SPE 29553
`
`Society of Petroleum Engineers
`
`Current Use of Limited-Entry Hydraulic Fracturing
`in the Codell/Niobrara Formations—DJ Basin
`
`M.J. Eberhard*, D.E. Schlosser**
`*Halliburton Energy Services, **HS Resources
`
`SPE Members
`
`Copyright 1995, Society of Petroleum Engineers Inc.
`
`This paper was prepared for presentation at the 1995 SPE Rocky Mountain Meeting, Denver, March 20-22.
`
`This paper was selected for presentation by an SPE Program Committee following review of information contained in an abstract submitted
`by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject
`to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineers,
`officers, or members. Papers presented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petro-
`leum Engineers. Permission to copy is restricted to an abstract of not more than 300 words.
`Illustrations may not be copied. The abstract
`should contain conspicuous acknowledgment of where and bv whom the Daoer is oresented. Write Publications Manaaer. SPE, P.O. Box
`.,.
`833836, Richardson; TX 75083-3836,
`U.S.A. Telex, 730989 SPEDAL.
`
`its
`
`Abstract
`
`has
`perforating
`limited-entry
`In the last several years,
`been used for hydraulically fracturing the Codell and
`Niobrara formations in the Denver-Julesburg (DJ)
`Basin. Limited-entry perforating reduces stimulation
`costs with no apparent effect on production.
`
`Several papers have presented guidelines for designing
`a limited-entry treatment. A primary concern for
`treating muitipie intervals is to ensure that both zones
`receive the necessary treatment. Currently, some
`operators simply ratio the number of perforations in
`each interval to the volume of treatment required for
`each interval. To ensure that both zones are being
`treated, a minimum pressure drop of 700 to 1,000 psi is
`usually used for limited-entry design. Changes in the
`perforation discharge coefficient and diameter during
`the treatment, combined with changes in the net treat-
`ing pressure, affect the perforation pressure drop
`calculation. To determine the actual pressure drop
`across the perforations, designers use a real-time
`spreadsheet calculation.
`
`will be presented, as well as the effect of proppant
`concentration and velocity through the perforation. The
`current spreadsheet calculation used on location to
`calculate the pressure drop across the perforations is
`also discussed.
`
`Introduction
`
`The Niobrara and Codell formations are the two
`prirn.aryproduction intervals for most of the wells being
`completed in the DJ Basin. The Nlobrara is a micntic
`limestone consisting of three benches. At a depth of
`approximately 6,800 ft, the overall interval is generally
`between 150 and 250 ft thick. The Ft. Hays formation,
`the lower member of the Niobrara group, separates the
`Niobrara and Codell. There is a transition at the top of
`the Codell from a carbonate to a calcareous sandstone
`to a fine-grained sandstone with a high clay content.2
`At a depth of approximately 7,000 ft, the Codell is
`typically 8 to 14 ft thick. Both the Codell and Niobrara
`are overpressured gas reservoirs with a low permeabili-
`ty ranging from 0,01 to 0.1 md.
`
`This paper reviews limited-entry treatments pumped in
`34 wells that verify spreadsheet calculations. Changes
`in the perforation discharge coefficient and diameter
`
`In the past, the Codell and Niobrara intervals were
`fractured separately. The Codell was fractured first
`with treatments ranging from 150,000 to 350,000 lb of
`
`References at the end of the paper.
`
`107
`
`Page 1 of 11
`
`

`
`SPE 29553
`
`Society of Petroleum Engineers
`
`Current Use of Limited-Entry Hydraulic Fracturing
`in the Codell/Niobrara Formations—DJ Basin
`
`M.J. Eberhard*, D.E. Schlosser**
`*Halliburton Energy Services, **HS Resources
`
`SPE Members
`
`Copyright 1995, Society of Petroleum Engineers Inc.
`
`This paper was prepared for presentation at the 1995 SPE Rocky Mountain Meeting, Denver, March 20-22.
`
`This paper was selected for presentation by an SPE Program Committee following review of information contained in an abstract submitted
`by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject
`to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineers,
`officers, or members. Papers presented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petro-
`leum Engineers. Permission to copy is restricted to an abstract of not more than 300 words.
`Illustrations may not be copied. The abstract
`should contain conspicuous acknowledgment of where and bv whom the Daoer is oresented. Write Publications Manaaer. SPE, P.O. Box
`.,.
`833836, Richardson; TX 75083-3836,
`U.S.A. Telex, 730989 SPEDAL.
`
`its
`
`Abstract
`
`has
`perforating
`limited-entry
`In the last several years,
`been used for hydraulically fracturing the Codell and
`Niobrara formations in the Denver-Julesburg (DJ)
`Basin. Limited-entry perforating reduces stimulation
`costs with no apparent effect on production.
`
`Several papers have presented guidelines for designing
`a limited-entry treatment. A primary concern for
`treating muitipie intervals is to ensure that both zones
`receive the necessary treatment. Currently, some
`operators simply ratio the number of perforations in
`each interval to the volume of treatment required for
`each interval. To ensure that both zones are being
`treated, a minimum pressure drop of 700 to 1,000 psi is
`usually used for limited-entry design. Changes in the
`perforation discharge coefficient and diameter during
`the treatment, combined with changes in the net treat-
`ing pressure, affect the perforation pressure drop
`calculation. To determine the actual pressure drop
`across the perforations, designers use a real-time
`spreadsheet calculation.
