Intelligent completion system nears deployment

Intelligent completion devices are being developed for downhole applications, especially for deepwater subsea completions, and wells with complex geometries and multilateral boreholes.

One such system (Fig. 1 [74,441 bytes]), designed by an alliance of Baker Oil Tools and Schlumberger Wireline & Testing, integrates downhole pressure, temperature, and flow sensors with a remote operated, fully adjustable choke for flow control.

The alliance indicates the system:

Reduces and eliminates costly subsea well interventions
Provides selective and remote control of drawdown and production rates of individual zones in producing wells
Provides selective and remote control of downhole water and gas injection into individual zones
Optimizes stacked/commingled production and injection
Prevents zonal crossflow in multilateral and horizontal wells
Increases reservoir knowledge and management capability.

System components

As described by the alliance, the main system components include a surface unit, tubing hanger, electrical cable, special packers, remotely operated flow-control devices, and sensors to measure pressure, temperature, and flow.

The alliance's surface unit provides real-time control of downhole flow-control devices while managing data received from the downhole sensors. The unit also can interface with supervisory control and data acquisition (scada) systems and can control multiple wells. The alliance plans for one version of the control unit to be installed in a subsea control pod.

Electric conductors (Fig. 2 [45,178 bytes]) provide the conduit for transmitting signals and power between the surface unit and downhole sensors and flow control devices. The two 18 AWG copper conductors, forming a twisted pair, are encapsulated in an epoxy-filled 0.25-in. metal tube. The outer metal jacket serves as a mechanical protector for the conductors as well as the electrical ground.

The alliance can provide the metal tube in several corrosion-resistant materials and also has alternatives for the epoxy fill.

The alliance designed special hydraulically set packers for the system. These packers are conveyed on the completion tubing and have no packer body movement while being set. They provide a penetrator-less feedthrough for the 0.25-in. electrical cable. The packers can be released with a retrieving tool run on coiled tubing.

The alliance's remotely operated flow-control device (Fig. 3 [89,703 bytes]) incorporates an electro-mechanical adjustable choke, and multiple pressure/temperature and mass-flow sensors. The alliance based the choke design on sliding sleeve technology with nonelastomeric sealing. The surface unit can precisely adjust the downhole choke.

Multiple flow-control devices can be run to provide zonal control and monitoring. When multiple devices are included, each device is independently addressable.

The alliance has tested the choke for erosion resistance at flow rates up to 25,000 b/d and with up to 3% solids.

In case the electric choke actuator fails, the alliance has designed the choke to be manually operated with a standard shifting tool run on coiled tubing.

The downhole flow-control device can included three high-precision quartz pressure gauges. Two gauges measure tubing pressure and one measures the annulus pressure.

Mass flow is computed from the pressure measured by the two gauges placed at the throat of a Venturi. The design allows the Venturi to be retrieved by conventional coiled tubing or slickline operations.

The annulus pressure gauge enables continuous sandface pressure monitoring, regardless of the choke size. Therefore, it provides both upstream production flow pressure, downstream injection flow pressure, and storage-free pressure build-up readings when the zone is shut in.

Reliability

The alliance says it used an innovative approach based on reliability growth testing in designing the system. The approach identifies all potential weak points and their impact from the operator's viewpoint. This is important because the system has to work with multiple components provided by different suppliers. Such components include downhole completion equipment, the subsea pod, the umbilical, and the platform and data management systems.

The first field trials of the system are scheduled for later in 1998.