Copyright 2007, Society of Petroleum Engineers This paper was prepared for presentation at the 15th SPE Middle East Oil & Gas Show and Conference held in Bahrain International Exhibition Centre, Kingdom of Bahrain, 11–14 March 2007. 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 Recent advances in horizontal drilling technology have allowed drilling longer horizontal sections in the reservoir more efficiently and economically. While operators benefit from the well-known advantages of horizontal drains, such benefits cannot be maximized during the lifetime of the well without a viable well intervention means for well service and monitoring operations. Coiled tubing has been recognized as an effective technique for such interventions but with limitation on the total length that can be accessed especially in extended reach wells . This paper summarizes the utilization of innovative coiled tubing Tractor technology to improve coiled tubing accessibility in long horizontal wells . Introduction

The paper discusses the aspects of well intervention using coiled tubing (CT) and coiled tubing tractor technology on four (4) open hole horizontal water injection wells and one (1) cased hole oil producing well . The results presented show that the use of a coiled tubing Well Tractor combined with coiled tubing along with proper well selection, design and planning can result in a significant improvement in Well accessibility both in cased hole and open hole . Well Accessibility with Coiled Tubing

For a well to be accessible with coiled tubing , the coiled

tubing need to be run to the end of the horizontal section and no “lock-up” should happen before reaching TD. Lock-up occurs when no weight can be transmitted to the end of a coiled tubing and hence no progress into the horizontal section is possible . Coiled Tubing simulation software is available that can predict the depth at which this lockup is reached and

whether it will occur . Such simulations are often used in the planning stage of a coiled tubing Intervention to decide on the type of coiled tubing pipe to be used (diameter and thickness). The following factors are taken into account in the simulation : Well trajectory ,coiled tubing pipe variables ( OD, thickness, strength , length ) , Diameter (s) in the wellbore , friction coefficients (cased/openhole),Well fluid type , temperature, pressure , and wellhead flowing conditions. Many techniques can enhance coiled tubing accessibility into the wellbore : The use of larger pipe, pipe straighteners, vibrating tools , pumping of Nitrogen , pumping of friction reducers or a combination of the above. A lot of literature has been published and is available about these techniques. Figure (1) shows coiled tubing Lockup depth using a typical output of a Well Intervention simulation program [ refer to point A on the graph]. This is the “theoretical” Lockup point. Actual Lockup point can only be found when the coiled tubing is run into the hole.

The advantage of using a coiled tubing Tractor at the end

of coiled tubing is that it provides a concentrated downhole force that can delay or prevent lockup by “pulling ”the coiled tubing from its end. This often results in improving well accessibility on extended reach wells. It is thought that when the CT locks up, a spiral type of form takes place at the end of the coiled tubing section; having a concentrated point load acting at the end of the coiled tubing will make this event unlikely thus improve the accessibility . Figure (1) shows the new lockup depth predicted by the well intervention Simulation program [ refer to point B on the graph] after applying a concentrated force of 4000 lbs by the Tractor at the end of the coiled tubing as per the well intervention simulation.

The Coiled Tubing Well Tractor

The idea of using a downhole Tractor was originally

conceived in 1994 when it was required to transport diagnostic and maintenance equipment in highly deviated and horizontal sections . Such Tractors were powered with electric current that drives an electric motor to generate downhole movement. Electric power is normally supplied from a power source at the surface through the wireline cable . Simply put , the wireline Tractor is an electro-mechanical device that generates a concentrated traction force downhole when activated. This

SPE 105225

Mazen Al Omari and Hans Plessing, SPE, Welltec

Innovation in Coiled-Tubing Tractor Technology Extends the Accessibility of Coiled Tubing in Horizontal Wells, Allowing Better Possibilities for Well Intervention

2 SPE 105225

force is needed to “pull” the wireline cable as well as “push” wireline tools in highly deviated or horizontal section of the hole . The coiled tubing Well Tractor operates around the same principal but is hydraulically powered . A turbine powered by the fluid drives the hydraulics system and moves the Tractor forward . The use of a turbine versus an electric motor allows more force to be generated from the coiled tubing Tractor when compared to that of wireline . Figure (2) two shows a typical schematic of the coiled tubing Well Tractor used in the interventions. Traction occurs when the wheels of the Tractor engage the inside diameter of tubing/casing/openhole and the force applied by the Tractor moves the string forward (downhole) .