`
`will be presented, as well as the effect of proppant
`concentration and velocity through the perforation. The
`current spreadsheet calculation used on location to
`calculate the pressure drop across the perforations is
`also discussed.
`
`Introduction
`
`The Niobrara and Codell formations are the two
`prirn.aryproduction intervals for most of the wells being
`completed in the DJ Basin. The Nlobrara is a micntic
`limestone consisting of three benches. At a depth of
`approximately 6,800 ft, the overall interval is generally
`between 150 and 250 ft thick. The Ft. Hays formation,
`the lower member of the Niobrara group, separates the
`Niobrara and Codell. There is a transition at the top of
`the Codell from a carbonate to a calcareous sandstone
`to a fine-grained sandstone with a high clay content.2
`At a depth of approximately 7,000 ft, the Codell is
`typically 8 to 14 ft thick. Both the Codell and Niobrara
`are overpressured gas reservoirs with a low permeabili-
`ty ranging from 0,01 to 0.1 md.
`
`This paper reviews limited-entry treatments pumped in
`34 wells that verify spreadsheet calculations. Changes
`in the perforation discharge coefficient and diameter
`
`In the past, the Codell and Niobrara intervals were
`fractured separately. The Codell was fractured first
`with treatments ranging from 150,000 to 350,000 lb of
`
`References at the end of the paper.
`
`107
`
`Page 1 of 11
`
`

`
`2
`
`Current Use of Limited-Entry Hydraulic Fracturing in the Codell/Niobrara Formations-DJ Basin
`
`SPE 29553
`
`sand.3 Next, all three benches of the Niobrara were
`fractured in a single treatment. As operators started
`moving into marginal acreage, the economics of
`fracture treatments had to be improved. In addition to
`optimizing fracture treatment sizes, other methods of
`reducing costs had to be found. One way of reducing
`cost while improving fracture treatments was to com-
`plete both intervals at once.
`
`Limited-Entry Technique
`
`Limited-entry perforating is one method for completing
`multiple intervais with a singie treatment. During a
`limited-entry treatment, operators maintain a pressure
`drop across the perforations (Pp,) greater than the
`stress differential between the intervals. A pressure
`drop across the perforations is created by forcing the
`treating fluid through a limited number of perforations
`of a known diameter. The size and number of perfora-
`tions placed opposite each interval are determined
`based on the percentage of the total treatment planned
`c-.
`--L : +a-~~oland th-
`nllmher
`nf n~rf~@~~n~
`IUI ea~ll mbU1v-1, -llU ...w.
`.. . ... ....
`_ ~
`total
`required to produce the necessary pressure drop.4
`
`During a limited-entry fracture treatment, PF,~should
`be monitored to ensure that all perforations are open
`and that the necessary pressure drop is maintained.
`With the advent of more advanced on-site computer
`systems, improved fluid friction correlations,5-7and
`better quality control programs, predictions of PPti are
`becoming more accurate.
`
`and fracture friction will be set to zero. As a result, PP,~
`will be the sole component of P,fwin Eq. 1.
`
`During a fracturing treatment, the wellhead treating
`pressure (WHTP), pump rate, and proppant concentra-
`tions are constantly changing. Computer-based data
`acquisition systems (DAS) are used to record these
`three variables. Additional programs are then used to
`calculate hydrostatic pressure (P~Y~)and tubular friction
`pressure (P~tiC).
`
`During a typical fracture treatment, the pump rate is
`stopped after the first half of the pad fluid is pumped to
`“--------------- .L..+ ‘- --a .,,r- (TCTP
`determinethe insmumurwuz+
`~llut-lll
`~lWsOUlw ~.ul.
`).
`When the rate is zero, Pp,~and PfriC,are also zero, and
`the BHTP can be expressed as shown below:
`
`BHTP = ISIP, + PhYd.................................. (2)
`
`where
`
`ISIP, = surface instantaneous shut-in pressure
`..-—
`When pumping is resumed, this MH1”J?vaiue can be
`used in Eq. 1 to estimate PP,~,However, for most cases,
`BHTP either increases or decreases during the treat-
`ment, depending on the fracture geometry.8’gThe effect
`this change in BHTP has on the calculation of PFr~can
`be significant and should be considered whenever
`possible during P~~ calculations.
`
`PP,~can also be calculated from the following equation:
`
`Calculations
`
`<7.$ = 0.2369?
`
`The standard equation for calculating the bottomhole
`treating pressure during a fracturing treatment is shown
`~ejo.w;
`
`where
`
`~
`
`72
`
`ND;cd ]
`
`[
`
`.................... (3)
`
`BHTP = WHTP + ~Yd - Pf,iC,- P,,aC.......... (1)
`
`Fracture-entry pressure (P’,=) has several components,
`including perforation friction, near-wellbore tortuosity,
`and fracture friction. ‘Whenthe rate per perforation is
`jow (<-~.~ bN1/mjn/peflJ, Ppfi is &3t3i~ii~
`CGfiSid~KXi
`tO
`be zero. In limited-entry jobs, however, this assumption
`is not the case, and determining the true bottomhole
`treating pressure (BHTP) becomes more difficult.
