Copyright 1998, Society of Petroleum Engineers, Inc.

This paper was prepared for presentation at the 1998 SPE Asia Pacific Oil & Gas Conference and Exhibition held in Perth, Australia, 1214 October 1998.

This paper was selected for presentation by an SPE Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Papers presented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petroleum Engineers. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A., fax 01-972-952-9435.

Abstract New wireline tractor technology has been developed and used successfully in Australia to deploy production logging tools in horizontal wells. The results of operations in the Wandoo field in Australia are presented. The dynamics of tractor operations have been modelled, and field data has been used to validate the model and to quantify borehole friction coefficients. The model may be used to assist job planning and to assess the feasibility of deployment by wireline tractors in general situations.

Introduction The growth in horizontal well drilling in recent years has renewed interest in electrically powered traction devices which connect in tandem with conventional downhole wireline equipment and assist descent into the well. By obviating the requirement for auxiliary deployment methods such as coiled tubing, significant cost-effective advantages are possible1. In addition, production log quality is expected to benefit from improved depth control and reduced alteration of the flow regime, vis-a-vis coiled tubing intervention.

This paper describes the development and operation of a versatile tractor which is compatible with standard wireline equipment and which is capable of horizontal well intervention through the wide range of completion strings. In parallel with the tractor development, the dynamics of wireline tractor well intervention have been modelled with a view to quantifying the feasibility and general range of application of well tractors in existing and future well designs.

Tractor Description The well environment imposes two major constraints on the design of tractors. The amount of continuous electric power that can safely be delivered through a mono-conductor wireline from the surface imposes an ultimate limit on the

mechanical output, which in turn imposes limits on the depth and speed of tractor intervention. Secondly, the tractor dimensions must be small enough to allow free passage through restrictions in the completion string while at the same time be able to open far enough to maintain traction against the wall of the largest casing size. The simultaneous requirements for high efficiency and small size introduce mutually opposing constraints into the design process.

The tractor layout is shown in Fig. 1. The tractor is connected between the logging head and the passenger equipment. Traction is achieved by forcing two drive wheels against the wall of the casing. The drive wheels are mounted on arms positioned on opposite sides of the tractor. The arms are activated by the deployment module. In the open position, the arms extend out to reach the casing wall and apply sufficient side forces between the drive wheels and the casing to create traction without slippage. The magnitude of the side forces is adjusted automatically in response to the applied load so that traction is sustained throughout the entire load range. In the closed position, the arms and the drive wheels retract fully within the envelope of the tractor body (54 mm OD). For safety reasons, whenever electrical power is removed from the cable, the drive wheels retract automatically. A secondary shear pin release mechanism allows over-pull at the cable head to increase the retraction force if required. The arm geometric profile is designed to push well debris such as sand sideways, helping to avoid a build up ahead of the tractor which could impede progress along the well. To minimise friction on the tractor itself, and hence maximise the net payload, the tractor is fitted with in-line centralisers fitted with rollers.

A key element of the tractor design was the development of a direct current permanent rare earth magnet motor which is both compact and has a power transfer efficiency in excess of 90%. The motor can maintain continuous full load output at 150 C. Torque is transmitted from the motor to the drive wheels through an arrangement of gears built into the arms. The motor can drive in both uphole and downhole directions. Speed is continuously variable and changes approximately by 1.5 m per minute for every 100 volts change at the cable head. Tractor load is derived from the cable current, which increases approximately by 0.35 amps per 1,000 N change of applied load. The tractor can sustain loads up to 3,000 N without exceeding the electrical ratings of standard 7/32 in. mono-conductor cables.

The tractor is microprocessor controlled and data transfer and communication between the downhole electronics and the surface control equipment is achieved through a single cable conductor, while power is

SPE 51612

Wireline Tractor Production Logging Experience in Australian Horizontal Wells Eddie Local, SPE, ORAD Ltd, and Thomas L. Searight, SPE, Sondex.

