Oilfield Review Summer 2011: 23, No
Conveyance—Down and Out in the Oil Field
Well productivity can be greatly enhanced by drilling high-angle wells or by directing the wellbore into multiple targets. In such wells, traditional methods for conveying evaluation, remediation and intervention tools are no longer practical. In response to the challenges presented by complex well trajectories, service companies have developed numerous innovations for accessing and evaluating these complicated wellbores.
Matthew Billingham You can’t push a rope. Many a frustrated wireline by a well, the measured depth of horizontal wells Roissy-en-France, France engineer has uttered those words when logging often far exceeds their true vertical depth tools failed to reach the bottom of a well, espe- (TVD). In 2010, more than 16,000 horizontal Ahmed M. El-Toukhy cially in high-angle wells. But the source of that wells were drilled worldwide.1 This number does Perth, Western Australia, Australia frustration has been overcome—at least in some not include thousands more wells drilled direc- respects—by the introduction of new convey- tionally to reach targets far from the surface Mohamed K. Hashem ance methods. These developments enable evalu- entry point or reach multiple zones separated by Saudi Aramco ation, completion and remediation not only in great lateral distances. Dhahran, Saudi Arabia high-angle wells but also in long horizontal With today’s technology, drilling engineers Mohamed Hassaan wellbores, environments that previously pre- can create such complex wellbore geometries Doha, Qatar sented insurmountable challenges to traditional that delivering downhole tools to a targeted logging methods. formation becomes a challenge. These wells Maria Lorente In the days when most wells were vertical, require evaluation information when they are Todor Sheiretov delivering logging tools to total depth and back drilled, and they will also require some means to Sugar Land, Texas, USA was a relatively straightforward task. A truck- access the reservoir for future evaluation and powered winch containing a spool of cable ran intervention.2 Matthew Loth the tools in and retrieved them from the well. The A number of technologies have been devel- Clamart, France tools were pulled to the bottom of a well by grav- oped to address the difficulties created by com- ity. The cable was also used to communicate with plex wellbore trajectories. Whereas in the past, Oilfield Review Summer 2011: 23, no. 2. Copyright © 2011 Schlumberger. the tools, provide power and send information the primary consideration was simply which Blue Streak, EcoScope, FMI, Litho-Density, MaxTRAC, about the downhole environment back to the sur- tools to run, today, engineers must also consider Multi Express, SFL, TLC and TuffTRAC are marks of face. This method of conveyance sufficed for how to optimally evaluate, access and perform Schlumberger. IntelliServ is a mark of National Oilwell Varco. openhole logging, cased hole evaluation and run- remedial work for the life of a well. Fortunately, ning mechanical services, which included perfo- the restrictive reliance on gravity to pull logging 1. Drilling and Production Outlook. Spears & Associates: Tulsa (June 2011): 17. rating. But today, gravity is not the only means of tools attached to a cable has been replaced by 2. For more on horizontal drilling practices: Bennetzen B, getting tools to the bottom of the well, and cables an expanding battery of methods, equipment Fuller J, Isevcan E, Krepp T, Meehan R, Mohammed N, Poupeau J-F and Sonowal K: “Extended-Reach Wells,” are not the only means of delivering data to the and techniques. Petrophysicists and engineers Oilfield Review 22, no. 3 (Autumn 2010): 4–15. surface; tool delivery, data transmission and now have a plethora of choices. This article equipment deployment methods abound. reviews some of these methods and also looks at This shift in techniques and methodology has recently introduced technologies that offer developed in large part to meet the needs of greater flexibility in data acquisition choices. wells drilled at high angles. Whereas TD once implied the deepest point in the Earth reached
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41615schD5R1.indd 18 8/12/11 8:02 PM WWireline ire line
CCoiled Tubing oile d Tu bing
LLoggingo Tools on Drillpipe ggin g To ols on D rill pipe
DDownhole Tractor own hole Tra ctor
LLoggingo While Drilling ggi ng W hile Dri lling
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41615schD5R1.indd 19 8/12/11 8:02 PM Surface units used for acquisition also became Advantages Disdavantages more and more sophisticated. But the well logging Wireline- • Suitable for both formation • Gravity dependent gravity evaluation and production services • Vulnerable to hole irregularities landscape experienced its most dramatic transfor- conveyance • Largest selection of tools mation in the 1980s with the introduction of • Fast logging-while-drilling (LWD) tools. Downhole • Compatible with wireline, slickline • Not suitable for every well LWD tools are an integral part of the drill- • tractors and coiled tubing conveyance Primarily a cased hole service string bottomhole assembly (BHA). In the early • Highest operational efficiency for • Retrieval risks with horizontal horizontal intervention intervention days, measurements were fairly basic; they • Requires minimal number of field • Expensive downhole equipment included gamma ray and resistivity, followed by personnel the addition of porosity measurements. The tools Pumpdown • High success rate • Requires a return or exit path Cable conveyed communicate via a series of pressure pulses conveyance • High operational efficiency for the fluid • Low cost • Limited applicability transmitted through the circulating drilling mud to convey commands downhole and deliver data Slickline • Highest operational efficiency of • Primarily cased hole all conveyance methods intervention to the surface. These pressure pulses are encoded • Low cost • Gravity dependent with data about well conditions, the status of the • Limited tool offerings BHA and the formations encountered by the bit. Coiled tubing • Suitable for a variety of logging, • Primarily cased hole and Mud pulse telemetry transmits data at rates conveyance stimulation, perforating and producing well intervention mechanical services • Limited reach due to that are several orders of magnitude lower than • High success rate helical lockup those achieved using logging cables; but, given • Ability to access horizontal and • Large footprint and crew deviated wells requirements compared with those the time required for drilling operations, this of other intervention methods method has generally proved to be sufficient.
