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Refracs: What can we decipher? - Mike Vincent

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A presentation by Mike Vincent, petroleum engineer and consultant with Insight Consulting, delivered in early May 2014 at an SPE local chapter meeting in Horseheads, NY. Mike reveals a great deal of …

A presentation by Mike Vincent, petroleum engineer and consultant with Insight Consulting, delivered in early May 2014 at an SPE local chapter meeting in Horseheads, NY. Mike reveals a great deal of information learned over the past 10 years or so of active hydraulic fracturing of shale wells across the U.S. These slides are loaded with hints, tips and superb data to help those in the industry do a better job with fracing and refracing.

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  • 1. 1 Mike Vincent Insight Consulting mike@fracwell.com 303 568 0695 Refracs – What can we decipher? SPE 134330 & 136757 Fracwell LLC Outline Introduction • Non-unique solutions, uncertainty, value of field data Refrac Field Results • Refrac definition • History of restimulation • Why do refracs work? – Mechanisms; cause/effect – Field examples • Why do refracs fail? Interpretations and Recommendations
  • 2. 2 Can I reinforce my misconceptions? SPE 106151 Fig 13 – Production can be matched with a variety of fracture and reservoir parameters 6 0 200 400 600 800 1000 1200 1400 1600 1800 2000 0 100 200 300 400 500 600 Production Days StageProduction(mcfd) 0 20 40 60 80 100 120 140 160 180 200 CumulativeProduction(MMscf) Actual production data Long Frac, Low Conductivity Medium Frac, Low Conductivity Short Frac, High Conductivity, Reservoir Boundaries 500' Xf, 20 md-ft, 0.5 uD perm, 23 Acres 4:1 aspect ratio 100' Xf, 20 md-ft, 5 uD perm, 11 Acres 4:1 aspect ratio 50' Xf, 6000 md-ft, 10 uD perm, 7 Acres 4:1 aspect ratio • History matching of production is surprisingly non-unique. • Too many “knobs” available to tweak • We can always blame it on the geology If I don’t uniquely match this, can I trust my refrac interpretation? Removing the Uncertainty • If we require a production match of two different frac designs, we remove many degrees of freedom – lock in all the “reservoir knobs”! – The difference in production must be explained with the difference in the FRAC descriptions, not the reservoir description, right? 7
  • 3. 3 Recent Recent attempts to history-match field production: • SPE 119143 – summary of 200 published field trials in which initial frac designs were altered • SPE 134330 – summary of 143 published reports of the outcome of refrac attempts (worldwide) • SPE 136757 – evaluation of ~ 100 Bakken refracs – Direct search - minimizes “publication bias” – First field to allow evaluation of proppant durability on refrac success • There are many surprising results that are difficult to explain with traditional models • “It’s awfully dark down there” • Fracs are not as efficient/durable as we anticipate • Keep an open mind, dig, challenge. • None of us have it figured out. Consider outlandish ideas! Refracs My Definition of Refrac • A second propped fracture treatment (with production data between!) • Also tri-fracs, quads-, and “cinco-de-fraco” restimulations • I have excluded a large dataset where propped fracs improve previous acidized or unpropped initial treatments – What can we learn about durability of unpropped portions of the frac? Goals • Identify restimulation opportunities • Improve initial designs • Understand fracture and refrac mechanisms • Improve production models and frac models
  • 4. 4 History1953 Observations: May recover or exceed initial productivity! Decline rate also reduced! 1955 – Refrac and Tri-Frac Adapted from Garland, 1957 Sallee&Rugg,1953 Does this outcome fit your intuition or model? – Through 1970 • 35% of the 500,000 stimulation treatments were refracs – 1996 • Only 2-3% of current stimulation activity was refracs – Why? • Did we improve design, implementation, durability of initial frac treatments? • Did technological evolution cease? • Did economic parameters change? • Are we no longer staffed to analyze refrac opportunities? • Did refracturing fall from vogue and become lost art? • Are refracs not as effective as initially believed? – Current: Desire to understand refracturing History
  • 5. 5 Where Have Refracs Worked? Well Types Oil Wells (under primary depletion, waterflood, or EOR) Condensate Wells Gas Wells Gas Storage Wells Water Production Wells Water Injection Wells Steam Injection Wells Huff-n-Puff , cyclic injection/withdrawal Wells Disposal Wells Formation Types Carbonates, limestones, dolomites, chalks, evaporites Sandstones, cherts, siliceous diatomites Coal (CBM), immature ductile shales, brittle shales Conglomerates, unconsolidated formations, siltstones 16-page Appendix is attached to SPE 134330 describing all field examples – Immediately post-frac • Unsuccessful implementation • To achieve new entry points, diversion, reorientation – Somewhat later • Most common published examples are 1-10 years later – Much Later • >20 years, Clinton Sand, high perm oil, Ohio • >30 years, Mesaverde tight gas sand, Colorado • >30 years, Rangely Field, high perm oil, water + CO2 flood, Colorado • >40 years, Pembina mature waterflood, Alberta • >30 years, Medicine Hat, Milk River shallow gas – Ideas available on the theoretically “optimal” time to refrac, but we need to discuss mechanisms first! When have Refracs been Performed?
