87S t i m G u n T e c h n o l o g y

A p p l i c a t i o n Ty p e : N e a r- W e l l b o r e S t i m u l a t i o n

The first applications of TCP underbalanced propellant jobs inshallow Rocky Mountain gas wells Ralph Affinito, Marathon Oil CompanyLarry Staten, Halliburton Energy Services

This article describes how TCP assemblies wererevised to allow effective use of the StimGun™

assembly ignition and immediate subsequentunderbalance to occur in shallow gas wells. Thefirst use of the technology was a successful recom-pletion of a gas reservoir in the Dakota formationlocated in northwest Wyoming in 1998.

Historical background

Uphole gas recompletions in the field utilizedcased hole wireline perforating in a balanced con-dition with 3% KCl water. Economic productionafter swabbing generally required a breakdown orproppant fracture treatment. Post-fracture ratesranged from 300 to 1000 mcfgpd (8500 to280,000 m3/d). This reservoir was generally fault-ed yielding relatively small accumulations of gasdepleted by less than three wells per fault block.Exploitation was through recompletions fromdeeper intervals.

Post-breakdown/fracture transient analysis of oneearlier completion indicated 31 md permeabilityand -3.5 skin. This zone was also extremely sensi-tive to fluids, as demonstrated in one Dakota com-pletion which tested 1000+ mcfgpd followingproppant fracture treatment and never returned toan economic production rate following loading thehole with completion brine and running tubulars.

General Reservoir parameters are as follows:

✳ Depth: 1400-1800 ft (427-549 m)

✳ Porosity: 17.60%

✳ Gross pay: 148 ft (45 m)

✳ Net pay: 52 ft (16 m)

✳ Water saturation: 26.67%

✳ SBHP: 325 psig (2.2 MPa)

✳ SBHT: 90°F (33°C)

Completion utilizing the StimGun™

assembly

The process leading to an improved completiondesign:

✳ Minimize liquid contact and provide as muchstimulation as possible. Reservoir evaluationindicated the kaolinite, chlorite, and illitemixed layer clays system of the reservoir wouldbest be stabilized by use of 3% NH4Clreplacing the KCl system.

✳ The permeability of an undamaged reservoirwas thought to be sufficient to allowproduction at economic rates without need forfracture stimulation.

✳ An adjacent clean sandstone which was waterprolific also made proppant fracturing toogreat a risk in this wellbore.

✳ Based upon the low SBHP of the reservoir,solely underbalanced perforating would notyield an adequate completion.

A system of underbalanced TCP in combinationwith the StimGun™ assembly to provide an ade-quate formation breakdown and near-wellborefracturing with minimal fluid contact appeared tobe the appropriate approach. The initial concernwith use of the StimGun™ assembly was therequirement that 600 psig of liquid hydrostatictamp exist for the propellant to effectively perform.

The novel approach employed in this applica-tion, for the first time in industry, was to trap afluid tamp of 600 lbs (4.1 MPa) of hydrostatic pres-sure below the packer but still have a minimumamount of fluid in the tubing to accommodate the325 psi (2.2 MPa) SBHP of the Dakota formation. Amaximum differential bar vent was used to achievethe closed system. The maximum differential barvent was held closed by a chamber of silicone fluidand a spring. When the detonating bar wasdropped and passed through this specialized vent,

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88S t i m G u n T e c h n o l o g y

it sheared a break plug, allowing the silicone fluid toescape and enabling the vent to open, communicat-ing the perforated interval to the tubing. A choke wasplaced in the break plug to slow down this action toenable the guns to fire and the propellant to beginignition while the hydrostatic pressure was still at 600 psi (4.1 MPa). This approach worked very well,and the job was successful. Additionally, the only fluidable to contact the perfs when the StimGuns werefired was 3% NH4Cl. A diagram of a typical comple-tion of this type is shown below.

Results

The StimGun completion in this well performed asdesigned. The bar vent established the necessary

hydrostatic pressure for the propellant to burn on theStimGun, while negligible fluid contacted the reser-voir. The well was immediately flow tested and placedon production following cleanup. This StimGun com-pletion practice was executed on four other wells inthis Big Horn Basin field from 1998–1999. Initial pro-duction rates ranged from 800 mcfgpd to 4500 mcfgpd (23,700 m3/d to 127,400 m3/d) withthe average being 2300 mcfgpd (65,100 m3/d).These resulted in higher production rates than oldercompletions and lower capital costs due to removingthe necessity to use proppant fracture stimulation.This methodology has now been applied to numer-ous wells throughout the world.

Cement retainer @ 1610 ft (491 m) with 5 sks cmt

Halliburton PLS pkr @ 1335 ft (407 m)

Dry tubing

Radioactive marker

Water

Water (KCl fluid)Maximum differentialbar vent and drop

bar firing head

Gross perforations from 1444 to 1592 ft (440 to 485 m) with 52 ft (16 m) of net perforations

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High-speed gauge data improvesjob success on wireline-conveyed near-wellbore stimulations Todd McAleese, Marathon Canada, Ltd.

This article describes the value of understandingand revising job designs by use of the high-

speed pressure gauges. Production on this exam-ple well was tripled using the StimGun™ assembly.After the first run, changes were made on locationusing the gauge data.

Marathon desired to perform an electric line re-perforating job on an older rod pumped well inCanada. The Pekisko formation in this well hadbeen originally completed in the 1970s. Productionhad steadily fallen off over the years to the pointthat the well was becoming uneconomic. The wellwas scheduled for a pump change, and it waselected to re-perforate the zone using theStimGun™ assembly. Two runs were required to

cover the zone. As per standard practice in a newarea at the time, it was decided to use StimGun™

assembly, with 50% sleeve coverage. high-speedgauges were used to obtain actual pressure dataand allow subsequent runs to be optimized. Thewell was thought to have sufficient hydrostaticavailable to ensure the proper burn of the propel-lant tools.