2 EDDIE LOCAL, THOMAS L. SEARIGHT SPE 51612

simultaneously delivered to the drive motor. The surface power supply and the control unit are compact and may be installed inside the logging unit or adjacent to the winch drivers console. A standard single-phase power supply is required. The drive motor and the arm deployment functions are initiated by simple keyboard commands from the surface computer. The tractor provides various downhole measurements including head voltage, head tension, tractor speed, CCL, temperature and pressure readings, all of which are measured and displayed at the surface as the tractor progresses along the well. This information allows the tractors performance and its interaction with the downhole environment to be monitored in real time, which facilitates operational control and safety. In addition, measurement of the drive wheel rotation provides a means for computing the distance travelled by the tractor. Tractor distance is also displayed in real time. Solid state switches, under microprocessor control, allow the cable to be selectively connected to the tractor or through to the passenger equipment. Unless the tractor and the passenger equipment have common downhole telemetry and power supply systems, it is generally not possible to log and tractor simultaneously. At full load, the electro-mechanical efficiency of the complete tractor system is better than 50%.

Tractor Field Experience The first successful application of the tractor was to convey production logging equipment on Mobils Wandoo field which is located on Australias North West Shelf. Prior to the job, a computer model was developed to assess the feasibility of the operation by calculating the tractor load and cable tensions expected during the survey. Data recorded during the job was later used to fine-tune the model, which is described in more detail below.

Operating procedure. The limited height of the mast required multiple deployment of the long multi-sensor production logging equipment. The logging tools were made up vertically in a single stage or two stages with a deployment bar, depending on the downhole tool configuration, followed by the tractor, which was made up together with the logging head in a single stage. The small diameter of the tractor permitted the use of standard 2 in. ID lubricator.

To facilitate vertical make up and to relieve cable torque downhole during the well operation, a swivel head was connected between the cable head and the tractor. Ideally, roller devices should be fitted to the passenger equipment to reduce friction. This has the benefit of both maximising the depth of descent under gravity and reducing the tractor load. However, the production logging program required the tools to be run eccentralised, and rollers were not in fact fitted. A 5/16 in. diameter co-axial logging cable was used. The cable was 24,000 ft. long and the conductor resistance was 250 ohms.

The tractor head tension and CCL were monitored while running into the well. As the well deviation built up, these measurements provided a means for detecting tool motion and confirming when the holdup depth had been reached. This method was found to be more sensitive than relying on the cable surface tension indication alone. At the holdup

depth, the drive wheels were deployed and the tractor was started up, initially taking up any cable slack until the head tension reading started to increase, confirming that the tractor was mobile and operating correctly. The winch was then engaged and the winch speed adjusted to maintain a constant surface tension reading, indicating that cable was being fed into the well at the same rate as cable was being pulled along the well by the tractor. With this procedure, the cable tension around the holdup depth remains close to zero throughout the tractor operation, and the tractor load is independent of the cable tension distribution above the holdup depth.

After entering the horizontal section, the tractor was stopped every 200 m and the drive wheels were retracted. The cable was then pulled up for a short distance to check the surface pull and the head tension readings. These were found to follow the trend predicted by the simulation model. Prior to stopping the tractor, the winch was stopped first and the tractor allowed to continue running for a few meters until the head tension started to increase, indicating that any slack cable had been taken up. If there was any back load on the tractor after it had stopped, the tractor was first reversed for a short distance to relieve head tension before retracting the drive wheels. The real time head tension and tractor speed curves provided a basis for excellent coordination between the winch and tractor movement. In addition, the cumulative distance travelled by the tractor drive wheels was compared continuously with the cable depth odometer, providing confirmation of synchronised motion.

Tractor performance. Production logs were run in three oil producing horizontal wells. In total, 15 tractor runs were made and over 8,300 m were tractored, the longest interval being 1,190 m. The maximum cable current was about 0.6 amps which is less than 50% of the specified cable rating. The maximum surface voltage was 600 volts. The average speed was 1000 ft./hr. The production logging objectives were in general accomplished and within budget. The log data is presented in a separate paper2. A summary of the tractor operations run on three horizontal wells, B1a, B9 and B4a follows. The wells have similar deviation profiles, the vertical depth being typically around 630 m with horizontal sections ranging from 1,000 m to 1,200 m. The maximum well deviation was 92o. The well completions are essentially mono-bore with 5 in. OD 13Cr pre-drilled production tubing with 48 x in. holes per foot.