  • 6. 6 Refrac after 25 years of Depletion? 15 refracs (shallow gas – Medicine Hat & Milk River) All 15 responded to restimulation Average increase 600-900% 6 of 15 achieved higher production than peak 25+ years prior 4 of 15 achieved rates within 25% of peak IP RatepriortoRefrac First3 months,Initial Frac 3monthaverage, Post Refrac Adapted from Gutor, 2003 Observation: Excellent success despite decades of production. Why Do Refracs Work? (mechanisms) Refrac success (worldwide) has been attributed to: • Enlarged frac (more reservoir contact) – Improved pay coverage (add pay in vertical wells) – Better lateral coverage (horizontal wells) • Increased frac conductivity – Restore conductivity lost – frac degradation – Address unpropped/poorly propped portions • Improve wellbore-to-frac connection/conductivity • Reorientation • Use of more suitable frac fluids • Re-energizing natural fissures • Other mechanisms
  • 7. 7 Improved Reservoir Contact • Bypassed Pay in Vertical Wells – Where radioactive tracers or detectable proppants indicated missed opportunities, refracs are frequently successful Adapted from Hecker, 1995 Refrac contacted initially bypassed pay Improved Reservoir Contact • Bypassed Pay in Vertical Wells – 50 discrete sands in Pinedale [Huckabee 2005] • Can we touch it all with 15-20 stages? – ~26 sand intervals in Piceance • 28% of those stages fail to produce measurable gas? [Esphahanian 1997] • Limited entry didn’t induce effective diversion? [Craig & Odegard 2008] – 30-40 sand intervals in Jonah? • 35 to 40% fail to contribute meaningfully [Eberhard 2003] – Almond, Cotton Valley, Delaware, Red Fork • In 40% of wells, at least one targeted interval failed to accept any RA tracer [Fisher 1995] • Touching Pay is Job #1 – If kv/kh is tiny, you MUST create conductive, durable, vertical breach of these horizontal laminations – Despite what a simple model will predict, not all gas molecules are hydraulically connected to a perforation – Is bypassed pay a primary refrac opportunity?