After successfully perforating the well on the firstrun, the gauge data were downloaded and thepressure data were reviewed on site. It was foundthat there was much less hydrostatic than originallythought, most likely due to the gassy nature of thefluid, and there was much more produced oil inthe wellbore. The pressure curve (see Figure 1, Run 1) showed only a peak pressure of 8000 psi(55 MPa) was achieved, much less than the com-puter model prediction of 13,500 psi (93 MPa)based on less compressible fluid. Burn time

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Time - seconds

0

10

20

30

40

50Marathon Canada well

-- run #1 5.1 MPa Hydrostatic 60% coverage

-- run #2 10.1 MPa hydrostatic 75 % coverage

Pres

sure

- M

Pa

Figure 1 – Using gauge data from Run 1, the operator greatly increased the effectiveness of the propellant burn byincreasing the fluid tamp and propellant coverage, shown in Run 2.

Before Stimulation: 17 BOPD (2.7 m3/d)

After Stimulation: 48 BOPD (7.7 m3/d)

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appeared to be in the range of 45 ms, much longerthan originally expected. Long burn times and lowpeak pressure are generally indicators that the hydro-static pressure is too low. The StimGun™ assemblyrequires confinement to burn properly, and high gascontent of the well fluids caused the propellant gasesto follow the path of least resistance and pressure upthe wellbore rather than leak off to the formation. Fluidwas added to increase the hydrostatic in the well. Thedecision was also made to increase the coverage ofStimGunpropellant to 75% on the second run.

The second perforating run was performed withoutincident, and the gauge data showed clear indication

of the improved job design (see Figure 1, Run 2). Byincreasing the hydrostatic in the wellbore assemblyto roughly 900 psi (6.2 MPa), and increasing theStimGun sleeve coverage to 75%, the peak pressuregenerated at the perforations increased to 13,000 psi(89.6 MPa). Burn time was reduced to 25 ms, allgood indicators that the StimGun™ assembly sleeveshad burned properly.

Marathon had expected the well to produce at 17 bopd (3 m3/d); instead the well came in at 48 bopd (7 m3/d) and barely declined over the nextseveral months.

Over 2000 successful StimGun technology jobs in Western Canada

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Combining StimGun™ assembly withEOB perforation and acid stimulationsignificantly improves New Yorkstate’s gas productionCraig Smith, The Expro Group (formerly with Halliburton Energy Services, Inc.)

Extreme overbalanced(EOB) StimGun™ assembly

jobs completed on the BlackRiver/Trenton zone in NewYork state have proved to bevery successful. This zone isdolomitic with considerable joints andfractures. Conventional completion techniqueshave rendered less than desired results. Typicallyoperators perforated with wireline, then attemptedhigh-rate acid/fracture jobs. The leak-off associatedwith the joints and fractures lead to screen-out,even with very low sand concentrations.Acceptable production was in the 750 mscfd to 1 mmscfd (2.1 to 2.8 E4m3/d) range.

The solution is to run the StimGun™ assembly ina tubing-conveyed perforating (TCP) gun configu-ration and apply extreme overbalance pressure.Propellant coverage is typically 40 to 50% of thenet pay perforated. TCP guns are generally rununder a 10,000 psi (69 MPa) packer with an on-off tool and tubing to surface. Job design also uses300 ft (91 m) of 20% acid as the incompressiblespearhead. The annulus is usually pressured up to

3500 psi (24 MPa), and then nitrogen pressure isused to create the EOB condition with 11,500 psi(79 MPa) of surface pressure typical. This translatesto ~15,000 psi (103 MPa) bottom hole treatingpressure. Upon detonation, nitrogen is used to dis-place the treatment at a rate of 8000 scf/min. forfive minutes, then nitrified 20% acid is pumped~1000 gals (4 m3) of acid at 5000 scf/min (142 m3/min), depending upon treating pressure.

Upon completion of the nitrified acidinjection, flow back is initiated imme-diately with a full open choke forone to two tubing volumes.

The wells respond splendidly. Thefirst well completed flowed at a rateof 3 to 3.5 mmscfd (8.5 to 9.9 E4m3/d). Subsequent wells pro-duce in the range of 3 to 10 mmscfd (8.5 to 2.8 E5m3/d).Considerable rig time is savedbecause wells are producing withinhours of the treatment. This hasnow become a best practice solu-tion to completing these wells.

91S t i m G u n T e c h n o l o g y

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0

1

2

3

4

5

6

7

8

9

10

Before StimGun After StimGun

Prod

ucin

g ra

te –

mm

scfd

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92S t i m G u n T e c h n o l o g y

Industry has had great success in removing near-wellbore damage caused by perforating wells in an

underbalanced condition. However, if the formationpressure is too low, this technique is not always suc-cessful. By using the combined stimulation and per-forating technique (StimGun™ assembly), the near-wellbore damage in depleted reservoirs can be suc-cessfully removed. Halliburton presented some oftheir results in the “SPE Paper 68101: A UniqueApproach to Enhancing Production from Depleted,Highly Laminated Sand Reservoirs Using a CombinedPropellant/Perforating Technique,” written by H. El-Bermawy, SPE, Agiba Petroleum Company and H. El-Assal, Halliburton Energy Services. This paper waspresented at the 2001 SPE Middle East Oil Show heldin Bahrain, 17-20 March 2001. This entire paper,with due recognition to the SPE for allowing itsrepublication, is included in Appendix.

