Coiled tubing (CT) has proven to be efficient and relatively inexpensive for a broad range of intervention operations. However, with increasing well complexity and expected low oil prices for the foreseeable future, the need for real-time data during intervention planning and execution is crucial to well efficiency, cost effectiveness and performance. Fishing is an excellent example. For decades it has been characterized as an art. But without knowledge and certainty about the position and location of the fish and the condition of the wellbore, complicated fishing operations might require multiple runs, adding nonproductive time (NPT) that can render an otherwise valuable well useless.

A new intelligent CT (ICT) intervention service from Baker Hughes incorporates real-time downhole intelligence to help field crews pinpoint fish locations, react quickly to changing downhole conditions and eliminate unnecessary runs. The TeleCoil ICT intervention service provides accurate real-time downhole monitoring of high-resolution depth correlation; differential pressure and temperature data; and tension, compression and torque (TCT) data.

TCT data are particularly valuable in applications where real-time knowledge of bottomhole assembly (BHA) loads and torque is important, for example:

  • differentiating between frictional lock-up and potential obstruction tagging;
  • ensuring effectiveness of extended-reach technologies such as fluid hammer tools, tractors and lubricants;
  • confirming jar activation during fishing jobs and the milling effectiveness over time; and
  • quantifying mill aggressiveness from the back torque and weight on bit (WOB) analysis.

The ability to provide power continuously to the downhole sensors or any electrically activated downhole tools without the time limitations imposed by the life of BHA batteries is a key advantage of this ICT service compared to other CT telemetry systems.

Unlimited real-time video and job-critical feedback enhance intervention efficiency.

Combining downhole power and communications with advanced camera technology makes it possible to clearly identify fish, execute an effective removal strategy and verify that the wellbore has been effectively cleared, all without changing the reel at the surface.

Real-time high-definition (HD) video offered with the ICT service makes it possible to see the fish and examine the condition and shape of the casing without limitations on battery life, memory or downhole visibility. Because power is supplied from the surface, the camera can stay downhole as long as necessary. Instead of having to save footage to memory for later review, live video is fed directly to surface for instant viewing. Pumping fresh fluid around the fish and across the camera lens provides clear images, even in murky conditions. This accurate understanding of the fish and the wellbore around it helps teams design and execute more effective fishing plans.

Simulation software is used both before and during intervention jobs to save runs, protect personnel and reduce operational time. Based on known well parameters, the job is first modeled using CIRCA software. As data from the job are collected, CIRCA RealTime software updates the pre-job models on the fly, enabling CT personnel to make critical decisions quickly if downhole conditions change. The software displays a virtual gauge that clearly delineates safety and operational limits as they correspond to the actual depth and time. Live updates on the remaining fatigue life of the CT string are provided continuously.

Using this ICT service, milling and cleanout operations also can be improved. The ability to monitor torque, tension and compression in real time makes it possible to track motor and mill performance accurately over time and adjust job parameters to enhance the entire milling process. Variances between milling plugs, stumps or washing sand can be identified more easily. Top of sand in highly deviated wells can be accurately located. Wells can be cleaned out more effectively by increasing fill penetration rates and adjusting bit length and wiper trip speed based on current equivalent circulating density. Additionally, the simulation software predicts pressures for two-phase flow, gels, acid and solids and continuously updates fluid rheology with temperature and pressure readings. Knowing the downhole pressures makes it possible to track fill removal dynamically and control well balance to prevent lost returns and formation damage.

In perforating operations, knowing accurate depth helps teams perforate the right zones, avoiding additional correlation runs. The perforation operation is more efficient because the ICT service can perforate up to 32 individual zones in a single trip and can convey more than 305 m (1,000 ft) of perforating guns in and out of the well under pressure without having to first kill the well. Perforations can be oriented to avoid damaging intelligent completion fiber optics and other components. Observers at surface can confirm in real time that guns have fired.

Case histories

While the ICT service has helped operators reap dramatic benefits offshore, it also has brought significant value to onshore intervention operations.

