cobed halli

June 2007

Chapter 7

Completions

7.1 InWell compbut modifpropertieswith deve

Coal produ

Coal hwellboto bloc

Adsororganifluids.

Bothe Highe

As a consstudy in chof conditioperations

7.2 OOpenholethe Warriofrom a sinCompletions 323

troductionletions in coalseams are similar to conventional gas well completions,

ications have been incorporated into the procedures because of unique of the coal. Some coal properties and attendant problems associatedloping the coals for methane include the following:is friable. The coal of optimum rank for coalbed methane (CBM)ction is also the most fragile.as an extensive natural fracture system that must be connected to there to provide adequate permeability. The fracture network is sensitivekage from cement or drilling muds.

ptive properties that lead to swelling of the coal matrix, especially fromc compounds, make the coal susceptible to drilling mud and fracturing

rsome coal fines are generated during completion and production.r treating pressures are often encountered in fracturing coals.

equence of these coal properties, completing CBM wells has become aoosing and modifying a method to give the best procedure for each setons.1 Costs of completing the well must be minimized in all CBM but particularly the many projects that are marginally economical.

penhole Completions completions of single seams were the first type of completion used inr basin where, before 1982, the completion goal was recovery of gas

gle seam with minimum formation damage.2 The technique was simple

Coalbed Methane: Principles and Practices

324 Comp

in principle, and it involved minimum risk. The single-seam, openholecompletions were directed toward the most prolific group, the Mary Lee/BlueCreek.

Basically, the procedure was the following:

1. A 2. Dr3. Th4. Th5. A

Similarly,the 1970shad no hywas less thThe procecasing obclean loos

During 1completiomarginal pwith an opcompletio7.1 for the

In this insThe Marythe other tletions June 2007

4 1/2-in. diameter casing was set above the coal. illing was completed through the coal.e seam was hydraulically fractured.e well was cleaned with compressed air. tubing string and pumping equipment were inserted.3

the CBM wells drilled in the Appalachian basin in the 1950s through were openhole completions of a single seam. These wells ordinarilydraulic fracturing, or at most a small-scale fracture. The gas productionan 150 Mscf/D in all cases4 and usually in the range of 3050 Mscf/D.

dure was favored by the mining industry because the open hole left nostacle for eventual mining through the coal. However, downtimes toe coal from the open hole were frequent.

98284, Taurus began initial developmental work on multizonens in openhole2 because of the potentially lower cost to developroperties. As a result, the single-seam completion was replaced brieflyenhole, multizone completion. A sketch of the openhole, multizone

n used early in the Warrior basin developmental period is shown in Fig. case of the Deerlick Creek field.2

tance, the Black Creek, Mary Lee, and Pratt groups were completed. Lee was the prolific producer, but significant production came fromwo groups.


June 2007

The openhole completion has these advantages: No casing is left to obstruct mining. The cementing process does no damage to the coal face. The open hole gives unobstructed access to the coal face from the wellbore.

Despite tcompletiothin coalswhere mu

Tubin

Inflat

Sand

Fig. 7.1Completions 325

hese secondary benefits, the time and expense of the multizonen by open hole proved prohibitive in the Warrior basin for the multiple,eams. Openhole completions were also common in the San Juan basinch thicker seams made the technique more practical.

g string

able packer

plug

Pratt Group( ~1,200 ft )

Mary Lee Group( ~2,000 ft )

Black Creek Group( ~2,500 ft )

Openhole multizone completion.2


326 Comp

7.3. Openhole Cavitation Process

7.3.1 Introduction

Reaming phenomensometimeand the hoin open hoof high pefairway, a

Thereforeinto two completio

The cavitreported completioJuan basinfractured necessaril

The cavitselection applicatiocavity com

Thick Good Extens Ranks Low a Overp High iletions June 2007

the coal face underneath the casing, as well as a natural cavitationon, led to the realization that great improvements in production coulds result in the San Juan basin if a cavity was created in the open holele was swept free of rubble. The dynamic cavity completion developedle as a specialized completion method for thick, overpressured seamsrmeability in a northwest to southeast trending area, referred to as thelong the Colorado/New Mexico border of the basin.

, completions in the thick seams of the San Juan basin have evolvedschools: openhole cavity completions and cased-hole perforatedns with fracturing.

y completion method grew rapidly after prolific production wasby Meridian in 1986, and within a few years almost 1,000 suchns had been made. In these wells of the fairway of the northwest San, cavity completions may produce at six times (or more) of the rate of

wells in the area.5 Outside the fairway, however, the technique is noty more successful than a fracturing technique.

y completions of the San Juan basin act as a standard for projectinternationally, and other sites in the United States are sought forn of the process. Factors identified as contributing to success of thepletion include:

seams. permeability. ive cleating. of coal beyond the coalification break. sh content. ressuring. n-situ stress.