In Egypt, an operator was not obtaining the desiredflow efficiency from conventional, tubing-conveyed,underbalanced perforating methods. Given the lowformation pressure, it was probable that during perfo-rating, the differential pressure created was insufficientto remove the induced perforating damage. Toimprove the effective conductivity from the reservoir,the StimGun™ assembly combination stimulation/per-foration technology was used to enhance the under-balanced perforating. This successfully reduced theskin and increased the flow efficiency.

The reader is encouraged to review the paper in itsentirety. The detailed discussion of the problem, thepossible solution, the results, and of operational pre-cautions is extremely informative and applicable –given the increased interest in stimulation of lowpressure reservoirs.

Case 1

Conventional underbalanced perforating

Skin: +23

Flow Eff.: 0.27

An overview of SPE paper 68101:A unique approach to enhancing production from depleted, highly laminated sand reservoirs using a combined propellant/perforatingtechniqueKim Hungerford, Halliburton Energy Services

Case 2

StimGun™ underbalanced perforating

Skin: -4

Flow Eff.: 1.19

Case 3

StimGun™ underbalanced perforating

Skin -2

Flow Eff. 1.25

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Successfully combining the StimGun™

assembly with Pow*rPerf™

technologies Frank Oriold, Canadian Completion Services – The Expro Group

Canadian Hunter, now Devon Energy, operatesthe Ring Border gas field which straddles the

Alberta/British Columbia border. In some cases thewells contain two producing horizons, the Blueskyand Monteny formations. The Bluesky, when pres-ent, requires stimulation to be productive. Typicaltreatments such as four or five tonne“batch fracs” tend to be risky due tothe close proximity to water. As a resultof these issues, the Pow*rPerf™ comple-tion technique was used to overcomeskin damage.

Pow*rPerf™ is a Marathon OilCompany patented process that com-bines extreme overbalance (EOB) per-forating with a specially modified gunbody that contains 20/40 mesh baux-ite. Special shaped charges open thebauxite carrier, ejecting the materialinto the fluid/expanding gas streamduring the extreme overbalance job.The erosive attributes of the bauxitecoupled with the high pressure andvelocity of the expanding gas and fluidstream make this a very effective toolin the treatment of near-wellbore dam-age in the perforations. CanadianHunter had performed transient analy-sis on some of the wells and discoveredthan skin was not completely removedutilizing this technique alone in someof the Bluesky wells.

Solution

Use of high-speed pressure gaugeshave also shown that pressure loss due tofriction can be significant in extremeoverbalance operations. This is especiallytrue in wells that use small tubing. In theRing Border gas field, the productiontubing is 23⁄8 in. (60.3 mm) OD and thewells are shallow at approximately

3000 ft (900 m). The maximum pressure that can besafely applied to the wells is around 6700 psi (47 MPa). It appears that this combination of shallowwells and small tubing combine to reduce the effec-tiveness of the Pow*rPerf™ process.

In an attempt to improve completion methods, it

Radioactive marker sub

Tubing with high pressure nitrogen

Tubing joint

Retrievable 10K packer

10 ft (3.1 m) pup joint

“X” profile

10 ft (3.1 m) pup joint

Jar up mechanical tubing release

10 ft (3.1 m) pup jointAuto venting pressure activated firing head

Gun with proppant

23⁄8 in. (60.3 mm) 6 spf (20 spm) 60° phase perforating gun with 75%coverage of 3.5 in. (89 mm) OD StimGun™ sleeve

S t i m G u n T e c h n o l o g y

A p p l i c a t i o n Ty p e : N e a r- W e l l b o r e S t i m u l a t i o n

Typical StimGun/Pow*rPerf™ TCP assembly.

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was thought that combining the StimGun™ assemblywith Pow*rPerf™ might increase the effectiveness of thetreatments, and it been a great success. The initial ener-gy provided by the StimGun™ assembly was used inthese completions to break down near-wellbore dam-age and initiate a small fracture. Because the StimGun™

assembly and the associated high energy gas pulse actto break down all the perforations, it is thought that thePow*rPerf™ portion of the job is more effective becausethe stored energy in the tubing would be needed onlyfor fracture extension as opposed to perforation break-down. By combining the two technologies, the issue offriction loss should be of lesser consequence.

Results

To date, more than 30 of these combination jobshave been performed in the area. It appears that theStimGun does indeed assist in reducing total skinbecause production numbers are up from these wellsby approximately 25%. The breakdown/leak-off profileof nitrogen into the formation is now significantly dif-ferent and seems to indicate that a more efficient pathto the formation has been created.

As a result of these successes, more than 80% of theextreme overbalance jobs performed by The ExproGroup in Canada now incorporate StimGun™ assemblyas a perforation breakdown tool.

StimGun sect 4c 9/19/02 8:58 PM Page 94

In May 2001, ExxonMobil contracted Tripoint toperform a StimTube™ tool stimulation on slick-

line for a well candidate on the Hondo Platform,offshore California. The well chosen was produc-ing from the Vaqueros formation. The H-36 STwell had been damaged during its initial comple-tion, and current production was lower than cal-culated reservoir performance. The H-36 ST oilproducer would require a high-rate, acid fracturestimulation to improve production at an estimat-ed cost of $500,000. Other issues involved in per-forming the fracture stimulation on this wellinvolved strict offshore environmental regulationsconcerning this type of work and a lack of rigspace available to perform the fracture stimula-tion that the well required.