Well B1a. The passenger equipment was 14.6 m long and weighed 105 kg including deployment bars. Tractoring commenced from the holdup depth at 714 m (deviation 76o). The logging tools were conveyed to the programmed survey depth (1,779 m). Various sections of log were run including stationery readings and three additional tractor passes were required. The total distance tractored was 2,464 m.

Well B9. The passenger equipment was 14.6m long and weighed 95 kg. The holdup depth was 753 m (deviation 78o)and the logging equipment was conveyed to 1,590 m. In total, the tractor made eight down passes, and the total tractored distance was 3,149 m. In Fig. 2, the tractor load and head tension data are plotted against measured depth from holdup to TD. The well was shut in during this pass.

SPE 51612 WIRELINE TRACTOR PRODUCTIONLOGGING EXPERIENCE IN AUSTRALIAN HORIZONTAL WELLS 3

The TVD profile is also shown. The maximum deviation was 91.68 at 1,076 m. The head tension, which is effectively a measure of the cable drag behind the tractor, is zero at the holdup depth and increases continuously with depth as the tractor travels along the well. The minor fluctuations in head tension arose from variations in the speed of the tractor relative to the cable feed. If the tractor moves faster than the cable feed, the head tension will increase as the cable slack is taken up. The tractor load, which is the tangential force exerted by the drive wheels against the casing, is equal to the sum of the cable drag, the drag on the logging tools and the drag on the tractor itself. The separation between the tractor load and head tension plots is then equal to the drag on the logging tools and the tractor alone. Below the holdup depth, gravitational assistance diminishes and tool drag increases, and as the well deviation builds up towards 90, the separation increases. In the horizontal section, the separation is relatively uniform but is modulated by minor changes in well deviation.

Well B4a. The logging equipment was 23.6 m long and weighed 159 kg including deployment bars. The holdup depth was at 738 m (deviation 80 deg). On the first run the production logging tools were conveyed to 1,930 m. After entering the horizontal section, the well was opened up and flow allowed to stabilise as the tractor progressed towards the end of the well. Fig. 3 is a plot of the tractor load and head tension data. An abrupt increase in both head tension and tractor load was observed around 1,100 m. This is attributed to the additional drag arising from the flow of well fluids. The data is analysed more fully below. Two additional runs were made and the total tractored distance was 2,755 m.

Wireline Tractor Operations: Theoretical Model A three-dimensional computer model has been developed which simulates both tractor loading and cable tensions arising during a wireline tractor operation. The model provides a means to quantitatively assess the capability of the tractor to achieve the intervention objectives, and to confirm that the cable can retrieve the tools from the well without exceeding acceptable safety limits. The underlying theory is similar to that used by Maidla3 et al. to investigate borehole friction on casing strings. The model makes use of the well survey data. Other input parameters are; cable linear density, diameter and safety limits; the passenger tool weight and dimensions; the tractor weight and dimensions; the well fluid levels and specific gravity; and the friction coefficients which are defined as the ratio between the tangential friction force and the normal contact force.

The unit vector tangential to the borehole at survey level di is given by,

)1(.........cossinsincossin iiiiii zyxu&&& IITIT

where z& is a unit vector in the vertical direction and x& and

y& are unit vectors in the horizontal plane. The unit vectors

normal and tangential to the borehole are respectively,

)2(.................../)( 1-ii1-ii uuuun&&&&

)3(..................../)( 1-ii1-ii uuuut&&&&

With the cable head positioned at depth dn, the surface cable tension is calculated by adding the head tension and the contributions of all cable elements back to the surface, ie,

)4(.......)(.)(

)cossin()(1

1

uuuu

uu i

niicii

nntns

Fktzdd

WdT

PU

TTP&&

where,

)5(....).arccos(. 1i.1i uuu iiiiii uuTnzddF&&U

The calculation is performed for both cable directions. When the cable direction is downhole (k=21), the calculation continues until a negative cable tension element is detected, and the depth at which this occurs is determined to be the hold up depth. The change in surface pull due to over-pull at the cable head is calculated by introducing a constant term representing over-pull on the right hand side of Eq. 4. Through an iterative process, the maximum head over-pull compliant with the surface pull safety limit is calculated. This result provides a guideline for weak point selection.