Drillpipe • Highest success rate in difficult • Not suitable for producing wells Other transmission methods are available; for combined conditions • Time-consuming example, electromagnetic telemetry is used as an with wireline • Gravity independent • Limited reach in very difficult alternative to mud pulse telemetry in air or foam • Cable-pipe conveyed Supports most conventional conditions formation evaluation tools • Not suitable for fragile tools drilling. And more recently, wired drillpipe, • Highest temperature and • Complications due to presence which can send data using an imbedded trans- pressure rating of logging cable • Maintains well control mission cable, has been introduced. Wired drillpipe promises high data rates: Drillpipe- • Highest chance of success in • Not suitable for cased hole or LWD difficult conditions intervention in producing wells 57,000 bits per second compared with 10 bits per • Gravity independent • Expensive second with mud pulse telemetry. Commercial • Maintains well control • Smaller selection of tools compared with wireline transmission systems, such as the IntelliServ Broadband Network, are currently available, Drillpipe- • High success rate in difficult • Limited tool offering wireless conditions • Limited logging time although this technology has yet to replace mud
Pipe conveyed • Gravity independent • Relatively slow pulse telemetry as the method of choice for ser- • Highest efficiency among • Expensive downhole equipment vice companies and operators. drillpipe conveyance methods • Maintains well control Whichever method is used, the ability to acquire real-time data from near the bit not only > Conveyance methods. offers a substitute for wireline logging, but also has led to a revolution in the application of rotary steerable drilling systems, ushering in a new age Getting to the Bottom and hybrid solutions that blend elements of the of horizontal and extended-reach drilling.4 Using Conveyance consists of more than the mecha- other. The various methods come with trade-offs, real-time information provided by LWD tools, nisms of pulling and pushing tools downhole. Its strengths and weaknesses, so there is rarely a directional drillers can remotely steer and guide greater purpose is to address the challenges cre- perfect solution. the bit to specific targets, making precise correc- ated by wellbore environments. These challenges Cable-conveyed tools have a long history. The tions in wellbore trajectory. include deploying tools at the surface, overcom- first electric log, acquired at Pechelbronn field in As well trajectories shifted from vertical to ing frictional forces, maneuvering past obstacles Alsace, France, on September 5, 1927, was run on horizontal, LWD data, in many cases, supplanted and adapting to unforeseen downhole conditions.Oilfield Review a cable. The survey instrument was lowered 300 m traditional wireline logging for formation evalua- Flexibility and adaptability are importantSUMMER factors 11[980 ft] into the well, and subsurface measure- tion. Meanwhile, the quality and scope of LWD Conveyance Fig. Table 1 that engineers consider when deployingORSUM11-CONVY tools ments were Table plotted 1 by hand as the tool was slowly data have improved, and sophisticated tool offer- downhole, but their tool choices often dictate the retrieved using a manually operated winch (next ings are now available while drilling. For instance, method of conveyance. page, top right). For the next 50 years, the logging the EcoScope multifunction LWD service offers Conveyance methods can be grouped into two industry remained tethered to a cable, even as log- resistivity, porosity, azimuthal density, ultrasonic basic types: cable conveyed and pipe conveyed ging tools evolved to include extremely complex caliper, capture spectroscopy and azimuthal (above). Within both categories are variations measurements that demand high data rates.3
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41615schD5R1.indd 20 8/12/11 8:02 PM gamma ray measurements in one compact tool (below right).5 Instead of a chemical radioactive source for neutrons, the tool uses a pulsed neu- tron generator powered by a turbine, which is driven by circulating mud. The tool also includes a variety of sensors that provide information to improve drilling operations. Logging companies can perform advanced services such as seismic, acoustic and magnetic resonance logging while drilling. Pressure mea- surements and sampling, which have long been exclusively in the wireline logging domain, can now be carried out with LWD tools as well. Engineers developing log evaluation pro- grams, however, have more to consider than mea- surement technology when deciding on which services to run. For example, temperature and > Birth of an industry. The first logging operation, which used a hand- pressure limits are generally lower for LWD tools. operated winch similar to the one shown, was performed in 1927 at the And there are size limitations because LWD tools Pechelbronn field in Alsace, France. Using a spool of cable containing a are designed for specific ranges of borehole conductor wire, operators lowered a survey instrument into the well and recorded resistivity measurements at the surface. Hand-plotted data were diameters, whereas wireline tools can be used in presented versus depth, and this first well log launched a new industry. a much broader range. There are also higher costs associated with deploying LWD equipment for long periods of time during the drilling pro- cess compared to logging with wireline tools. Holding on or Cutting the Wire engineers developed and attempted various Although the gap between wireline and LWD Drillers can negotiate high-angle and difficult methods to get past obstructions. Operators have offerings continues to narrow, there are some wellbores because drillpipe is stiff and heavy. welded chains to the bottom of tools hoping that services that are not available while drilling. This is not the case with tools at the end of a wire- the chain would pile up on a ledge and eventually These include high-data-rate services, such as line. In the past, when TD could not be reached fall off and pull the tool downhole. Weight the FMI formation microimager tool, tools requir- with logging tools because of well conditions, bars, friction-reducing wheels and rollers have ing high power, such as sidewall coring tools, and other technologies that have yet to migrate to LWD platforms. Eventually, the rig moves on to drill the next Porosity Sigma well, and LWD tools can no longer be used for Spectroscopy data transmission. Even if they were available, Neutron gamma density LWD tools were not developed to perform cased Annular pressure Azimuthal density hole services. Wireline tools are needed to evalu- while drilling and photoelectric factor Oilfield Review ate and access the reservoir, although getting SUMMER 11 them to the bottom of horizontal and high-angle Azimuthal natural Conveyance Fig. 1 gamma ray wells is problematic. Thus, alternative means of ORSUM11-CONVY 1 2-MHz and conveyance have been developed to deliver 400-kHz resistivity these tools.