`Although near-wellbore tortuosity can be significant,
`for the purposes of this paper, near-wellbore tortuosity
`
`108
`
`p = density of fluid (lb/gal)
`
`Q=
`
`N=
`
`total pump rate (bbllmin)
`
`number of perforations
`
`W-henabrasive fluids, such as those containing sami,
`+.. ~~*L=m.arfnratinn
`m ) and
`are piirnped, ih~ dxmet=l WIcll~~~,, u, -..”..
`,-
`, ----
`the coefficient of discharge(C~) will change wi!h
`respect to P@ and sand concentration during the
`treatment. Several attempts have been made to quantify
`changes in DPand Cd. Crump and Conway’0 demon-
`
`Page 2 of 11
`
`

`
`SPE 29553
`
`M.J. Eberhard, D.E. Schlosser
`
`3
`
`strated that Cd can increase by 15Y0.Willingham, et al.,
`showed that the values for Cdcan range from 0.62 to
`0.95,1i depending on whether abrasive fluid has been
`pumped through the perforations. Crameriz presented
`a hydraulic perforation erosion constant of
`0.00418 in./l ,000 lb of 20/40 mesh sand pumped. This
`constant is used to calculate the diameter increase of a
`0.375-in. perforation, based on proppant volume
`pumped through a perforation. Changes in DPand Cd
`will also be evaluated in this paper.
`
`Well Information
`
`In 1994, over 300 limited-entry treatments were
`pumped within the Wattenberg field. For this paper,
`limited-entry treatments in 34 wells were evaluated. All
`treatments are in the Codell/Niobrara intervals.
`
`Of the 34 wells evaluated, 27 were completed with
`4 l/2-in., 11.6-lb/ft, 1-70 casing cemented in a 7 7/8-in.
`hole. Each well was perforated with six shots in the
`Niobrara and 12 shots in the Codell.
`
`The remaining seven wells were completed with
`2 7/8-in., 6.40-lb/ft, N-80 casing cemented in a 7 7/8-in.
`hole. Each of these wells was perforated with four shots
`in the Niobrara and seven shots in the CodeIl.
`
`Both well types were perforated with jets. In the 27
`wells having 4 l/2-in. casing, 3 l/8-in. OD carrier guns
`with 10-g charges were used. For the seven wells
`having 2 7/8-in. casing, 2 1/16-in. OD carrier guns with
`8-g charges were used. Both gun types had a 0.3 l-in.
`perforation diameter. 13
`
`During a standard treatment, 412,000 lb of sand and
`104,000 gal of fluid were placed into both intervals.
`The perforation placement was designed to place one-
`third of the treatment into the Niobrara and the remain-
`ing two-thirds of the treatment into the Codell. Table 1
`shows the various stages of a typical Codell/Niobrara
`treatment.
`
`the initial BHTP in the
`When treated individually,
`Niobrara is typically 450 to 700 psi higher than in the
`CodeIl. (To help break down the Niobrara perforations,
`HC1 is pumApedahead of the treatment.) Based on this
`stress differential,
`the proper ratio of perforations is 7
`in the Niobrara and 11 in the Codell. However, a
`
`109
`
`typical net pressure increase in the Niobrara is between
`Oto 200 psi, while typical increases in the Codell are
`400 to 600 psi. As a result, the BHTP is essentially the
`same for both intervals at the end of the treatments. The
`6-to-12 ratio of perforations is based on these BHTP
`conditions. Final results from multiple tracers run in
`early treatments indicate that all intervals were taking
`fluid throughout the entire treatment. Fig. 1 (Page 4)
`shows the results of one of the tracer surveys. Produc-
`tion results from limited-entry treatments are compa-
`rable to wells treated individually, further validating
`that the proper proportion of the treatment is being
`placed in each interval.
`
`Table 1: Typical CodelUNiobrara
`Schedule
`
`Treatment
`
`Stage
`
`Clean
`Volume
`
`Fluid
`Description
`
`Sand
`Concentration
`
`I 30 lb CMHPG*
`6
`I
`4.000
`I
`4.000 I
`M/at
`171
`. .–ler
`lPer 1,OOO’gal-
`I
`
`,
`
`,
`
`i
`‘
`I
`
`8
`—
`
`I
`1
`
`Data Acquisition
`
`All treatments were recorded on the same data acquisi-
`tion system. In addition to recording the standard
`pressure, rate, and density variables, this system also
`records all real-time calculated values. All the treat-
`ments used for this paper were recalculated using the
`same program.
`
`The software program calculates BHTP at time t
`(BHTPC,,C)based on the following equation:
`
`BHT&C = ‘HTP + ‘h@ -
`
`‘frict
`
`““”””””””””””””””(4)
`
`To calculate P~Y~and Pf,ic,,the program breaks the
`wellbore into 15 segments and then tracks each seg-
`ment as it moves down the wellbore. The software also
`hnc
`~c.varal
`nntinnc
`nwailahl-
`fnr
`ealei,lntino
`Am-
`n,-.
`.-~
`-. u, wybnunn.
`n v usm4c.Ixu *w. WCLWUZU . ...5
`Y,YU
`friction.
`
`Page 3 of 11
`
`

`
`4
`
`Current Use of Limited-Entry Hydraulic Fracturing in the CodelVNiobrma Formations-DJ
`
`Basin
`
`.