Tractor Selection parameters The following are the main factors considered when selecting the coiled tubing Well Tractor .

• Size: Tractors exist in two standard nominal sizes of

2 1/8 inch and 3 1/8 inch. The minimum ID restriction in the wellbore pretty much governs the selection of the Tractor size to be used. The larger the Tractor size the more force it will be capable of generating. In all cases presented in this paper a tractor size of 3 1/8 inch was used .

• Wheel/Arm Configuration: The wheels have to be small enough to pass through the minimum ID restriction of the well and large enough to reach the biggest ID in the wellbore. For an openhole operation normally the largest size of wheels available will be selected as the maximum hole diameter is often unknown and depends on the hole conditions and the type of formation .

• Wheel Type: Special wheels with “optimized” edge are usually used when Tractoring in the open hole; this allows better traction in the open hole section .

• Force Required: Well Intervention simulation will indicate the theoretical force required to reach TD . This has to be compared to the force available from the Tractor and a safety margin needs to be added . Previous experience however has shown that it is often much more advantageous to run two Tractors in tandem in an open hole situation as this will provide more force and more grip especially in situations where a washed-out section of the well has to be overcome . Theoretically, when two Tractors are run in tandem , the force available multiplies by two .

• Tractor Setup : Two setups of the coiled tubing Tractor exist . The flow-trough Tractor is setup to allow fluid pumped through the coiled tubing to flow through; either to power a bottom Tractor which is run in tandem or when it is necessary to have flow below the tractor to hydraulically activate any mechanical tools run below . The top-vent Tractor “vents” the fluid through ports below the turbine, it is normally a simpler design than the flow-through type.

• Turbine Setup : The turbine is setup to engage the Tractor above a threshold pump rate . As it is often necessary

to be pumping while running in hole without engaging the Tractor and prior to reaching lockup depth, normally the turbine will be setup to activate above 0.6 BPM but this can be increased depending on the operation and coiled tubing size.

Figure three (3) summarizes the general specifications of the Tractor used . Candidate Selection – Open hole Horizontal wells

Open hole wells present a special challenge for tractoring

technology. Besides looking at the Well trajectory, performing intervention simulation and selecting proper wheel size and wheel design, the formation type and the well history need to be considered . Harder formations are easier to “drive through” than softer formation. Also harder formations have less likelihood of developing large washouts across the open hole section. Often “new” wells which have not been subject to large acid treatments will have a larger success ratio than older wells where large amounts of acids has been pumped . However and given all that, most of the time quantitative data may not be available to make a concise engineering judgment. This is why it is often necessary to review the well history, field history, previous experience in the area and attempt to gather as much information as possible prior to selecting the best candidate. Job Objectives and Well Data - Open Hole water injectors

The four open hole wells stimulated are water injection

wells completed with a 4 ½ in tubing with a minimum ID (restriction) of 3.75 inches and a 6 1/8 inch open hole. Figure (4) four shows a typical schematic of these wells.

The Objective of the intervention was to stimulate the

openhole by pumping 20% inhibited diverted HCL acid to remove the drilling damage and to enhance near wellbore permeability. Even though diverters were used along with the acid , effective stimulation meant that acid had to be spotted across each of the zones with coiled tubing . Previous experience showed that 2 inch coiled tubing would lockup around 60% of the open hole sections, thus most of the acid had to be spotted at that lowest point. Alternatively and in some situations , acidizing was done after drilling the openhole utilizing drillpipe which added to the well cost not to mention the safety issues and the practicalities of pumping large quantities of acid using drillpipe. CT theoretical Lockup The table below summarizes results of the theoretical coiled tubing lock-up (Measured Depth) predicted by the Well Intervention simulation , a 2”coiled tubing was used in the simulations . The column labeled as “openhole” shows the depth from upper casing shoe to the bottom of the open hole drilled section, all depths refered to in this table are measured depths. .

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Well Openhole

(7”shoe MD – MD) Length Lockup,

MD 1 11,800 -18,000ft 6,200ft 13,540 2 8,350-17,100 ft 8,750ft 12,100 3 10,745 -16690 ft 5,945ft 13,000 4 12,150 - 18,000ft 5850 ft 14,500

Well intervention job results- open hole water injectors A total of four wells were stimulated using coiled tubing combined with the Well Tractor . The table below summarizes well accessibility results achieved in these operations .