3. For more on advances in cable-logging systems: Alden M, Ultrasonic caliper Arif F, Billingham M, Grønnerød N, Harvey S, Richards ME and West C: “Advancing Downhole Conveyance,” Oilfield Review 16, no. 3 (Autumn 2004): 30–43. Three-axis 4. For more on rotary steerable drilling: Williams M: “Better shock and vibration Turns for Rotary Steerable Drilling,” Oilfield Review 16, no. 1 (Spring 2004): 4–9. Inclination 5. Japan Oil, Gas and Metals National Corporation (JOGMEC), formerly Japan National Oil Corporation > (JNOC), and Schlumberger collaborated on a research Logging-while-driling tools. The EcoScope multifunction LWD service is a reflection of the advances project to develop LWD technology that reduces the need that have taken place in drillpipe-conveyed logging services. This compact tool provides the basic for traditional chemical sources. Designed around the measurements of a wireline triple-combo log—resistivity, density porosity, neutron porosity and gamma pulsed neutron generator (PNG), EcoScope service uses ray—plus neutron capture spectroscopy. Using neutrons produced from a pulsed neutron generator technology that resulted from this collaboration. The PNG and the comprehensive suite of measurements in a single (PNG), capture spectroscopy provides crucial information about lithology and mineralogy. Formation collar are key components of the EcoScope service that evaluation data are acquired as well as information about drilling operations, including shock, vibration, deliver game-changing LWD technology. annular pressure while drilling and tool inclination.
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Oilfield Review SUMMER 11 Conveyance Fig. 2 ORSUM11-CONVY 2 Before After Deployment Deployment
Connection to drillpipe Logging truck
Ejector
Logging cable Deployment outside Logging cable head drillpipe setup in CSES Drillpipe Cable clamp Multi Express Cable side tools entry sub Packoff seal (CSES) assembly Concentric Check valve housings Logging cable inside drillpipe Casing shoe Wet-connect adaptor Logging string
Horizontal openhole section Receiver Receiver and shoe and shoe > Tough logging conditions. Before LWD tools were widely available, the Deployment TLC system conveyed wireline tools via drillpipe. Logging tools are attached head to the drillpipe using a crossover adaptor with a wet-connect device. Tools are run in the hole to the bottom of casing, and a mating connector, Multi Express attached to the logging cable, is threaded through a side entry sub and tools pumped down the drillstring until it engages the downhole connector. Once communication and power are established, the tools are pushed out into open hole and down to the bottom of the well. Because the cable is exposed above the side entry sub, it is not allowed to exit the bottom of casing for fear of damage to the cable, and extreme care must also be exercised while running in the hole to avoid crushing the cable. The logging tools, which are at the end of the drillpipe, are also at risk of being damaged in open hole. Most wireline logging tools can be run using this system.
been developed to facilitate tool movement. A modified technique, logging while fishing > Schlumberger engineers even designed an articu- (LWF), uses a concept similar to the TLC system. Carrier conveyed logging. Special logging tools can be conveyed inside a protective carrier and lated bottom nose that could be manipulated Should a conventional wireline logging tool run in hole on drillpipe (left). Once the desired from the surface to locate the wellbore path become stuck in the well while logging, a cut-and- depth is reached, the tools are ejected through when the tools stopped on ledges or where the thread fishing operation is performed to engage the bottom of the drillpipe (right). The tools then hole exhibited large washouts. These attempts to the stuck tool with a grapple attached to the end of acquire data, which are stored in memory, as the drillpipe is pulled out of the hole. At surface, data overcome geometry and borehole irregularities drillpipe. The severed cable is reconnected at sur- are read and merged with a depth-time reference typically met with limited success. face to provide power and communication to the log. Conventional depth-based logs are generated However, before the widespread acceptanceOilfield Review downhole tools, and then data are acquired as the from the merged data. The tools must have small SUMMER 11 diameters to fit inside the carrier; one example, of LWD tools, methods existed for conveying con- pipe and tools are pulled out. This operation has 1 the 2/4-in. Multi Express service provides a ventional openhole logging tools at theConveyance end of beenFig. 3performed when crucial data were needed ORSUM11-CONVY 3 triple-combo toolstring plus a sonic tool option. drillpipe. Among them was the TLC tough logging but hole conditions made logging impossible. This carrier conveyanceOilfield Review system permits fluid conditions system. Logging tools, minus the Both TLC and LWF methods are still in use circulation andSUMMER pipe rotation 11 while running into the well and while logging. cable, were attached to the end of the drillpipe today, offering the capability to acquire informa- Conveyance Fig. 4 ORSUM11-CONVY 4 and pushed to the bottom of casing. Next, a spe- tion that would otherwise be unobtainable. cially designed connector, attached to the logging However, the process of running in the hole and cable, was pumped down through the inside of logging can be slow. Perhaps more significant, drillpipe and BHAs, the relatively fragile logging the pipe (above left). A wet-connect device the operator has little control over the tools at tools can be easily crushed or damaged. Engineers latched onto the downhole toolstring to provide the end of the drillpipe during TLC operations. have designed specialized hardware and protec- power and communication to the tools. The drill- Drillers must also take precautions to avoid dam- tive equipment as accessories to protect the pipe then pushed the tools into the open hole and aging the exposed logging cable and the tools tools, but a risk associated with pushing exposed on to the bottom of the well. while running them in the hole. Compared with tools through open hole remains.
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41615schD5R1.indd 22 8/12/11 8:02 PM Telemetry–Neutron–Gamma Ray Tool Length 3.1 m [10.2 ft], weight 33.1 kg [73 lbm]
Litho-Density Tool Length 3.1 m [10.2 ft], weight 40.8 kg [90 lbm]
Sonic Tool Length 4.3 m [14.4 ft], weight 40.8 kg
Audio-Temperature Tool Length 2.0 m [6.5 ft], weight 20.4 kg [45 lbm]
Spherically Focused Resistivity Tool Length 3.8 m [12.5 ft], weight 30.4 kg [67 lbm]
Induction Resistivity Tool Length 4.9 m [16.0 ft], weight 40.8 kg
> Multi Express platform. The compact, lightweight Multi Express platform offers gamma ray–neutron (thermal and epithermal), Litho-Density, sonic, audio-temperature, spherically focused resistivity and induction resistivity tools. The sonic tool includes a cement bond logging option and the telemetry cartridge includes a casing collar tool.