ExxonMobil decided to use the StimTube™ tool asa near-wellbore stimulation method as an alterna-tive to the fracture stimulation. PulsFrac™ modelingsuggested fractures could be created 2 to 3 ft (.6 to 1 m) from the wellbore, and the operator feltthis was sufficient to reach past the near-wellboredamage as well as break down plugged perfora-tions. The StimTube™

tool would eliminateenvironmental impactrisk, reduce productiondown time, and at thesame time be more costeffective. The desiredresult was additional per-foration breakdown andthe initiation of a fracture near the wellbore. Thisjob was designed to be conveyed on slickline,which was also one of the first such applications forthe technology. A slickline gamma ray correlationmemory tool was deployed first to establish positivedepth control for the subsequent operations. TheStimTube™ tool was then deployed utilizing a mem-ory tool slickline firing system. Two separate runswere conducted to intervals 12,674 to 12,689 ft(3863 to 3868 m) and 12,649 to 12,674 ft

(3855 to 3863 m) with 15 ft (4.6 m) of StimTube™

tool on each run. The well was then returned toproduction. Before and after producing rates are asfollows:

✳ Before: 356 BOPD (57 m3)

✳ After: 890 BOPD (141 m3)

✳ Stabilized Rate: 800 BOPD after 6 weeks (127 m3)

Clearly, the work was very successful. ExxonMobilsubsequently planned and executed furtherworkovers using this technology as well as theStimGun™ assembly combined with tubing-con-veyed underbalanced perforating for new well com-pletions in the field. As a result of this successfulprocedure, four more wells were treated withStimTube™ tools in this field. In three of the fourcases production increased over original numbers.Accurate production numbers were not availablebecause of the limited amount of gas available forlifting operations on the platform. The operatorstated, however, that the platform was deliveringmore than 10,000 barrels of oil per day (bopd) forthe first time in five years.

This is one of many examples showing removalof near-wellbore damage via the use of the propel-lant technology. In the US, the propellant technol-ogy has been most effective as a near-wellborestimulation in formations where fractured reser-voirs damage, and fracture plugging exists.Internationally, use of the technology for near-wellbore stimulation has been successful wherehigher permeability reservoirs are damaged bynon-optimal drilling or completion practice.

Slickline-conveyed StimTube™ toolstimulation: an alternative to high-rate acid fractureBill Barton, Tripoint, Inc. – The Expro Group

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The StimTube™ tool eliminated environmental impact risk, reduced

production down time, and at the sametime was found to be more cost effective.

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Propellants have dramaticallyincreased production from heavy oilwells: the need for hydraulic fracturinghas been reducedKevin Newmiller, Precision DrillingPerry M. Huber, Plains Perforating Ltd.

In order to effectively obtain productionfrom heavy oil sands in

Canada, either ahydraulic fracture or thecreation of sand produc-tion (along with the oil), orboth, have been required.Propellant tools have greatlyreduced the need for hydraulicfracturing; and have greatlyincreased sand/oil production inareas where this is necessary.

Bakken formation – replacing hydraulic fracturing

The Bakken formation is an unconsolidated sand-stone within the Mannville group of sands. Locatedin Western Saskatchewan, the zone contains 14° to 19° API gravity oil. The average porosity is30% and the average perforation interval is 11.6 ft(3.5 m). Traditionally, wells have been stimulatedthrough the use of 32,500 lbs (15 tonne) sand fracsat an average cost $25,000 per fracture.

As of this writing, over 100 wells have been pro-pellant stimulated in this field. The operator hasindicated that wells with an average porosity equalto or greater than 30% do not require a hydraulicfracture stimulation following the propellant stimu-lation. In total, 58% of the wells fall into this cate-gory. The remaining wells required hydraulic frac-turing but less pressure was needed to initiate thefracture stimulation.

High-speed pressure gauges and computer modelsusing the PulsFrac™ software are run in conjunctionwith each propellant stimulation to monitor resultsand to aid in refining the amount of propellantrequired to obtain satisfactory results. As a result ofthis optimization, perforation shot density has beenincreased to 6 spf (20 spm) from 5 spf (17 spm), andthe propellant coverage has been increased to anaverage of 80% from an initial average of 60%. Thishas resulted in a more complete propellant burnwith improved burn pressures and fracture lengths.

The use of StimGun has reduced the need forhydraulic fracturing in the Bakken formation by 58%.

Heavy oil areas in Western Canada.

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Case 1

Bakken formation: 34% porosity

5.6 ft (1.7 m) perforation interval with 3.9 ft (1.20 m) propellant sleeve

Maximum burn pressure: 3900 psi (27 MPa)

Fracture extension: 7.5 ft (2.3 m)

Results: Successful stimulation – no fracture treatment required.

0.000 0.003 0.006 0.009 0.012 0.015 0.018 0.021 0.024Time - seconds

0

5

10

15

20

25

30

35

40

45

50

55

Penn West Hoosier111/13-23-031-27 W3/00

Bakken 833 m86 mm, 24 gm, 17 spm, 60° x 1.7 m

High-speed pressure data

Pres

sure

- M

Pa

Bakken Examples

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Case 2

Bakken formation: 33% porosity

6.6 ft (2.0 m) perf interval with 4.9 ft (1.5 m) propellant sleeve

Maximum burn pressure: 4930 psi (34 MPa)

Fracture extension: 7.5 ft (2.3 m)

Results: Successful stimulation – no fracture treatment required. Increase in shot density improvedburn pressure.

