Understanding Downhole TractorsGulf Coast Section, SPE Northside, December 12, 2000

AUTHOR :

Bruce Henderson, SPE, SmarTract, Inc.

What is a Tractor ?

• A method of conveyance for use in high angle and horizontal wellbores.

• Competes with coiled tubing and drill pipe conveyed systems.

Background

Tractor history :

• early-mid 1990s

• North Sea

• increase in extended reach wells

Trends in horizontal drilling

Extended-Reach Drilling - Evolution in the 1990s0

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Trends in horizontal drilling

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(m)Amethyst Andrew

Bruce ChiragColombia FoinavenGoodwyn HardingMiller Milne PointNiakuk PedernalesPompano MagnusMarnock SchiehallionUla/Gyda ValhallWytch Farm

bp drilling envelope

Colin MasonPhil Hearn, Sept 00

Background

Tractor designs :

• wheels - initial designs uni-directional, no CHT.

- 5+ designs in N.Sea.

• crawlers

• mechanical

• others

Applications

• Production logging

• Perforating

• Fishing

• Plug setting

• Cement bond logging

• Seismic data acquisition

Tractor and logging string configuration

Cement bond logging tool

Compensated neutron logging tool

Tractor

Cost saving opportunities

Tractor vs alternative services:

• 15 minutes additional rig up time.

• CT/tractor onshore log off – 2 identical wells - rigged up, 2 log runs, rig down - 12 hours. CT rigging up.

• Offshore platform – avoid CT upgrade. Savings can easily be in six figures.

Minimal rig up time

Further applications

• Open hole tractoring

• Logging while tractoring (LWT)

• Intelligent use in zones of interest -sliding sleeves, gas lift mandrels, other mechanical applications

A “crawler” Tractor

• Fully bi-directional - speed and power(1000lbs)

• Four modules

The TechnologyCable: Single or Multi ConductorOutside Diameter: 2 1/8”ID of Casing: 2.44 - 7.125” or largerMax Pulling Force: 1000 lbsMax Speed: 1800 + ft/hr Length: 32 ft (modular)Max Pressure: 15 KpsiMax Temperature: 3000FTensile Strength: 24,000 lbsWeight: 260 lbsBuild rate: 30 degrees/100 ftReal Time Monitoring: CHT, CHV, tool parameters

(pressures,temperatures, motor RPM, others)

Pulling Direction: Bi-directional, equal force

Tractor SchematicWireline & cablehead

Electronics

Hydraulics

Upper stroke

Lower stroke

Logging tools

Anchors

Example anchor arms

The technology

Prejob planning

Main areas :

• Wellbore profile, loads

• Hole configurations

• Well plan - model vs actual

• Unexpected problems

Prejob planning

Prejob planning..

Hole configurations :

• many changes in hole size, small IDs, restrictions, doglegs, combinations of all these – easier to go in than come out.

Model vs actual :

• well conditions may have changed, do not have the safety margin expected.

Prejob planning

Prejob planning..

Unexpected problems (an example) :

• Identical wells ( # 8) - Logging tools (with nuclear source) unexpectedly stuck below tractor.

• Weak point set at 3500 lbs – pulled up to 3000 lbs on wireline with no success.

• Choice - try tractor to free logging tool or use service rig.

Risk reduction using fully bi-directional tractor

• Tractor + wireline pull = 800 + 3000 = 3800 lbs

• Cablehead weakpoint = 3500 lbs

• Free within 10 minutes.

• Savings made of 7-10 days service rig time, supervision, tools.

Conclusion

• Horizontal and high angle wells are becoming more common.

• Tractors are being used more frequently as a cost effective alternative to other methods of conveyance.

• Higher level of awareness of “tractors” will lead to increased use and applications.