June 2007

The procedure has been successfully applied in 30- to 80-ft thick seams of coal ofat least high-volatile A bituminous rank. Good permeabilities are present (22md); third and fourth order cleats are present and the cleats are closely spaced. A30% overpressuring has been reported in areas of successful applications.6 Onlya small paskin facto

To explaimodeled tand cavityof exceptinaturally network tthe formamechanicresult in lvalue of meffective.

There are that make

Fractuwellbofines effect.accum

The clfractur

A fracadjaceThis fmaxim

AlthoughcompletioopenholeCompletions 327

rt of the success of a cavity completion comes from the reduction inr at the wellbore7 or the effective enlargement of the wellbore.8

n the mechanism of the dynamic cavity effect on production, Weida7he interactions of in-situ stresses, coals bulk mechanical properties, dimensions. The results were stress-relaxed and stress-altered regionsonal permeability emanating from the cavity elliptically to intersectoccurring fractures and to effectively connect the formation cleato the wellbore. In the model of Weida, high natural permeabilities oftion are symptomatic of a high-order cleat system that reduces

al properties of the coal for the process to be successful; thick seamsonger stress-relaxed regions of enhanced permeability. A thresholdinimum in-situ stress was suggested for the cavity mechanism to be

some negative aspects of the fracturing process in the San Juan fairway the cavity completion excel in comparison, including the following. ring may cause near-wellbore damage where fines collect around there to hinder gas flow. The hvAb to mvb coals are most susceptible to

generation. (Fines may accumulate in the cavity without immediate Near the wellbore, the cavity creates a repository where fines canulate without deleterious effects on production.) osely spaced primary, secondary, and tertiary cleats are susceptible toing fluid infiltration and damage. ture is apt to follow the trend of the face cleat, to increase the stress of nt coal, and to close the parallel face cleats in the low-modulus coal. orces the flow of gas through the butt cleats of lower permeability. For um gas production, flow should be directed through the face cleats.

costly, holes already cased may be recompleted with a cavity-typen or converted from a cased and hydraulically-fractured well to an cavity completion. By jet-milling through the casing above the


328 Comp

coalseam, the hole can be sidetracked and redrilled through the coal. It is thencavity completed.

As a result of cavity completing, production was increased by a factor of 7.8 in7-ft seams at 3,396 ft and 14-ft seams at 3,417-ft depths in the South Shale Ridge#11-15 woperation,extendingthe 14-ft sfractures t

Different will be dis

7.3.2 Ca

Using twResearch Itechnique Mexico bgives averletions June 2007

ell of Conquest Oil Company.9 In a computer simulation of the Weida7 predicted a stress relaxation region of enhanced permeability 10.8 ft from the cavity in the 7-ft seam and 23.1 ft from the cavity ineam; these extended regions are postulated to have intersected naturalo increase production.

field procedures for the cavitation process have been investigated andcussed in the following sections.

se Study: Cavitation Research Projecto producing wells and three observation wells, Amoco, the Gasnstitute, and Resource Enterprises Inc. (REI) evaluated the cavitationalin the fairway region of the San Juan basin near the Colorado and Neworder.10 The original reservoir permeability was 22.5 md. Table 7.1age characteristics of the wellsite.

Table 7.1Average Reservoir Properties10Depth, Top of Coal (ft) 3,150Coal Thickness (ft) 47Gas Content (scf/ton) 553Ash Content (%) 30%Langmuir Volume, Ash-free (scf/ton) 1,118Langmuir Pressure (psia) 606Sorption Time (hr) 4.1Coal Density (g/cc) 1.50Temperature (F) 120Initial Pressure (psia) 1,525Permeability, Horizontal (md) 22.5


June 2007

A flow diagram of the surface facilities used in the test well is presented in Fig.7.2.11

Samp

Culvert

w6 ft

Hamm

erunion

or

(stakedow

n) 21/2-in. li


10 ft

16-in.

2 1/2-in

. Line

Pick-up Eye 1/2-in. a

ngle iron

Muffler-top view

Dogleg

Baffle Plate

150 ft-6-in.

le Box

3 1/2-in. Line

gas

ater

Anchors

Res

erve

Pit

1. Run blow lines into flare pit to minimize overspray.2. All blooie lines equipped with floor controlled motor valves.3. All blooie lines to be secured with anchors, cable, and cement pads.4. Stake down 2 1/2-in. flare lines and test lines-every joint.5. Equip blooie lines with common igniter system.6. End secondary blooie dogleg to be converted to mud flowline with 4-in. hose.7. Choke manifold to be targeted.8. Primary blooie line to have sample catcher and gas sniffer.9. Set light stand at sample box.

threadedne

Secondary

blooie line

Second

ary

jet

>2-in. - 3,000 psichoke manifold

Primary

blooie line

Cement pads9 5/8-in. casing/cement

1,700 lb

Test Se

parator

1. heate

r

2. vess

el

3. mete

r run

Flow diagram of surface facilities.11


330 Comp

After drilling through the Fruitland coal, cavities were established by REI in thetest well by injection cavitation, a process inducing sloughing of coal into thewellbore by pressure cycles, in which the following steps were taken in eachcycle:

1. Pu2. Cl3. Cl

su4. In

the5. Op

The cavitaand McBa

ElsewherePiceance bto 108 Mcface-cleat

Natural canatural informationwas evaluwere taken

1. Pu2. Se3. Cl4. Al5. Opletions June 2007

ll drillpipe and bit into the casing above the open hole.ose pipe rams around the drillpipe, sealing the annulus.ose hydraulically operated valves in the blooie lines to give complete pres-re sealing.ject 25 bbl water and follow with 2,625 scfm of air (approximately 10% of rate to fracture12) through the drillpipe until 1,350 psig is reached.en the blooie lines. Allow the hole to blowout into the flare pit.

tion cycles were continued by the consortium as reported by Mavorne10 through 9 days. Cost was estimated at $10,000 per day.

, a jetting tool to facilitate a cavity formation has been used in theasin. Consequently, the production rate of methane increased from 22f/D.5 Permeability in the butt-cleat direction was 913 md and in thedirection 23.525.0 md.

vitation is the process of coal sloughing into the wellbore by release of-situ stresses. The controlled blowout in the process comes from pressure buildup rather than injected air. A natural cavitation processated by Mavor and McBane in a test hole where the following steps:10

ll drillbit into casing.al annulus with pipe rams.ose hydraulic valves of blooie lines.low surface pressure to increase to 500 psig (approximately 30 minutes).en valves; let well blow out into flare pit.


June 2007

The steps are similar to the injection cavitation except there is no injection ofwater or air.

The sequence of steps was repeated 29 times. After production flow tests, the60-mesh to 1/4-in. particles that had entered the cavity during flow periods wereremoved. remove th

During thand naturaflow reachaway wascycles is gimprovem


Water and air were circulated through the drillpipe at total depth toe debris.

e eighth day of cavitation cycling after about 15 injection cavitationsl cavitations, a breakthrough was achieved.10 Not only did the test gas a maximum at that time, but the pressure of an observation well 176 ft

substantially affected. A production profile as a function of number ofiven in Fig. 7.3 that illustrates when additional cycles gave no moreent in production.

Cavity cycles at Amoco test site.11


332 Comp

7.3.3 Case Study: Devon Cavity Process

In the fairway of the San Juan basin, 50 miles east of Farmington, New Mexico,and 50 miles south of the Fruitland coal outcrops at Durango, Colorado, 102wells werecavity merequired 8

Although 3,000 ft. Oseam thick

A sketch location isdepth whewater or, a

3,00

50

Fig. letions June 2007

drilled by Devon on 320-acre spacing and completed by the openholethod.13 The cost of creating the cavities was $180,000 per well and14 days to accomplish.

the maximum burial at one time was 8,800 ft, coal in the unit is now atverpressured by 30%, the high-volatile bituminous coals average a

ness in the region of 50 ft; maximum thickness reaches 80 ft.

of the cavity completion technique as practiced by Devon at this presented in Fig. 7.4. An uncemented, perforated liner was run to totalre the perforations were kept clear of fines buildup by circulating freshs a last resort, by pulling the liner.

300 ft

0 ft

ft

Top of Fruitland

Cavity Cavity

7-in. Casing

9 / -in. Surfacecasing

5 8

Liner

Preperforated1-in. D holes12 holes/ft

7.4Openhole cavity completion.13


June 2007

From a horizontal distance of 0.20.4 miles away, wells were drilleddirectionally in an S-shaped hole to a destination under Navajo Lake to minimizethe environmental impact.12

The openhole section completed in the coal was kept vertical since shale stringersthat do nowells wertested at a

A direct cDevon rep6.7 times An even gcavity rate

The cavityby Mavor7.5). Theremains insonar evalCompletions 333

t cavitate would otherwise have restricted pipe placement.13 Four suche drilled to a depth of 2,000 ft underneath the lake and subsequently total rate of 35.3 MMcf/D.

omparison between fracturing and cavity methods is possible here, aslaced 10 fractured wells with nearby cavity completions, which gave

as much stabilized gas flow as the initial rate of the fractured wells.14reater contrast of initial flow ratio existed in a 21:1 ratio of initials to the initial fracture rates.

dimension from a sonar probe agrees with the cavity size calculated from a material balance on solids collected at the surface14 (see Fig. sonar probe gives a profile of the cavity in which fingerlike shale the 8-ft diameter cavern. The gamma ray and density logs verify theuation.


