1. Selective Fracturing of a Series of Perforations in a Horizontal Well Using a Resettable Straddle System
SPE
Josh Thompson
Weatherford International Ltd

2. Index Introduction The Jet Pack Straddle System Operational Details
Field Location
Well Profiles
The Jet Pack Straddle System
Conventional system
Reverse circulation system
Operational Details
Background
Well Schematic
BHA Configuration
Case History
Conclusions
Acknowledgments

3. Field Location Viking Formation Redwater Operations Area
Approximately 50 km NE of Edmonton
Discovered in 1948
Edmonton, 30 miles
(50 km)
The Viking formation is found at relatively shallow depths in the Redwater operations area of Central Alberta, Canada, which was discovered in (For a map of the area see Fig. 1). About 30 miles (50km) NE of Edmonton.

4. Well Profiles
Typically either vertical with the zone being fractured to enhance productivity
Horizontal with slotted liner completions
Some selective fracturing operations in low deviation wells using cup style straddles
With increased deviation they have proved to be unreliable when more than one zone is to be treated on the same run in the well
stuck straddle assemblies are not uncommon

5. The Jet Straddle System
Conventional System
Used for Acid Stimulations
Multiple Set capable
No pipe movement required to set
Pack of force created by fluid velocity through orifice
Ideal for setting in deviated wells
Adjustable straddle lengths
5000 psi differential rating
Sets with as little as .5 bpm
Up to 17 bpm flow rate (CT dependant)

6. The Jet Straddle System
Reverse Circulation System
Used for Proppant Stimulations
Multiple Set capable
Tension set
Pack off force created by overpull
Suitable for setting in deviated wells
Adjustable straddle lengths
5000 psi differential rating
Up to 17 bpm flow rate (CT dependant)
Allows for reverse circulation (clean-up)
Elements Removed

7. Background New horizontal well drilled early in 2009
cement casing through the productive zone, perforate several intervals and fracture them in an attempt to improve productivity.
Research done to find new approach to selective treatment of each set of perfs
Desired approach would allow for;
Set across the zone
fracture,
unset,
circulate the well clean,
move to next interval
In a new horizontal well drilled early in 2009 it was decided to cement casing through the productive zone and then perforate several intervals and fracture them in an attempt to improve productivity.
Fracturing of horizontal sections in the past has proved problematic with the use of diverters being ineffective and cup packers being unreliable, so a new approach to allow for selective treatment of each set of perforations was researched. As a result a selective “jet pack” straddle system was chosen which allows for setting it across the zone, fracturing, unsetting the straddle, circulating the well clean and providing for the possibility of moving it further uphole to treat the next set of perforations. The well was drilled to a total vertical depth (TVD) of 650 meters (2133 ft.) and a measured depth (MD) of 1481 meters (4859ft.), with a maximum inclination of 91°. A 4-1/2” 11.6lbs/ft casing string was then cemented in place and the well perforated with six sets of perforations each one meter in length with depths ranging from meters ( ft.). A straddle system was then deployed on 2-7/8” coiled tubing with the objective of selectively fracturing each interval with some 45 metric tones (99,180 lbs) of sand at pump rates of Bbls/min with breakdown pressures ranging from MpA ( psi).

8. Operational Details Well Schematic TVD 2,133ft (650m)
MD 4,859ft (1,481m)
Max inc. 91°
4-1/2” 11.6lb/ft casing
Six (6) sets of perfs
1 m in length
From 2,681-4,813ft ( m)
The well was drilled to a total vertical depth (TVD) of 650 meters (2133 ft.) and a measured depth (MD) of 1481 meters (4859ft.), with a maximum inclination of 91°. A 4-1/2” 11.6lbs/ft casing string was then cemented in place and the well perforated with six sets of perforations each one meter in length with depths ranging from meters ( ft.).