Even with protective hardware, openhole log- Because they are deployed inside drillpipe, acquire both thermal and epithermal neutron ging tools may encounter ledges, bridged sec- the tools must have a smaller diameter than porosity data. It includes a casing collar locator tions of open hole and large washed-out conventional logging equipment. The recently for depth correlation, which can be used with wellbores, making it impossible to push the tools introduced Multi Express slim, multiconveyance cement bond logging. The sonic tool can be run to bottom. Drillers often attempt pipe rotation to formation evaluation platform is an example of a in openhole mode for borehole-compensated get around obstructions, which is not an option set of tools that can be deployed using the protec- sonic data or in cased hole mode for cement 1 when tools are attached with TLC operations. tive drillpipe carrier. With a 2/4-in. [5.7-cm] diam- bond logging. A recent adaptation of the TLC concept has eter, these tools fit inside the 5-in. [12.7-cm] OD While developing this tool platform, engi- been developed that uses drillpipe to convey log- carrier with enough clearance to circulate mud neers focused on minimizing tool length and Oilfield Review ging tools. The main differences are that the tools downhole.SUMMER The ability 11 to circulate is an important weight. A triple-combo toolstring—induction, are protected inside a carrier while they are being feature forConveyance running drillpipe Fig. 5 into the well, espe- density and neutron tools—consists of three run in the hole and no logging cable is required cially in longORSUM11-CONVY horizontal openhole 5 sections in devices of approximately 3 m [10 ft] each and is (previous page, top right). Once the drillstring which cuttings can accumulate. 9.75 m [32 ft] long when fully assembled. The reaches the logging depth, the field engineer uses The Multi Express platform includes induc- 4.3-m [14.4-ft] sonic tool can be included as well. an ejection mechanism to deploy battery-powered tion, Litho-Density, thermal and epithermal neu- The Multi Express family of tools was designed to tools. Extended beneath the bottom of the drill- tron porosity and array acoustic tools (above). be handled by one person; the heaviest tool pipe, these tools acquire downhole data, which are The induction tool acquires data at two depths of weighs 40.8 kg [90 lbm]. stored in memory while the drillpipe is being investigation—deep and medium resistivity— The Multi Express tools are ideal for logging pulled out of the hole. Pipe movement is recorded and an optional tool section can acquire shallow small wellbores, shallow wells and air-filled versus time during retrieval. At surface, the time- SFL spherically focused resistivity data. The holes. The platform includes the tools mentioned based data from downhole are recovered using a density tool has an articulated pad and caliper to above plus an audio-temperature tool, which sup- laptop computer and then merged with the depth provide good borehole contact. The compact plies important measurements in coalbed meth- data from pipe movement to generate conven- telemetry–neutron–gamma ray section can ane and shallow air-drilled tight gas wells. These tional depth logs. A logging truck is not required.
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41615schD5R1.indd 6 8/19/11 11:05 PM types of wells can be difficult to evaluate with conventional logging units because the wells have small drilling pads and the rigs move quickly from wellsite to wellsite. Logging engineers can access wells for both openhole logging and cement bond logging using fit-for-purpose logging trucks with integrated masts, such as the Blue Streak high-efficiency unit (left). Drilling and workover rigs are not required when engineers use these small, self-contained logging units. Monocables—logging cables with a single conductor—are generally used instead of multiconductor cables that are common with con- ventional logging tool systems. With the memory recording option, the Multi Express tools can also be run with cables that have no conductor. This adds the capability of using slickline units for openhole logging, although there is no surface readout using this method. Data acquisition and quality are con- firmed after the tools have returned to the sur- face and the stored information is retrieved. > Fit-for-purpose conveyance. The Blue Streak logging truck is a self-contained unit with its own mast, Smart Iron cable and acquisition system. Conventional openhole logging units commonly use large cables with multiple conductors to provide power, control downhole tools and acquire logging data. The Multi Express Conveyance at the end of pipe is not limited to tools can be run with a smaller monoconductor cable, which allows a smaller winch and spool. The LWD and TLC operations; pipe-conveyed methods memory logging mode of the Multi Express tools, utilized with the drillpipe-carrier method, can also be include coiled tubing (CT) logging (below left). used with slickline units (inset), allowing logging without the need for surface-supplied power. This proven system of tool deployment, intro- duced in the mid-1980s, is often used for produc- tion logging (PL) and perforating. CT units may include a cable inside the tubing to provide power to downhole tools and relay real-time mea- surements to the surface. In the absence of an integrated wire, logging can be performed in memory mode using tools that store data for retrieval once they return to the surface. Perforating, as with conventional tubing- conveyed perforating (TCP) operations, can be initiated with surface-applied pressure to acti- Oilfield Review SUMMER 11 Injector head vate guns, but the integrated wire gives greater Conveyance Fig. 6 control and offers engineers the option of send- ORSUM11-CONVY 6 ing power from surface to fire guns sequentially. Tubing reel A major limiting factor in using CT is that it Control cabin ceases to make progress, or locks up, beyond Power pack about 900 m [3,000 ft] of horizontal section. Lockup occurs because the tubing assumes a helical shape as it comes off the reel, resulting in increased friction between the casing and the tubing. When frictional forces reach a critical point, more tubing can be injected into the well, but the end of the string cannot be pushed deeper into the wellbore. Several options can be > employed to extend this limit: CT straighteners Coiled tubing unit. A CT unit is made up of four basic components: a reel to store and transport reduce residual bend and friction, filling the tub- the coiled tubing (diameter ranging from 1 in. to 3.25 in.), an injector head designed to drive the CT downhole and retrieve it from the well, a control cabin and a power pack. The tubing may include a ing with nitrogen can provide added buoyancy, monoconductor cable for wireline logging and perforating. friction reducers may extend length capability