334 Comp

The diameimprovem

Dep

th, f

t

3,2

3,1

3,1

3,1

3,1

3,1

3,1400.0 GAPI 200

Gamma Ray 1 # 2-8.0 Feet 8.0

Cavity Radius

Fig. 7.5letions June 2007

ter of the cavity should be 68 ft; a larger cavity provides only limitedent of production rate.5

1.0 3.0Density, gm/cc

00

90

80

70

60

50

Sonar probe of cavity.15


June 2007

7.4 Cased-Hole Completions

7.4.1 Conditions for Cased Hole

Characterare typicaWarrior seserve as mworld. CoThe seamCreek, anpermeabitarget froseams hav

The genergroups beFig. 7.6. research sestablishe

Many comInfluencin

Mult Thin Marg Larg Norm Dept Coal Optim GoodCompletions 335

istics of multiple groups of coals with thin seams in the Warrior basinl of the other coals in the eastern United States. Completions in therve as models for these other thin seams in Appalachia, and they mayodels for completions of multiple, thin seams in basins around the

mpletion of these multiple seams must be done as cheaply as possible.s in a typical Warrior well may consist of the Pratt, Mary Lee/Blued Black Creek coals. The shallow Pratt group has relatively highlity and low gas content, the intermediate Mary Lee is the primarym which most of the production comes, and the deep Black Creeke high gas content but low permeability.

alized configuration of the borehole and casing through the three coalfore entry is made to the formation by slots or perforations is given inThe diagram refers to the experimental P2 well at the Rock Creekite.16 Note the 5 1/2-in. diameter casing in the 7 7/8-in. diameter holed from surface into a sump below the lowermost seam.

pletion techniques have been used throughout the Warrior basin.g their choice are the following:

iple seams per well. seams of inches to a few feet thick.inal economics for producing.

e volumes of water produced early in the life.ally pressured (some underpressured).

h (1,0004,500 ft). fines.

um coal rank, hvAb-lvb. permeability.


336 Comp

Conditions usually combine to require a cased hole with access to the seams thatallows maximum control of fracturing. Economics requires simplicity.

7.4.2 Ac

The slottecontrol an


cess by Slotting

d-casing technique was introduced to correct problems with fracturingd fines control in openhole completions while retaining the best

Generalized diagram of cased hole at Rock Creek prior to seam entry.16


June 2007

attributes of the openhole completions used early in the development of theWarrior basin. The concept aims to retain a large area open to the face of the coalwhile providing a means to isolate each zone and control fracturing fluid entrymore easily.

The proceA jetting tthe casingsolution.

A sketchhigh-presdiameter tcyclicallymaximum

During thetool, and especiallytraverse small-scaformation

Slotted cperforatio

Unfortunathe advant

1. Pl2. Sl3. Ad

The additifalloff tesplugging.Completions 337

dure involves drilling and cementing casing through the coal intervals.ool is attached to the end of the tubing string, and slots are cut through and cement with high velocity streams of an abrasive water-sand

of the slotting tool is presented in Fig. 7.7. A high-velocitysure water and sand fluid (4 bbl/min) is pumped through a 3/16-in.ool to impinge on the casing; two nozzles are set 180 apart. The tool is lowered and raised to create slots approximately 48-in. long by a of 1.4-in. wide.17

slotting operations, sand control in the carrier fluid, orientation of theovercutting prolong slotting times and increase costs. Overcutting is troublesome because early breakthrough at some point on the casingwill expose the coal to the high-pressure jet. The result can bele fracturing that affects any subsequent permeability tests of the.

asing prevents fines and spallings from plugging access as inns.

tely, the problems associated with the slotting technique overshadowages.2

acing and orienting the cutting jet are difficult.ots weaken the casing and make it susceptible to failure during fracturing.ditional time to perform the slotting operation adds to the cost.onal cost of slotting limits its use to those wells used for injection andts, where it is useful because of the slots large entry area and lack of


338 Comp


Jet slotting tool.17


June 2007

7.4.3 Access by Perforating

After the slotting attempts, a more conventional approach was taken. Casing wasset to total depth, and a sand plug was placed successively below each zonebefore perforating at four shots per foot and fracturing above the sand. Althoughadditionalreduced fcoalseams

Perforatinestimate aPerforatinfollowing

Inexpe Versat Select Forma Routin A repe

A difficuland chipsaccommodsummariz

Greate Plugg Dange

Despite thmethod opreferred perforatintreated, a allows coopenhole Completions 339

time was required to clean sand from the hole, completion times wererom 2 weeks to about 2 days, and the completion was for all of the present.11

g is inexpensive compared to slotting. Schraufnagel and Lambertn 80% greater cost for slots to give access to an equivalent section.18g as the conventional method of accessing the formation has theadvantages:nsive.ile.ive stimulations.tion stability around borehole; reduction of fines.e operation understood and performable by workers in the field.atable process, applicable to large-scale field development.

ty with perforating is the plugging of the perforations with coal fines. It is especially troublesome if casing strength is inadequate toate high fracturing initiation pressures in coals. Disadvantages may be

ed as follows:r costs for casing to total depth.

ing of perforations.r of formation damage.

