slickline signaling a change - semantic scholar · the scope of slickline operations that use...

16 Oilfield Review

Slickline Signaling a Change

Well intervention techniques have long been dependent on mechanical and

hydraulic systems for actuation and measurement. As a consequence, the outcomes

of many downhole operations—for which depths were often approximate—

depended as much on the skill of the operators as on the design of the tools.

For one intervention method, these limitations were eliminated when engineers

developed digital slickline.

Matthew Billingham Vincent ChateletStuart MurchieRoissy-en-France, France

Morris CoxNexen Petroleum USA Inc.Houston, Texas, USA

William B. PaulsenATP Oil & Gas CorporationHouston, Texas

Oilfield Review Winter 2011/2012: 23, no. 4. Copyright © 2012 Schlumberger.For help in preparation of this article, thanks to Blaine Hoover, Buddy Dearborn, Chuck Esponge, Douglas Guillot and Scott Milner, Broussard, Louisiana, USA; Farid Hamida, Rosharon, Texas; and Fabio Cecconi, Pierre-arnaud Foucher and Keith Ross, Roissy-en-France, France.D-Jar, D-Set, DSL, D-Trig, FloView, GHOST, Gradiomanometer, LIVE, LIVE Act, LIVE Perf, LIVE PL, LIVE Seal, LIVE Set, PS Platform, Secure and UNIGAGE are marks of Schlumberger.

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Slickline operations in oil and gas wells have been performed for more than 75 years, and until recently, practices have changed little. Technicians and engineers in the field perform basic downhole operations through manipulation of downhole tools attached to the end of a single-strand thin wire called a slickline; the name dis-tinguishes it from a conducting cable used in electric line or a braided cable used for heavier mechanical work. These downhole operations may be as simple as running a gauge ring to TD or more complex wellbore maintenance and pro-duction optimization procedures such as setting or pulling valves and plugs. Operations also include removing production-hindering debris such as sand or paraffin from the well. More recently, devices with electronic memory have been run on slickline to gather data for pressure transient surveys or production logging.

Slickline has remained a staple of well inter-vention because it is cost-effective, reliable, effi-cient and logistically uncomplicated. It is deployed with relative ease using compact equip-ment that may be moved to and situated at a well-site of nearly any size located anywhere in the world. It may be used in all types of wells, includ-ing HPHT, sour gas, high-angle and flowing. On locations with space or weight limitations, slick-line is often the only feasible intervention option.

But the simplicity of slickline is also the source of its drawbacks. Engineers designed slickline initially to perform rudimentary mechanical operations. At that time, absolute depth was not an essential consideration for such operations. Drillers could not place tools pre-cisely, and as a consequence, it was difficult to verify a tool’s precise downhole location. For some operations, particularly perforating or the setting of isolation tools, knowledge of exact tool depth is critical. Similarly, to ensure sensitive instruments and other tools are not damaged during setting or pulling operations, or to confirm the intended downhole action, it is sometimes imperative that a force—which must fall within a narrow range—be delivered downhole. Using slickline, it is impossible to determine with any certainty exact tool depth or amount of force delivered downhole.

All tubulars, wires and cables stretch to some extent as they are moved into and out of a well. Stretch in slickline wire, however, is significantly greater than that of other conveyance methods. Therefore, depth measurements taken using a mechanical device and displayed at the surface may not accurately represent the tool location. Indeed, displayed information is not a measure-ment of tool depth but of how much wire has been

spooled on or off the drum. As a consequence, the standard accuracy for slickline depth measuring systems is about 30 cm/300 m [1 ft/1,000 ft].1 This degree of accuracy is often sufficient for slickline operations for which depth is reckoned to within a few feet of some fixed point in the completion string. In wells that have no downhole marker, the margin of error may be unacceptable. Engineers have devised systems to correct for stretch as well as other variables, but such corrective measures are based on data estimates only, and sophisti-cated operations typically require more accuracy than these systems could deliver.

In addition, wellbore deviation can cause considerable inaccuracies in the weight indica-

tor readings at the surface; these readings are the only indicator of forces being applied down-hole. Typically, the weight downhole is measured using a load cell attached to a wellhead and then to a pulley through which the slickline is directed from the drum to the top of the lubricator (above). As the angle of deviated wells has increased, along with the number of such wells, there has been a corresponding increase in the frequency and degree of inaccurate weight read-ings. Such depth and weight inaccuracies may

1. King J, Beagrie B and Billingham M: “An Improved Method of Slickline Perforating,” paper SPE 81536, presented at the SPE 13th Middle East Oil Show and Conference, Bahrain, April 5–8, 2003.

> Basic slickline rig-up. A load cell, which is attached to a sheave, is activated by tension in the wire running through the sheave. The wire runs from the slickline drum to the sheave, which redirects it upward at an acute angle. It is turned 180° by a second sheave and fed into the stuffing box where it enters the well through the lubricator. The wireline valve above the Christmas tree contains opposing rams (not shown) that may be closed to seal against each other without removing the wire, thus providing a pressure barrier alternative in the event the stuffing box sealing mechanism fails.

