DRILLING TECHNOLOGY

RFIDs for drilling and completion-
ingenious applications

 We wave a card or keychain and the door opens, or the item is charged to our account. We also think of them for inventory control, but Marathon has far more innovative uses for the little tags.

Perry A. Fischer, Editor

Wal-Mart has been threatening for years to gets its suppliers to include a Radio Frequency IDentification (RFID) tag on all their products. A few experimental grocery stores have them; you just wheel your grocery cart out the door, and a machine prints out a receipt on the way-no bar code scanning. This writer recently received a call from a company that specialized in RFID tracking of oilfield assets, such as rig assets and chemical tanks.

Not many folks doubt that at some point in the near future, bar codes will give way to RFID as the fastest way to identify an object. Soon, you’ll hear about new laws that will have to be passed to address privacy and security concerns. Unlike bar codes, RFIDs can be read through coats, purses and wallets. But what does any of this have to do with drilling and completion?

For the past eight years, Marathon Oil Corp. has been working on downhole uses for RFIDs, while quietly pursuing certain RFID intellectual property rights. Its aim is to save money for itself, while making money through such intellectual property. Marathon created a company along with other investors called In Depth in 2002. In March of this year, In Depth signed a deal with Petrowell to develop RFID for completion and permanent installations. In Depth also signed a similar deal with IIITec for developing RFID drilling and coiled tubing applications. Both companies are UK firms.

RFID requires a “dumb ID chip” that is usually passive and merely reports a number, and a “reader,” which is active and requires power to operate. The reader and chip must pass within a certain proximity to each other-exactly how close is a function of power and RFID design. Generally speaking, there are three categories of uses for RFID:

1. Inventory control, i.e., simple identification at surface or downhole.

2. The ID chip is placed downhole, and subsequent downhole runs of the “reader” from surface perform the application.

3. The reader tool is placed downhole, and subsequent downhole runs of the ID chip passing across the reader perform the application.

This article focuses on the last two categories for drilling and completion applications.

HOW IT WORKS

There are two types if RFID: induction based and capacitance based. Capacitance requires much closer distance between the chip and the reader. Induction, which is far more common, can typically act at a distance ranging from a few inches to several feet, and is what is used in oilfield applications.

Induction works by moving a wire or loop of wire through a static magnetic field. Electricity is induced in the wire by such movement. Conversely, it can also be the wire that is stationary, and the magnetic field that is changing. Or both the wire and the field can be changing (i.e., moving). Any of these arrangements creates a small electrical current in a wire that has an RFID circuit. The circuit varies, or modulates, the electrical current and radiates that modulated signal like an output antenna. A reader generally provides the magnetic field that creates the current in the passive RFID device, and the reader also detects and interprets the modulated signal. Most folks are familiar with the technology as a card that is waved at a box to open a door or to charge an item at a checkout counter.

There are three parts to a typical inductively coupled RFID tag: the silicon microprocessor chip, a metal coil that acts as the tag’s antenna, and the encapsulating material that wraps around the chip and coil, which is generally glass or polymer material.

RFID tags are usually inexpensive, costing anywhere from $0.25 to $1 or so for passive chip tags. Tags costing a little bit more allow reprogramming of the ID number. So, basically, price is not an issue in oilfield applications.

SURFACE APPLICATIONS

During the last eight years or so, RFID has been used for the classic asset tracking for which it was first envisioned. An RFID chip on drill pipe is, in effect, a number. However, unlike a bar code, it does not have to be kept clean, nor pointed at to be read; and once the attachment and packaging issues are worked out, it can be very useful in determining unambiguously how much pipe is on deck or in the hole. It can also keep track of the downhole history of a particular tubular or LWD/MWD component. If attachment requires any sort of recessing into the pipe, the issues of strain and strength assurance of the tubular come into play. A reader at the drill floor can do all the recording directly into a computerized system, tied to the Internet.

DOWNHOLE APPLICATIONS

The simplest downhole use is for reassurance. If there is any doubt about which components are in, for instance, the BHA, an RFID reader could be run downhole. This almost foolish use of rig time would hopefully never occur, but it does point out that, like RFID-tagged drill pipe, it can help eliminate human error.