  • 8. 8 Improved Reservoir Contact • Improved Coverage of Horizontal Laterals – Where radioactive tracers or detectable proppants indicated missed opportunities, refracs are frequently successful Adapted from Lantz, 2007 • Montana Bakken, cemented laterals believed drilled for longitudinal growth • Initial fracs ~300,000 lb 20/40 RCS • RA tracer showed incomplete coverage • Add perfs, refrac 600,000 lb 20/40 sand, 10 ppg slugs, ball sealers Improved Reservoir Contact Adapted from Lantz, 2007 Refrac reduced GOR, increased oil rate and reserves • Lower breakdown pressures, but 50% greater net pressure • We should revisit this issue! • Oil rates up, GORs down • Refracs diverted into undrained areas of the reservoir • EUR increased 1,300,000 bbls in 16 refractured wellbores • 1 mechanical problem, but 16 of 17 successful (94%)
  • 9. 9 Refrac on a Schedule? Pagano, 2006 – Gas Condensate wells in DJ Basin – up to 5 restimulations – Rangely oilfield – 1700 refracs 1947-1989. Most wells have received 3-4 refracs yet remain viable restimulation candidates. – Pembina oilfield – Conductivity was understood to degrade over time, with production falling to unstimulated rates in 6-7 years. Does Conductivity Degrade? 0 0.2 0.4 0.6 0.8 1 0 15 30 45 60 75 PermeabilityRatio Days at Constant Stress IDC at 10,000 psi (69 MPa) LWC at 10,000 psi (69 MPa) Sand at 5000 psi (35 MPa) Cobb, 14133 200F, 5000/10,000 psi [93C, 35/69 MPa] All non-corrodible surfaces, prop in Teflon tube, continuous flowing 2% KCl McDaniel , 15067 275F, 8000 psi [135C, 55MPa] showed importance of using silica saturated, deoxygenated brine
  • 10. 10 100 1000 10000 0 10 20 30 40 50 Conductivity(md-ft) Days at Constant Stress, 8500 psi IDC - Intermediate Density Ceramic Proflow - Precursor to LWC RCS - Resin Coated Sand Ottawa Sand 0 20 40 60 80 100 0 30 60 90 120 150 180 210 240 270 %OriginalConductivity Days at Constant Stress, 5000 psi 20/40 Sand at 75F 10/20 Sand at 250F Hahn, SPE Drilling 1986 300F, 8500 psi [149C, 59 MPa] Teflon tube, continuous flowing 2% KCl, Non-silica saturated Montgomery (12616) 1984 75/250F, 5000 psi [23C/121C, 34 MPa] API “short term” cell: Metal plates, continuous flowing 2% KCl, Non-silica saturated 25 Does Conductivity Degrade? Previous testing Handren 110451 250F, 6000 psi [121C, 41MPa] Modern conductivity cell, Ohio Sandstone Deoxygenated, Silica Saturated 2% KCl, Does Conductivity Degrade? All proppants degrade, but at different rates. Is replacing degraded proppant a major factor in refrac success?
  • 11. 11 Perhaps this makes sense? Pagano, 200627 Provocative Statements • Refrac DJ with minimal data – >5000 refracs performed – Few wells individually metered, even fewer with production log or single-zone test (comingle J Sand, Codell and Niobrara) – >8 papers written – arguing different mechanisms that account for success – We don’t know where, why, or how these refracs work • No correlation between reorientation and production? (Wolhart) • Which do you agree with? – “Engineering malpractice” – “Statistically validated approach to blanket refrac” – “Honestly? Do this 5000 times without actually trying to investigate whether we can address durability?” – “Financially prudent approach”