Oilfield Review WINTER 11/12 Slickline Fig. 1 ORWNT11/12-SLKLN 1

Stuffing box

Lubricator

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18 Oilfield Review

lead to extended operation times or, in more complex well completions, to operational issues. In slickline perforating, for example, placing a gun a few feet above or below target depth may mean the difference between producing water, oil or gas—or nothing at all.

In recent years, engineers have developed numerous improvements to traditional slickline equipment. Most of these are incremental changes applied to tools run on slickline rather than to the wire itself. Battery-powered elec-tronic tools, which acquire and store data in memory, have overcome some slickline shortcom-ings pertaining to actuation and confirmation of downhole actions. But once these tools have been deployed, they do not provide real-time downhole data or give the operator the ability to change settings, such as the depth or temperature at which triggers are activated. As a result, battery-operated tools cannot address the time and effi-ciency shortcomings that characterize many traditional slickline operations.

The most ambitious attempt to overcome these hurdles—using the slickline itself to deliver two-way signals between the tool and the surface—has been pursued for decades. Such a solution could be used to provide operators with precise tool

depth, tool status, downhole weight, wire tension and wellbore data such as pressure and tempera-ture measurements in real time.

Despite many years of effort, manufacturers had been unable to develop an acceptable solu-tion using a slickline wire and equipment. That changed when engineers at Geoservices, a Schlumberger company, developed DSL digital slickline services.

This article describes enhancements made to slickline in the form of battery-powered and memory tools that allow engineers to expand slickline applications to include accurate depth measurements for perforating and production logging. Also discussed is DSL technology, which is an engineering breakthrough, rather than a slickline enhancement. Using telemetry over slickline, coupled with battery-powered elec-tronic tools that incorporate a memory and telemetry interface, DSL services allow com-mands and data communication between the sur-face and downhole without compromising the mechanical integrity of the wire. These features expand slickline capabilities significantly by offering accurate depth correlation, tool status information and tool control to the operator in real time; this is critical to delivering precise, efficient and low-risk operations on slickline-

conveyed mechanical, remedial and measure-ment operations.

Upgrading SlicklineHistorically, depth accuracy has critically limited the scope of slickline operations that use conven-tional measuring devices. The primary factors affecting depth accuracy are elastic stretch, tem-perature, buoyancy, slickline and toolstring fric-tion against the wellbore wall, lift and measuring wheel precision. The variety of sizes and materi-als used for slickline wire may also impact mea-surement readings. The most common slickline wire diameters are 0.092, 0.108 and 0.125 in. [2.34, 2.74 and 3.18 mm]. The materials from which they are manufactured—depending on their application—include carbon steel, stainless steel alloys and nickel- and cobalt-based alloys.2

Elastic stretch—the factor that causes the most variability in slickline depth accuracy—is a function of line tension and the modulus of elasticity of the wire.3 Length measurements may be increased or decreased by out-of-tolerance or poorly calibrated measuring wheel diameters. Changes in measuring wheel diameters can result from wheel wear, debris buildup or the disparity in the temperatures at which the measuring wheel was manufactured or

> Battery-powered tools. The PS Platform service is a suite of battery-powered tools that can perform both memory and surface readout operations. The GHOST gas holdup optical sensor tool (top left) uses four sapphire optical probes to measure gas and liquid holdups, bubble count, average hole caliper measurements and bearing. The Gradiomanometer specific gravity profile tool (top second from left) measures the average density of the wellbore fluid and wellbore deviation, from which water, oil and gas holdups can be derived. The bubble count from the FloView holdup measurement tool (top center) identifies first fluid entry, water holdup and bubble count and includes a centralizer and average hole caliper measurements. The UNIGAGE pressure gauge system carrier (top second from right) contains a crystal quartz gauge that offers the option of a high-resolution pressure measurement. The optional inline spinner (top right ) provides a bidirectional fluid velocity measurement inside the tubing. The basic measurement sonde (bottom left ) provides gamma ray (GR) and casing collar locator (CCL) data for correlation, plus pressure and temperature measurements. The flow-caliper imaging tool (bottom right ) measures the average fluid velocity, water and hydrocarbon holdups and bubble count from four independent probes. It also provides dual-axis X-Y caliper measurements and relative bearing measurements. Well deviation and accelerometer measurements provide the deviation correction for the measured fluid density.

Oilfield Review WINTER 11/12 Slickline Fig. 2ORWNT11/12-SLKLN 2

7.1 ft[2.2 m]

GHOST Tool

Basic Measurement Sonde Flow-CaliperImaging Tool

Gas holdup, gas andliquid bubble count,

average caliper, bearingDensity, deviation

Batteries and recorder, gamma ray,casing collar locator,

temperature, pressureFlowmeter, X-Y caliper,

water holdup, bubble count,relative bearing, centralizer

Water holdup, bubblecount, centralizer,average caliper

Quartz pressuregauge

Flowmeter

FloView Tool UNIGAGECarrier

BidirectionalInline Spinner

GradiomanometerTool

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calibrated and the temperature at which it operates. Measurement errors can be in excess of 0.6 m [2.0 ft] at well depths of 3,000 m [10,000 ft].4 Temperature differences in the hole also affect wire length as the wire is lowered into the well. Unless wellbore tem-perature gradients remain constant, or temperature and measurement variations are included in depth corrections, it is difficult to compensate for this vari-able. In addition, buoyancy, friction and lift—which are functions of wellbore parameters such as fluid viscosity, flow rate, fluid type, deviation, tortuosity and wellbore geometry—affect tension measure-ments at the surface.