The tractor load is assumed to be zero at the holdup depth, and below the holdup depth, it is equal to the sum of the cable drag and the tool drag, i.e.

)6(...........)(sin)( nntn dHWdL uu TP

Where;

)7(.............)(.)()( 1

uuu

ni

HUDiiciiiin FtzdddH PU

&&

Fi is given by Eq. 5.

The friction coefficients are not known precisely and in the absence of prior field experience, a range of values must be assumed. A diverse range of values for borehole friction coefficients is published in the literature. For example, Maidla4 et al report that friction coefficients for drill strings ranging from less than 0.1 to as high as 0.45 have been measured under various well conditions. Bratovich5 and al. have found average values of 0.4 for the coefficient of friction of logging cables in casing and values around 0.15 for logging tools fitted with wheels. The tractor data collected on the Wandoo wells has been used to quantify the friction coefficients by finding values which give the best fit between the field data and the theoretical model. The tractor data allows cable and tool friction coefficients to be estimated independently. The head tension measurement, being independent of the tool friction, is used to estimate the casing friction coefficient and the difference between the tractor load and the head tension is used to estimate the tool friction coefficient.

Cable friction calculation. From Eq. 7, the incremental

4 EDDIE LOCAL, THOMAS L. SEARIGHT SPE 51612

change in head tension with measured depth along the horizontal section of the well is given by:

)8(.......................** cdH PGUG

Fig. 4 shows a composite of head tension logs recorded on four tractor runs in the three wells, including runs made with the well flowing and the well shut in. The head tension gradient is observed to be non-linear, decreasing as the tension increases. Cable friction is plotted against head tension in Fig. 5 and the best fitting trendline takes the form:

)9(...................)/exp( bHac u P

where a = 0.61 and b = 730 N. When applying Eq. 9 to the simulation model, a lower limit of 0.13 is imposed on the value of c, this being the lowest value measured in the range of the Wandoo data set. Further analysis of tractor data over a wider range of cable sizes and well conditions is required in order to establish the range of applicability of the relationship in Eq. 9.

Tool friction calculation. The tool friction coefficient is calculated from Eq. 6, The results for well B9 are plotted in Fig. 6. In this case, the well was shut in. The trendline is flat with an average value of 0.08. The observed tractor load variations are due primarily to the random interaction between the casing perforations and the tractor drive wheels and the centraliser rollers. The friction is highest around 1,150 m and 1,350 m. The TVD plot shows that the well curvature is also highest at these depths, suggesting that there are additional side forces on the long tools as they are forced to flex around the bend in the casing.

Tool friction for the B4 well is plotted in Fig. 7. This tractor run was made with the well flowing. The oil and water flows rates are also shown. Compared to Fig. 6, thetool friction is generally higher. This is attributed to additional viscous drag from the well fluids moving against the tools. There is a good correlation between tool friction and the oil flow rate, which declines steadily toward the toe of the well2.

Comparison between field data and the simulation model. Fig. 8 shows the simulation model applied to the B9 well, using Eq. 9 for the cable friction, and a value of .08 for the tool friction. Two cable surface tension plots are shown, one running into the well and the other pulling out. The tractor load and the head tension are plotted from the holdup depth to TD. Fig. 9, which combines the tractor data from Fig. 2 and the simulated data, confirms that there is good agreement between the two. Good agreement was also found between the calculated holdup depths and actual holdup depths, the difference being less than 15 m in each of the three wells. Descent under gravity was limited in the first instance by the cable, which has a higher friction coefficient than the logging tools.

The cable tensions recorded at the pick up checks taken during the tractor run, and when pulling out of the hole, were also found to fit closely with the model. The contribution of the tool weight to the cable tension increases

as the well deviation decreases, and consequently, for this particular well profile, the cable tension increases while pulling out of the well, which is contrary to normal experience in a vertical well. The maximum surface cable pull occurs at 500 m where the well deviation is around 308.