e drawbacks, perforating cased holes has developed into the preferredf accessing the coalseams in the eastern U.S. basins (Fig. 7.8). Theprocedure is to cement casing to total depth followed by successivelyg and fracturing each zone up the hole. After a lower zone has beenwireline bridge plug is set to isolate the zone above. The procedurempleting two or three zones per daya much faster procedure thanor slotting methods.19


340 Comp

7.5 M

7.5.1 Ba

In the bafinstalling be individball than tplacement

Sand


ultizone Entry in Cased Hole

ffled Entry

fled fracturing technique, baffle plates are placed on the casing beforeand cementing the casing for locations between coal groups that are toually fractured. The upper baffle is a template that will pass a largerhe lower baffle. A sketch of the process is given in Fig. 7.9 where the of baffles and the relative size of the balls are indicated.16,20

plug

Pratt Group( ~1,200 ft )

Mary Lee Group( ~2,000 ft )

Black Creek Group( ~2,500 ft )

Perforated multizone completions.2


June 2007

From Fig. 7.9 it is seen that after perforating and fracturing the Black Creek, asealing ball was dropped into place to isolate the Black Creek, whereupon theMary Lee group was perforated and fractured. Finally, the Pratt group wasisolated with a sealing ball, perforated, and fractured. In such manner, multiplezones can be treated in 1 day.

At the expthe Gas R

G

Fig. 7Completions 341

erimental P3 well at the Rock Creek research site in the Warrior basin,esearch Institute fractured eight seams of the Black Creek group, which

Mary LeeBlue Creek

1,022 ft1,028 ft

A1,207 ft1,219 ft

BC

4-in. baffle at 1,268 ft

D

E

FG

BlackCreek

roup 1,315 ft1,319 ft3 / -in. baffle at 1,328 ft1 2

1,349 ft

1,372 ft

2 / -in. baffle at 1,410 ft7 81,417 ft1,420 ftH

Well P3Warrior Basin Density Log

1,300 ft

1,400 ft

1,200 ft

1,100 ft

1,000 ft

1,000 ft

.9Baffled fracturing technique.20


342 Comp

contain 12 net feet of coals in four stages using three sets of baffles preset on the5 1/2-in. casing. Fig. 7.10 shows their casing configuration with the three sets ofbaffles of 4 in., 3 1/2 in., and 2 7/8 in. and with decreasing diameters proceedingdown the hole.20

Taurus andfollows:

1. Peba

2. Peba

3. Co

Fig. 7letions June 2007

GRI developed a sequence of operations for baffled entry that goes as

rforate and fracture bottom seam at eight shots per ft. Drop ball to 2 7/8-in. ffle to seal off bottom seam.rforate the target seam directly above. Stimulate. Drop ball to 3 1/2-in.ffle.ntinue the procedure uphole until all seams are treated.

Class A cement 12 / -in. hole1 49 / -in. OD36-lb/ft casing

5 8

8-in. hole

Spherelite cement

5 / -in. OD17-lb/ft casing

1 2

Sump TDCasing TDHole TD1,601 ft

1,598 ft1,562 ft

1,267 ft

1,028 ft

54 ft

PrattCoal

Group

Mary Lee/Blue CreekCoal Group

BlackCreekCoal

Group

Note:Well P3Warrior Basin

1,329 ft1,411 ft

4-in. baffle3 / -in. baffle1 22 / -in. baffle7 8

.10Use of baffles to fracture multiple seams.16


June 2007

7.5.2 Frac Plug Entry

Frac plugs originated from the desire of the operator to individually treatdifferent zones after the casing had already been cemented in place. With thebenefits seto set a plabove (Fig

A frac plutechnique,casing (beAny numbstaging ofcombinatibe used iperforatioplugs was

Fig. 7.11conventiCompletions 343

en in the baffled fracturing technique, frac plugs allowed the operatorug-type tool on electric wireline in the casing after perforating a zone. 7.11 shows a composite bridge plug).

g is hollow through the center. A ball, much like that used in the baffle could be dropped or placed in the top of the tool to allow shutoff of thelow) when initiation of the next frac stage (above) has commenced.er of plugs could be set coming out of the hole to allow for individual treatments. While the frac plugs cost more than the baffle and ballon, no restrictions for the perforators meant normal casing guns couldn a pressurized well under lubricator. This allowed for betterns and reduced breakdown pressures. One drawback of the steel frac the removal time. Use of two or three steel frac plugs led to lengthy

A bridge plug made of composite materials is easily drilled out with onal bits.


344 Comp

drillouts as the top tool would partially drill up, then fall down on the next plugand spin, preventing timely removal. It was not uncommon for an operator totake 710 days to remove the steel frac plugs. Steel frac plugs also meant that alarge amount of iron debris would settle to the bottom of the well.