9. Operational Details
Areal photographs of location

10. CT Stretch

11. Required Setting Loads

12. Operational Details BHA Configuration
Total Length 30ft (9.25m), Distance between element centerline 8ft (2.45m)

13. Operational Details Case History Run 1
RIH to 705 ft. (215 m), anchor set and a surface load (CT weight plus applied tensile load) of 10.3K lbs (4.6 kdaN) applied to set straddle in blank pipe
Successful pressure test to 4,350psi (30MPa) for 5 min
Straddle moved to 3,031 ft (924m)
Successful blank pipe test was carried out (26,976 lbs (12 kdaN) surface load applied to test in horizontal.
POOH to prepare for fracturing operations the next day.
RUN # 1
The assembly was run in the hole (RIH) to a depth of 215 meters (705 ft.), the anchor was set and a surface load (CT weight plus applied tensile load) of 4.6 kdaN (10,340 lbs) applied to set the straddle packers in blank pipe – note all setting depths referenced are MCL depths. A pressure test was then carried out down the CT to 30MPa (4350 psi) for 5 minutes to test the straddle pack-off in the vertical. This test was successful and so the anchor and the packers were unset and the assembly moved downhole to a depth of 924 meters (3031 ft.) where a second blank pipe test was carried out, with a surface load of 12 kdaN (26,976 lbs) applied to the assembly, to test the straddle assembly in the horizontal. At this point it was decided to shut down operations and pull out of the hole (POOH) to prepare for fracturing operations the next day.

14. Operational Details Case History Run 2 Next day, same assembly RIH
Objective of fracturing zone 6
Casing meters (4814 ft.)
Pulled up to set at meters (4799 ft.) with a surface load of 14 kdaN (31,472lbs).
Leak appeared at pressure of 9 MPa (1305 psi)
Pumps were shut off and a surface load of 16.8kdaN (37,766lbs) applied
leak returns
RUN # 2
The next day the same assembly was RIH with the objective of fracturing zone 6, the casing collar was located at meters (4814 ft.) and then the assembly pulled to set at meters (4799 ft.) with a surface load of 14 kdaN (31,472lbs). The fracturing process was then started but at a pressure of 9 MPa (1305 psi) a leak appeared, so the pumps were shut off and a surface load of 16.8kdaN (37,766lbs) applied, but once again on starting up the pumps a leak appeared. The straddle was unset and then reset at a depth of meters (4790 ft) and a load of 15kdaN (33,729 lbs) applied but this time, upon starting the pumps, indications were that the safety shear release on the anchor had been activated. It was then necessary to shut down and POOH to inspect the assembly when the packer elements were found to be damaged and the anchor had sheared indicating that the straddle had been set across the perforations.

15. Operational Details Case History Run 2 (Cont)
Straddle unset and then reset at a depth of meters (4790 ft)
load of 15kdaN (33,729 lbs) applied
Indications were that the safety shear release on the anchor had been activated
POOH to inspect the assembly
packer elements damaged and the anchor had sheared
Conclusion that the straddle had been set across the perforations
RUN # 2
The next day the same assembly was RIH with the objective of fracturing zone 6, the casing collar was located at meters (4814 ft.) and then the assembly pulled to set at meters (4799 ft.) with a surface load of 14 kdaN (31,472lbs). The fracturing process was then started but at a pressure of 9 MPa (1305 psi) a leak appeared, so the pumps were shut off and a surface load of 16.8kdaN (37,766lbs) applied, but once again on starting up the pumps a leak appeared. The straddle was unset and then reset at a depth of meters (4790 ft) and a load of 15kdaN (33,729 lbs) applied but this time, upon starting the pumps, indications were that the safety shear release on the anchor had been activated. It was then necessary to shut down and POOH to inspect the assembly when the packer elements were found to be damaged and the anchor had sheared indicating that the straddle had been set across the perforations.