Although minimal differences in measure-ment occur at shallow depths, discrepancies may increase and become more significant with increasing depth. In recent years, engineers have addressed the depth accuracy issue through the development of electronic measurement devices that attempt to automatically correct for wire stretch.

Another slickline limitation has been the mechanical means by which tools are activated. Engineers addressed this issue through develop-ment of battery-powered tools. These tools, which store downhole data in memory that is accessed once the tool returns to the surface, may perform downhole slickline operations when activated by a timer or a when a signal is generated through a predefined cable movement sequence. Memory devices have been used in remedial services, such as perforating and device setting, and have been used in measurement services such as pro-duction logging, while offering a cost or access advantage over electric line.

Battery-powered electronic triggering can enable safe detonation of explosives used for tub-ing and casing cutting and perforating, and elec-tromechanical setting tools can replace explosive devices. The industry has welcomed electronic fir-ing heads because they can be programmed to dis-arm automatically on retrieval to the surface if the pressure window that is a condition of their arm-ing has been selected correctly.5 These concerns were formerly met using mechanically or hydrauli-cally actuated firing heads.

The industry has also embraced the use of nonexplosive, electronically actuated setting tools

in environments where logistics associated with explosives are restrictive or complex. Firing delays or pressure windows are two examples of safety measures added to traditional devices. But these add complexity and compromise precision because of variations in downhole conditions such as temperature and pressure and because of the time the tool has spent downhole. Electronic firing heads are immune to these variations and provide improved accuracy and control.6

Many services that were performed using elec-tric line or coiled tubing are now possible as slick-line services because of battery-operated tools. These include sensors for pressure, temperature, gamma ray (GR), casing collar locator (CCL), flow-meter, caliper, bubble count, tool orientation, water holdup and gas holdup (previous page).

Despite these improvements, engineers con-tinued to seek the next major advance in slickline capabilities—a method by which they could send signals to, and receive data from, downhole tools in real time. Their objective was to gain the versatility and accuracy of electric line telemetry communication without sacrificing the advan-tages of slickline.

For example, because slickline is a single component it is naturally balanced and so lends itself to operations such as jarring. In contrast, jarring with electric line may lead to destruction of the insulator between the conductor and the cable’s armor.7 Electric line includes an outer and inner set of protective armor wires wound in opposite directions around the central conduc-tors (above right). This creates an inherent torque level within the cable that must be man-aged to avoid wire damage, particularly in deep or highly deviated wells. This damage may take the form of overlapping outer armor, or wires, that quickly wear and break and then hang up in pressure control equipment. When an overlap-ping wire breaks, it unravels as it enters wellhead pressure control equipment, which results in an extensive operation to remove the stranded armor wire.

The sealing mechanism at the top of the slickline lubricator also offers an advantage over that used for braided or electric line. A slickline stuffing box is far less complex than

the grease tube assembly used for braided or electric line. A rubber packing element main-tains a pressure seal even when a wire passes through it (below). It is thus easier to rig up than a braided cable grease-control flow-tube

2. Larimore DR and Kerr WL: “Improved Depth Control for Slickline Increases Efficiency in Wireline Services,” Journal of Canadian Petroleum Technology 36, no. 8 (August 1997): 36–42.

3. Modulus of elasticity is the ratio of longitudinal stress to longitudinal strain.

4. Larimore and Kerr, reference 2.5. A pressure window is a preset condition that allows the

tool to arm only when it is at a pressure greater than surface pressure.

6. Goodman KR, Bertoja MJ and Staats RJ: “Intelligent Electronic Firing Heads: Advancements in Efficiency,

> Armored electric cable. Cables used for electric line, or wireline, operations include multiple armored and insulated conductors. In this case, seven insulated wire conductors are packaged within a semiconductive jacket. The wires and insulators are wrapped in inner and outer sets of armor wound onto the bundle in opposite directions.


Inner armor

Semiconductivejacket

Insulatedconductors

Outer armor

> Simple pressure control. A slickline stuffing box (orange) is a relatively simple sleeve lined with sections of polymer packing (black) that act as a pressure seal against the wire as it moves out of the wellbore, through the pressurized lubricator and the stuffing box, into the atmosphere and up and over the sheave. When tightened, a packing nut (red) compresses the packing against the wire, increasing the sealing force. The same sealing mechanism holds pressure as the slickline is going into the well.


Sheave

Flexibility, and Safety,” paper SPE 103085, presented at the SPE Annual Technical Conference and Exhibition, San Antonio, Texas, USA, September 24–27, 2006.

