. Today, operators can install temperature and pressure sensors as well as a distributed temperature array that uses fiber optics and provides a real-time instantaneous temperature profile over the entire length of the fiber. In addition, downhole multiphase flowmeters are available as well as seismic sensors. Data from these sensors are telemetered to surface, often using a single conductor, where they are input to dynamic reservoir models. Powerful reservoir management simulators can turn the data into timely information to enable production decisions.
The other half of the IWS picture is control. Not only can operators find out what's going on in their reservoirs, they can do something about them. A wide array of downhole flow-control valves is available. Some are electrically actuated, others use hydraulics. Some valves are simple on/off devices, others act as variable chokes with the most sophisticated being infinitely variable over the full range from open to closed.

The ability to control production from an individual completion can virtually eliminate interventions and delay the requirement for workovers. The ability to understand production dynamics enables operators to manage production over the life of the asset leading to optimized rates of return, increased recovery factors, control of gas and water production, reduced surface facilities and lower well costs. And with zonal monitoring, commingling, once plagued with uncertainties, could be effectively managed.
How real are the benefits?

Early in the development of IWS, Brunei Shell installed a low order hydraulic system to test its number one driver, reduced interventions. Even with the rudimentary system, Brunei Shell was able to project potential savings for the Shell Group of between US $500 million and $1 billion over a 10-year period. Shell developed a screening methodology to select the most viable candidate wells and reservoirs for IWS solutions. In April 2001, Shell Technology Ventures and Halliburton Energy Services formed a joint venture company called WellDynamics with the goal of maximizing the potential of IWS by combining complementary technologies of the two companies. WellDynamics engineers can help operators screen their assets for IWS opportunities, design the IWS completion and install it. Most operators are now approaching IWS technology as an investment opportunity and are undertaking project screening studies to evaluate economic benefits before submitting their proposals to the normal corporate value assurance process. Screening can take as little as half a day for a single well to several months for full field development optimization. A valuation tool is then used to match the best technical solution to the individual customer's economic situation and needs. As a result, customers have a high degree of confidence that the proposed solution is right for their reservoir, and right for their company, before the completion is implemented.

Choose your weapons

Customized solutions are possible due to the wide range of devices to monitor and control wells. WellDynamics uses an integrated multidrop communication, control and acquisition system called SCRAMS. The heart of its system is the digital hydraulics downhole decoder that allows several valves to be controlled hydraulically using the minimum number of control lines. The decoder receives and interprets a unique series of pressure pulses for each action required, then enables a hydraulic sequence to be performed. For less demanding completions, there is the direct hydraulics system that uses two control lines, one for opening and one for closing connected directly to the valve. Multiple valves can be operated using a common close line, thus three valves require four lines and so on. A mini hydraulics installation is a pure hydraulic system that uses a single line to open and close each device to be controlled. A small amount of hydraulic fluid vents to the production tubing with each actuation. A variety of valves is available as mentioned earlier. The most sophisticated is the infinitely variable interval control valve. This device has electrical or hydraulically actuated versions, and is driven by a SAM sensor actuation module that contains

the pressure and temperature gauges. Incremental control is provided by Accu-Pulse, which routes a predetermined volume of actuating fluid to shift the valve slightly each time it is pulsed. As many as 100 increments are possible, which amounts to virtual continuous choke control. A high-performance interval control valve boasts metal-to-metal seals for demanding conditions. It can be provided in an on/off configuration or in a stepped variable configuration. Communication with downhole sensors and valves is enabled by installing a flat pack umbilical to the tubing string as it is run. Flat packs can be custom-made and contain combinations of hydraulic lines, electrical power and data conductors and steel bumper lines that provide tensile strength as well as guard against crushing. All lines terminate in a hydraulic systems cabinet at surface. This device contains a rack for each well control module as well as the hydraulic pumps and controls. Additionally, the surface control unit can be operated remotely using a secure Internet connection. Its modular design permits expansion to control as many wells as desired.

Reliability is key

Not only must an intelligent well system provide timely and accurate data over the life of the well, but its valves must operate reliably when they are commanded to do so. This means that a downhole choke may lie dormant for a year or two before reservoir conditions call for its position to be changed. Some prudent operating procedures such as periodic exercising of each valve can go a long way toward assuring they will be ready to operate on command. In addition, redundant electrical and hydraulic lines ensure the available options in operating the system. WellDynamics uses a SegNet communications protocol that improves reliability by providing the capability to steer around any electrical or hydraulic failure. In addition, critical components are cycled thousands of times during acceptance testing to ensure they will perform reliably in the well.

To accommodate more sophisticated designs, a fiber optic disconnect head (FOODH) has been developed that allows the upper completion to be removed without disturbing the lower completion. This
could occur, for example, if an electrical submersible pump (ESP) required servicing during its life. The pump and the FOODH could be pulled, leaving the hydraulic valves and decoders in place, then reconnected after pump servicing. Four hydraulic lines can be disconnected/reconnected and a fiber optics sensor package can be reinserted through the tool's bore.

Complex solutions

IWS systems are the key to enabling complex multilateral completions. Each branch of a multilateral well can be controlled with all options open - multizone completions,

with separate or commingled production, artificial lift completions or combination producer/injector wells. Over time, IWS systems will pay for themselves many times in these situations because they allow the well to be operated under optimum conditions over its lifetime without costly interventions.

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