16. Operational Details Case History Run 3
logging run was made with a memory tool on CT
Perforations found to be off by 1m (3.3ft).
62cms (2.03 ft.) of spacer added between the packers
total length of 10.16m (33.3ft)
(longest that could be accommodated in the lubricator)
RIH and set at a depth of meters (4795 ft.) with a surface load of 14.5 kdaN (32,596 lbs)
Straddle zone 6
RUN # 3
The tools were completely redressed the next day while a logging run was made with a memory tool on CT in order to recheck the location of the perforations which were found to be off by 1m (3.3ft). The BHA was made up again with an additional 62cms (2.03 ft.) of spacer between the packers making a total length of 10.16m (33.3ft) – this represented the longest assembly that could be accommodated in the lubricator. It was then RIH and the assembly set at a depth of meters (4795 ft.) with a surface load of 14.5 kdaN (32,596 lbs) to straddle zone 6 and the zone was successfully fractured with a breakdown pressure of 22 MPa (3190 psi) using a total of 84 m³ of gelled fluid with 45 metric tonnes (99,180 lbs) of sand. RIH to 1464 meters (4803 ft.) to unset the anchor and packers and, after a short wait to allow the packing elements to retract, reverse circulation was established to flush the CT and the surface lines. The BHA was then POOH to be inspected and redressed – the packers were found to be in good condition with no evidence of damage.

17. Operational Details Case History Run 3 (Cont)
Zone successfully fractured
breakdown pressure of 22 MPa (3190 psi)
total of 84 m³ of gelled fluid
45 metric tonnes (99,180 lbs) of sand
RIH to 1464 meters (4803 ft.) to unset the anchor and packers
after a short wait to allow the packing elements to retract, reverse circulation was established to flush the CT and the surface lines.
POOH to inspect - packers found to be in good condition with no evidence of any damage.
RUN # 3
The tools were completely redressed the next day while a logging run was made with a memory tool on CT in order to recheck the location of the perforations which were found to be off by 1m (3.3ft). The BHA was made up again with an additional 62cms (2.03 ft.) of spacer between the packers making a total length of 10.16m (33.3ft) – this represented the longest assembly that could be accommodated in the lubricator. It was then RIH and the assembly set at a depth of meters (4795 ft.) with a surface load of 14.5 kdaN (32,596 lbs) to straddle zone 6 and the zone was successfully fractured with a breakdown pressure of 22 MPa (3190 psi) using a total of 84 m³ of gelled fluid with 45 metric tonnes (99,180 lbs) of sand. RIH to 1464 meters (4803 ft.) to unset the anchor and packers and, after a short wait to allow the packing elements to retract, reverse circulation was established to flush the CT and the surface lines. The BHA was then POOH to be inspected and redressed – the packers were found to be in good condition with no evidence of damage.

18. Operational Details Case History Run 4
BHA set at 1341 meters (4400 ft.) with a surface load of 9.4kdaN (21,131 lbs)
Top packer leak detected
BHA unset and reset at meters (4398 ft.)
Another leak (upper element was set across the perforations)
Good set at 1340 meters (4397 ft.)
zone 5 fractured
maximum pressure of 37.5 MPa (5437 psi)
RUN #4
The redressed BHA was run in to set at 1341 meters (4400 ft.) with a surface load of 9.4kdaN (21,131 lbs) On starting the pumps a top packer leak was detected so the BHA was unset and reset at meters (4398 ft.) and, after another leak (apparently because the upper element was set across the perforations), at 1340 meters (4397 ft.) where a good set was obtained and then zone 5 was fractured according to the program with a maximum pressure of 37.5 MPa (5437 psi). The BHA was then run down to 1348 meters (4423 ft) to unset the anchor and packers and reverse circulation established to flush the CT and surface lines clean. It was then POOH to be reset across zone 4 but without success so it was POOH for inspection and redress. It was found while tripping the BHA to surface that the CT had been perforated by sand. This was due to the frac. breaking down the casing cement and beginning to communicate with Zone 4 (the next zone above) from outside the casing to inside (around the casing annulus).