Depth control/correlation is another (and less trivial) use. If RFIDs are embedded in casing or couplings as a reservoir horizon nears, they become distinct markers whose use is akin to casing-collar patterns. An odd/unique pattern of short and long casing joints are usually placed in the well near the reservoir. Such casing collars generally form a distinct pattern that can serve as a marker after a (usually) gamma ray confirms the collar pattern relative to the formation. On rare occasion, the collar pattern is not sufficiently unique. In other rare cases, the metallurgy of the collars may not be sufficiently magnetic to allow collar locators to work. In such cases, RFID tags, permanently imbedded in the collars, offer inexpensive depth-control solutions.

Taking this idea a step further, any operation that requires depth control, such as setting packer and plugs, could see cost savings. An obvious application for this sort of depth control is perforating off a workstring or slickline. In the latter case, an RFID tag would be placed somewhere near the reservoir during completion, probably during the final liner run, perhaps in a special purpose-built collar, and depth-verified with cement bond (with gamma-ray/RFID reader) or another logging run that occurs near the end of the completion. Subsequently, perhaps even after rig-down, a battery-powered reader/actuator on slickline (or workstring), mounted atop a perforating gun(s), would detect the RFID tag. Once the reader detects the unique tag, a signal, perhaps acoustic, is sent uphole to alert the crew, and a countdown timer is started. Ample time is given to further position the gun across the perforating zone using a surface odometer (or pipe measurement), which is sufficiently accurate for short distances. Then, after a “safety/comfort factor” wait time has elapsed, the reader/actuator fires the gun. This would provide highly accurate perforating depth control at less cost than electric line.

If an RFID tag or reader is placed exactly at (or very close to) the spot that needs to be perforated, the gun and reader could simply be dropped in the hole and programmed to fire when it encounters the marker.

Completion. Perforating field tests in Alaska and the North Sea have proven successful. Marathon pioneered the Excape completion process-a proprietary casing-conveyed perforating system used in multi-zone completions. The Expro Group and BJ Services market and provide services for the system, through an agreement with Marathon. Excape has been used in more than 80 wells.

The system is composed of external perforating guns, a control line and isolation valves, all of which are run with the casing into the openhole, positioned by gamma ray correlation, and cemented in place. Thereafter, each gun may be detonated in succession using a surface-controlled hydraulic line. After each detonation, a sliding sleeve is shifted, allowing an integral isolation flapper valve to fall into place.

Four years ago, Marathon activated this system using RFID technology instead of the control line, by dropping a “dart” through the well, which fired a particular perforating segment, on an 8,000-ft deviated gas well near Kenai, Alaska. This is believed to be the first commercial use of this RFID technology in the oil field. Since that success, the use of RFID for the Excape system has languished, but it’s now receiving another look.

In what will surely be the first of many RFID-actuated drilling tools, a downhole circulating sub (Fig. 1) has been developed for well cleanup. The sub is run as part of the drillstring and is activated by passing RFID tags through the circulating sub, which has a reader built in. The signal activates the electronics, which in turn triggers mechanical devices within the sub. A sleeve is opened or closed depending on the unique coding of the RFID tag. RFID tags can be made programmable such that they can be coded onsite to either open or close the circulation sub. The sub has been used in the field.

Fig. 1. RFID controlled, downhole circulating sub for well clean-up, which was used in the North Sea by operator CNR.

Operator CNR was drilling in the UK sector of the North Sea, on its Ninian North platform in August 2005. Well N46z was at about 15,000 ft. As part of the completion process, an RFID circulating sub was run to clean up the well before running the completion string. RFID tags were dropped into the drillstring. When they reached the sub, the circulating ports opened, and inhibited seawater was circulated from just above the liner top at 10,000 ft. RFID tags with a different code were then circulated to close the sub’s ports. Everything went according to plan. This was the first time an RFID-actuated sleeve was used in the oil and gas industry. The sub can also be used to spot a different fluid in a section of the hole, which might be desirable on long horizontal runs.

Because each sub can be programed to react to different RFID codes, multiple RFID circulating subs can be run in a single tubing string, and each be controlled individually. The RFID tag used in this application is shown in Fig. 2.

Fig. 2. RFID tag used in circulation sub application: a small glass pill about 3 mm in diameter and 3 cm long.

Drilling/other applications. The somewhat universal concept of an RFID reader and mechanical-power actuation system, triggered by a passing RFID tag, can be adapted to many other drilling and completion needs. RFID tags can be made small enough that they will likely survive being pumped through a drilling motor (Fig. 3), which would allow tools below the motor to be RFID activated.

