by Rienk Reitsma & Alex Goodwin
May 5, 2016

The ongoing challenges of low commodity prices and market pressures are pushing production companies to consider nontraditional tools as well as innovative deployment strategies to optimize one of the most important aspects of wellbore economics: drilling efficiency. Achieving that objective sometimes requires the ability to seamlessly integrate multiple technologies into a single bottomhole assembly (BHA), reducing the number of trips downhole and saving valuable 
rig time.

In a first-of-its-kind application that resulted in considerable time and cost savings for a major offshore operator, a multinational oil field services company ran a drilling reamer and a circulation sub, both activated by radio frequency identification (RFID) tags, in tandem in the same BHA. The approach, which represented a departure from conventional methods that rely on mechanical actuators, enabled rathole-reaming and wellbore-cleaning operations to be completed in 
a single run.

Image 1. Circulation subImage 1. Circulation sub (Images courtesy of Weatherford)

Downhole RFID Activation

The drilling reamer and circulation sub used on this job operate on similar principles. In both cases, the tools are activated when a field technician drops pre-programmed RFID tags from the surface into the inside diameter (ID) of the drillpipe, where they are pumped downhole via the drilling fluid. As the tags pass through the ID of each RFID-enabled tool, antennas pick up the instructions transmitted by the tags and initiate the appropriate action.

RFID technology enables the tools to be activated or deactivated at any time while drilling and also permits multiple RFID-enabled tools to be run in tandem and controlled independently. The tools are engineered to operate with low flow rates when necessary to protect sensitive formations. They also record downhole events and parameters that provide the operator with comprehensive data for post-job analysis.

Tool Functionality

When used to kill a rathole, the RFID-enabled drilling reamer is installed near the bit and can be activated using RFID tags or pressure cycle activation—a method in which a series of pressure pulses are sent downhole at carefully calculated intervals to open the tool. Adding to its operational flexibility, the reamer can be used with either a rotary-steerable system or a rotary BHA.

Image 2. Drilling reamerImage 2. Drilling reamer

The drilling reamer’s polycrystalline-diamond-cutting (PDC) structure provides high-impact strength and erosion resistance. Cutters are strategically placed to disperse workloads more evenly across all stages of the cutter block to improve performance. The cutter blocks, which are capable of underreaming and backreaming, grip the reamer body at full actuation to minimize vibration while drilling, extending the life of 
the cutters. Once activated, the cutter blocks extend out from the reamer 
to simultaneously drill and enlarge 
the wellbore.

Leveraging the same technology, the RFID-actuated circulation sub provides remote, selective and unlimited actuation, which enables multiple operations to be completed without tripping in and out of the hole. Applications include hole cleaning, jetting blowout preventer stacks, and spotting of lost-circulation material (LCM) and kill-weight fluids. The ability to actuate the system without relying on downhole hydraulics expands the operating window for use in a variety of scenarios, including low-flow and under-balanced drilling jobs.

Because the ID is not restricted by mechanical actuators such as ball-seat mechanisms, the sub maintains full through-bore flow and a large total flow area throughout the operation. This enables higher annular velocity and turbulent flow than conventional devices. The circulating valve also logs time, drillpipe pressure, hydraulic micro-pump pressure, temperature and battery capacity in the internal memory of the sub.

Field Case Study: 
A Commanding Single Run

During the winter, combined use of the drilling reamer and circulating sub helped an operator in the Azerbaijan sector of the Caspian Sea to efficiently ream a 154-foot (47-meter), 71-degree rathole and conduct a cleanup job to prepare the wellbore for completion. The directional offshore well has a measured depth of 16,043 feet (4,890 meters). Especially suited for complex and offshore wells, the approach was implemented to meet the operator’s objective of minimizing drilling time by making fewer trips. Previously, the operator had used a conventional reamer that could not be deactivated downhole prior to beginning circulation, which resulted in additional trips.

The oilfield services provider initiated the operation from a platform rig, deploying the RFID-activated reamer and circulating sub in the same BHA. In this case, the reamer was deployed in the closed position and installed just above the roller-cone drillbit to minimize the length of the rathole. To initiate the underreaming operation, a field technician dropped RFID tags pre-programmed with “open” commands downhole. Within minutes, the tags transmitted instructions to the electronic reader on the reamer controller.

The tags instructed the cutter blocks to extend from the reamer body to simultaneously drill and underream the rathole section. The reamer, using a 1.38-specific-gravity synthetic oil-based mud, enlarged the 6.25-inch rathole to 8 inches in less than 12 hours, drilling from a depth of 14,282 feet (4,353 meters) to a total depth of 14,436 feet (4,400 meters).

When the underreaming operation was complete, a second set of RFID tags programmed with “close” commands initiated the movement of the cutter blocks back into the reamer body. With the reamer in the closed position, it could remain downhole during cleaning without the risk of creating additional cuttings that could damage the casing and cutting structure.

After reaming, the field technician used RFID tags to open the circulating sub to clean the cuttings from the borehole and displace the drilling mud with completion fluid. After receiving the RFID signal, the battery-powered electric motor, which operates a hydraulic pump, moved a sleeve into the pre-configured “open” position.

This enabled the sub to redirect fluids back to the surface with high-velocity, turbulent annular flow for efficient wellbore cleaning. Because RFID actuation is not pressure-dependent, the operator could initiate the wellbore-cleaning operation while maintaining hydrostatic pressure.

Over the course of three days, the circulation sub cleaned the wellbore and displaced the wellbore fluids to prepare the well for completion. A final set of RFID tags dropped downhole gave the command to re-close the sub.

Both the rathole reamer and the circulation sub recorded downhole hydraulic data to deliver a complete analysis of pressure changes during the reaming and cleaning operations, which enabled the team to validate that the tools had functioned properly.

RFID technology enabled both systems to be deployed downhole and activated in a single trip, eliminating the need for the operator to pull out the underreaming BHA before cleaning the wellbore and make a dedicated well-cleanup trip. The single-trip operation saved an estimated two to three days of rig time valued at between $700,000 and $1 million.