Simulation Model Applications The simulation software is integrated with the tractor control software and the actual cable tensions and tractor loads may be compared with the simulation model predictions during the tractor operation. This feature contributes to general operational safety by allowing anomalous events to be more rapidly identified.

The model provides a useful planning tool. By comparing the tractor pulling capacity with the computed tractor loads at the toe of the well or at the deepest survey depth, the feasibility of wireline tractor conveyance may be assessed and compared with other methods of deployment. The model is also used to confirm that the wireline may be retrieved from the well without exceeding acceptable safety limits. Although larger cables have a higher pull rating, this advantage is offset partly because more pull is required to retrieve the cable itself from the well, and in particular, because the heavier cables give rise to more cable drag in the horizontal pipe, which in turn increases the load on the tractor. For example, the drag arising from cable weight is approximately double for a 5/16 in. compared to that for a 7/32 in. cable.

To assist job planning, different cable scenarios may be considered. Fig. 10 compares three typical cable sizes, 7/32 in., 5/16 in. and 7/16 in. The plots are extrapolated horizontally to give an indication of the maximum intervention achievable. In general, the intervention limit will be imposed by either the cable safe pull rating, the cable current rating, the cable voltage rating, the voltage rating of the surface equipment, or the tractor pull rating. In this example, the limit is set by the tractor load which in this case is assumed to be 3,000 N, being about 50% of the tested tractor pull limit. The results are listed in Table 1.With a 7/32 in. cable, the intervention limit is 3,800 m, which is 1,400 m more than what would be possible with a 5/16 in. cable. In deeper wells, the intervention limit may be the cable rating rather than the tractor pull rating. Another factor affecting cable selection is the over-pull which may be applied at the cable head without exceeding the cable safety limit, which in turn determines the head weak point rating. In the example, the allowed head over-pull with a 7/32 in. cable is 8,700 N (1,950 lbf.). A conventional weak point would typically be set to 75% of this value. If the weak point setting is too low for practical applications, a head release mechanism will be required. The tractor is bi-directional and it could be reversed to relieve head tension and hence assist cable retrieval. However, this feature is not taken into account in the weak point calculation, because in the worst case, this advantage would be negated by equipment failure.

The model may be used to compare different well trajectories, and to optimise the well design to facilitate wireline tractor intervention. Ideally, the holdup depth should be as deep as possible, and preferably deeper than any restrictions or abrupt changes in tubing diameter, which

SPE 51612 WIRELINE TRACTOR PRODUCTIONLOGGING EXPERIENCE IN AUSTRALIAN HORIZONTAL WELLS 5

are likely to impede tractor progress. The model may also be used to direct future tractor development work by defining hardware specifications required to achieve successful intervention in existing or planned well profiles.

Further field experience is required to fine-tune the selection of parameters for the well model, and appropriate safety margins should be adopted particularly in extended reach wells where errors in the friction coefficients will be compounded over long distances. Factors such as well flow and the presence of debris and sand, which will increase tractor loading, should also be taken into account.

Conclusion and Further Developments The experience gained on the Wandoo wells has confirmed the feasibility of wireline tractor conveyed production logging operations in horizontal wells. The though tubing capability of the tractor, combined with its capacity to drive in large casing sizes, make wireline tractor deployment possible in a wide range of well completions. Data recorded from sensors incorporated in the tractor has increased the understanding of the dynamics of tractor operations. This data has been used to calibrate a simulation model which may now be used more generally with greater confidence to assist job planning, and to quantitatively assess the general feasibility of tractor conveyed well interventions.

In order to extend applications to as wide a variety of wells, and as wide a range of services as possible, further design refinements need to be made. Work is continuing on a revised design with improvements in the following areas: Capability to negotiate complex down-hole hardware.

For example, with the current drive arm configuration, the tractor has a limited ability to pass severe changes in diameter. There are also problems to traverse features such as holes that cover a large proportion of the pipe circumference such as the inlet from a down-hole pump. Tests have shown that the performance in these situations can be greatly improved by the addition of a second set of drive wheels.