In 1997, Hplugs to besingle daythat contafrac plug, because itweight andamage cprevents sImproved

7.5.3 Pa

Thin seameconomicato multiplproducer,potential shallow PThe problsupplemenrates of reresearch s

A single eof propagainterval asletions June 2007

alliburton introduced a composite frac plug that would enable multiple set in the hole for stage completions and easy removal via drillout in a. Composite plugs consist of composite material and rubber elementsin minimal metal content. During the drilling operation of a compositethe composite material drills up and will float out with the return fluids is lighter than water. Drilling time for a plug using the recommendedd drill bit averages 30 minutes. This saves rig time and reduces casingaused by a long drillout. The design of the lower shoe on the toolpinning of the upper tool remnants after they drop onto the next tool.efficiency of completions in CBM was noted by Guoynes, et al.21

rtings Entry

s of the Warrior basin and Appalachian coals are often marginallyl to develop because of the expense of completing and gaining access

e seams. For example, the Mary Lee group may be the most prolific but the low-permeability Black Creek group below may have theof adding substantial gas flow from the same well. Similarly, theratt group above the Mary Lee may have potential for the same well.em becomes one of tapping the reserves of the secondary seams tot the flow from the Mary Lee but doing so at acceptable incrementalturn for the investment. The problem was addressed at the GRI fieldite at Rock Creek in the Oak Grove Field of the Warrior basin.22

ntry into the bottom of the Black Creek group was made with the goalting a vertical fracture through the seven seams dispersed over a 250-ft depicted by Spafford22 in Fig. 7.12.


June 2007

Such a psurroundithat wouldRock Creewould appstresses loseams of bottom of

Depth in Feet (Surface) 0

170 Cobb Group

Thompson Mill Seam


rocedure is dependent upon having stress data on the coal andng rock; it depends on a favorable minimum horizontal stress profile give assurances of fracture containment. Stresses in the formation atk are presented in Fig. 7.13. Vertical growth downward of a fractureear to be limited to the bottom of the Black Creek coal group by highcated at 1,440 ft.23 There would be the hope of encompassing all eightthe Black Creek group in one fracture initiated at an entry near the the coal group but above the stress barrier.

480

1,050

1,250

1,440

Black Creek Group

Mary Lee Group

Pratt Group

Note:Generalized StratigraphicSection, Rock Creek Site,AlabamaLower Pennsylvania AgePottsville Formation

Rock Creek stratigraphic column.22


346 Comp

820685

800

Minimum Stress, psiLithologyGamma Ray1,000

1

1

1

1

1

1

1

1

1

Blue

MaryLee

Fig. 7.letions June 2007

HI

(perfs)

D

E

F/G

A

BC

500 700 900 1,100

800

760

760

760

760715

1,000

760

683

683

811

760

523

598

685

685656

656

,050

,100

,150

,200

,250

,300

,350

,400

,450

Coal

Shale

Sandstone

Creek

BlackCreek

13Stress profile at Rock Creek.23


June 2007

The hypothesis was evaluated by Schraufnagel, Spafford, and Saulsberry.24Consequently, perforations were made in the lower seam in a control well and inthe rock parting between G and H seams on another well with the expectation ofa fracture in each well encompassing the area of Fig. 7.14. Fracturing with acrosslinkeCreek seahigh stresMary Lee

Perforatinrock reduoccur fromfrom the eadditionareaching tthat might

M


d gel resulted in a single, vertical fracture through the eight Blackms. As expected, the fracture was limited in downward growth by as. A water tracer dye later showed the fracture to have penetrated the group also.

g and gaining access to the formation through the adjacent inorganicces generation of fines at the point of fracture initiation that would bursting of the coal. When producing water and gas, fines generated

roding of coal at high fluid velocity near the wellbore are reduced, andl fines are collected in the partings segment of the fracture beforehe wellbore. Multiple, parallel fractures occurring at higher pressures occur in coal are avoided.

ary Lee/Blue Creek

Black CreekABC

DEFGH

1,031 ft

1,202 ft

1,426 ft

Projected fracture geometry

Desired fracture geometry.24


348 Comp

However, when accessing the formation through noncoal partings, there is thepossibility of communicating with adjacent sands that could create questionableproduction to qualify for the Section 29 tax credit. Unless the stress profile of theformation is certain, the operator will not have the confidence of containing thefracture or of connecting all of the seams to the wellbore. Finally, shales adjacentto the coaconductiv

Spafford2than usualas compamaintenanCreek seamthe coal gr

7.5.4 Co

Advancesdiameter,assembly treat as mwell. Pinpon conduoperationimpossible

Rodvelt, eas many aVirginia. Tstage at anletions June 2007

ls may not offer a medium in which to generate and to maintain ae fracture.