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Oilfield Review SUMMER 11 Conveyance Fig. 7 ORSUM11-CONVY 7 and larger diameter tubing can often go deeper Pumpdown Return but requires much larger surface equipment.6 side side ExxonMobil, in developing the Sakhalin Island land-based offshore Chayvo field in Russia, tested a hydraulically actuated CT tractor to extend the reach of operations.7 The field is located offshore, but drilling and production facilities are located on land. To access their wells, ExxonMobil engi- Tubing string neers needed to increase the CT range beyond Cable that possible with existing hardware. Although much of the equipment was standard for CT units, Tubing string engineers made several modifications to accom- 3 modate a 35,006-ft [10,670-m] reel of 2/8-in. OD Casing coiled tubing. Swab Casing shoe cup This hydraulic CT tractor was powered and Centralizers controlled by differential pressure between the tubing and the annulus. The assembly was tested prior to job commencement and had 9,700 lbm Stinger [43,148 kg] of pull and nominal operating speed of 950 ft/h [290 m/h]. During the job, a 31,938-ft
[9,735-m] well was successfully logged with PL 7-in. slotted liner PL tool tools and 1,050 ft [320 m] was perforated with > Horizontal production logging. A production log (PL) can provide a flow profile of horizontal wells and 3 8 3/8-in. [8.57-cm] casing guns. identify producing zones. But, in the 1980s, getting tools to TD in a horizontal well was a problem. One Although the operation was a success, engi- early scheme used a dual completion to circulate and flow the well through one string. The other string neers discovered that using coiled tubing for fre- was used to pump tools down to the bottom of the well. A stiff stinger was attached to the tool and quent PL runs was not viable. Excessive wear fluid pressure was applied to the swab cups at the top of the stinger to provide locomotion. Although the necessary data were acquired, this type of operation is not feasible in most wells. (Adapted from experienced by the coil, high cost and poor data Joly et al, reference 10.) quality at low flow rates led to the eventual aban- donment of the CT technique for PL logging in the field.9 For routine operations, the industry needed an alternative to logging with a CT unit. were attached to a stiff upper section—a flexibility, efficiency and cost savings to cased stinger—outfitted with swab cups for locomotion hole evaluation and intervention in horizontal Going Around the Bend (above). Pressure applied to the top of the stinger wells. Within 10 years of Elf’s pumpdown logging In 1988, Elf Aquitane made one of the first forced the tool out the bottom of the tubing until experiment, operators were routinely using trac- recorded attempts to log a cased horizontal well it reached the end of the horizontal section. A tors for the majority of their well interventions in with PL tools.10 The operator was developing the 600-m [1,970-ft] stinger was necessary to ensure horizontal and high-angle wells.11 Rospo Mare pilot project offshore Italy to pro- the PL tool reached TD while the top of the 6. AL-Amer AA, AL-Dossary BA, AL-Furaidan YA and duce viscous oil trapped in a karst formation. The stinger remained inside the tubing. After a trial Hashem MK: “Tractoring—A New Era in Horizontal company drilled three pilot wells: a vertical, a run in an onshore horizontal test well, the tech- Logging for Ghawar Field, Saudi Arabia,” paper SPE 93260, presented at the 14th SPE Middle East Oil high-angle deviated and a horizontal well. The nique was successfully applied to OilfieldElf’s offshore Review and Gas Show and Conference, Manama, Bahrain, SUMMER 11 vertical and deviated wells penetrated approxi- well and provided essential information for fur- March 12–15, 2005. Conveyance Fig. 8 7. Moore NB, Krueger E, Bloom D, Mock PW and Veselka A: mately 30 m [100 ft] of formation. The horizontal ther field development. ORSUM11-CONVY 8“Delivering Perforation Strings in Extended-Reach Wells contacted more than 600 m [1,970 ft] of the The complex nature of the design required to With Coiled Tubing and Hydraulic Tractor,” paper SPE 94208, presented at the SPE/ICoTA Coiled Tubing reservoir. The surprisingly high productivity run the PL tool underscores the challenges of Conference and Exhibition, The Woodlands, Texas, USA, obtained in the horizontal well compared with evaluating, completing and performing remedia- April 12–13, 2005. that in the conventional wells led to a pressing tion of wells with horizontal and high-angle tra- 8. Moore et al, reference 7. 9. Fitz DE, Guzmán-Garcia A, Sunder R, Billingham M and need to discover the drainage mechanism. A jectories. Few operators have the luxury of Smolensky V: “Pushing the Envelope for Production proper understanding of the production profile running dual tubing strings just to acquire pro- Logging in Extended Reach Horizontal Wells in Chayvo Field, Sakhalin, Russia—New Conveyance and Flow would greatly impact future development plans duction logs, but in the late 1980s there were not Profiling Approach,” paper SPE 103589, presented at the for the field. many alternatives. SPE Russian Oil and Gas Technical Conference and Exhibition, Moscow, October 3–6, 2006. Elf engineers, in conjunction with field opera- This dearth of options for accessing horizon- 10. Joly EL, Dormigny AM, Catala GN, Pincon FP and tions staff from Schlumberger, designed an elab- tal wells was first addressed with the introduc- Louis AJP: “New Production Logging Technique for orate method to run a PL tool across the tion of wired CT units. As ExxonMobil discovered Horizontal Wells,” paper SPE 14463, presented at the SPE Annual Technical Conference and Exhibition, producing interval and generate a flow profile. A in the Chayvo field, PL logging on coiled tubing Las Vegas, Nevada, USA, September 22–25, 1985. dual-tubing completion string was installed to can be expensive, and data quality can suffer. 11. Hallundbæk J, Haukvik J, Østvang K and Skeie T: “Wireline Well Tractor: Case Histories,” paper OTC 8535, allow fluid circulation in one string and to pro- Downhole wireline tractors, developed in the presented at the Offshore Technology Conference, duce the well through the other. The PL tools 1990s, provided an alternative to CT units, adding Houston, May 5–8, 1997.
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41615schD5R1.indd 8 8/19/11 11:07 PM Continuous Drive Reciprocating Drive Wheels Tracks Corkscrew Hydraulic Mechanical
> Tractor types. Service companies have developed many different topologies for downhole tractors. Continuous drive units (left) have wheels, tracks and even corkscrew drives. Reciprocating units (right) use locking devices and imitate an inchworm’s motion with an anchor, extend, release and re-anchor movement.