  • 12. 12 Proppant Durability Affect Refracs? • SPE 136757 – Examines refrac success of ~100 horizontal wells in Bakken – Large number of wells completed with: • Sand • RCS • Ceramic – Large number of refracs attempted on each type • ~90% success restimulating Sand or RCS completions • <50% success restimulating wells initially completed with Ceramic – More durable proppants appear to delay or avoid the need to restimulate this field Increase Conductivity in Refracs? Dozens of examples in literature Shaefer, 2006 – 17 years later, tight gas 0 500 1000 1500 2000 2500 3000 3500 Jan-90 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan-00 Jan-01 GasRate,MCFD 0 50 100 150 200 250 300 350 400 450 500 WaterRate,BWPD Gas Water Initial Frac in 1989: 48,000 lb 40/70 sand + 466,000 lb 12/20 sand May 1999 Frac: 300,000 lb 20/40 LWC May 1995 Frac: 5,000 lb 100 mesh + 24,000 lb 20/40 Sand Vincent, 2002 – 9 years later, CBM 0 500 1000 1500 2000 2500 3000 3500 4000 May-84 May-86 May-88 May-90 May-92 May-94 May-96 May-98 May-00 Date ProductionfromFracture(bfpd) Original Fracture (20/40 Sand) Phase I refrac (20/40 Sand) Phase III refrac (16/20 LWC) Incremental Oil Exceeds 1,000,000 barrels Incremental Oil exceeds 650,000 barrels First Refrac Second Refrac Pospisil, 1992 – 6 years later, 20 mD oil 0 500 1000 1500 2000 2500 StabilizedRate(MSCFD) Pre Frac 10,000 gal 3% acid + 10,000 lb glass beads 80,000 gal + 100,000 lb 20/40 sand 75,000 gal + 120,000 lb 20/40 ISP Ennis, 1989 – sequential refracs, tight gas 0 20 40 60 80 100 120 Well A Well B Well C Well D Well E ProductionRate(tonnes/day).. Initial Frac Refrac Dedurin, 2008, Volga-Urals oil 30
  • 13. 13 Refrac Reorientation Barnett - Cipolla, 2005 • Refrac Reorientation Documented in: – Lost Hills Diatomite – Austin Chalk – M. Bakken Dolomite – Codell, DJ Basin – Barnett Shale – Van oilfield – Ansai oilfield – Daqing oilfield – Xin Zhan field • Diversion/reorientation evidence: – Mounds cuttings disposal site – Black Warrior CBM – Undisclosed locations 31 Cross Sectional View 0 100 200 Xf, ft Core Projections 2400 2500 2600 2700 2800 2900 -50 0 50 100 150 200 250 300 350 GR& Hor. Dist., ft Depth Core# 4 Core#1 Fracture Intersections Core#3 GR and Hor. Dist., ft Mounds Wilcox Interval Tiltmeter & µS Mapping No hydraulic fractures present in Sidetrack #3, confirming vertical containment. -100 -75 -50 -25 0 25 50 0 25 50 75 100 125 150 175 Easting (feet) Northing(feet) Wellheads Perforation Locations Wellbores Core Frac Intersections Mapped Fractures Average azimuth N 71° W ± 11° Sidetrack #1 Sidetrack #4 Note: Dips of vertical fracs are not properly represented on this plan view. Plan View - 5 diagnostic injections and 17 cuttings slurry injections - Core #1 detected ~20 hydraulically induced fractures - Core #3 detected no hydraulically induced fractures - Core #4 detected ~9 hydraulically induced fractures Sidetrack 4 ABOVE fracture center Case C-01 See also: SPE 63032
  • 14. 14 Mounds Cuttings Injection Reference: 77553, after Moschovidis, SPE 59115, 63032, 48987 • Core through verified multiple fracs in recovered core • Core above Wilcox confirmed containment in mapped interval Why Do Refracs Work? (mechanisms) Refrac success (worldwide) has been attributed to: • Enlarged frac (more reservoir contact) – Improved pay coverage (add pay in vertical wells) – Better lateral coverage (horizontal wells) • Increased frac conductivity – Restore conductivity lost – frac degradation – Address unpropped/poorly propped portions • Improve wellbore-to-frac connection/conductivity • Reorientation • Use of more suitable frac fluids • Re-energizing natural fissures • Other mechanisms – Fracturing past condensate block, inducing complexity, rearranging existing proppant pack, better containment of refrac, etc