2 reported positive results at Rock Creek. Fines gave fewer problems; a sucker rod pump for water removal was maintenance-free for 1 yearred to ordinarily being down three to four times per year force. There was evidence that the fracture connected all eight Blacks to the wellbore, and the fracture was contained by high stress below

oup.22

iled Tubing and Packer Completions

in the use of large-bore coiled tubing (CT) strings, 2 3/8- to 2 7/8-in. in conjunction with development of a unique bottomhole packer(BHPA, Fig. 7.15) finally enable the stimulation engineer to isolate andany coalseams as required on an individual basis with one trip to theoint placement of treatments can be tailored for each coalseam basedctivity requirements. An integrated CT rig (Fig. 7.16) allows the to proceed in a safe, timely, and economical manner that was to repeat with prior completion methods.

t al.25 used a 2 3/8-in. CT string and proprietary BHPA to fracture-treats 19 stages (21 coalseams) in a CBM pilot in Buchanan County,his project used 70-quality nitrogen foam to place proppant in each

average rate of 8 bbl/min and 4,000 psi.


June 2007

Fig.Completions 349

7.15Bottomhole packer assembly.


350 Comp


Integrated coiled-tubing rig.25


June 2007

The operation consists of perforating all prospective intervals in the well in 1 or 2days before the fracturing equipment arrives on the well site. An integrated CTrig picks up the BHPA and trips into the well to a known depth on bottom. TheBHPA is then positioned across the lowest, prospective coalseam with thebottom packer approximately 24 in. below the bottom perforation. CT movementsets the locups and bbegun dowequalized the BHPAstarted. Incirculatedupward peand restarfor the com

CT fractucommingreductionfracturingupper-mocleanout pwell on pthrough cstring.

Jetting thpreviouslmethod oBenefits orate, maxaccordingperforate speed andCompletions 351

wer packer, and circulation is begun through the annulus past the upperack up the coil string. Once the hole is circulated clean, a new stage isn the CT. At the completion of the treatment stage, the pressure is

across the BHPA, which is then moved to the next upward zone. After is positioned and set, the hole is circulated clean and the next stage the event of a screenout, the BHPA is moved, reset, and the hole

clean. If communication between treatment perforations and the nextrforations is observed, the treatment is moved to the next upward zoneted; additional treatment volume can be added to this stage to account

municated zone.

ring has been used with foamed fluids, crosslinked fluids, andled gas-fluid systems. Other benefits of CT and the BHPA include of screenouts, less environmental impact, and fewer pieces of equipment to achieve the same outcome. At the end of fracturing thest interval, the BHPA can be withdrawn from the well and a CTerformed. No baffles, plugs, or sand-fill remain to hinder placing theroduction. Negatives include higher treatment pressures (frictionoil) and limited rates and proppant concentrations through the coil

rough the casing to allow entry to the coalseam has been discussedy (7.4.2). Advances in jet technology coupled with CT provide af completing multiple intervals at the speed and versatility of coil.ver the CT and packer (CTP) technique allow for maximum injectionimum proppant volume, and maximum proppant concentration to formation need. This completion technique allows the operator toand fracture-treat a well during the same trip into the hole with the versatility of coiled tubing.


352 Comp

The process entails pumping through a CT string using a proprietary jet (Fig.7.17) to create perforations and to initiate fractures (Fig. 7.18).26 Fractureextension and placement is done via the CT/casing annulus. At the completion ofthe treatment, a sand plug is placed to pack the perforations and provide isolationfor the nexsand pluglowered tprospectivback to bbaffles, pl

Fig. 7.letions June 2007

t stage. At the completion of pumping, the jet tool is raised through the to clear the pipe. The casing is then reverse-cleaned as the CT iso spot the jet for the next interval treatment (Fig. 7.19). Once alle coals have been stimulated, the jet tool can be removed and coil runottom to clean the casing to bottom. As with the CTP method, nougs, or sand-fill remain to hinder placing the well on production.

17Jet-perforation nozzles.


June 2007


CT string performing jet perforation and initiating fractures.

Fig. 7.19Jet-perforating tool being lowered into the next interval to be treated.


354 Comp

References1Holditch, S.A.: "Completion Methods in Coalseam Reservoirs," paper SPE 20670 presented at the 1990 SPE Annual Technical Conference and Exhibi-tion, New Orleans, Louisiana, 23-26 September.

2Lambert,Well Com11, 1360

3Lambert,J. (Nove

4Hunt, A.Mchian Ba(July 199

5Mavor, M1992 Eas

6Logan, T(Decemb

7Weida, SDegasific

8Mavor, MLaboratoInc. (Dec

9Close, J.quest OWesternprises, In

10Mavor, Quarter9, No. 2

11Mavor, Quarter1991) 9letions June 2007

S.W., Niederhofer, J.D., and Reeves, S.R.: "Multiple-Coal-Seam pletions in the Deerlick Creek Field," JPT (November 1990) 42, No.

-1363. S.W. and Graves, S.L.: "Production Strategy Developed," Oil & Gas mber 1989) 87, No. 47, 55-56.