Pulling a Rope well interventions without the high cost associ- approximately 80% of the interventions performed Although earlier attempts were recorded, down- ated with CT services, downhole tractors dramat- by one operator had shifted to wireline tractors.14 hole tractors successfully arrived in the oil field ically changed the way North Sea operators Not only did this reduce costs, it expanded both in the mid-1990s. In 1996, a device to access hori- planned and managed their fields.13 the frequency and scope of interventions. zontal boreholes performed the first tractor ser- Prior to 1996, interventions had been per- vice on a well in Norway.12 Developed to perform formed almost exclusively by CT units. By 2009,
> Climbing the borehole. Engineers designed the reciprocating, gripping mechanism of the MaxTRAC tractor based on rock-climbing gear. The cams located on the extended arms (inset) rotate into position and grip the inside of the casing or borehole. Once the cams are securely locked, the tractor can move forward, but backward movement is nearly impossible.
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Oilfield Review SUMMER 11 Conveyance Fig. 10 ORSUM11-CONVY 10 Rear anchor locked Forward anchor free
Tool moving forward
As tool moves forward, front anchor moves into position.
Anchor free Anchor locked
Tool moving forward
Rear anchor moves into forward position.
Anchor locked, cycle repeats
> Inchworm movement. The MaxTRAC reciprocating system uses a minimum of two synchronized tractor sections, but up to four sections can be combined. Locomotion is achieved when the rear gripping section locks (red) and pushes the tool forward until it is fully extended as the forward anchor, which is free (black), moves into position and locks in place (red). The rear anchor then releases and the front section pulls the assembly forward. After the tractor advances, the rear section again locks in place, and the toolstring is pushed forward. These actions are repeated until the tool reaches TD or the desired depth.
Service companies offer a variety of downhole range from 2.44 in. [6.20 cm] to 11.3 in [28.7 cm]. but more can be added as needed. With each tractors. They include tractors with rotating It has the ability to log in forward direction or, with power stroke, the tool moves forward in inch- wheels, motorized tracks and corkscrew designs some specific limitations, in reverse while being worm fashion (above). The MaxTRAC tractor (previous page, top). In a departure from these retrieved by wireline. has been deployed in a number of openhole and systems, Schlumberger engineers developed a The reciprocating grip system uses cams to cased hole applications and, with the TuffTRAC reciprocating gripping mechanism for the grip the inside ofOilfield the casing Review or borehole. This cased hole services tractor, holds a number of MaxTRAC downhole well tractor system (previous design is similar to devices used to secure ropes SUMMER 11 12. Hallundbæk J: “Well Tractors for Highly Deviated and 1 page, bottom). This 2/8-in. [5.4-cm] diameter tool during rock climbing:Conveyance Once the Fig. cam 11 is in position, Horizontal Wells,” paper SPE 28871, presented at the has a maximum pull of approximately 4,448 N backward pull causesORSUM11-CONVY it to expand and 11 lock more SPE European Petroleum Conference, London, October 25–27, 1994. [1,000 lbf] while exerting 13,335 N [3,000 lbf] securely in place. It can easily be pushed forward, 13. Schwanitz B and Henriques K: “The Development of maximum force on the casing or borehole wall. It but it is almost impossible to pull backward. The Wireline-Tractor Technology,” The Way Ahead 5, no. 2 (2009): 18–20. can advance at 670 m/h [2,200 ft/h] while pulling tractor requires at least two gripping sections, 14. Schwanitz and Henriques, reference 13. 2,224 N [500 lbf] and operates in hole sizes that
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41615schD5R1.indd 27 8/12/11 8:02 PM World’s longest openhole 4,238 m (13,904 ft) Loss of power to the tool is not the only con- Although downhole tractors were originally tractor pass Two descents for a total of cern when engineers design a tractor job. With developed for cased hole intervention, operators 8,476 m (27,808 ft) continuous forward motion, the equipment can have used the MaxTRAC tractor system to run a World’s deepest PL 8,650 m (28,380 ft) on tractor eventually reach a point that exceeds the capa- variety of openhole services. For instance, the bility of the logging unit to retrieve the tool using FMI tool is often combined with the tractor sys- Most cumulative distance 85,987 m (282,109 ft) traversed using a tractor the cable. To ensure successful return to surface, tem for fracture identification. Horizontal wells in a single well the field engineer can model the downhole forces drilled through fractured reservoirs are difficult > MaxTRAC-TuffTRAC records. with job-planner software (below). Using infor- to evaluate with LWD services alone because of mation that includes deviation, pushing force, the high data density required for imaging the friction and job variations, modeling software factures. The FMI tool can help identify the opti- operational records (above). Should the tool ever provides a go–no-go determination (next page, mal intervals for production along the horizontal lose power, the arms with the gripping cams auto- top right). The planner also determines the num- section. The MaxTRAC tractor has also been used matically return to a retracted position for ease ber of drive sections needed and helps establish in openhole completions to deploy PL tools and of tool retrieval. the weakpoint for cable release in the event the to deploy Multi Express tools in both open and tool becomes stuck downhole. The field engineer cased wells. can fine-tune the model with real-time data.
Dogleg Severity as a Function of Measured Depth Cable Tension at Surface
6 Maximum safe pull on cable
Dogleg severity 80 Cable tension, retrieving 80 Wellbore deviation 4,000 Wellbore deviation Cable tension, moving forward 4 60 60
40 40
Tension, lbf Tension, 2,000 2 Wellbore deviation, degree Wellbore 20 deviation, degree Wellbore 20 Dogleg severity, degree/100 ft Dogleg severity,
0 0 0 0
0 10,000 0 10,000 Depth, ft Depth, ft
Oilfield Review Tractor Force Pseudo-3D Well Profile Projections SUMMER 11 0 ConveyanceMaximum Fig. Table force available 2 from tractor 1,000 ORSUM11-CONVY Table 2 Tractor force 80
Wellbore deviation 5,000
60 0
500 40 10,000
5,000 0 Wellbore deviation, degree Wellbore 20 TVD, ft
Tractor force required to go down, lbf Tractor 5,000
0 0 10,000 East, ft 10,000 0 10,000 –5,000 05,000 Depth, ft North, ft > Prejob planning. From well data, tractor job planner software provides operational limitations and critical go–no-go analysis before the job commences. The planner can then be updated with downhole data while the tractor is operating. The well profile data (top left) includes deviation and dogleg severity— a measure of how rapidly the wellbore trajectory is changing per unit of distance. Modeled cable tension at the surface indicates whether tension will exceed safe operation limits (top right). The forces acting on the tractor are also modeled (bottom left) to ensure the limitations of the tractor are not exceeded. A pseudo-3D profile, created from client-provided deviation and inclination data, helps visualize borehole geometry (bottom right). The wellbore path (red) is presented versus TVD (blue), surface location (magenta) and north departure (green).