7. Slickline jarring uses a downhole mechanical device called a jar to deliver an impact load to another downhole component. Jars include a lower section attached to a tool or other component, and an upper section that can travel freely. The jar may be opened upward and then quickly lowered to use the weight of the toolstring to deliver a downward blow to the lower section. In reverse, the slickline is reeled in at high speed to deliver an upward force to the lower section of the jar.

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assembly, which requires grease to be injected across flow tubes at a pressure greater than that of the wellhead during the entire operation. Electric line operations performed under pres-sure require additional equipment, including a grease pump and a grease supply, which have implications for logistics and the environment. In addition, because moving the line through the grease tubes may break the grease seal, braided cable is restricted to running speeds of about 1,200 to 3,000 m/h [4,000 to 10,000 ft/h] in and out of the well. The mechanical slickline tools can be run at a faster rate without losing the pressure seal, saving valuable rig time.

A Matter of Live and DepthWhile a true slickline telemetry system eluded engineers for decades, they were able to develop a power–telemetry slickline link using coaxial cable. However, because the cable sacrifices the tensile strength and inherent robustness that are essential to slickline applications, the technology has been abandoned.

Developing an insulator was the stumbling block to slickline telemetry, and engineers were further challenged to find a method to bond the insulating material to the wire. In 2002, engi-neers at Geoservices began work on a telemetry system based on previously developed MWD electromagnetic technology. However, telemetry

was not the issue; the challenge was finding an insulating material and a method by which it could be bonded to wire that would allow it to survive the rigors of slickline operations. Initially, the team tested seven polymers, based on their resistance properties, as insulation material can-didates. Under well conditions, however, these coatings did not adhere to the wire.

After years of effort, researchers developed a complex wire-coating material and an exacting bonding procedure. The finished product is made continuous, uniform and with a precise diameter to within 0.002 in. [0.05 mm] throughout its length.8 Applied to standard 0.108- and 0.125-in. [2.74- and 3.25-mm] stainless steel alloy line, the outside diameter of the coated slickline is 0.138 and 0.153 in. [3.51 and 3.89 mm], respectively.

The resulting LIVE digital slickline retains all the strengths of the original wire upon which it is built. The system maintains tool power require-ments delivered from batteries and uses the slick wire as a telemetry conduit rather than as an electrical conduit. Because engineers designed the service to be a digital telemetry system rather than an electrical conduit, they were able to reduce insulation performance requirements and so hasten development. Engineers created another advantage by not sending power through the slickline. This feature eliminates concerns

about transmission reliability through an electric line, associated accessories such as sinker weights and the point at which the wire is con-nected to the toolstring. But the mechanical demands on the insulation-wire bond remain sig-nificant; the wire deployed using standard slick-line equipment must withstand the rigors of spooling on and off the drum, running around sheaves and through pressure-control equip-ment. It must also endure an often punishing downhole environment, and when it emerges from the well through the stuffing box, it is exposed to instantaneous decompression from wellhead to atmospheric pressure.

In 2009, those hurdles had been overcome and the first commercial jobs were performed successfully in Africa, France, Italy and Indonesia. Since that time, various applications within digital slickline services have been per-formed in France, Indonesia, China, the US and Saudi Arabia.

The core of the LIVE toolstring includes the computer baseboard management controller (BMC) that handles the telemetry downhole; delivers surface readouts of shock, line tension, deviation and movement in real time; and con-firms the success of operations such as perforat-ing (below). Surface equipment includes a slickline unit furnished with a computer and transceiver, pressure control equipment and the

> Surface confirmation of detonation. Multiple measurements displayed at the surface show the instantaneous effects of the firing of perforating guns just before 03:29:00. The shock curve (red) indicates a negative acceleration of more than 100 gn. At the same time, head tension (purple) increases from approximately 80 lbf [356 N] to more than 120 lbf [534 N] and pressure (blue) drops from 1,364 psi [9.4 MPa] to about 1,220 psi [8.4 MPa]. Tool movement is apparent on the CCL curve (green) immediately after gun detonation as the tool moves in the tubing, creating voltage across the CCL coil. Oscillation of the cable and gun after detonation is reflected in both the head tension and pressure curves. After the guns are fired, a decrease in temperature (orange) indicates cooler fluid is entering the tubing from the annulus. These indicators are independent verifications that the gun has been detonated on command.


Acce

lera

tion,

gn

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03:28:45 03:29:00 03:29:15 03:29:30 03:29:45 03:30:00

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digital line. Optional core downhole equipment includes a depth correlation cartridge, which delivers real-time CCL and GR measurements to provide depth accuracy during any slickline ser-vice; a digital pressure-temperature gauge may also be added for downhole measurements.