Well Length

(1) CT Lockup (2)

Tractored ft (3)

Access % (4)

1 6,200ft 2,050 ft 3,353 87 % 2 8,750ft 2,100 ft 4,400 74 % 3 5,945ft 555 ft 1,000 26% 4 5850 ft 1,200 ft 4150 91%

(1) This is the length of the 6 1/8inch open hole section. (2) Actual coiled tubing lock-up point in the openhole or

the length CT was run successfully in openhole section (3) Feet tractored in the open hole beyond coiled tubing

Lockup. This is progress due to the coiled tubing Well Tractor .

(4) Accessibility of coiled tubing and Tractor combined calculated by adding (2) + (3) divided by (1).

Bottom Hole Assembly The BHA run on 2 inch coiled tubing during these jobs : 1- 2”coiled tubing (CT) connector 2- CT disconnect Sub 3- CT circulating Sub 4- Deployment bar 5- Check Valve 6- Cross-over 7- Upper Tractor Flow-Through type 8- Lower Tractor Top-Vented type Typical CT/Tractor Stimulation Job Procedure 1- Function test CT Tractor on surface. See Figure 5A

and 5B 2- Rigup and deploy Tractors and coiled tubing BHA ,

enough lubricators should be made available to deploy the Tractors.

3- Pressure deploy the Tractor utilizing a slickline unit 4- Pressure test prior to start RIH 5- RIH CT keeping pump rate below than threshold rate

that engages Tractor. 6- Perform pull test prior to reaching openhole 7- Once CT lockup point is reached , pickup 100 ft

8- Start pumping to engage the Tractor and maintain the same rate .

9- Continue RIH until new lockup is reached . Work the CT through “washout spots“ disengaging tractor, picking up and then re-engaging the Tractor again .

10- Once the lowest depth is reached drop the ball opening the circulating sub. It is not possible to engage the tractor after this point .

11- Pump desired acid treatment moving upwards and stopping as necessary.

12- POOH and un-deploy Tractors. 13- Flow the well back as needed .

Lessons Learned

These wells were among the first wells where coiled tubing Tractor technology was utilized in open hole environment and following are some of the lessons captured :

1- A circulating sub was incorporated in the BHA to

allow pumping of the acid without exposing it to the turbine . Once the maximum depth is reached with Tractor , a ball is dropped that activates this sub .

2- Special coating was applied to the Tractor housings to improve corrosion resistance of the Tractor . Due to the considerably high temperature (250F) and the high acid concentration , this was deemed necessary . Protective sleeves were incorporated on the body of the Tractor that was later eliminated as it was not contributing to corrosion protection .

3- Extensive corrosion testing needs to be conducted for particular well conditions and acid designs. Standard Acid inhibition designs which can inhibit corrosion in coiled tubing will not have the same effect of inhibiting Tractors since the metallurgy is different .

4- Candidates need to be properly selected. Wells with history of washouts or severe damage or plugging in the open hole should be avoided . In this context poor results were achieved on Well No. 3 due to the fact that the open hole was plugged with lost circulation materials used in previous work-over.

Job Objectives and Well Data - Cased Hole case history

The objective of the operation on this cased hole oil producer was to isolate lower perforated interval in the 5-1/2 inch Liner to close off unwanted water production and to re-perforate higher up . It was decided to use Coiled tubing for the perforation to save time and reduce number of runs with wireline . The well schematic of this cased hole oil producer is shown in Figure 6 . Prior to this operation a Plug was set above the old perforations .

Old perforations = 3,360m – 4730 m New proposed perforations : Run 1 = 3047m-3350m Run 2 = 2750m – 3019m Coiled Tubing size : 2inch , tapered

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Coiled Tubing theoretical Lockup @ 3,100 m. To convey the perforating strring to perforating depth , a coiled tubing tractor was recommended . Well intervention simulations showed that one CT Well Tractor pulling force was sufficient for reaching the desired depth but tandem tractors were used as a safety measure . Bottom Hole Assembly – CT / Tractor /Perforating The following BHA was run (two runs) :

1- 3 3/8in Guns with bull nose (303m , approx 14000lbs weight )