  • 15. 15 Why Do Refracs Fail? (poorer candidates) Refrac failure (worldwide) often attributed to: • Low pressure – depleted wells (limited gas reserves) – poor recovery of frac fluids • Inadequate reservoir quality • Diagnostics indicated drainage to reservoir boundaries • Undesirable existing perforations • Poor mechanical integrity • Failure to clean out well prior to restimulation • Inadequate procedures to select refrac candidates – Poor wells often make poorest refrac candidates – Unless there was a failure in initial frac design or implementation 35 Additional Examples Horizontal Well Refracs
  • 16. 16 Bakken Refracs (Lantz, 2007: 108117) • Montana, cemented laterals believed drilled for longitudinal growth • Initial fracs ~300,000 lb 20/40 RCS • RA tracer showed incomplete coverage • Add perfs, refrac 600,000 lb 20/40 sand, 10 ppg slugs, ball sealers upper track of Figure 4. The effect of depletion was observed in the treating records, as breakdown pressures averaged 669 psi lower than initial treatments. However, net pressure generated during the refracs was approximately 50% greater than during the initial fracs. Figure 4 – Tracer logs in horizontal well indicate coverage was increased by refrac. [Figure adapted from Lantz, 2007] Tracer from original frac▲ ▼Tracer from refrac • Lower breakdown pressures, but 50% greater net pressure • Oil rates up, GORs down • Refracs diverted into undrained areas of the reservoir • EUR increased 1,300,000 bbls in 16 refractured wellbores • 1 mechanical problem, but 16 of 17 successful (94%) Observations: Can refrac into new rock from cemented wellbores 37 Bakken Refracs (Dunek, 2009: 115826) • Uncemented liner. N-S oriented lateral. Surface tiltmeter mapping • Unintentional termination of frac job (wellhead isolation tool failure) – 3892 bbl crosslinked fluid and 296,000 lb proppant at 48 bpm • 2nd stimulation treatment 6 weeks later – 6533 bbl slickwater and 193,000 lb proppant at 61 bpm Transverse: 45% heel Longitudinal: 30% Horizontal: 10% Oblique: 15% Transverse: 45% toe, mid Longitudinal: 35% Horizontal: 20% Observations: Diversion/ Initiation at new locations Both Transverse and Longitudinal Growth
  • 17. 17 Bakken Refracs (Eberhard, 2008: WBPC) Cemented laterals initially treated with sand/RCS • Reperf/jet new entry points • Diversion slugs • 100% success rate – 30 days prior – 46 bopd – 30 days post refrac – 144 bopd Uncemented Liners initially treated with sand/RCS • Retreat existing perfs • 87% success rate (27 wells) – 30 days prior – 64 bopd – 30 days post refrac – 122 bopd Observations: Adding entry points helps. Initial cemented laterals failed to drain all rock Bakken wells frac’ed with sand usually benefit from refrac (~90% of time) 39 Bakken Refracs (Besler 2007/2008, SPE 110679 + 2008 WBPC) Bakken wells initially stimulated with ceramic • Only ~50% success rate with refracs using ceramic – Refrac success appears to correlate with wells in which RA tracer indicated poor diversion – In pre-refrac cleanouts, only minimal quantities of ceramic proppant recovered from wellbore Observations: Less need to refrac if wells treated with ceramic? Perhaps due to reduced proppant flowback or better durability? 40
  • 18. 18 Bakken Refracs (Phillips 2007 SPE 108045) Bakken wells initially stimulated with ceramic and XLG • Showed 1st month benefit refracturing with sand/slickwater 41 Bakken Refracs (Operator B) • 3 Wells initially stimulated with 20/40 ceramic in XLG • Restimulated 13-39 months later with >200,000 lb 30/50 or 40/70 Ottawa (much information unavailable via public data) • 2 of 3 wells subsequently TA, but did give short term benefit. 0 20000 40000 60000 80000 100000 120000 0 12 24 36 48 CumulativeOilProduction,Barrels Months on Production Well B-1 Well B-2 Well B-3 Refrac Refrac Abandon Trifrac Abandon Refrac Sand refracs of initial ceramic completions have been successful, but 2 of 3 abandoned?