19. Operational Details Case History Run 4 (Cont)
The BHA run down to 1348 meters (4423 ft) to unset
Reverse circulation established to flush the CT and surface lines clean.
POOH to be reset across zone 4 but without success
POOH for inspection of straddle
CT had been perforated by sand
Frac. breaking down casing cement establishing communication with Zone 4 (the next zone above) from outside the casing to inside (around the casing annulus).
RUN #4
The redressed BHA was run in to set at 1341 meters (4400 ft.) with a surface load of 9.4kdaN (21,131 lbs) On starting the pumps a top packer leak was detected so the BHA was unset and reset at meters (4398 ft.) and, after another leak (apparently because the upper element was set across the perforations), at 1340 meters (4397 ft.) where a good set was obtained and then zone 5 was fractured according to the program with a maximum pressure of 37.5 MPa (5437 psi). The BHA was then run down to 1348 meters (4423 ft) to unset the anchor and packers and reverse circulation established to flush the CT and surface lines clean. It was then POOH to be reset across zone 4 but without success so it was POOH for inspection and redress. It was found while tripping the BHA to surface that the CT had been perforated by sand. This was due to the frac. breaking down the casing cement and beginning to communicate with Zone 4 (the next zone above) from outside the casing to inside (around the casing annulus).

20. Operational Details Case History Run 5
RIH to be set at a depth of meters (4038 ft.) to straddle zone 4
leak developed (packers maybe set in the perforations)
Unset and reset at meters (4036 ft.)
Leak detected again (communication with zone 5 below)
Zone 4 attempts abandoned
BHA was unset reset at meters (3582 ft.)
surface load of 13.3 kdaN (29,898 lbs).
RUN #5
The same assembly was redressed and then RIH to be set at a depth of meters (4038 ft.) to straddle zone 4 but a leak developed indicating that the packers maybe set in the perforations. It was unset and reset at meters (4036 ft.) but again there was a leak which appeared to indicate communication with zone 5 below. Attempts to treat zone 4 were abandoned and the BHA was unset and POOH to be reset at meters (3582 ft.) across zone 3 with a surface load of 13.3 kdaN (29,898 lbs). The zone was then successfully fractured according to program with a maximum pressure of 15 MPa (2175psi), however the job was terminated early due to pressure jacking. As a result, when the BHA was unset and reverse circulation started, no returns were obtained, likewise with direct circulation, and attempts to POOH with a surface load of 13 kdaN (29,224 lbs) were unsuccessful. The BHA was worked down to meters (3621 ft) still without any returns and then down to meters (3635 ft.) where the assembly came free with a surface load of 9 kdaN (20,232 lbs) from where it was POOH with a continuous overpull of 4kdaN (8992 lbs) all the way to surface. When it was retrieved it was found that sand was on top of the BHA, the packing elements were not fully retracted due to sand contamination and the CT was packed with sand. The tools were then shipped to the warehouse in Red Deer and operations were shut down for the Easter holiday.

21. Operational Details Case History Run 5 (Cont)
Zone 3 successfully fractured
maximum pressure of 15 MPa (2175psi)
Job terminated early due to pressure jacking
As a result, when the BHA was unset and reverse circulation started, no returns were obtained
Attempts to POOH with a surface load of 13 kdaN (29,224 lbs) were unsuccessful
BHA worked down to meters (3621 ft) (no returns)
Down to meters (3635 ft.) free with a surface load of 9 kdaN (20,232 lbs)
RUN #5
The same assembly was redressed and then RIH to be set at a depth of meters (4038 ft.) to straddle zone 4 but a leak developed indicating that the packers maybe set in the perforations. It was unset and reset at meters (4036 ft.) but again there was a leak which appeared to indicate communication with zone 5 below. Attempts to treat zone 4 were abandoned and the BHA was unset and POOH to be reset at meters (3582 ft.) across zone 3 with a surface load of 13.3 kdaN (29,898 lbs). The zone was then successfully fractured according to program with a maximum pressure of 15 MPa (2175psi), however the job was terminated early due to pressure jacking. As a result, when the BHA was unset and reverse circulation started, no returns were obtained, likewise with direct circulation, and attempts to POOH with a surface load of 13 kdaN (29,224 lbs) were unsuccessful. The BHA was worked down to meters (3621 ft) still without any returns and then down to meters (3635 ft.) where the assembly came free with a surface load of 9 kdaN (20,232 lbs) from where it was POOH with a continuous overpull of 4kdaN (8992 lbs) all the way to surface. When it was retrieved it was found that sand was on top of the BHA, the packing elements were not fully retracted due to sand contamination and the CT was packed with sand. The tools were then shipped to the warehouse in Red Deer and operations were shut down for the Easter holiday.