Intervention in completions with widely differing tubing diameters. For example it may be necessary for the tractor to drive through small diameter highly deviated tubing before reaching the larger diameter liner in the producing zone. As the tractor drive arms have to be selected to match the tubing size in order to achieve the maximum pulling capacity, a tractor with two or more pairs of drive arms could be set-up with each pair of arms optimised for each tubing diameter.

While the tractor was initially conceived to push logging tools it may be used for other forms of well intervention such as perforating, packer setting and general mechanical services which are conventionally performed on slick line and coiled tubing.

Finally, the tractor will be repackaged to upgrade temperature and pressure ratings and to reduce overall length to facilitate deployment.

Acknowledgments The author would like to thank Mobil Exploration & Production Australia, and in particular Jack Goodacre, Ian Clyne, Mark Pogson, Nigel Roberts and Ian Ure for their

support and encouragement during the Wandoo logging campaign. The author would also like to acknowledge the support of the Energy Research and Development Corporation, the Department of Industry Science and Tourism, the Commonwealth Scientific & Industrial Research Organisation and the University of Technology, Sydney, the latter two being the joint developers of the tractor motor technology.

Nomenclature d = measured depth = well bearing k = direction modifier, uphole (+1), downhole (21) = cable linear buoyant density = well deviation = dynamic friction coefficient F = normal force between cable and casing H = head tension L = tractor load W = buoyant weight of downhole tools CCL = casing collar locater HUD = holdup depth ID = inside diameter OD = outside diameter TD = total measured depth TVD = true vertical depth

Subscripts cc = casing to cable

ct = casing to wireline tools s = surface

References G. McInally and J. Hallundbk: The Application of New

Wireline Tractor Technology to Horizontal Well Logging and Intervention.: A review of Field Experience in the North Sea, paper SPE 38757 presented at the 1997 SPE Annual Technical Conference and Exhibition held in San Antonio, Texas, 5-8 Oct.

A. Carnegie, N. Roberts and I. Clyne: Application of New Generation Technology to Horizontal Well Production Logging- Examples from North West Shelf of Australia paper SPE 50178 presented at the 1998 SPE Asia Pacific Oil & Gas Conference and Exhibition held in Perth, Australia, 1214 Oct.

E.E. Maidla and A.K. Wojtanowicz: Field Comparison of 2-D and 3-D Methods for the Borehole friction Evaluation in Directional Wells, paper SPE 16663 presented at the 62nd

Annual technical Conference and Exhibition of the Society of Petroleum Engineers held in Dallas Texas, 27-30 Sept 1987.

E.E. Maidla and A.K. Wojtanowicz: laboratory Study of Borehole friction factor With a Dynamic-Filtration Apparatus SPE Drilling Engineering, Sept 1990.

M.W. Bratovich, W.T. Bell and K.D.Kaaz: Improved techniques for logging High-Angle Wells paper SPE 6818 presented at the 52nd Annual Fall technical Conferences and Exhibition of the Society of Petroleum Engineers of AIME held in Dallas Texas 9-12 Oct 1977.

SI Metric Conversion Factors ft x 3.048 E-01 = m in x 2.54 E+00 = cm lbf x 4.448 E+00 = N

6 EDDIE LOCAL, THOMAS L. SEARIGHT SPE 51612

Fig. 1 Tractor layout showing the major components. Traction between the two drive wheels and the casing is maintained by automatically varying the side forces in response to the applied load.

0

200

400

600

800

1000

700 900 1100 1300 1500 1700

TRACTOR MEASURED DEPTH m

TR

AC

TO

R L

OA

D &

HE

AD

TE

NS

ION

N

623

625

627

629

631

633

635

637

639

TV

D m

HEAD TENSION

TRACTOR LOADu

TVD

Fig. 2 - Well B9: Head tension, tractor load and true vertical depth versus measured depth.

SPE 51612 WIRELINE TRACTOR PRODUCTIONLOGGING EXPERIENCE IN AUSTRALIAN HORIZONTAL WELLS 7

0

200

400

600

800

1000

700 900 1100 1300 1500 1700 1900 2100

TRACTOR MEASURED DEPTH m

TR

AC

TO

R L

OA

D &

HE

AD

TE

NS

ION

N

WELL STARTS TOFLOW

HEAD TENSION

TRACTOR LOAD

Fig. 3 - Well B4a: Head tension and tractor load versus measured depth. The tractor load increases when the well starts to flow.