0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040 0.045 0.050

Time - seconds

0

5

10

15

20

25

30

35

40

45

Penn West Hoosier131/05-06-031-26 w3/00

Bakken 871 m 86 mm, 26 gm BH, 20 spm, 60° x 2.0 m

High-speed pressure data

Pres

sure

- M

Pa

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Case 3

Bakken formation: 25% porosity

9.8 ft (3.0 m) perf interval with 8.9 ft (2.7 m) propellant sleeve

Maximum burn pressure: 9100 psi (63 MPa)

Fracture extension: 8.4 ft (2.55 m)

Results: Successful stimulation – well had a slight blow on the casing following stimulationdespite the reduced formation porosity in this example. Increased coverage yieldedhigher burn pressure and resulted in a complete propellant burn.

l

0.000 0.005 0.010 0.015 0.020 0.025 0.030Time seconds

0

5

10

15

20

25

30

35

40

45

50

55

60

65

perf gun

Penn West Milton B14121/14-16-30-28 W3/00

Bakken 86mm, 24 gm, 17 spm, 60 deg

High-speed pressure data

Pres

sure

- M

Pa

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100S t i m G u n T e c h n o l o g y

Case 4

Bakken formation: 33% porosity

17.8 ft (5.4 m) perf interval with 14.8 ft (4.5 m) propellant sleeve

Maximum burn pressure: 8400 psi (58 MPa)

Fracture extension: 10.3 ft (3.13 m)

Results: Successful stimulation – no hydraulic fracture required. Optimized shot density and propel-lant coverage resulted in improved fracture extension.

Time - seconds

Penn West Loverna141/04-24-031-28 w3/00

Bakken 845 m 86 mm, 26 gm BH .8, 20 spm, 60° x 5.4 m

High-speed pressure data

perf gun

-- propellant ignition

0.00 0.01 0.02 0.03 0.04 0.050

5

10

15

20

25

30

35

40

45

50

55

60

Pres

sure

- M

Pa

l

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In Lloydminster, Canada, to achieve oil productionfrom the majority of unconsolidated heavy oil

wells, both the sand and oil must pumped to sur-face. The sand is separated from the oil at surfaceand discarded (Figure 1). All too frequently, theproduction in these wells unexplainably declines.This is normally attributed to a lack of sand mobili-ty or the bridging of the sand grains. Propellanttechnology using the WST has been very success-fully used to disrupt the presumed sand bridgesand re-establish economic production rates.

The procedure is to pull all pumps, rods, andtubing from the well. If the well bottom is within 6.56 ft (2 m) of the stimulation interval, any fillmust be removed. The WST propellant has aunique ignition system and can be successfullyignited and combusted under shallow, high per-meability conditions. After initiation the propel-lant burn must be contained by as much back

pressure as possible or propellant burn velocitywill rapidly decrease to zero. To maintain backpressure it is necessary to have as much fluid(produced fluid, blended with lighter oil or KCIwater) in the wellbore as possible. In some cases

Enhancing sand/oil production in the Lloydminster Canada areaDavid Cuthill, Computalog Wireline ServicesLane Merta, Computalog Wireline Services

Propellant ignition,rapid pressure leak-off,and prolongedburn normallyobserved due to lackof confinement.

0 0.005 0.01 0.015 0.02 0.025Time - seconds

0

10

20

30

40

50

60

70

Pres

sure

- m

Pa

Figure 2 – Typical pressure vs. time high-speed gauge data from WST heavy oil applications in the Lloydminster area.

Figure 1 – Sand and oil are pumped to surface and theoil is separated from the sand. The sand is subsequentlydiscarded and stockpiled.

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where the formation will not support a fluid column,packers can be set and then released after the well-bore is full and the propellant tool is positioned andready to fire. Alternatively, fluid can be pumpedbefore and during the stimulation. Several successfulstimulations have been carried out while pumpingwith pressure on the wellhead. Generally, underthese conditions, any method that will provide afluid column with as much back-pressure as possible,will enhance tool burn efficiency and the effective-ness of the stimulation. After the stimulation, produc-tion should be resumed as soon as practical. Due toincreased sand cut a sand pump or foaming with

coiled tubing may be required until the sand cut,declines to a manageable level where commonpumping methods can be used.

When the high-speed pressure gauge is used, agraphical presentation of the stimulation event can begenerated for analysis with the help of the PulsFrac™

software. It is sometimes difficult to get a completepropellant burn in this application so the pressurepulse is viewed to determine the burn efficiency.Propellant ignition followed by a rapid pressuredecline is indicative of the observed response in thisshallow unconsolidated environment, as shown inFigure 2.

Case 2

Objective: Well was suspended due to low productivity

Solution: A propellant WST was proposed as a method of reinitiating economic production

Configuration:

Orientation: Vertical

Formation: Rex sandstone; 1935 ft (590 m)

Casing size: 7 in. (177.8 mm)

Tool: 2.5 in. (63.5 mm) WST, conveyed on wireline with high-speed gauge

Tamp: Oil blend

Results. After stimulation sand inflow increased significantly. Production sustained at 60 bpd (9.5 m3/d), oil.

Case 1

Objective: Well had been shut in for a period of three years due to low productivity

Solution: A propellant WST was proposed as a method of reinitiating economic production

Configuration:

Orientation: Vertical

Formation: Basal Mannville sandstone; 2165 ft (660 m)

Casing size: 7 in. (177.8 mm)

Tool: 2.5 in. (63.5 mm) WST, conveyed on wireline with high-speed gauge

Tamp: Oil

Results: Added 63 bbls (10 m3) of fluid prior to propellant ignition to maintain sufficient tamp column height.After stimulation production sustained at 44 bpd (7 m3/d), oil.