LIVE digital slickline services are divided into the typical intervention service classifica-tions: mechanical, remedial and measurement.The mechanical LIVE Act digital slickline ser-vices include conventional tools deployed as they would be on a standard slickline. Remedial ser-vices include LIVE Set setting services, which are nonexplosive, hydraulically set plug and retainer services; LIVE Seal sealing services, which use nonelastomeric sealing for monobore comple-tions; and LIVE Perf perforating, punch and pipe cutting services.9 The measurement segment of the service is the LIVE PL comprehensive suite of production logging tools. These services are run in conjunction with the core and optional tools and with real-time measurement and control.

In addition, LIVE services expand on tradi-tional capabilities and requirements by adding the digital D-Jar downhole adjustable jar, which can be commanded to repeatedly activate and deliver a specific force downhole. When using tra-ditional hydraulic or mechanical jars, operators rely on their experience and a weight indicator to determine jar action downhole. The D-Jar tool, in contrast, provides control and efficiency to jar-ring operations without requiring trips to the sur-face to adjust the impact force. It does so through repeated upward jarring using elasticity of the cable to store energy while the jarring action is delivered via the electrically triggered mechani-cal firing function. Downhole tension and shock are measured and monitored at the surface dur-ing operation, which allows an optimized jarring force without unnecessary stress on the tool-string or jarring of components. Engineers set jarring force by adjusting cable tension, which can be reset when and as often as necessary.

The digital controlled release (DCR) tool is another LIVE tool that may be added to any digi-tal slickline operation. In the event the toolstring becomes stuck downhole and cannot be freed, conventional slickline options include using a cutter bar to sever the wire as close to the tool-string as possible. The resulting fishing job may require numerous runs to gather, cut and retrieve any wire that remains in the well, sometimes fol-lowed by attempts using a braided wireline to latch onto and retrieve the stuck tool. This can be problematic if wire remains on top of the object

8. “GEM-Line Goes LIVE,” GeoWorld—The Geoservices Group Magazine 54 (December 2010): 4–7.

9. Punchers are perforating devices designed to penetrate the inner tubing string without damaging the surrounding casing.

being retrieved or the fishing neck has been dam-aged. Often, it requires numerous attempts to determine the nature and amount of the debris that is on top of the stuck tool and to then remove it before the stuck tool can be latched onto and retrieved. In contrast, the DCR tool provides a controlled separation of the toolstring assembly at or near the tool head, which instead of leaving wire behind, leaves only a defined internal and external fishing neck profile (above).

LIVE Set digital slickline setting services pro-vide a means for setting devices such as casing and tubing plugs and cement retainers without using traditional explosives-based systems. Using

> Digital controlled release. In the event a slickline tool becomes stuck, a signal from the surface decouples the DCR tool, allowing the operator to pull the top portion of the tool and all the wire from the hole, leaving clean internal and external fishing neck profiles facing upward (bottom). Depending on the DCR tool’s position in the well, or other factors affecting access, the operator may then use a cable wire or coiled tubing and either a fishing tool with collets that latch an internal profile (left) or an overshot-type tool (right) with collets that latch an external profile to retrieve the stuck tool.


Collet

Collets

Internalfishing

neckExternalfishing neck

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the surface-controlled D-Set digital electrohy-draulic setting tool, this service allows placement of downhole components on depth (left). This tool is a battery-powered electrohydraulic power unit that can generate up to 25 tons [249 kN] of force—sufficient to set permanent plugs, packers and other devices. Microhydraulics—miniatur-ized hydraulic pumps—can generate this force with limited power in a small package. Engineers control the depth of the tool accurately using a downhole GR and CCL. The D-Set tool uses a battery-powered electrohydraulic pump to gener-ate the power to create pull or movement, or stroke, necessary to set the device. During the setting sequence, diagnostic motor current, tool-string shock and head tension information is sent to the surface to confirm each step of the process.

The retrievable locking mandrel, one of the most versatile tools in the slickline toolbox, allows well intervention in monobore wells or completions with damaged landing nipples. Traditional slickline locking mandrels feature rubber seals that are extruded outward against the tubing wall for pressure containment. They are activated by an inner mandrel that moves downward behind them at the same time it forces slips to move out and grip the tubing. Engineers use these locking mandrels to carry plugs, pres-sure and temperature sensors and other tools to points in the tubing or casing that do not have landing nipples.

Unlike traditional locking mandrels, the LIVE Seal GeoLock digital sealing service uses a non-rubber kinematic sealing mechanism that does not deform when the tool is set (left). It can thus be used in the presence of gas and at high tem-peratures and pressures for prolonged periods—circumstances that often lead to failure of extruded rubber seals—and can be easily retrieved with standard slickline pulling tools. The anchoring and sealing devices maximize the mandrel’s internal flow area and, when retracted, reduce the mandrel OD while running in and out of the hole.

The GeoLock mandrel is run with the D-Set setting tool and a sequence consisting of central-izing, anchoring and sealing. Engineers can mon-itor the procedure from surface using a time plot of the complete sealing sequence. The tool and mandrel use a calibrated shear disk instead of a shear pin, which ensures a fully open flush tube with no internal restrictions once the tool is set.