Texas. An operator of a well in Texas attempted to mill the 10th plug after completing a 43-stage fracturing operation when the milling BHA encountered an impassable obstruction at about 2,950 m (9,700 ft) measured depth. The well was 4,237 m (13,900 ft) long with the kickoff point to horizontal at 2,052 m (6,731 ft) and perforations between 2,608 m and 4,209 m (8,558 ft and 13,810 ft). Suspecting that collapsed casing was impeding progress, the operator tripped the mill out of hole and rigged up a wireline camera and tractor to attempt to clearly identify the problem. After 50 hours of unsuccessfully trying to position the camera and retrieve images, a 21⁄8-in. ICT with a HD camera and flow-through lens-cleaning BHA was run in hole, while filtered fresh water was pumped down the CT and casing annulus to help provide a clear-fluid environment so the camera could return clear images. As expected, the Camera BHA encountered murky fluid below the first perforations at 2,635 m (8,650 ft) because of a thief zone that was stealing the clear fluid. To reduce murkiness and clean the camera lens, filtered fresh water and surfactant pills were pumped through the CT and Camera BHA at 0.25 bbl/min. The obstruction was tagged and then clearly identified at 2,936 m (9,632 ft). Clear imagery showed the severity and type of collapse, which allowed the operator to plan a solution quickly. The entire operation was performed in one 21-hr run.

Europe. An onshore well with a 3½-in. cemented completion in a partially depleted reservoir was left with 800 liters of cement in the tubing. As a result, the tubing was cut above a 5-in. liner at a depth of 2,763 m (9,064 ft) in the 3,603-m-long (11,820-ft-long) well with a packer set above the cut. The objective was to perforate the well using 2-in. guns and establish productivity. The 21⁄8-in. ICT system provided beneficial downhole data that contributed significantly to overall job success. Motor stalls were detected quickly by real-time pressure data, which also helped monitor downhole pressure for reservoir influx. Casing collar locator (CCL) data improved depth measurement accuracy to ensure that sufficient rathole was milled for perforating, and gamma ray and CCL data were monitored for real-time logging and perforation depth correlations.

The guns were detonated electrically at desired depth. This saved time and reduced risk compared to ball-operated or pressure-activated firing heads. The downhole pressure and temperature gauges indicated that the guns had fired when intended. Finally, the BHA plugand- play capability that offers the ICT system avoided the need for additional equipment such as wireline unit and tractor, saving operational time and cost.

Caspian region. For an onshore operator in the Caspian region, using the ICT service with simulation software and an EasyReach fluid hammer tool helped to successfully mill and clear a bridge plug in an extended- reach well with no motor stalls or NPT. The J-shaped well contained 5% hydrogen sulfide, and the operator wanted to mill out the composite bridge plug from where it was set at 6,080 m (19,950 ft) and push it to the toe of the well at 6,400 m (21,000 ft). The setting depth of the bridge plug made it difficult to reach with sufficient WOB to effectively mill it out. Previous milling runs had been ineffective and made no progress after 8 hours of rig time. The job was complicated further by mandatory shut-in conditions during milling time. The shut-ins blocked milled particles from being circulated out of hole, which increased both risk to surface personnel and the likelihood of sticking the BHA in solids and fill buildup.

The modeling software provided an accurate operational plan, including accurate total flow analysis, wellbore hydraulics, extended-reach modeling, WOB simulation and on-the-job force matching.

The modeling software provided an accurate operational plan, including accurate total flow analysis, wellbore hydraulics, extended-reach modeling, WOB simulation and on-the-job force matching. When completed, the ICT BHA consisted of a CT connector, motorhead assembly, integrated sensor assembly, extended-reach fluid hammer tool, centralizer, X-treme series positive displacement motor and a mill. Real-time data enhanced motor performance, prevented stalls and monitored real-time downhole pressures and temperatures.

The team completed the millout in just 34 minutes— 10% of the time that had been spent in previous attempts. After the mill broke through, the remnants were easily pushed to the toe of the well.