. and Steele, D.J.: "Coalbed Methane Development in the Appala-sin," Quarterly Review of Methane from Coalseams Technology1) 8, No. 4, 10-19..: "Cavity Completion Well Performance," paper presented at the tern Coalbed Methane Forum, Tuscaloosa, Alabama, 1 September..L.: "Western Basins Dictate Varied Operations," Oil & Gas J. er 1989) 87, No. 49, 35-39..D.: "The Mechanics of Dynamic Cavity Completions for Coalseam ation Wells," MS thesis, Mississippi State U. (December 1993) 147..J.: "Summary of the Completion Optimization and Assessment ry Site," GRI Contract No. 5088-214-1657, Resource Enterprises,ember 1991).C., Pratt, T.J., Logan, T.L., and Mavor, M.J.: "Summary of the Con-il Company South Shale Ridge #11-15 Well, Piceance Basin, Colorado," GRI Contract No. 5088-214-1657, Resource Enter-c. (April 1993).

M.J. and McBane, R.A.: "Western Cretaceous Coalseam Project," ly Review of Methane from Coalseams Technology (January 1992), 17.M.J. and McBane, R.A.: "Western Cretaceous Coalseam Project," ly Review of Methane from Coalseams Technology (November, No. 1, 19.


June 2007

12Duckworth, J.M. and Rector, C.A.: "Devon Blends Drilling Methods in Fruit-land Coal," Western Oil World (July 1991) 47, No. 49, 26-27.

13Mavor, M.J.: "Coal Gas Reservoir Cavity Completion Well Performance," paper presented at the 1992 International Gas Research Conference, Or-lando, F

14Petzet, (Novem

15Palmer,hole Capaper Sand Exh

16Schraufterly Re3 and 4

17Schraufterly ReNo. 2, 2

18Schraufterly ReNo. 2, 2

19Zebrow& Gas J

20Spaffordterly ReNo. 2, 1

21Guoynein CoalbSPE Roposium

22SpaffordRestrictloosa, ACompletions 355

lorida, 16-19 November.A.G.: "Devon Pressing Fruitland Coalseam Program," Oil & Gas J. ber 1990) 88, No. 45, 28-30. I.D., Mavor, M.J., Seidle, J.P., Spitler, J.L., and Volz, R.F.: "Open-vity Completions in Coalbed Methane Wells in the San Juan Basin,"PE 24906 presented at the 1992 SPE Annual Technical Conferenceibition, Washington, DC, 4-7 October.

nagel, R.A. and Lambert, S.W.: "Multiple Coalseam Project," Quar-view of Methane from Coalseams Technology (March 1988) 5, Nos., 33-44.nagel, R.A. and Lambert, S.W.: "Multiple Coalseam Project," Quar-view of Methane from Coalseams Technology (December 1987) 5,5-36.nagel, R.A. and Lambert, S.W.: "Multiple Coalseam Project," Quar-view of Methane from Coalseams Technology (November 1988) 6,7-34.itz, M. and Thomas, B.A.: "Coalbed Stimulations Are Optimized," Oil . (October 1989) 87, No. 41, 67-70., S.D. and Schraufnagel, R.A.: "Multiple Coalseams Project," Quar-view of Methane from Coalseams Technology (October 1992) 10,7-21.s, J.C., et al.: "New Composite Fracturing Plug Improves Efficiencyed Methane Completions," paper SPE 40052 presented at the 1998cky Mountain Regional Meeting/Low Permeability Reservoirs Sym-

and Exhibition, Denver, Colorado, April 5-8., S.D.: "Stimulating Multiple Coalseams at Rock Creek with Access

ed to a Single Seam," Proc., Coalbed Methane Symposium, Tusca-labama (May 1991) 243-246.


356 Comp

23Schraufnagel, R.A. and Lambert, S.W.: "Multiple Coalseam Project," Quar-terly Review of Methane from Coalseams Technology (June 1989) 6, No. 3and 4, 28-37.

24Schraufnagel, R.A., Spafford, S.D., and Saulsberry, J.L.: "Multiple SeamCompleMethan

25Rodveltulation AssembMeeting

26Hallibur2004. letions June 2007

tion and Production Experience at Rock Creek," Proc., Coalbede Symposium, Tuscaloosa, Alabama (May 1991) 211-221., G., Toothman, R., Willis, S., and Mullins, D.: "Multiseam Coal Stim-Using Coiled-Tubing Fracturing and a Unique Bottomhole Packerly," paper 72380 presented at the 2001 SPE Eastern Regional, Canton, Ohio, October 17-19.ton Energy Services, Inc., Internal Data-CobraMaxSM data sheet,

Completions7.1 Introduction7.2 Openhole Completions7.3. Openhole Cavitation Process7.3.1 Introduction7.3.2 Case Study: Cavitation Research Project7.3.3 Case Study: Devon Cavity Process

7.4 Cased-Hole Completions7.4.1 Conditions for Cased Hole7.4.2 Access by Slotting7.4.3 Access by Perforating

7.5 Multizone Entry in Cased Hole7.5.1 Baffled Entry7.5.2 Frac Plug Entry7.5.3 Partings Entry7.5.4 Coiled Tubing and Packer Completions

References

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