Digital slickline also includes LIVE Perf perfo-rating services. With these services, operators can confidently and safely cut pipe for recovery, punch tubing and perforate at specified depths. The ser-vice employs the D-Trig digital activation device,

>D-Set electrohydraulic setting tool. The D-Set electrohydraulic unit contains three principal components: a high-temperature lithium battery, an electronics package and a hydraulic power unit (HPU). The lithium battery provides power. The electronics package converts the DC battery output to three-phase alternating current for the HPU’s electric motor and commands the hydraulic circuit. The battery and electronics package are isolated by means of a pressure barrier from the HPU. The HPU, which consists of the electric motor, microhydraulic pump and a solenoid valve is 54 mm [2.1 in.] in diameter by 510 mm [20.1 in.] in length. A smaller 43-mm [1.7-in.] diameter pump can generate nearly 6 tons [60 kN] of force. Within the HPU, the brushless electric motor is coupled to a fixed-displacement, microhydraulic axial piston pump (not shown). The motor is run at high speed for low-torque requirements, such as tool stroke, and switches to low speed for high-torque needs such as setting a tool or shearing a setting stud. Hydraulic pump output is routed to the tool’s mechanical section (not shown) through surface-controlled solenoids.


Microhydraulicpump

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> Setting without profiles. With a GeoLock mandrel, tools may be set in smooth tubulars having no internal setting profiles. When the tool is in the running position, the slips and seal elements (inset, bottom) are retracted, which minimizes the mandrel’s outside diameter and allows it to pass through tubing. Once the tool has been run to the desired depth, it is set using a LIVE D-Set digital setting tool or explosive setting tool to compress the tool, forcing cones to travel beneath the slips and seals. This expands the seals (inset, top) against the tubing wall. The mandrel may be retrieved using an electric or hydraulic tool that latches and returns the cones, seals and slips to their original positions.


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which allows surface-controlled activation of both explosive and nonexplosive devices. Like other DSL equipment, the D-Trig device uses the depth correlation cartridge real-time GR or CCL data to achieve accurate depth control. It is equipped with multiple fail-safe systems and is compatible with most industry perforating, punching and set-ting technologies.

The D-Trig activation device represents a sig-nificant advance in slickline triggers because it can be correlated in real time with surface read-out GR and CCL when deployed in combination with the depth correlation cartridge tool (right). This tool can fire all Schlumberger through- tubing perforating guns, hollow carrier guns, casing and tubing cutters and some third-party systems. The D-Trig system can also be used to initiate explosive setting tools.

The combination of the D-Trig system and the baseboard management controller (BMC), and other devices such as a quartz pressure gauge, enhances downhole shot detection. Crews can confidently identify misruns prior to retrieving the tools to surface. Within the BMC, shock detection and head tension changes give conclu-sive evidence that a device has fired. This can also be confirmed with downhole pressure and temperature measurements.

Another safety feature of the D-Trig service is a fuse that can be blown to disarm the trigger under certain conditions including disagree-ment between the microprocessors, drift in clock frequency within electronics, low BMC battery voltage and excessive time gaps in com-munication; the fuse can also be blown by opera-tor command.

When engineers replace high explosives with exploding bridgewire detonators or exploding foil detonators, the system becomes immune to early detonation caused by a number of factors:•radiofrequencyradiation•impressedcurrentcathodicprotection•electricwelding•high-tensionpowerlines.

The introduction of LIVE PL production log-ging services changed the industry’s dependence for these surveys on battery-operated memory tools or electric line. Arguably the most powerful tool for diagnosing the health of a well, produc-tion logs provide in situ measurements that describe the nature and behavior of fluids in the borehole during production or injection; produc-tion logs also help engineers determine which zones are contributing to fluid flow. But at wells with surface locations where space, weight or accessibility limits exclude use of large electric line units, the only option for obtaining a produc-tion log has been a battery-powered memory

slickline tool. The LIVE PL service offers an alternative to the larger electric line unit and delivers more accurate depth correlation than is possible with memory tools; in addition, the ser-vice sends logging data to the surface in real time while simultaneously storing it in memory.

Additionally, when engineers perform tran-sient buildup tests with digital slickline, they can monitor downhole pressure and temperature in real time and detect when the well has reached maximum bottomhole pressure (BHP). Obtaining this information in real time can reduce shut-in times. Data can therefore be used efficiently for reservoir monitoring, updating models and diag-nosing certain individual well conditions such as the existence and location of water sources.

Two for One Combining real-time downhole measurements with traditional slickline creates numerous ben-efits. For example, one operator discovered inherited wellbore schematics were in error. Had engineers chosen to shoot tubing perforations as originally planned, based on depths displayed on the schematic and without a CCL and GR for cor-relation, they would have tried and failed to puncture a blast joint located where the well schematic showed the target tubing joint. In this case, changes were made immediately as the job was progressing based on real-time GR and CCL data seen on the surface, allowing engineers to carry out the operation without additional time and, more importantly, without error.