28 Oilfield Review
41615schD5R1.indd 28 8/22/11 12:19 PM Oilfield Review SUMMER 11 Conveyance Fig. 12 ORSUM11-CONVY 12 Tackling a Giant Saudi Aramco has been instrumental in develop- 10,000 Maximum safe pull on cable ing tractor technology.15 For the Ghawar field, the Well deviation 80 largest onshore oil field in the world, engineers Force to go forward Force to retrieve have increasingly turned to horizontal, extended- 60 reach and multilateral wellbores as part of the ongoing development program. The expense of 5,000 using CT units, as well as the difficulty of access- 40 Tension, lbf Tension, ing complex completion geometries for conveying Break weakpoint
diagnostic and surveillance tools, has led Aramco 20 deviation, degree Wellbore to investigate alternatives.16 Aramco, which extensively tested various 0 0 downhole tractors, views them as an enabling technology for intervention services. The com- 0 1,000 2,000 pany has determined that tractors can effectively Depth, m log horizontal wells, far exceed the reach of con- > Critical decisions. In this plot from the job planner, the MaxTRAC tractor ventional CT units, provide significant cost bene- can travel forward with tensions (red curve) that are well below the fit and offer safer operations compared with maximum safe pull (dashed green line). However, the cable tension while 17 retrieving the tool (purple curve) approaches unsafe conditions beyond complex CT mobilization and deployment. about 2,000 m [6,560 ft]. Should the tool exceed the maximum safe pull limit, However, Aramco’s earlier experience with it may not be possible to break the weakpoint and release the cable from openhole logging, starting in 2004, was not as the tool should the tool become stuck. The alternative is to not advance all positive as with cased hole tractor operations. the way to TD but to keep the tension within the safe operating margin. The software provides a high and low range for modeled tensions based on Aramco and Schlumberger engineers determined data uncertainty, and downhole data can be used to improve the model as that the cams used with the MaxTRAC system the tool approaches the critical safety point. could successfully grip in formations with uncon- fined compressive strength (UCS) greater than 5,000 psi [34.5 MPa]. Below that cutoff, the cams would dig into the formation and lose gripping Openhole tractors are not suitable for every longer reach than CT units and require fewer per- force. Engineers working with field operations well, particularly those with long washed-out sec- sonnel and less hardware on location. Today, staff developed an add-on kit to distribute the tions or irregularly shaped boreholes. However, openhole tractors are in use not only in Saudi force more uniformly, which maximized the grip- Aramco determined that the use of openhole Arabia but also in several other locations in the ping force in soft formations (below right).18 tractors can deliver significant cost savings over Middle East. The newly designed gripping assembly was conventional CT logging. Tractors have a much 1 first tested in a 6/8-in. wellbore completion in a formation with a high UCS. A 5,072-ft [1,546-m] horizontal openhole section was successfully logged with a PL toolstring. Eight more openhole wells in high UCS formations were successfully logged before engineers attempted operations in Oilfield Review a soft formation. The soft formation candidate, SUMMER 11 with a 7,553-ft [2,300-m] lateral section, was then Conveyance Fig. 13 ORSUM11-CONVY 13 logged with PL tools to determine oil entry points Wedge and establish a flow profile along the lateral sec- Gripping action tion. The job was successfully completed and the Formation well evaluated using the new design.
15. AL-Amer et al, reference 6. Saddle 16. AL-Amer et al, reference 6. Grip geometry Bow springs locked 17. AL-Amer et al, reference 6. 18. Hashem MK, Al-Dossari SM, Seifert D, Hassaan M and Direction of Foubert B: “An Innovative Tractor Design for Logging grip motion Openhole Soft Formation Horizontal Wells,” paper SPE 111347, presented at the SPE North Africa > Conference and Exhibition, Marrakech, Morocco, Openhole tractor logging. The MaxTRAC tractor gripping mechanism lost traction in soft formations. March 12–14, 2008. Saudi Aramco and Schlumberger engineers collaborated on an improved design that could deploy openhole logging tools. An added bowspring with a saddle and wedge (inset) distributed the gripping force more evenly; the tractor was able to successfully navigate in wells with formations that had UCS less than 5,000 psi.
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Oilfield Review SUMMER 11 Conveyance Fig. 14 ORSUM11-CONVY 14 Pickup Truck TuffTRAC (8 drives) Weight of unit 2,560 kg [5,645 lbm] 277 kg [610 lbm] Additional radial force 0 4,448 N [1,000 lbf] per wheel Weight per wheel 640 kg [1,411 lbm] 522 kg [1,152 lbm] Size of wheel 76 cm [~30 in.] 7.6 cm [3 in.] Towing capacity 44,927 N [10,100 lbf] 106,757 N [24,000 lbf] Towing force 4,448 N [~1,000 lbf] 10,676 N [2,400 lbf]
> TuffTRAC pulling power. The TuffTRAC tractor can use up to eight drive wheels (right). In the maximum pull configuration, it has 106,757 N [24,000 lbf] of pulling capacity. For comparison, the pickup truck shown has a towing capacity of 44,927 N [10,100 lbf].