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Case 4

Objective: Horizontal heavy oil well, completed with a slotted liner, producing at 19 bpd (3 m3/d) with a 35%water cut. Propellant was suggested as a method of increasing productivity

Solution: A propellant WST was proposed as a method of clearing the liner slots and stimulating the forma-tion behind the liner

Configuration:

Orientation: Horizontal

Formation: McLaren sandstone; 6100 ft (1850 m)

Casing size: 7 in. (177.8 mm) slotted liner

Tool: 2 in. (50.8 mm) WST, conveyed on tubing with high-speed gauge

Tamp: Produced water

Results: After stimulation well producing at 82 bpd (13 m3/d) at a 35% water cut. Liner was not damagedduring stimulation treatment.

Case 5

Objective: New well completion – on perforating no measurable inflow

Solution: A WST was proposed as a method of initiating production

Configuration:

Orientation: Deviated

Formation: Cummings sandstone; 1755 ft (535 m)

Casing size: 7 in. (177.8 mm)

Tool: 2 in. (50.8 mm) WST, propellant conveyed on wireline with high-speed gauge

Tamp: Oil

Results: Pumped 63 bbls (10 m3) of tamp fluid prior to propellant ignition. After stimulation well producingat 82 bpd (13 m3/d), oil.

Case 3

Objective: Well was producing at an uneconomic rate of 6 bpd (1 m3/d), oil

Solution: A propellant WST was proposed as a method of increasing production rate

Configuration:

Orientation: Vertical

Formation: Sparky sandstone; 1739 ft (530 m)

Casing size: 7 in. (177.8 mm)

Tool: 2.5 in. (63.5 mm) WST, conveyed on wireline with high-speed gauge

Tamp: Oil blend

Results: After propellant stimulation production increased to a sustained rate of 38 bpd (6 m3/d), oil.

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Case 8

Objective: Well was suspended due to low productivity

Solution: A WST was proposed as a method of reinitiating production

Configuration:

Orientation: Vertical

Formation: Basal Mannville sandstone; 2050 ft (625 m)

Casing size: 7 in. (177.8 mm)

Tool: 2 in. (50.8 mm) WST, conveyed on wireline with high-speed gauge

Tamp: Oil

Results: After the propellant stimulation production increased to 31 to 44 bpd (5 to 7 m3/d), oil.

Case 7

Objective: Well was suspended due to low productivity

Solution: A WST was proposed as a method of reinitiating production

Configuration:

Orientation: Vertical

Formation: Basal Mannville sandstone; 1657 ft (505 m)

Casing size: 7 in. (177.8 mm)

Tool: 2 in. (50.8 mm) WST, conveyed on wireline with high-speed gauge

Tamp: Produced oil

Results: After propellant stimulation the well began producing at 38 bpd (6 m3/d), oil.

Case 6

Objective: Well was producing at an uneconomic rate of 22 bpd (3.5 m3/d), oil

Solution: A WST was suggested as a method of stimulating increased production

Configuration:

Orientation: Vertical

Formation: Colony sandstone; 1854 ft (565 m)

Casing size: 7 in. (177.8 mm)

Tool: 2 in. (50.8 mm) WST, conveyed on wireline with high-speed gauge

Tamp: Oil

Results: After propellant stimulation production increased to and stabilized at 53 bpd (8.5 m3/d), oil.

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Case 10

Objective: Well was producing at unacceptable rates

Solution: A WST in combination with a solvent soak/squeeze was proposed as a method of reinitiating pro-duction

Configuration:

Orientation: Vertical

Formation: Waseca sandstone; 1115 ft (340 m)

Casing size: 7 in. (177.8 mm)

Tool: 2 in. (50.8 mm) WST, conveyed on wireline with high-speed gauge

Tamp: Xylene & oil blend

Results: After the propellant stimulation production increased to 25 bpd (4 m3/d), oil.

Case 11

Objective: Well was suspended due to low productivity

Solution: A WST was proposed as a method of reinitiating production

Configuration:

Orientation: Deviated

Formation: Upper Waseca sandstone; 1476 ft (450 m)

Casing size: 7 in. (177.8 mm)

Tool: 2 in. (50.8 mm) WST, conveyed on wireline with high-speed gauge

Tamp: Oil

Results: After the propellant stimulation no sustainable production was possible due to an extremely highsand cut. A foam cleanup was used to remove sand and debris. Production increased to economicrates.

Case 9

Objective: Well was producing at 6 bpd (1 m3/d), oil

Solution: A WST was proposed as a method of increasing production

Configuration:

Orientation: Vertical

Formation: General petroleum sandstone; 1460 ft (445 m)

Casing size: 7 in. (177.8 mm)

Tool: 2 in. (50.8 mm) WST, conveyed on wireline with high-speed gauge

Tamp: Oil

Results: After the propellant stimulation production increased to 38 to 44 bpd (6 to 7 m3/d), oil.

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Stimulation of shallow gas wellsDavid Cuthill, Computalog Wireline Services

Successfully completing shallow gas wells can be achallenge – especially in intervals that are near

water. In many instances perforating alone will notprovide sufficient inflow performance. Low reservoirpressure does not generally provide adequate differ-ential pressure and inflow velocities to flush the near-wellbore region. Remedial efforts such as modest“skin fracs,” for near-wellbore stimulation, run therisk of connecting to water.

The StimGun™ assembly has been demonstrated toprovide sufficient stimulation energy to clean up thenear-wellbore region while remaining in the zone.Shallow gas wells stimulated using this advanced per-forating technique have performed to potential with-out the need for additional costly and sometimesunpredictable stimulations. When dealing with near-wellbore production restrictions, propellant stimula-tion devices can be an inexpensive and effective

method of clearing the formation and perforations.The focused nature of the stimulation means that itcan be used in applications where more aggressivestimulations may result in the increase of undesirablenear-water production.