22. Operational Details Case History Run 5 (Cont)
POOH with a continuous overpull of 4kdaN (8992 lbs)
Sand on top of the BHA
Packing elements not fully retracted
CT packed with sand.
Tools shipped to Red Deer Ops shut down for Easter
RUN #5
The same assembly was redressed and then RIH to be set at a depth of meters (4038 ft.) to straddle zone 4 but a leak developed indicating that the packers maybe set in the perforations. It was unset and reset at meters (4036 ft.) but again there was a leak which appeared to indicate communication with zone 5 below. Attempts to treat zone 4 were abandoned and the BHA was unset and POOH to be reset at meters (3582 ft.) across zone 3 with a surface load of 13.3 kdaN (29,898 lbs). The zone was then successfully fractured according to program with a maximum pressure of 15 MPa (2175psi), however the job was terminated early due to pressure jacking. As a result, when the BHA was unset and reverse circulation started, no returns were obtained, likewise with direct circulation, and attempts to POOH with a surface load of 13 kdaN (29,224 lbs) were unsuccessful. The BHA was worked down to meters (3621 ft) still without any returns and then down to meters (3635 ft.) where the assembly came free with a surface load of 9 kdaN (20,232 lbs) from where it was POOH with a continuous overpull of 4kdaN (8992 lbs) all the way to surface. When it was retrieved it was found that sand was on top of the BHA, the packing elements were not fully retracted due to sand contamination and the CT was packed with sand. The tools were then shipped to the warehouse in Red Deer and operations were shut down for the Easter holiday.

23. Operational Details Case History Run 6
Operations resumed five days later
RIH to be set across zone 2 at meters (3087 ft)
Surface load of 11 kdaN (24728 lbs)
Zone successfully fractured
maximum pressure of 38 MPa (5510 psi).
Return line became plugged preventing bleed off
BHA unset and RIH to 962 meters (3156 ft)
Operations shut down to allow the well to bleed to the formation overnight.
RUN #6
Five days later operations were resumed and the same BHA, fully redressed, was RIH to be set across zone 2 at meters (3087 ft) with a surface load of 11 kdaN (24728 lbs) and the zone was successfully fractured according to the program at a maximum pressure of 38 MPa (5510 psi). However attempts to bleed off at surface after the job failed as the return line became plugged. The BHA was unset and RIH to 962 meters (3156 ft), but being unable to circulate in either direction due to the plug, operations were shut down to allow the well to bleed to the formation overnight. The next day operations continued and after cleaning out the surface lines circulation was established with considerable amounts of sand in the returns which plugged the return line twice. The BHA was RIH to meters (3174 ft) and with reverse circulation the returns became clean enough to POOH and the BHA was recovered and found to be in good condition.

24. Operational Details Case History Run 6 (Cont)
Next day operations continued
After cleaning out the surface lines circulation was established
plugged the return line twice
The BHA was RIH to meters (3174 ft) and with reverse circulation the returns became clean enough to POOH
BHA was recovered and found to be in good condition.
RUN #6
Five days later operations were resumed and the same BHA, fully redressed, was RIH to be set across zone 2 at meters (3087 ft) with a surface load of 11 kdaN (24728 lbs) and the zone was successfully fractured according to the program at a maximum pressure of 38 MPa (5510 psi). However attempts to bleed off at surface after the job failed as the return line became plugged. The BHA was unset and RIH to 962 meters (3156 ft), but being unable to circulate in either direction due to the plug, operations were shut down to allow the well to bleed to the formation overnight. The next day operations continued and after cleaning out the surface lines circulation was established with considerable amounts of sand in the returns which plugged the return line twice. The BHA was RIH to meters (3174 ft) and with reverse circulation the returns became clean enough to POOH and the BHA was recovered and found to be in good condition.