When the Going Gets Tough tools have been used to run and position perfo- mechanically powered wheels (above). The Logging is not the only operation that takes place rating guns, but the shock that the downhole TuffTRAC tool is bigger and stronger than the
in horizontal wells. Initial completion operations equipment can receive—up to 20,000 gn—can MaxTRAC tractor and has a much simpler design; often use drilling or workover rigs to run TCP damage sensitive electronic and mechanical it has minimal downhole electronics. Maximum guns, which can traverse extremely long inter- components. running speed is 975 m/h [3,200 ft/h] and maxi- vals. However, after the rig has moved on, reme- Recognizing the need for a more robust trac- mum pulling force is 10,676 N [2,400 lbf]. It is dial perforating in horizontal wells can be tor for perforating services, Schlumberger engi- designed primarily for perforating and cement difficult to perform. CT units are an option for neers designed the TuffTRAC cased hole services evaluation. The TuffTRAC system also offers trac- this task but they have depth limitations. Tractor tractor. Tool movement is accomplished using tion control, which dynamically adjusts the grip- ping force while the tractor is in forward motion. The TuffTRAC equipment is currently the only tractor qualified for perforating that can reverse out of the well. This has proved beneficial in hori- zontal well sections where guns were trapped by debris in the wellbore. On at least one occasion, surface-applied tension was not sufficient to free the guns because the high angle of the well pro- hibited pulling force from being transmitted to the tools. By moving in reverse, the tractor was Oilfield Review able to free the guns, which were then retrieved SUMMER 11 without a costly fishing operation. Conveyance Fig. 15 Although perforating can damage electronics ORSUM11-CONVY 15 and mechanical components, the TuffTRAC ser- > Qualification testing. The TuffTRAC tractor was designed to withstand the vice has demonstrated that properly engineered rigors of perforating. The tool was attached to loaded casing guns, which solutions can mitigate some of the effects of high were fired at the surface, shown here, without significant damage to the explosives (left). Tested to extreme limits, this tool. The design-for-purpose and qualification testing resulted in a robust new tractor design has been field qualified. In system that has been proved in the field. one North Sea well that had initially been com-
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Oilfield Review SUMMER 11 Conveyance Fig. 16 ORSUM11-CONVY 16 XX,200 100
XX,400 90
XX,600 80
XX,800 Well profile 70 Phase 2 perforation XY,000 60 Phase 1 perforation TVD, m XY,200 Inclination, degrees 50 Inclination, degree
XY,400 40
XY,600 30
XY,800 20 XX,000 XX,250 XX,500 XX,750 XY,000 XY,250 XY,500 XY,750 MD, m > Well profile for North Sea injector. The operator perforated this well in two stages. Together the stages covered approximately 1,250 m. Holes were spaced approximately 7 m apart across the intervals. A total of 180 shots were attempted. Only one shot failed to fire. During the course of 12 descents, the tractor tool traversed 8,670 m.
pleted as a commingled oil producer from two run as many as 20 single-shot carriers per descent Wireless downhole communication may separate zones, only water was being produced. to perforate the Phase 1 interval and as many as become more readily available to the oil and gas Engineers ran the TuffTRAC system to set two 33 single-shot guns for the Phase 2 interval. industry, and there are already commercial sys- 7 plugs, ran 73.1 m [240 ft] of 2/8-in. high shot den- During the execution of the job, the tractor tra- tems that communicate with downhole tools via sity guns in four runs and made six trips to retro- versed a total of 8,670 m [28,450 ft] in the course radio waves. Depth and data limitations for wire- fit sand screens. For this single intervention, the of 12 descents. less systems exist at present, but controlling tractor traversed 22,500 m [73,819 ft] without Although CT perforating was an option, using downhole devices and receiving data without the incident. The procedures resulted in resumption more than 1,250 m of gun stock to perforate 180 use of cables and wires open new possibilities of oil production without a costly workover and holes was neither cost-effective nor an efficient and applications for operators and service recompletion. use of resources. Another option would have been companies. In another North Sea horizontal well, an oper- multiple runs—perhaps as many as 60—with a LWD tools, coiled tubing and downhole trac- ator needed to perforate approximately 1,250 m conventional switched-gun system. The applica- tors create opportunities in drilling, completions [4,100 ft] of reservoir section for a water injec- tion of this new technology greatly reduced the and production that previously did not exist. The Oilfield Review tion project. One objective was to achieve a par- number of runs,SUMMER equipment 11 wear and the time on oil and gas service industry continues to develop 5 ticular perforation hole size in heavy-wall 6/8-in. location for personnel.Conveyance Fig. 17 new methods that reduce costs, decrease equip- liner with one shot every 7 m [23 ft]. The plan ORSUM11-CONVY 17 ment requirements and minimize the number of called for perforating in two phases across sepa- Change Brings Opportunity personnel on location. rate intervals (above). The two phases included Game-changing technology often creates a As conveyance techniques evolve, they intro- 90 holes per interval for a total of 180 shots. bridge to better methods of operation and offers duce opportunities to improve production and, in Because of logistics and cost, it would have a wider range of choices. For instance, in many general, function more efficiently than earlier been difficult to justify perforating with TCP guns developing countries, telephone service provid- methods. If you can’t push a rope, you may be using a CT unit—180 shots would have required ers are investing in cellular phone systems able to pull it. Or perhaps, in the future, it may be at least 1,250 m [4,101 ft] of gun stock. For lim- rather than traditional landline infrastructures. easier just to cut the rope completely. —TS ited-entry perforation operations such as this, The benefits to consumers include smart phones engineers at Schlumberger Rosharon Completions and wireless internet access, which go far Center (SRC), in Texas, USA, have developed an beyond eliminating the inconvenience of being addressable-switch perforating system that uses tied to a telephone cord. radio-safe detonators and allows up to 40 single- In a similar fashion, LWD tools have changed shot carriers to be run in a single descent. The the way operators approach drilling. Memory system requires surface power to communicate logging has changed the way data acquisition is with and detonate each shot. Because the carried out while simultaneously offering a TuffTRAC tractor is combinable with the address- broader range of opportunities. In the near able-switch system, field engineers were able to future, wired drillpipe promises to provide even greater opportunities.
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