`
`SPE 29553
`
`-. .-.-—..
`Ana
`frirtinn
`P..I,...lOA--
`computer syslems. Uakulaclqj
`plpu
`IImw..wl.
`changes in the BHTP are not as accurate, however.
`
`zmrl
`.
`. . .
`
`When Eq. 1 is used to calculate Pwr the value for
`BHTP is generally calculated from Eq. 2, and an ISIP is
`.1 -z. DIJ-
`.,-1..- :. +k-m,~csrlfm- thp
`taicen during paa. 1ms Dm I r
`valuG
`la LIIW1l Ucw-
`.“.
`. . . .
`Tn ~m-tell/NiOhrara treat-
`.__-:
`-A_
`,.4 .L.
`tr=ntmant
`rmnimmm
`U1 LUG UWUWVM.O
`-.
`-w-----
`.-_–_—
`-.
`ments, the net pressure cart increase from 50 to 500 psi
`during pumping. If the increase in net pressure is
`ignored, Pm will be overcalculated by the net pressure
`value, as the following equation shows.
`
`P
`pe~,
`
`= BHTPca[c–
`
`(BHISIp@
`
`+NWt,)
`
`. . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
`
`(5)
`
`Fig. 2 shows the effect that the change in net pressure
`has in calculation PWfifor one well. In this paper, ANet
`is the difference between the ISIP taken during the pad
`and the final ISIP at the end of the treatment. For the
`final ISIP, the DAS-calculated value for BHTP was
`used, which is a more accurate calculation of the finai
`P~Y~.The ANet was then divided by the number of da+a
`points and applied linearly throughout the treatment.
`
`For real-time calculation of PP,f, an accurate prediction
`of the ANet is required. Net pressure can be determined
`based on other treatment results on wells in the area, or
`3-D models can be used to predict ANet throughout
`the
`treatment.
`
`Pipe friction is dependent on the tubular configuration,
`fluid rheology, sand concentration, and treatment rate.
`Because of varying sand concentrations and fluid
`
`Fig.
`
`l—Multiple
`
`tracer log of a limited-entry
`
`treatment.
`
`Evaluation of Pwti
`
`To evaluate PF,t and its associated variables Cd and DP,
`the program compares the PP~ calculated from Eq. 1 to
`the PP,~calculated from Eq. 3. Independent variables are
`used by each equation to calculate PP~. This method
`was also used in early versions of the real-time perfora-
`tion friction spreadsheet to verify the number of open
`perforations as well as PP...
`
`WHTP is a direct measurement; with the accuracy of
`today’s transducers, WHTP will be very consistent.
`Calculating the hydrostatic pressure of the wellbore
`fluid is also fairly straightforward with current on-site
`
`110
`
`Cumulative Sand Volume Pure@
`
`(lb)
`
`Fig. 2—PWfl calculated with and without the chunge in
`BHTP.
`
`Page 4 of 11
`
`

`
`.
`
`SPE 29553
`
`M.J. Eberhard, D.E. Schlosser
`
`5
`
`rheology in the wellbore, the friction pressure calcu-
`lated by the DAS for determining Pm must be used. A
`fracturing fluid system of CMHPG polymer crosslinked
`..,itk .+-r.fifih,- .,,oc ,,c.a~;m9112A xx)t=llc Anmwih.d
`in
`WLLL1 L.lltiullausll
`WU.Y U.ltiu
`,11 u.
`a-r w-a..
`Uti.tilauuu
`all
`this paper. To help ensure accurate P~,iCvalues, each
`treatment was reviewed to verify that the wellbore
`configuration and fluid properties for each stage were
`correct.
`
`For the fracturing fluid system used in these wells, DAS
`has three different friction calculation options:
`
`l
`
`Option 1 calculates friction based on an integration
`of the base fluid and crosslinked fluid properties
`depending on wellbore temperature.
`
`Adiustad Frlctkm
`
`p-
`
`DASCalculatsd Frkllon
`
`o
`
`so,molw,mO
`
`lso#00200@0250#O0
`
`m0,m10 sWOOW@J04so@0
`
`Cumulative
`
`Sand Volume Pumpad (lb)
`
`Fig. 3—Ppti based on DAS-calculatedfriction
`adjusted friction (4 l/2-in. casing)
`
`vs.
`
`‘ Option 2 uses the A, e, ands method developed by
`Melton and Malone14to calculate friction based on
`lha h.c,a “,al
`“t
`.“.4
`u!
`11
`allu
`1>
`
`L1lG
`
`uaou
`
`~bl
`
`.
`
`l
`
`Option 3 uses a modification of the equation
`developed by Lord and McGowen.5
`
`After results from all three calculations were compared,
`Option 3 seemed to best represent the observed friction
`in 4 l/2-in. casing.
`
`Option 3 was used to recalculate all 27 of the treatments
`down 4 l/2-in. casing, and Eq. 5 was used to calculate
`PP,~.The values calculated for PW,~in the later stages of
`the treatment were surprisingly low when ANet was
`included.