> Digital trigger. The D-Trig device is controlled by redundant dual microprocessors and incorporates multiple fail-safe systems. A signal sent from surface is received by the tool, which generates a pulse to fire the detonator of the cutter or explosive tool (not shown). The device includes a battery that can fire either third-party exploding bridgewire detonators or Schlumberger Secure detonators. A separate smaller battery is mounted in the baseboard management controller (not shown) to power the electronics within the electronics cartridge. This design allows for a safety fuse to be placed between the firing battery and detonator (not shown) and adds a level of security to operations. In addition, a safety sub is placed between the detonator and the D-Trig tool and includes a safety pressure switch that automatically grounds the detonator when the device is at atmospheric pressure. The D-Trig device shown is electrically plugged into the detonator using a single spring monopin box connection.


Battery

Electronics cartridge

Safety fuse

Safety pressure switch

Spring monopin box connection

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24 Oilfield Review

In addition to risk management, efficiency and precision advantages, LIVE digital slickline services also enable engineers to perform certain types of jobs—operations that once required use of traditional slickline and electric line with a unit and a crew for each—with a single digital slickline unit and crew. For example, engineers often use both conventional electric line units with surface readouts to gather real-time mea-surements, and a slickline unit to perform mechanical operations on the same well. When performing such interventions in each of four producing zones, engineers traditionally first use a slickline unit to prepare the well for logging by running gauge rings, installing plugs and shifting sliding sleeves. They then run production logs using a separate electric line unit. This move-ment of equipment and personnel can lead to complicated logistics, high costs, increased

potential risks and lengthy operating time. Because LIVE digital slickline services can per-form the full scope of work, the single unit and crew cuts logistics and manpower requirements by half and reduces risks while saving significant overall rig time (above).

ATP Oil & Gas Corporation engineers seeking to capitalize on these efficiencies selected DSL services for a recompletion operation at Eugene Island Block 71, offshore Louisiana, USA. The zone isolation and recompletion operation was performed from the deck of a jackup vessel by first setting a through-tubing cast iron bridge plug and dumping 50 ft [15 m] of cement in 27/8-in. tubing to shut off a depleted lower zone at 12,790 to 12,875 ft [3,898 to 3,924 m].

Once the lower zone was plugged, the opera-tor planned to perforate a shallower interval at 12,668 to 12,678 ft [3,861 to 3,864 m] using six

shots-per-foot perforating guns (next page). Because the shallower target sand was thin, depth precision and accuracy were critical and could be achieved efficiently and in real time through the use of CCL and GR, an option for-merly available only with electric line. Because other parts of the operation, such as dump bail-ing the cement, required slickline tools, two crews would have been required to perform numerous rigging operations and equipment moves on the deck of the vessel. Using the LIVE depth correlation package with the LIVE Perf services, a single unit and crew accomplished the plug back and perforation operations. Total cost as a result of time saved was US$ 80,000 below the original authorization for expenditure.

In this instance, the operator realized savings by reducing the time required to mobilize and move electric line and slickline units on and off the well and around the deck and by eliminating the standby costs associated with a second crew. In other cases, there may be additional savings because space and weight requirements are reduced when only one unit is deployed, allowing the operator to hire a less expensive lift vessel with reduced deck capacity. In some instances, because of the slickline equipment’s relatively small footprint and light weight, an operator may be able to place the unit directly on the deck of a platform too small to accommodate larger, heavier electric line equipment. This may elimi-nate the cost of a service vessel entirely, resulting in significant savings.

Cost reduction as a function of time can quickly multiply depending on environment. For example, in relatively shallow waters, interven-tions may be performed from the deck of lift boats for which the day rate ranges from about US$ 4,000 to as much US$ 40,000 as a function of water-depth capabilities and deck space. However, savings can skyrocket when work is slated for water beyond lift boat depth capabili-ties, which is about 60 m [200 ft], in relatively calm waters such as offshore West Africa and in the Gulf of Mexico. The cutoff depth is even shal-lower in areas of typically rougher waters such as the North Sea.

In deeper waters, an operator may use a semi-submersible or dynamically positioned drilling unit whose costs are much higher than jackup vessels. And in deep and ultradeep water, opera-tors must use specially designed deepwater drill-ing units. The day rate for these giant units is around US$ 1 million. Saving a few days or even a few hours to perform slickline and electric line work can quickly yield significant savings.

> Single-unit logging operation. Typically, operators use a slickline unit to prepare a well for logging by first performing gauge ring runs, installing plugs and locking out the surface-controlled subsurface safety valve (SSV). They then use an electric line unit to acquire production log data. For one typical operation requiring a static pressure gradient, drawdown and shut-in pressure and temperature survey for each producing zone, the operator scheduled the program to take 168 hours using slickline and electric line independently. By using DSL services to perform both conventional slickline and electric line surface readout operations, the operator saved more than 10 hours and eliminated an extra crew and logging unit.


Day

1

2

3

4

5

6

7

Rig up and runfirst gauge ring.

Digital Slickline Slickline Plus Electric Line

Performstatic gradient

survey andfirst shut-in.


survey and flow well.


survey, flow welland perform buildup.

Install plugs, shift sliding sleeves and

run fourth gauge ring.

Perform buildup survey and rig down.