Mechanism

The stimulation mechanism for a StimGun treatmentis identical to the stand-alone propellant tools with theunique difference that the propellant event takes placeat the time of perforating. Once positioned on depth,detonating the shaped charge contained within theperforating carrier ignites the propellant sleeve. As thepropellant burns, a surge of high-pressure gas is pro-duced that enters the newly created perforation path,breaking through the damage around the perforationtunnel. For underbalanced stimulations, an increasedback-flushing effect has been demonstrated to furtherenhance the stimulation.

Propellant devices require confining pressure in orderto promote an efficient burn. Confining pressure isobtained by placing a fluid column of sufficient heightover the propellant tool > 650 ft (>200 m) for theStimGun™ assembly. Twice the minimum amount isideal. In shallow wells adequate fluid height sometimescannot be obtained due to the depth of the well. Inaddition, placing excessive fluid over the interval isundesirable due to the low reservoir pressure and con-cern over fluid injection into the formation followingperforation. An efficient propellant burn can beobtained by placing a minimal amount of a formationcompatible fluid over the interval and applying ade-quate nitrogen pressure at the surface over that fluidcolumn (see Figure 1). Effective confinement isobtained and the StimGun™ assembly can be ignited.After initiating the StimGun™ assembly, the nitrogenpressure is immediately released to minimize fluid injec-tion and allow back-flushing of the formation.

Pressure data

When a high-speed pressure gauge is used, agraphical presentation of the stimulation event canbe generated for analysis. The analysis can be used todetermine the effect of the stimulation on the forma-tion and to evaluate the burn of the propellant. Theconfiguration and job execution for this application

Nitrogen

Compatible liquid

Perforating carrier

Propellant sleeve

Sleeve retainer ring

Figure 1 - Wellbore schematic illustrating how nitrogenpressure has been utilized to increase propellant confiningpressure.

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0 25 50 75Time - minutes

0

5

10

15

Run Inhole

On depth

Toolignition

Pressurize withnitrogen from surface

Bleed offnitrogen

POOH

Pres

sure

- M

Pa

Figure 2 - Example pressure plot illustrating well pressurization and post stimulation pressure bleed-off to minimize fluidinjection.

Case 1

Objective: The interval has near water. Hydraulic fracturing brings in water production and standard perforat-ing does not provide maximum expected inflow.

Solution: A StimGun™ assembly was run to initiate localized near-wellbore clean up.

Configuration:

Orientation: Vertical

Formation: Bluesky sandstone; 1132 ft (345 m)

Casing size: 41⁄2 in. (114.3 mm)

Tool: 3.375 in. (85.7 mm) StimGun™ assembly over 2.75 in. (70 mm) ERHSC loaded at 6 spf (20 spm)& 60° phasing conveyed on wireline

Tamp: KCl with 1000 psi (6.9 MPa) Nitrogen over pressure

Results: After completion with StimGun™ assembly, the well was producing at an acceptable rate of 225 mcf/d (6.4 E3m3/d), gas, with no observed water production. Hydraulic fracturing was avoided.

Case histories

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Case 4

Objective: The completion interval has near water. Previous fracing attempts in the field have brought in water pro-duction, and standard perforating does not provide maximum expected inflow.

Solution: A StimGun™ assembly was run to initiate localized near-wellbore clean up.

Configuration:

Orientation: Vertical

Formation: Bluesky sandstone; 1335 ft (406 m)

Casing size: 41⁄2 in. (114.3 mm)

Tool: 3.375 in. (85.7 mm) StimGun™ assembly over 2.75 in. (70 mm) ERHSC loaded at 6 spf (20 spm) & 60°phasing conveyed on wireline.

Tamp: Water/methanol with 1000 psi (6.9 MPa) nitrogen over pressure.

Results: After completion with StimGun™ assembly, the well was producing at 153 mcf/d (4.3 E3m3/d), gas, witha WGR of 6.7 bbl/mmcf (3.0 m3/100 E3m3). Hydraulic fracture was avoided – production at acceptablerate.

Case 3

Objective: The completion interval has near water. Previous fracing attempts in the field have brought in water pro-duction, and standard perforating does not provide maximum expected inflow.

Solution: A StimGun™ assembly was run to initiate localized near-wellbore clean up.

Configuration:

Orientation: Vertical

Formation: Bluesky sandstone; 1335 ft (407 m)

Casing size: 41⁄2 in. (114.3 mm)

Tool: 3.375 in. (85.7 mm) StimGun™ assembly over 2.75 in. (70 mm) ERHSC loaded at 6 spf (20 spm) & 60°phasing conveyed on wireline

Tamp: Water/methanol with 1000 psi (6.9 MPa) Nitrogen over pressure

Results: After completion with StimGun™ assembly, the well was producing at 5.9 E3m3/d (210 mcf/d), gas, witha WGR of 24.9 bbl/mmcf (11.3 m3/100 E3m3). Hydraulic fracturing was avoided – production at accept-able rate.

Case 2

Objective: The completion interval has near water. Previous fracing attempts in the field have brought in water pro-duction, and standard perforating does not provide maximum expected inflow.

Solution: A StimGun™ assembly was run to initiate localized near-wellbore clean up.