`
`Next, all seven treatments down 2 7/8-in. casing were
`recalculated based on Option 3, and negative Pw# were
`calculated. Since a negative PPf is not possible, the
`calculation of P~,iCtwas incorrect. When the results from
`Option 3 were compared to values calculated for Pm
`based on Eq. 3, it was determined the PftiClvalue gener-
`ated from the DAS needed to he reduced hv ~~?Q.Th~s
`—--------- ---- —....
`..-~---,-.-- --- --------
`-,
`correction was made to all 2 7/8-in. treatments, result-
`ing in realistic calculations of PW,..The same comection
`was made to the friction numbers calculated for
`4 l/2-in. casing, also resulting in more realistic calcula-
`tions of Ppfi. Fig. 3 compares Pw~based on both DAS-
`calculated friction and adjusted friction for a 4 l/2-in.
`well. Fig. 4 shows the same comparison for a 2 7/8-in.
`well.
`
`111
`
`n
`
`o
`
`Somo
`
`loom
`
`150JO0 zoo#OO 25@100 mom
`
`3Wm0
`
`4WO0
`
`Cumuiativa Sand voiurna F%mpad (ii)
`
`Fig. 4—Pp,tibased on DAS-calculatedfiiction
`adjusted friction (2 7/8-in. casing)
`
`vs.
`
`Calculation of Cdand Dp
`
`To calculate Cd and DP,designers setup a table for each
`well. This table includes the following information:
`
`l
`
`l
`
`P= calculated from Eq. 5
`
`pump rate, and sand concentration calculated from
`the DAS
`
`“
`
`cumulative clean fluid or sand volumes (optional)
`
`Page 5 of 11
`
`

`
`6
`
`Current Use of Limited-Entry Hydraulic Fracturing in the Codell/Niobrara Formations-DJ
`
`Basin
`
`SPE 29553
`
`.
`
`TabIe 2 is an example of a C#DP data table. Based
`on this data, the initial values of the perforations,
`and the information
`developed by the earlier refer-
`enced authors,lO-*1designers can estimate Cd and DP
`by using Eq. 3. This analysis procedure is also used
`on location for real-time calculations of PPfi
`
`Table 2: Calculation of Cd and DP Based on
`Eq. 5 and Eq. 3 Results
`
`1,168 I 31.4 I 0.0
`1.129 I 31.4 I 0.0
`1,064 I 31.6 I 2.8
`914 i 31.8 I 2.4
`
`18
`I 0.74 I 0.31 ]
`18
`i 0.74 ! 0.31 I
`I 0.85 I 0.31 I 18
`i 0.92 I 0.31 I 18
`
`I
`
`I
`
`1,190
`1.184
`1,083
`912
`
`between all wells. Table 3 summarizes treatment
`results from the 274 1/2-in. wells treated. As shown in
`Table 4, results from the seven 2 7/8-in. wells were
`similar.
`
`As soon as sand enters the perforations, Cd changes
`immediately. Within the first 5,000 lb of sand per
`perforation, Cd has increased to 0.95. Final perforation
`diameters ranged from 0.36 to 0.49 in. The average
`final DPwas 0.41 in. for an increase of 27.2?Z0.This
`increase is twice as high as what was observed by
`Cnmnn and Conway.1° Perforation diameter vs. the
`.= —..—
`volume of sand pumped was plotted for all wells. These
`charts did not reveal a linear increase in DPwith the
`volume of sand pumped throughout the treatment, but
`rather two separate erosion rates. Perforation erosion
`was fastest during the 3.5- to 5-lb/gal sand stages, with
`erosion rates ranging from 0.00376 to 0.0089 in./
`1,000 lb of sand. For the 5.5-to 8-lb/gal sand stages,
`perforation erosion slowed to rates ranging from 0.0019
`to 0.0043 in./l ,000 lb of sand. Fig. 5 shows no clear
`correlation between these two variables.
`
`4.7
`18
`0.36
`0.95
`37.2
`734
`18
`0.38
`0.95
`5.3
`39.3
`698
`18
`0.39
`0.95
`6.0
`39.6
`629
`18 I
`I 0.95 I 0.40 [
`572 ] 40.5 T 6.8
`18
`I 0.95 I 0.41 I
`549 I 40.6 I 6.9
`52~14~07~
`7.6 lnaGln49i
`f~
`~
`IV..7.JIU.
`G,
`i 0.95 i 0.43 ] 18 I
`.7 I 7.9
`,
`._
`,
`467]
`40..
`.._
`, _.__,
`-.._,
`
`716
`659
`618
`601
`549
`~~p ]
`469 i
`.__,
`
`I
`
`To evaluate the effect that rate has on perforation
`erosion, treatments were pumped at three different
`rates:
`
`‘
`
`l
`
`l
`
`constant low rates (=31 bbl/min)
`constant high rates (=40 bbilmhi)
`various increasing rates (=30 to 50 bbl/min)
`
`For the initial calculation, Cd= 0.72, DP= 0.31 in., and
`N = 18 are used for a pad fluid. If these values calculate
`a PP,~higher than Eq, 5, the perforation diameter and Cd
`are increased until a reasonable match exists. Several
`data points are taken during the pad, and the same Cd
`and DPare used for all data points. Once sand is
`pumped, DPis held constant and Cd is increased until
`Cd= 0.95. From this point forward, Cd is held constant,
`and the perforation diameter is increased.
`
`Results
`
`In the 4 l/2-in. wells, treatment rates during pad ranged
`from 29.5 to 42 bbhin with an average of 32.6 bbl/min.