2- Perforation Safety Sub 3- Firing sub with Flow sensor . 4- Flow Through CT Well Tractor No.1 5- Flow Through CT Well Tractor No. 2 6- Crossover 7- Swivel 8- Circulating Sub 9- Hydraulic Disconnect 10- Dual back pressure valve . 11- CT connector 12- 2 inch Coiled Tubing

Job Summary – Cased Hole case history Three runs were completed on this well . Here is a short

summary of the results

Run No. 1 Total length of guns = 303 m Required Depth of Guns = 3350 m CT Lockup = 2975m ( depth of engaging tractor) Maximum Tractored distance = 174 m , Total depth = 3149m POOH , Misrun . Discovered clogging in the Tractor turbine due to dirty fluids used . All fluids pumped from this point onward were properly filtered .

Run No. 2 Total length of guns = 303 m Required Depth of Guns = 3350m CT Lockup = 2890 m (depth of engaging tractor) Maximum Tractored distance =497 m, Total depth = 3387m Guns fired at desired depth, Good Run Run No. 3 Total length of guns = 303 m Required Depth of Guns = 3019m CT Lockup = 2970 m (depth of engaging tractor) Maximum Tractored distance =92 m , Total depth = 3062m Guns fired at desired depth , Good Run

Recommendations The intervention needs for horizontal wells are on the rise

as more and more wells are being drilled horizontally and with extended reach. There is a room for future developments to allow better accessibility on such wells , some of the areas which require more attention are :

1- Integration of coiled tubing Tractor with Mechanical

tools to allow isolation of horizontal to prevent water or gas breakthrough. This will enable identifying the problem and fixing it .

2- Adopting more quantitative methods for selecting open hole well candidates especially with regard to formation strength and hole gauge .

3- Combining Tractor technology with other techniques for improving well accessibility .

4- During early stages of the well design , more emphasis needs to be given to the accessibility issue . This has to be taken into account in designing the completion. Often wells completed with “small” tubing with restrictions are not good candidates for this technology and reduce opportunities for future intervention .

Acknowledgements

The authors wish to thank Welltec for giving them the permission to publish this paper and for providing the information and resources required. References

1. H.A. Nasr-El-Din , N.S. Al-Habib, M. Jemmali, A.Lahmadi,M.Samuel SPE 90385 “A Novel Technique to Acidize Wells with Extended reach “ SPE Houston , Texas 26-29 September 2004 2. Ian A Allahar , K. Kreiger SPE 81118 “Horizontal Production Logging using Tractor Technology- a first for Trinidad ” SPE port-of-Spain, Trinidad, West Indies , 27-30 April 2003 . 3. A.A.Al-Amer, B.A. Al-Dossary, Y.A Al-Furaidan,M.K. Hashem “Tractoring- A New Era in Horizontal Logging for Ghawar Field , Saudi Arabia “SPE , Bahrain , 12-15 March 2006. 4. H.A.Nasr-El-Din, SPE, and I.H. Arnaout , Saudi Aramco, and J.B. Chesson,SPE,and K.Cawiezel,SPE,BJ Service Co. “Novel Techniques for Improved CT Access and Stimulation in an Extended-Reach Well “SPE ICoTA , 12-13 April, The Woodlands , Texas

SPE 105225 5

Coiled Tubing Simulation

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-5000

0

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10000

15000

20000

25000

30000

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0 2000 4000 6000 8000 10000 12000 14000 16000 18000

Measured Depth, ft

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, lb

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A B

Figure 1- Well Intervention Simulation - Point A shows lockup of 2inch Coiled Tubing at a depth of 13,000 ft , Point B shows “new” Lockup after a Tractor force of 4000 lbs is applied

Figure 2 - The coiled tubing Well Tractor

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Body Tool OD 3 1/8 “ Length 22.7 ft Weight 450 lbs Max Reach OD 9.6 “ Max Speed 3600 ft/hr Traction Force 3500 lbs @ 1.4 bbl/min Max Flow Rate 3.0 bbl/min Flow rate config 0.60 bbl/min Max Dogleg 32/100 Deg @ 4.0@ ID

Figure 3 – Typical specifications of a coiled tubing Well Tractor .

Figure 4 – Typical Water Injection Well Schematic – 6 1/8 in Open Hole

Figure 5 A – Function testing of the Coiled Tubing Tractor

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Figure 5 B – Function testing of the Coiled Tubing Tractor

Figure 6 – Schematic of horizontal cased hole Oil Producer