Zonal Isolation in a U-shaped Well using Coiled Tubing and Well Tractor®
- T. Saelensminde (Hydro O&E) | H.F. Schjott (Hydro O&E) | H.M. Koldal (Schlumberger) | T. Skeie (Welltec) | T.O. Meberg (PI Intervention)
- Document ID
- Society of Petroleum Engineers
- SPE/ICoTA Coiled Tubing Conference and Exhibition, 23-24 March, Houston, Texas
- Publication Date
- Document Type
- Conference Paper
- 2004. Society of Petroleum Engineers
- 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 2.2.2 Perforating, 5.2.1 Phase Behavior and PVT Measurements, 1.6 Drilling Operations, 1.6.9 Coring, Fishing, 4.1.4 Gas Processing, 3.3.1 Production Logging, 2 Well Completion
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An 80m long retrievable "one-run" straddle assembly was successfully installed in order to shut off a gas breakthrough in the 130 degrees deviated reservoir section of a "U shape/Fish hook" sub sea oil producer in the Njord field. Coiled tubing with an internal electric line in combination with a tandem fluid driven tractor was used to convey the straddle assembly.
Njord is a sub sea completed oil field operated by Hydro, located offshore northwest Norway. Njord "A" is a floating drilling and production unit. The well is an oil-producer in the Tilje formation, completed with a 7-in" production tubing and a 7-in" perforated liner (Fig 1&2).
The objective was to isolate selected intervals in the reservoir section at 130 degrees inclination in the "toe" of the well in order to reduce the gas to oil ratio (GOR). The chosen method was to install a purpose designed straddle packer assembly utilizing coiled tubing and tractor.
Based on computer simulations, it soon became clear that it would not be possible to reach the desired depth using coiled tubing and conventional "extended reach" techniques alone.
Computer simulations using reduced friction coefficients and/or altered fluid densities only improved results marginally and indicated that the 2-in" (optimized taper) coiled tubing at best would go into a lockup 174 meters away from target depth. Computer simulations using 2-3/8-in" coiled tubing also showed similar results with a little added penetration. CoilCAT* software was used for modeling of tubing forces in the well.
Based on these simulations a coiled tubing tractor (Fig 3) was recommended to extend the conveyance reach to the target depth. The tractor supplier stated that 3000 lbs pull force would be available from the fluid driven coiled tubing tractor. Computer simulations performed using 3000 lbs (13kN) pull force on the straddle assembly in combination with the available coiled tubing push, indicated that bottom of well could be reached. (Fig 4 presents plot of simulation result with and without tractor). This would be the first time electrical tools were used in combination with the fluid driven tractor.
A new adapter sub was required to use tractor with e-line integrated for surface data readout. The adapter design was based on an existing coiled tubing cable head design with added functionality to allow higher flow rates directed down through the emergency disconnect section instead of the normal circulation path into the coiled tubing annulus.
A test of the new cable head adapter with tractor was performed onshore to verify the flow-through characteristics, disconnect functionality, tractor performance and electrical integrity. The measured parameters from the test were later used when setting up the tools and tractor for the operation.
To be able to run the required tool string (Fig 5) for the straddle packer assembly the tractor top connector and compensator were re-designed.
Special attention was given to the connection between the setting tool and the casing collar locator. On standard tools, this is a relatively weak connection, mainly meant for tools to be run on wireline. In order to ensure that tools were not accidentally lost in hole, the top adapter thread on the setting tool was changed to a CAL-B connection, which is larger and will give more resistance to bending forces that would occur during the run in and setting operations.
A tandem tractor configuration was required to achieve required pull force based on the available flow rate.
The packers at each end of the straddle packer assembly (Fig 6) were custom-made to special outer diameter of 5.5-in" in order to pass a 5.75-in AOF nipple and several doglegs in the well. The internal diameter of the packer setting area was 6.094-in. It was identified that the bottom hole assembly could become heavy and therefore difficult to get to the target depth. Based on simulations, a 3-1/2-in" 9.2pounds per foot spacer pipe was selected.
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