`Initial values for Cd ranged from 0.72 to 0.90 with an
`average of 0.78; values for DPranged from 0.31 to 0.36
`in. with an average of 0.32 in. Overall, there was very
`good agreement in the initial values for Cd and DP
`
`112
`
`Treatments at a constant iow pump rate had iess
`perforation erosion but similar final Pmr} as treatments
`at constant high pump rates. Realistic ‘values for Pw,r
`later in the treatment are 450 to 600 psi—not 700 to
`1,000 psi.
`
`0.3J
`
`o
`
`10,OOO
`5.OM
`13,000
`Cumulative SanWNumber Perh’etione
`
`20,000
`(lb)
`
`Z3Joo
`
`Fig. 5—Change in DP vs. volume of sand pumped.
`
`Page 6 of 11
`
`

`
`.
`
`SPE 29553
`
`M.J. Eberhard, D.E. Schlosser
`
`7
`
`Well
`
`ID No. Rate
`30.9
`1
`30.2
`2
`3
`30.8
`4
`29.9
`5
`30.9
`31.0
`6
`29.6
`7
`8
`30.6
`9
`31.4
`10
`30.8
`11
`31.8
`12
`30.4
`13
`30.1
`32.6
`14
`15
`31.0
`16
`30.6
`17
`41.7
`41.9
`18
`19
`39.2
`38.7
`20
`21
`31.2
`22
`29.4
`25.9
`23
`40.4
`24
`35.4
`25
`26
`33.6
`29.9
`27
`32.6
`Average
`4.1
`Std Dev
`
`Initial
`DD
`0.33
`0.33
`0.31
`0.31
`0.31
`0.31
`0.31
`0.31
`0.31
`0.31
`0.31
`0.31
`0.31
`0.33
`0.31
`0.34
`0.36
`0.34
`0.33
`0.34
`0.33
`0.33
`0.33
`0.31
`0.32
`0.33
`0.31
`0.32
`0.01
`
`cd
`0.90
`0.80
`0.75
`0.72
`0.78
`0.75
`0.76
`0.78
`0.74
`0.72
`0.75
`0.78
`0.75
`0.90
`0.82
`0.75
`0.75
`0.85
`0.75
`0.75
`0.72
`0.75
`0.80
`0.80
`0.90
`0.80
`0.68
`0.78
`0.06
`
`pm.
`605
`733
`1,110
`1,134
`1,032
`1,124
`1,001
`1,015
`1,083
`1,211
`1,186
`1,003
`1,064
`675
`942
`760
`1,121
`1,109
`1,406
`1,214
`967
`747
`1,447
`1,285
`1,055
`907
`1,274
`1,045
`206
`
`v
`304
`337
`411
`433
`389
`410
`385
`350
`410
`437
`423
`376
`388
`306
`365
`343
`386
`394
`453
`425
`372
`344
`443
`“--4Jd
`403
`374
`440
`390
`40.2
`
`Rate
`40.2
`40.4
`35.8
`38.7
`40.3
`39.0
`35.8
`33.1
`40.5
`37.1
`40.0
`41.3
`31.4
`37.0
`34.6
`41.2
`49.2
`44.5
`43.7
`42.0
`37.3
`33.1
`32.4
`
`
`
`‘n4U.
`7I
`39.0
`38.7
`32.5
`38.5
`4.1
`
`Final
`Do
`0.43
`0.42
`0.39
`0.39
`0.43
`0.41
`0.37
`0.38
`0.41
`0.38
`0.40
`0.42
`0.36
`0.39
`0.39
`0.42
`0.46
`0.45
`0.44
`0.49
`0.38
`0.38
`0.49
`
`0.41
`0.41
`0.39
`0.35
`0.41
`0.04
`
`cd
`0.9
`0.9
`0.9
`0.9
`0.9
`0.9
`0.9
`0.9
`0.9
`0.9
`0.8
`0.9
`0.9
`0.9
`0.9
`0.9
`0.9
`0.9
`0.9
`0.9
`0.9
`0.9
`0.9
`
`0.9
`0.9
`0.9
`0.9
`0.9
`0.02
`
`PM
`449
`504
`540
`621
`459
`519
`658
`427
`564
`639
`546
`529
`571
`575
`500
`532
`522
`450
`515
`296
`415
`357
`471
`
`572
`465
`632
`638
`517
`86
`
`Y. Increase
`Rate
`DO
`30.1
`30.3
`33.8
`27.3
`16.2
`25.8
`29.4
`25.8
`30.4
`38.7
`25.8
`32.3
`20.9
`19.4
`8.2
`22.6
`29.0
`32.3
`20.5
`22.6
`25.8
`29.0
`35.9
`35.5
`4.3
`16.1
`13.5
`18.2
`11.6
`25.8
`34.6
`23.5
`18.0
`27.8
`6.2
`32.4
`11.5
`33.3
`8.5
`44.1
`19.6
`15.2
`12.6
`15.2
`25.1
`48.5
`Qo e
`C8c. o
`28.1
`18.2
`12.9
`27.2
`8.6
`
`0.7
`10.2
`15.2
`8.7
`18.8
`10.0
`
`v
`225
`225
`241
`280
`219
`230
`258
`220
`247
`260
`237
`232
`243
`241
`225
`238
`231
`217
`220
`171
`235
`212
`223
`
`Me
`218
`256
`265
`234
`20.5
`
`I
`
`Initial
`
`I
`
`1 -.-— 1
`1
`1:1 0.31 I 1:238 I
`
`--- 1 —-. . ,
`4301 25.4]
`
`Final
`
`0.44
`0.39
`0.41
`0.371
`
`.