Configuration:

Orientation: Vertical

Formation: Bluesky sandstone; 1181 ft (360 m)

Casing size: 41⁄2 in. (114.3 mm)

Tool: 3.375 in. (85.7 mm) StimGun™ assembly over 2.75 in. (70 mm) ERHSC loaded at 6 spf (20 spm) & 60° phasing conveyed on wireline

Tamp: Water/methanol with 1000 psi (6.9 MPa) Nitrogen over pressure

Results: After completion with StimGun™ assembly, the well was producing at 300 mcf/d (8.5 E3m3/d), gas, with aWGR of 8.4 bbl/mmcf (3.8 m3/100 E3m3). Hydraulic fracturing was avoided – production at acceptablerate.

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Case 5

Objective: The completion interval has near water. Previous fracing attempts in the field have brought inwater production, and standard perforating does not provide maximum expected inflow.

Solution: A StimGun™ assembly was run to initiate localized near-wellbore clean up.

Configuration:

Orientation: Vertical

Formation: Bluesky sandstone; 1345 ft (410 m)

Casing size: 41⁄2 in. (114.3 mm)

Tool: 3.375 in. (85.7 mm) StimGun™ assembly over 2.75 in. (70 mm) ERHSC loaded at 6 spf (20 spm)& 60° phasing conveyed on wireline

Tamp: Water/Methanol with 1000 psi (6.9 MPa) Nitrogen over pressure

Results: After completion with StimGun™ assembly, the well was producing at 127 mcf/d (3.6 E3m3/d), gas,with no observable water production. Hydraulic fracturing was avoided – production at acceptablerate.

Case 6

Objective: The completion interval has near water. Previous fracing attempts in the field have brought inwater production, and standard perforating does not provide maximum expected inflow.

Solution: A StimGun™ assembly was run to initiate localized near-wellbore clean up.

Configuration:

Orientation: Vertical

Formation: Bluesky sandstone; 1207 ft (368 m)

Casing size: 41⁄2 in. (114.3 mm)

Tool: 3.375 in. (85.7 mm) StimGun™ assembly over 2.75 in. (70 mm) ERHSC loaded at 6 spf (20 spm)& 60° phasing conveyed on wireline

Tamp: Water/Methanol with 1000 psi (6.9 MPa) Nitrogen over pressure

Results: After completion with StimGun™ assembly, the well was producing at 92 mcf/d (2.6 E3m3/d), gas,with no observable water production. Hydraulic fracturing was avoided – production at acceptablerate.

Case 7

Objective: The completion interval has near water. Previous fracing attempts in this field have brought inwater production, and standard perforating does not provide maximum expected inflow.

Solution: A StimGun™ assembly was run to initiate localized near-wellbore clean up.

Configuration:

Orientation: Vertical

Formation: Bluesky sandstone; 1843 ft (257 m)

Casing size: 41⁄2 in. (114.3 mm)

Tool: 3.375 in. (85.7 mm) StimGun™ assembly over 2.75 in. (70 mm) ERHSC loaded at 6 spf (20 spm)& 60° phasing conveyed on wireline

Tamp: Water/Methanol with 1000 psi (6.9 MPa) Nitrogen over pressure

Results: After completion with StimGun™ assembly, the well was producing at 107 mcfd (3.0 E3m3/d), gas,with no observable water production. Hydraulic fracturing was avoided – production at acceptablerate.

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Case 8

Objective: The completion interval has near water. Previous fracing attempts in this field have brought in waterproduction, and standard perforating does not provide maximum expected inflow.

Solution: A StimGun™ assembly was run to initiate localized near-wellbore clean up.

Configuration:

Orientation: Vertical

Formation: Bluesky sandstone; 1119 ft (341 m)

Casing size: 41⁄2 in. (114.3 mm)

Tool: 3.375 in. (85.7 mm) StimGun™ assembly over 2.75 in. (70 mm) ERHSC loaded at 6 spf (20 spm) & 60° phasing conveyed on wireline

Tamp: Water/methanol with 1000 psi (6.9 MPa) nitrogen over pressure

Results: After completion with StimGun™ assembly, the well was producing at 236 mcf/d (6.7 E3m3/d), gas, witha WGR of 2.6 bbl/mmcf (1.2 m3/100 E3m3). Hydraulic fracturing was avoided – production at acceptablerate.

Case 9

Objective: The completion interval has near water. Previous fracing attempts in this field have brought in water pro-duction, and standard perforating does not provide maximum expected inflow.

Solution: A StimGun™ assembly was run to initiate localized near-wellbore clean up.

Configuration:

Orientation: Vertical

Formation: Bluesky sandstone; 1171 ft (357 m)

Casing size: 41⁄2 in. (114.3mm)

Tool: 3.375 in. (85.7 mm) StimGun™ assembly over 2.75 in. (70 mm) ERHSC loaded at 6 spf (20 spm) & 60° phasing conveyed on wireline

Tamp: Water/methanol with 1000 psi (6.9 MPa) nitrogen over pressure

Results: After completion with StimGun™ assembly, the well was producing at 206 mcf/d (5.8 E3m3/d), gas, witha WGR of 11.69 bbl/mmcf (5.3 m3/100 E3/m3). Hydraulic fracturing was avoided – production at accept-able rate.

makes the pressure recording an important tool todetermine if the propellant burned correctly.

Conclusions

Applications have demonstrated that the StimGun™

assembly can be an effective method of stimulatingshallow wells.

✳ In many instances perforating alone will notprovide sufficient inflow performance because the

low reservoir pressure does not clean up the near-wellbore region.

✳ Remedial efforts such as modest “skin fracs” runthe risk of connecting to water.

✳ The StimGun™ assembly has been demonstratedto provide sufficient stimulation energy to cleanup the near-wellbore region while remaining inzone.

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