10 hours saved

Run second gauge ring.

Run third gauge ring.

Install plugs, shiftsliding sleeves and run fourth gauge ring.

Close sliding sleeve,install SSV and rig down.

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Winter 2011/2012 25

In the deepwater Green Canyon area of the Gulf of Mexico, Nexen Petroleum USA leased the deepwater rig Ocean Saratoga to plug and aban-don (P&A) a well in about 900 ft [275 m] of water, about 100 mi [160 km] off the Louisiana coast. Typically, this phase of the P&A operation would have required preparatory work on slickline, fol-lowed by tubing punching and tubing cutting, which require accurate depth correlation using electric line. Nexen engineers turned to digital slickline to perform all P&A operations using a single slickline unit. Their objective for this high-cost environment was considerable savings through operational efficiencies—such as fewer rig-up and rig-down operations.

Digital slickline was used successfully for depth correlation and the subsequent tubing punching operation at 10,030 ft [3,057 m]. Tool shock measurements displayed at the surface in real time clearly indicated the successful firing of the puncher. The operator benefited from the value of a smooth, depth-correlated puncher oper-ation, and as a result, realized significant savings in this high-cost environment. Some of these sav-ings were achieved because the operator was not forced to pay standby costs for two crews when unforseen delays idled the rig for several days.

Executing such interventions with digital slickline instead of electric line also reduces risk because its pressure control equipment is less complex. During pressure control events, if it becomes necessary to cut the line, it is easier to cut slickline than thicker electric line that may be across the wellhead.

A Very Large NicheAs operating environments become increasingly more challenging in places such as the Gulf of Mexico and the North Sea, operators are actively seeking ways to control costs. Digital slickline, which offers the robust simplicity of slickline while maintaining the versatility of electric line, is poised to play a significant role in that quest. Its suitability for P&A operations will no doubt draw particular attention as aging wells in the North Sea and the Gulf of Mexico drive a push by regulators for large-scale platform decommissioning.

Engineers are likely to adopt digital slickline technology as part of a well’s completion strat-egy. It maintains the basic simplicity and famil-iarity of slickline and is thus far less intrusive than other recent innovations such as intelligent completions or monobore wells, whose complex-ity sparked years of resistance from an industry as concerned with the cost of failure as with potential benefits. A failure of an intelligent well or a monobore installation may result in loss of

an entire wellbore and almost certainly in the loss of many thousands of dollars spent in repair costs and delayed production. In contrast, the worst-case scenario of a digital slickline opera-tion failure is lost time while an electric line unit is brought in to finish the job.

In a post-Macondo world, operators are eager to seize any safety advantage, which means the benefits of digital slickline may be more than cost and time savings. Because digital slickline often allows a single crew with a single unit to provide services that once required two units and crews, it can significantly ease personnel and equip-ment movement logistics and thereby enhance safety and reduce environmental risk. This may be especially important in remote locations where transportation is difficult and offshore, where space, weight and environmental consid-erations are paramount.

There are also some simple but important and practical advantages to choosing digital slickline over electric line for certain offshore operations. For example, several industry efforts to develop riserless intervention techniques on subsea wells are ongoing. Slickline may have an edge over wireline in this application because it is very dif-ficult to manage a grease seal during subsea riserless operations. In this environment, the slickline-style stuffing box used in conjunction with digital slickline could prove to be one of the critical components that brings deepwater riser-less intervention into the mainstream. This tech-nology upgrade is long overdue for a service that has been used since the turn of the last century; digital slickline services may soon move from technology trial status to best practice. —RvF

>Wellbore schematic. Operator ATP Oil & Gas decided to plug the reservoir C sand at its Eugene Island Block 71 field and move uphole to perforate the B sand. Because the B sand is just 10 ft [3 m] thick, depth accuracy was critical. Obtaining that level of accuracy traditionally required the use of an electric logging unit for perforating. For this operation, the crew used only a LIVE digital slickline unit to first set a cast-iron bridge plug in the lower tubing string, dump 50 ft of cement on top of it and perforate the casing across the thin B sand precisely on depth. Unless otherwise marked, all depths are measured depth (MD).


60-in. by 48-in. casing at 224 ft

16-in. casing at 810 ft

10 3/4-in. casing at 3,970 ft

75/8-in. casing at 12,032 ft

5 1/2-in. packer at 12,487 ftB sand perforations12,668 ft to 12,678 ft MD12,070 ft to 12,080 ft TVD

C sand perforations12,790 ft to 12,875 ft MD12,144 ft to 12,200 ft TVD

D upper sand perforations13,448 ft to 13,472 ft MD12,588 ft to 12,604 ft TVD

5 1/2-in. packer at 12,700 ft

Cast-iron bridge plug

Isolation packer at 12,886 ft

Isolation packer at 13,311 ft

Sump packer at 13,482 ft

13,802 ft MD12,817 ft TVD

5 1/2-in. casing at 13,802 ft

Sliding sleeve at 12,870 ft

50 ft of cement

Sliding sleeve at 13,449 ft

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