Coiled-Tubing Telemetry Intervention in Shut-In Conditions
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When a new horizontal well in Asia was incapable of unassisted flow, coiled tubing (CT) was selected for the perforation and stimulation intervention. Mechanical isolation was required to ensure that the stimulation fluids entered only the new zones. Accurate depth control was required for three runs: setting two composite bridge plugs (CBPs), deploying CT-conveyed perforating guns for opening two intervals, and milling out the two CBPs without taking returns to surface. For the first time, a tension, compression, and torque (TCT) subassembly was used to improve the milling operation.
CT telemetry (CTT) systems have proved to be effective in enhancing operations by providing real-time monitoring of downhole data including depth, pressure, temperature, force, and torque. For data transmission from downhole sensors to surface, these telemetry systems can use either insulated wire or optical fiber. With insulated wire, power can be transferred from surface to the downhole sensors. With optical fiber, downhole batteries are required in the bottomhole assemblies (BHAs) to power the downhole sensors. When compared with braided systems using the 0.125-in. insulated electrical cable (Fig. 1 above), the main advantages of the CTT system are its low weight and the fact that balls can be pumped through the CT. A small wire has a minimal effect on the CT cross-sectional area. Balls up to ⅞ in. in diameter do not become stuck, and there is a minimal effect on the CT fluid pressure drop.
Description of the Wire CTT System
The 0.125-in.-wire CTT system has several components, such as surface hardware and software; the ⅛-in. insulated electrical conductor inside the CT string; and a BHA with different sizes, including 2.125, 2.875, and 3.5 in. The 2.875-in. BHA with three subassemblies is shown in Fig. 2.
The 2.875-in. sensor assembly has the following components:
- Tubing end connector
- Head that secures the wire downhole, seals the exterior of the wire, and provides downhole electrical connection
- 0.875-in. ball-operated wire-release mechanism
- Double-flapper check-valve housing
- Electronic module with a casing collar locator (CCL) and
- pressure/temperature sensors (internal/external)
- Motorhead section, where a ¾-in. ball-release mechanism is located followed by a circulating port activated with 0.625-in. balls
- Burst-disk section enabling 0.5-in. balls to pass through to activate downhole tools
The logging adapters in all three sizes are designed to connect any logging tools with the 0.125-in. wire. The adapters are crossovers, providing electrical connections to the logging tools, and are compatible mechanical threads for the electric tools. The adapters also contain separate burst disks to open circulating ports. Camera adapters connect one or two cameras with front and lateral views. The camera adapter allows fresh fluid to be pumped through to wash the camera lenses and improve downhole images. Downhole data and images are transferred through the 0.125-in. wire to surface. The wire exits the CT string through the bulkhead. A slip collector provides electrical connection through the rotating drum to the surface data connection and power system. Finally, the data are displayed on the monitors at the surface and can be interpreted in real time.
Description of the TCT Subassembly
The TCT subassembly enables real-time monitoring of axial forces and torque exerted on the BHA. This subassembly consists of foil strain gauges that are glued with epoxy resin onto the inside wall of the pressure housing. Five printed circuit boards are mounted on the outside of the annular ring of the atmospheric chamber. The atmospheric chamber has a central flow passage such that the electronic component must fit on the annular ring mounted inside the module housing. The TCT electronics module uses predefined tables for pressure and temperature compensation.
Operational Benefits of the TCT Subassembly
- Real-time torque readings help the CT crew optimize the weight on bit (WOB) to extend the mill and downhole motor life. In addition, torque data can be used to differentiate between several milled materials.
- TCT data can be used to confirm the BHA is latched to a fish. The data can also be used to verify that a downhole jar has been successfully activated.
- Receiving the TCT feedback in real time can help monitor the static and dynamic coefficients of friction, understand how well a specific extended-reach technology is working, and optimize its effectiveness.
- Real-time torque and compression data enable more-effective identification of the top of sand in deviated wellbores and differentiation between friction lockup and wellbore obstructions, reducing operational time and stuck-pipe risk.
- Real-time tension and compression data enable application of the specific WOB required for inflatable devices. Personnel can also ensure that WOB is neutral when setting casing patches and can see if downhole sliding sleeves were properly closed while pulling out of hole (POOH).
Milling in shut-in conditions has become a conventional CT operation in this field, mainly because of operator limitations in handling water-based sour fluids at surface. After the arrival of the TCT subassembly on location, a CBP milling operation was performed using the CTT system and the TCT subassembly. To describe the benefits of adding a TCT sensor into the milling BHA, a case history is offered here; another is discussed in detail in the complete paper.
Well A. This well was stimulated with the multistage selective acid-stimulation technique. Because of the unexpected high viscosity of the formation oil, the well could not flow without assistance (i.e., nitrogen lifting). A CBP was placed at 5293 m measured depth (MD) at the heel of the horizontal section in 4.5-in. tubing (3.826-in. inner diameter) to perforate and acid-stimulate the upper zones to increase the gas/oil ratio and lower the formation-fluid equivalent density.
Perforations were discharged electrically with the CTT logging adapter. The 2-m-long 2.875-in. guns were deployed to perforate the interval between 5285 and 5287 m. This interval of interest was confirmed by comparing the depth data acquired in real time with a previous log.
After performing all the previous operations above the CBP, the milling operation was performed with the shut-in wellhead pressure. For this operation, the CTT system was run above the downhole motor (DHM) to perform real-time monitoring of the downhole pressure (inside and outside the BHA), the temperature (inside and outside the BHA), and the depth-correlation data from the CCL.
Six milling attempts were performed with several flow rates ranging from 1.5 to 1.75 bbl/min. Because the differential pressure between the DHM (internal) and the annulus (external) was monitored in real time, the CT crew at surface knew when the motor was milling the CBP; up to 530 psi of differential pressure was recorded. Taking advantage of the actual differential pressure across the DHM, the total milling time for all six attempts was 187 minutes. After the sixth milling attempt, one trip was completed without pumping for dry-tag purposes to measure progress. Then, in the next trip, while pumping at 1.5 bbl/min, the CBP was milled out and the milling BHA went down with normal run-in-hole (RIH) weight. The total time since the CBP was dry-tagged until the time it was milled out was 4 hours. A total of 380 bbl of working fluid was used after the CBP was dry-tagged. When the CBP was milled out, its remaining debris was pushed down on top of a deeper CBP set at 5535 m MD and the CT was POOH.
- Use of CTT systems improves CT operations significantly by providing real-time downhole information, including pressure, temperature, and CCL data as well as axial forces and torque on BHA, with the addition of a 2.875-in. TCT sensor. The last two parameters are extremely useful during milling operations.
- The challenges of performing CBP milling in shut-in conditions have been encountered in this field. Under the shut-in scenario, as the job progresses, part of the debris becomes packed between the mill and the CBP and other debris is found behind or around the BHA, increasing the complication of the operation. Use of the CCT real-time downhole data with the TCT sensor has proved helpful in performing these operations safely without compromising well integrity and in avoiding stuck-pipe events.
- CT software output used to predict tubing RIH and POOH weight during the design stage can be verified with recorded data from the TCT sensor to create a more-accurate scenario for future CBP-milling operations. This is extremely important when dealing with CBP-milling depth in the toe section of the well.
Coiled-Tubing Telemetry Intervention in Shut-In Conditions
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12 June 2018