Fig. 3. RFID chips can get even smaller than this, small enough to survive passing through a mud motor.

Stuck-pipe/free-pipe point determination might be possible with a special sub (or more likely, a series of subs) that disconnects the drill pipe when a certain RFID tag is passed. If the drill pipe becomes stuck, a sequential method of dropping a tag that disconnects the drill pipe, say, just above the BHA, establishes whether it’s free at that point.

If not, you then move to the next disconnect sub and repeat the process. Eventually, you should be able to determine the lowest free point and proceed to recover pipe from there. Design of this particular tool is under way. Initial design calls for a timer that, after the first disconnect RFID is dropped, will start a countdown that will attempt to reconnect the pipe after a pre-programed amount of time has passed, giving the rig crew time to determine if the pipe is free above that point. If the pipe is pulled loose, the tool cannot reconnect.

Another interesting twist is using RFIDs for nearly continuously variable control. Suppose you want a downhole choke to vary from closed to 2.5 in. open, in 0.05-in. increments. Each time a properly coded RFID chip passes the choke, a ratchet- or screw-type mechanism is activated and opens the choke a little more. A differently coded RFID could close the choke. Downhole stabilizers can be expandable and retractable in increments in this manner, as can underreamers, orientation tools and adjustable bent subs, to name a few.

There are many more applications in the drilling arena, such as air- and foam-drilling applications, where fluid-pulse or pressure-activated systems do not work. Other uses include anywhere that ports/valves can be opened or closed, such as cement stage collars, actuating hydrostatic bailers, and splitting fluid streams between the bit and a circulating sub. Locking and unlocking drilling jars can be done, as well as uses in coiled tubing, retracting casing scrapers near nipple profiles, indexing fishing tools, changing fishing grapple sizes-wherever remote activation of something downhole is useful.

Technical issues. Any new technology has technical hurdles to overcome. Many of these issues are interrelated, such as: temperature, iron/magnetics, packaging, battery life and durability.

Any fine-wired chip will have problems performing at high temperatures, as will batteries. Brine and ferrous metals attenuate the signal between reader and tag. This can be somewhat mitigated by choosing the right frequencies, orienting the reader to the tag at right angles, using ferrite-cored coils to make the antenna more sensitive, and using non-ferrous metals/composites whenever feasible. Also, passive RFID tags can be made into various levels of active or powered tags, which can further mitigate the signal strength problem.

Robustness and durability is an issue that effects how long the application might be useful. Improvements are need in this regard for tags that are embedded downhole. Obviously, an application will not likely be developed if it is felt that the downhole RFID tag or reader will not last long enough to be useful.

Another related issue is packaging. Packaging the readers and tags can be half the challenge. If an RFID tag were deemed sturdy enough to last for years embedded in drill pipe, casing or tubing, it would be essential that the embedding process not weaken the pipe. Stress and strain testing, perhaps extensive, would be needed to confirm pipe integrity.

None of these issues is a show stopper; most, if not all, can be overcome. But collectively, they will likely drive early applications to have readers in retrievable tools, and tags pumped past them.

SUMMARY

Now in the early stages of development, the future of RFIDs for downhole use seems assured. Marathon has estimated that “a major oil and gas operator could realize at least $17 million in annual savings, as well as improved operational safety benefits, with even limited acceptance and use.”

The company realized that developing the technology might not always be in the best interest of the large, established downhole service companies. For example, a company heavily invested in hydraulically operated (via control lines), downhole, sliding-sleeve valves might not want to see those quickly replaced with RFID-actuated sleeves. Or gamma-ray or casing-collar-located depth control for, say, perforating, replaced with RFID depth control. Marathon says that it wants to see the technology developed quickly and implemented industry-wide. Considering what has already been accomplished, that should not be a problem.   

 

ACKNOWLEDGEMENT 

The author thanks Scott Scheffler, Marathon Oil, for his help in obtaining the graphics used in this article.

BIBLIOGRAPHY

Snider, P., Fraley, K., “Marathon, partners adapt RFID technology for downhole drilling, completion applications,” Drilling Contractor, March/April 2007.

http://www.touchbriefings.co.uk/pdf/2590/Fraley.pdf, from Exploration & Production-Oil & Gas Review 2007-OTC Edition.

Snider, P., PowerPoint presentation from the 2006 DEA Workshop, Galveston, Texas, 20-21 June 2006