`.
`0.9
`9
`
`432
`730
`567
`99
`8!
`
`I
`
`-.
`I QYoIncrease
`I
`I Rate I
`Dp
`19.6
`37.5
`25.8
`19.8
`32.3
`92.3
`24.0
`19.4
`
`v
`199
`267
`243
`304
`
`7
`Averaae
`
`1
`
`~7.6i~
`] 18.71
`
`0.7
`
`--
`
`.-
`
`113
`
`Page 7 of 11
`
`

`
`8
`
`Current Use of Limited-Entry Hydraulic Fracturing in the Codell/Niobrara Formations—DJ Basin
`
`SPE 29553
`
`.
`
`The plots shown in Figs. 6 through 8 show typical
`perforation erosion for the three treatments described
`above. Fig. 6 shows that for a constant-rate treatment,
`the change in Cd is gradual, and DPdoes not start to
`increase until 4.5 lb/gal slurry is going through the
`perforations. Fig. 7 shows a constant high-rate treat-
`ment. Note that the change in C.dis rn.!!c!lt?mn?i!mrxK!i-
`ate, and DPstarts to increase when 3-lb/gal slurry enters
`the perforations. Fig. 8 shows an increasing rate
`treatment.
`
`0.5
`
`I
`
`#
`
`0.2 L
`o
`
`.1
`
`D,
`
`Pump Rem
`
`veloci2y
`
`5,000
`
`10,000
`
`15,r410
`
`20,2410
`
`Cumulative Sand/Number
`
`Perioretions (lb)
`
`Lo
`25.UM
`
`through the perforations was investigated. The equation
`for the velocity (v) through a nozzle is shown below:
`
`P
`v = 35.2 ~
`i
`
`P
`
`........................................ (6)
`
`Velocity was calculated for each data point for all the
`treatments. Initial values during the pad ranged from
`304 to 453 ft/sec with an average of 389 ft/sec. Final
`values for were between 171 and 260 ft/sec with an
`average of 234 ft/sec (Table 3). A steep decrease in v
`occurs when the sand first starts; this decrease contin-
`ues until the velocity reaches = 350 ft/see; below 350
`ftisec, the rate of decrease becomes slower. Fig. 8
`shows that an increased pump rate does little to in-
`crease the velocity through the perforations.
`
`Real-Time Spreadsheet Calculation
`
`For the real-time calculation of PP,~,Eq. 5 is used.
`Table 5 shows the spreadsheet currently being used. A
`total net pressure increase value is entered along with
`total fluid. These values are used to calculate the ANet
`throughout the treatment. Next, the volume pumped
`when the ISIP is taken is entered into the spreadsheet.
`The net pressure increase used is based on the fluid
`-.,-— -
`pumped from tihe131P. 1he DAS vaiue calculated for
`~;pe f~ ----
`based cm~ptioii ~, is reduced by ~i %.
`Iulk)ii,
`When Pw~is calculated, the friction correction value is
`added in. Perforation friction and the velocity through
`the perforations are also calculated based on Eqs. 2 and
`6. As described earlier, C,, and Dn are adjusted to match
`r
`both pW,ts.
`
`0.51/’
`
`c,
`
`Fig. 6—Constant
`
`low-rate treatment.
`
`L-’
`
`.
`
`c,
`
`II
`0.21
`0
`
`30,raro
`WfJ
`10,WO
`13,000
`CumulativeSenrUNumberPerforations(lb)
`
`Fig. 7—Constant high-rate treatment.
`
`Velocity through a Perforation
`
`i
`0.9
`
`0.7
`
`0.6
`
`I0.8
`0.5I0.4
`
`03
`
`0.2
`t 0.1
`10
`25,0D0
`
`Based on the observed relationship between pump rate
`and perforation erosion, the effects of the velocity
`
`0.2v
`0
`
`3$m
`
`moo
`
`13,00Q
`
`20,000
`
`Cumulative Sand/Number Petiomtlons
`
`(lb)
`
`10
`2r@oo
`
`Fig. 8—Increasing rate treatment.
`
`114
`
`Page 8 of 11
`
`

`
`SPE 29553
`
`M.J. Eberhard, D.E. Schlosser
`
`9
`
`Table 5: Current Spreadsheet Calculation of PP,ti, Cd, DP, and v
`
`BHISIP
`Total Net
`Total Fluid
`
`psi
`6,385
`psi
`295
`104,000 gal
`
`Well Name
`
`1,531
`
`Fluid
`Volume
`(9 al)
`5,767
`12,126
`21,476
`32,309
`65,449
`73,080
`
`,DAS Infmnatim
`BHTP
`Pump
`Calc.
`Rate
`(p “)
`(bbUmin)
`7,::8
`31.3
`7,438
`31.7
`7,239
`31.8
`7,255
`34.4
`7,086
`39.3
`7,017
`39.6
`
`Pipe
`Friction
`(P )si
`542
`539
`592
`677
`910
`1,013
`
`Sand ‘
`Cone.
