New technology saves drowning gas wells

Have you ever wished you could deploy an electrical submersible pump (ESP) through tubing? The possibility was broached by Ziebel AS at the recent International Coiled Tubing Association (ICoTA) meeting in The Woodlands, Texas. Officials from Ziebel were in The Woodlands to accept the ICoTA Best New Technology Award for its innovative Z-System intervention technology.

Artificial lift applications
Parallel to the Z-System development, Ziebel’s engineers are developing a slim-profile downhole pump for gas well dewatering that is 1.8-in. in diameter, 30 ft (9.1 m) long, and can be deployed to 10,000 ft (3,000 m) in bottomhole temperatures up to 250°F (120°C).

The lightweight reel can store 32,500 ft (10,000 m) of carbon fiber rod containing five fiberoptic cables encased in a steel tube.

Because its diameter is small, the pump can be run through 23/8-in. tubing. For wells without packers, it can be powered by a 0.7-in. electrical cable. Water can be pumped to surface through the tubing, while gas is produced up the annulus.

For applications with packers, the pump can be deployed with a 1.5-in. umbilical. In that case, the umbilical also is the conduit for the pumped fluid, with the gas being produced up the production tubing.

The 1.8-in. diameter pump has the capacity to lift 120 b/d of fluid using approximately 25 kW of surface power. The linear motor is driven and controlled by a surface variable frequency drive.

For oil well production, an advanced high-speed rotary permanent magnet motor is being developed, together with a high-speed centrifugal downhole pump, for oil well production through 3½-in. tubing. The 2.8-in. diameter pumps are 30 ft long, and can be deployed on wireline type cable and a lightweight spooling unit. The larger pumps have a capacity of 1,000 b/d of liquid from 10,000 ft. They can be suspended in the production tubing on their own reinforced electrical cable.

Potential advantages include reduced electrical power equipment and eliminating the workover unit or rig by not having to pull the tubing.

Z-System enables new techniques
The key that opens so many interesting possibilities is in the form of a 0.59-in. diameter flexible carbon fiber rod stored

An artist’s sketch illustrates typical “‘tween-decks” rigup for offshore platform use where height limitations may exist.

on a 32,500-ft (10,000-m) capacity steel reel. Deployed like coiled tubing using an injector head, the rod is stiff enough to be pushed to bottom, but lacks the helical “set” that causes coiled tubing to lock up in lateral sections. Inside the carbon fiber rod is a stainless steel conduit containing five fiberoptic cables. Thus, fiberoptic telemetry and sensors can be deployed to conduct intelligent operations downhole. These include point pressure and temperature sensors and telemetry functions, as well as distributed temperature sensing (DTS) and distributed acoustic surveying (DAS). The reel can be deployed from land, a floating vessel or platform, and even from a subsea location, operated by a light well intervention vessel.

The carbon fiber rod can be used as a mechanical deployment device, or if real-time monitoring is required, it can use its fiberoptic capabilities to telemeter downhole data to surface from a variety of sensors. Deployment is achieved through the use of a lightweight spooling unit with a mast or derrick truck. No pulling unit or workover rig is required.

Using the carbon fiber rod to convey downhole gauges and sensors is easy and economical. For example, rigup/rigdown time is about 1/10 that of a typical wireline system with full lubricators, or that of a coiled tubing unit. Jobs have been performed with rigup taking two hours vs. 24 hours, and with five workers vs. 10 to 12 workers at the well site.

The system can deploy all types of production logging tools (PLTs), singly or in combination. Because of the rod’s natural stiffness, it can get to bottom in a lateral well without a tractor. Alternatively, the rod can convey a variety of fiberoptic sensors, including DTS and DAS. When used in this mode, there is no bottomhole assembly. There is only a 2-ft (0.6-m) bullnose that contains the point sensors and terminations for the fibers. This makes it adaptable to getting information out of horizontal wells where wireline and coiled tubing may be highly challenged. The DTS/DAS gives engineers a look at the entire reservoir section at once so temperature anomalies can be quickly detected and measured.

Measurement resolution and accuracy are precise. For example, temperature changes as low as 0.018°F (0.01°C) can

An artist’s conception of a subsea deployment shows the reel and injector head are lowered and latched onto the wellhead from a light intervention vessel, which carries the surface controls and data recording devices.

be measured over 3.28 ft (1 m). Because of the rod’s slim profile, the system is minimally obtrusive to flow measurements. For long-term reservoir monitoring applications, the carbon fiber rod can be parked in the well for weeks or months at a time. It also can be permanently installed.

Spooling units require little headroom – 10 ft (~ 3 m) – so the units can be deployed between decks on offshore production platforms. Because an injector head is used, no lubricator is required, as is the case for wireline systems. The slim rod can traverse changes in diameters of downhole tubulars with ease.

In an exclusive interview with David Ottesen, CEO of Ziebel AS, based in Tanager, Norway, Hart learned that the second-generation Z-System will include an electrical cable alongside the fiber conduit so electrical downhole manipulation tools can be operated and monitored via two-way communication with surface controllers. Ottesen said that presently his team is looking at the possibility of conveying perforating guns using the system, but that considerable work remains to determine how to deal with the mechanical shock when the gun detonates. The objective would be to develop a ruggedized system that could withstand the detonation and make continuous measurements throughout the sequence.