0

100

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300

400

500

600

700

800

800 1000 1200 1400 1600 1800 2000

MEASURED DEPTH m

HE

AD

TE

NS

ION

N

B4A: RUN 2

B4A: RUN 1

B9: RUN 1

B1A: RUN 1

Fig. 4 - Head tension versus measured depth from four tractor runs. The head tension gradient diminishes as the tension increases.

8 EDDIE LOCAL, THOMAS L. SEARIGHT SPE 51612

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 500 1000 1500 2000 2500

HEAD TENSION N

CA

BL

E F

RIC

TIO

N C

OE

FF

ICIE

NT

Fig. 5 Cable friction coefficient versus head tension. Cable friction diminishes as cable tension increases.

0.00

0.05

0.10

0.15

0.20

700 900 1100 1300 1500 1700

MEASURED DEPTH m

TO

OL

FR

ICT

ION

CO

EF

FIC

IEN

T

625

626

627

628

629

630

631

632

633

634

635

TV

D m

TVD

TOOL FRICTION & TRENDLINE

Fig. 6 Well B9: Tool friction coefficient measured with the well shut in.

SPE 51612 WIRELINE TRACTOR PRODUCTIONLOGGING EXPERIENCE IN AUSTRALIAN HORIZONTAL WELLS 9

0.00

0.05

0.10

0.15

0.20

900 1100 1300 1500 1700 1900

MEASURED DEPTH m

TO

OL

FR

ICT

ION

CO

EF

FIC

IEN

T

0

1000

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4000

5000

6000

7000

8000

FL

OW

RA

TE

b/d

OIL FLOWRATE

WATER FLOWRATE

Fig. 7 Well B4a: Tool friction coefficient measured with the tractor running against the well flow. There is a good correlation between tool friction and the oil flow rate.

-500

0

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2500

0 500 1000 1500 2000

MEASURED DEPTH m

TR

AC

TO

R L

OA

D &

CA

BL

E S

UR

FA

CE

PU

LL

N

-300

-200

-100

0

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400

500

600

700

TV

D m

TVD

SURFACE CABLE TENSIONPULLING OUT RUNNING IN

HOLD UP DEPTH

TRACTORTOTAL LOAD & HEAD TENSION

Fig. 8 Well B9 simulation: shows cable surface tension running in and pulling out, tractor load and head tension, and TVD. The surface cable tension is higher in the build up zone than it is in the horizontal section.

10 EDDIE LOCAL, THOMAS L. SEARIGHT SPE 51612

0

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TRACTOR MEASURED DEPTH m

TR

AC

TO

R L

OA

D &

HE

AD

TE

NS

ION

N

TRACTOR LOADSIMULATION

HEAD TENSIONSIMULATION

Fig. 9 Well B9: Simulation results overlay the field data

0

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4500

0 500 1000 1500 2000 2500 3000 3500 4000

MEASURED DEPTH m

TR

AC

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OA

D &

CA

BL

E S

UR

FA

CE

TE

NS

ION

N

CABLE SURFACE TENSIONCABLE 1 CABLE 2 CABLE 3

TRACTOR LOADCABLE 3

CABLE 1

CABLE 2

Fig.10 Hypothetical well with extrapolated horizontal section. The simulation model is used to compare the cable surface pull and tractor load for three cable sizes. The combined tractor and production logging equipment weight is 300 kg, and the well fluid specific gravity is 0.9. The data is summarised in Table 1.

Cable ID Cable Diameter

Depth to reach 50% tractor full load

Max pull compared to allowed pull

Max allowed over-pull at TD

1 7/16" in. 1,750 m 9% 30,600 N 2 5/16" in. 2,400 m 14% 15,300 N 3 7/32" in. 3,800 m 21% 8,700 N

Table 1. Summary of the data plotted in Fig.10. The intervention limitations of wireline tractors decrease as cable size increases.