25. Operational Details Case History Summary
4 of the 6 sets of perforations treated
Ceased operations to evaluate the results
Total of 6 trips
Set and unset successfully 12 times
Four (4) zones treated
total of 180 Metric tonnes (396,720 lbs) of sand
combined density of 1000kg/m³ (8.4 lbs/gallon)
fluid viscosity of approx 400cp, with no indications of any untoward abrasion of the BHA.
Summary:
With 4 of the 6 sets of perforations having been treated it was decided to cease operations and evaluate the results. The jet pack straddle system was run in the well a total of 6 times and was set and unset successfully 12 times during the program, four zones being treated with a total of 180 Metric tonnes (396,720 lbs) of sand in gel fluid with a combined density of 1000kg/m³ (8.4 lbs/gallon) and a fluid viscosity of approx 400cp, with no indications of any untoward abrasion of the BHA.
After a lengthy clean up period the well was put on production at a rate of 50bbl/day which represents the highest initial rate for any well in the field and the 4 months of steady production at that rate is also the longest on record.

26. Operational Details Case History Summary (Cont)
After clean up period well was put on production at a rate of 50bbl/day
Highest initial rate for any well in the field
4 months of steady production at that rate is also the longest on record.
Summary:
With 4 of the 6 sets of perforations having been treated it was decided to cease operations and evaluate the results. The jet pack straddle system was run in the well a total of 6 times and was set and unset successfully 12 times during the program, four zones being treated with a total of 180 Metric tonnes (396,720 lbs) of sand in gel fluid with a combined density of 1000kg/m³ (8.4 lbs/gallon) and a fluid viscosity of approx 400cp, with no indications of any untoward abrasion of the BHA.
After a lengthy clean up period the well was put on production at a rate of 50bbl/day which represents the highest initial rate for any well in the field and the 4 months of steady production at that rate is also the longest on record.

27. Conclusions Correctly placing the straddle proved difficult
Short distance between the element centerlines.
Dictated by the maximum assembly length that the lubricator assembly could accommodate.
In future operations it would be advisable to make plans for a longer lubricator.
Stretch and load characteristics of the CT are critical to the operation and the modeling of them is a very important part of job preparation!
Accurate perf depths very important.
Properly sized manifold for returns is equally important
Quality of the cement bond (communication between sets of perfs)
24 hour operations is a must for optimizing costs.
Conclusions
This first run of the tandem tension jet pack straddle assembly in a horizontal well proved the viability of the approach and although some difficulties were encountered the tools functioned according to design and the results achieved were very positive. Following is a breakdown of the difficulties encountered and the conclusions reached that should greatly enhance the success of future such operations:
Correctly placing the packers to straddle the perforated intervals proved difficult due to the short distance between the packer centerlines. This was dictated by the maximum assembly length that the lubricator assembly could accommodate. In future operations it would be advisable to make plans for a longer lubricator to be available so as to accommodate a longer straddle and make the accurate placement of the BHA less critical.
The stretch and load characteristics of the CT in the horizontal are critical to the operation and the modeling of them is a very important part of job preparation.
The accuracy of the perforation depths was very important and discrepancies led to several problems. Logging, or another means of obtaining perforating depth accuracy may be advisable in order to achieve accurate placement of the straddle.
Plugging of the CT and lines with sand, due to screening out, lead to difficulties in establishing circulation, either direct or reverse, and therefore in cleaning up the well and retrieving the BHA. In reviewing the problem it was concluded that the flow back manifold was inadequately sized and a larger capacity assembly is recommended in the future. The quality of the cement bond in this well was also critical as communication between sets of perforations as happened in Run # 4. In this case sand was jetting behind the casing uphole through the perforations on the next zone resulting in cutting a hole in the CT, causing an emergency shut down.
Multi zone horizontal operations should be carried out in 24 hour operations. Some of the shut downs in this series of operations were due to the day being over, thus extending the overall operational time.
If these aspects of the operation are properly addressed it is probable that multiple zone treatments can be made in a single trip as planned.

28. Looking Forward
Our experience has lead us to improvements to optimize performance these improvements include:
Increased pressure rating – Up to 54Mpa
Improved bottom packer equalization / release – Allowing for quicker movement between zones.
Debris barriers designed to “survive screen outs”
Improved Operating Procedures

29. Questions?