`(lb/gal)
`0
`0
`2.3
`3.1
`5.3
`5.9
`
`ANet
`(psi)
`
`16
`34
`61
`92
`186
`207
`
`P~ti
`(psi)
`
`1,150
`1,132
`917
`921
`706
`637
`
`I
`
`I
`
`Pm
`(psi)
`
`cd
`
`d%#’t@@Qm@a ;
`Perf
`Dia.
`(in.)
`I 0.31 I 18 I
`1,18010.74
`1.210 I 0.74 I 0.31 I 18 I
`I
`o.31 I 18 I
`m 1 I n.92
`t---%d%
`I I 18 I
`-.95
`0.32
`I
`0.37 I 18 I
`----
`---
`734
`I 0.95
`, 0.39 ] 18 [
`617 ] 0.95 I
`
`No.
`
`Velocity
`(fthec)
`
`I
`
`-
`4241
`342 I
`337 ]
`288 I
`261 I
`
`1
`
`Conclusions
`
`Nomenclature
`
`bottomhole treating pressure (psi)
`bottomhole treating pressure
`at time t (psi)
`bottomhole ISIP during pad (psi)
`coefficient of discharge
`diameter of perforation (in.)
`(nci)
`;ric+nmtnnen,,
`c chllt-;n
`nr~cclmr=
`“,OLLU,. CUI””LJ*
`011-. –,,,
`yLw.70 UUw \y”.,
`surface instantaneous shut-in
`pressure (psi)
`number of perforations
`hydrostatic pressure (psi)
`tubular friction pressure (psi)
`fracture-entry pressure (psi)
`perforation pressure drop (psi)
`pressure drop across the perforations
`at time t (psi)
`total pump rate (bbl/min)
`velocity through a nozzle (ft/see)
`wellhead treating pressure (psi)
`change in net pressure at time t (psi)
`density of fluid (lb/gal)
`
`BHTP
`BHTPC,,C
`
`BHISIP,,
`cd
`
`D~
`
`&p
`ISIP,
`
`N P
`
`hyd
`Pfrict
`Pfrac
`Pperf
`Ppxft
`
`Q v W
`
`HTP
`ANet
`P
`
`l
`
`l
`
`9
`
`l
`
`l
`
`l
`
`T~~C~~
`SUI-v~vs
`nrrxlucf~~n
`and
`results
`!nd~c~te
`- —.. — r--——-
`--- —..-
`,
`perforation scheme being used is placing the
`necessary treatment in each interval.
`
`the
`
`An accurate value for pipe friction is essential for
`the calculation of PP,~.
`
`AN~t
`h~
`chn,lld
`inr.lllrkd
`in the
`rnlmllatinn
`nf P
`-
`.“.
`“.J” U,W ““
`111”1”..”-
`11.
`. ..”
`“...
`-..1...1”..
`“1 .
`If ANet is not included, final PP,f values are
`undercalculated by 50 to 500 psi for these treat-
`ments.
`
`perf”
`
`Perforations will erode to a steady-state Pw,f.The
`final value for PW,~is dependent on the velocity
`through the perforations. Increasing the pump rate
`during sand stages only has short-term effects on
`Pv,. For these wells, a constant Pw,fof 1,000 psi is
`not realistic.
`
`In all cases, all of the perforations were taking
`fluid. “Balling off’ the perforations to ensure that
`all were open was not required. There is no evi-
`dence that any perforations were lost in any of
`these treatments.
`lm th~
`nl
`h..k
`;tw..~..in~
`th~
`n,lmn
`iC nnt
`rate
`.1.
`*IIW -.
`“-0,11,
`,’lw.wuol..~
`“1”
`y“.1.p
`.W.w 10 11”.
`necessary to maintain limited entry. Therefore,
`horsepower requirements can be reduced.
`
`115
`
`Page 9 of 11
`
`

`
`10
`
`Current Use of Limited-Entry Hydraulic Fracturing in the Codell/Niobrara Formations-DJ
`
`Basin
`
`SPE 29553
`
`10.
`
`11.
`
`12.
`
`13.
`
`14.
`
`Crump, J.B. and Conway, M.W.: “ Effects of
`Perforation-Entry Friction on the bottomhole
`Treating Analysis,” JPT (Aug. 1988), 1041.
`
`Willingham, J.D., Tan, H.C., and Norman, L.R.:
`“Perforation Friction Pressure of Fracturing Fluid
`Slurries,” paper SPE 25891 presented at the SPE
`1993 Rocky Mountain Regional Meeting and Low
`Permeability Reservoir Symposium, Denver, April
`12-14.
`
`Cramer, D.D.: “The Application of Limited-Entry
`Techniques in Massive Hydraulic Fracturing
`Treatments,” paper SPE 16189 presented at the
`SPE Production Operations Symposium, Oklahoma
`City, March 8-10, 1987.
`
`Hessler, R.: Phone conversation on Nov. 10, 1994,
`Bran-Dex Wireline Services, PO Box 1061, Ster-
`ling, CO., 80751.
`
`Melton, L.L. and Malone, W.T.: “Fluid Mechanics
`Research and Engineering Applications in Non-