  • 19. 19 0 10000 20000 30000 40000 50000 60000 0 10 20 CumulativeOilProduction,Barrels Months on Production Well C-1 Well C-2 Refrac Refrac Bakken Refracs (Operator C) • 2 wells initially stimulated with sand > 1,000,000 lbs (staged) • Restimulated 8-11 months later, slickwater with 100,000 lb 30/50 lightweight ceramic (bullhead; overflushed) Limited data, but: 100,000 lb LDC refracs in slickwater diagnostic plots similar/superior to initial fracs 0.00001 0.00010 0.00100 0.01000 0 0.5 1 1.5 2 2.5 3 3.5 1/BOPM SquareRoot of Months on Production Well C-1 Well C-1 Refrac Well C-2 Well C-2 Refrac Saskatchewan Bakken Refracs Vincent, 2010 - 136757 • 9 refracs identified in Viewfield area • 8 initially completed barefoot with 7-8 stages coiled tubing • 8 recompleted uncemented, ball activated sliding sleeves • 1 recompleted-cemented liner, abrasive jet, annular refrac • All 9 show oil increase. Watercut down in 7 of 9 refracs! 0 200 400 600 800 1000 1200 1400 0 20 40 60 80 100 120 140 160 180 200 0 10 20 30 40 50 GOR(mcfd/bbl) BOPDandWatercut% Months on Production BOPD BOPD normalized for downtime Watercut GOR Refrac Observations on this well •Oil increased from ~25 to ~140 bopd •Water decreased from ~250 to <100 bwpd! •GOR temporarily dropped 44
  • 20. 20 Restimulation of Gas Wells Dick Leonard, ProTechnics Expanding Shale Plays – 2009. PNR Energy Forum, Brookhaven College May 28, 2009 Barnett Shale Refracture Treatment • Min/Max stress are very similar in the Barnett. • There are now over 4000 traced HZ wells in the Barnett, about 50% show anomalies (unstimulated perfs, cement integrity, casing problems) • “Refracs are, and will become, critical to these shale plays”. It appears that we are not draining very far past the fractures. Refracturing of Barnett Dick Leonard Tri
  • 21. 21 Refracturing of Barnett Dick Leonard Barnett Refrac SPE 131783 Curry, Maloney (Range Resources) • Denbury Winston A3 well: – Original Completion: – 3000 ft cemented lateral – Original perfs spaced at 450 ft – Restimulated 2007 – Added intermediate perforations as shown on next page – Two stage refrac, placing 855klb proppant – Stage 1: 240 klb 40/70 + 290 klb 20/40 – Stage 2: 220 klb 40/70 + 105 klb 20/40 – Slickwater at 102 bpm – RA tracer shows diversion of treatment into new areas – Incremental EUR 1.0 BCF 53
  • 22. 22 Refracturing of Barnett Dick Leonard Green bars denote new perf clusters evenly spaced between old existing perfs. Note that on this stage, the new perfs took most of the refrac Apparent stress diversion. This is one of the best cases This well was identified as the Denbury Winston A3 well in SPE 131783 Refracturing of Barnett Dick Leonard A packer was set to isolate the lower (red) stage. It appears the middle green new perfs took proppant, but upper/lower did not? This well was identified as the Denbury Winston A3 well in SPE 131783
  • 23. 23 Refracturing of Barnett Dick Leonard Marcellus Refrac - Public SPE 131783 Curry, Maloney (Range Resources) • Range Nancy Stewart 4H well: – Original Completion: – 3000 ft cemented lateral – 100 ft perf spacing – 8 stages, placing 1.9 mmlb 100 mesh + 1.1 mmlb 30/50 sand – Crosslinked gel & slickwater used at average of 54 bpm – Restimulated Aug 2008 – Added “intermediate perforations” – Single stage refrac, placing 880klb 100 mesh + 390klb 30/50 – Slickwater at 131 bpm – RA tracer shows diversion of treatment into new areas – Incremental EUR 0.8 BCF 57
  • 24. 24 Marcellus Refrac SPE 131783 Curry, Maloney (Range Resources) • Range Nancy Stewart 4H well: – Incremental EUR 0.8 BCF 58 New perfs appeared to preferentially receive RAT in refrac Refracturing of Marcellus Buddy Woodruff, ProTechnics SPE ATW, Banff, May 3 2011 Original FG = 0.99 psi/ft Refrac FG 1.05 psi/ft Orig EUR 1.7 BCF Post ReFrac EUR 2.5 BCF
  • 25. 25 – I am aware of 7 refracs performed in EF • Swift • Pioneer • Results are not yet disclosed • Also in Eagle Ford, hesitation fracs have been shown by some operators to have induced diversion via microseismic mapping Eagle Ford – Immediately post-frac • Relax-a-frac? SPE 136873 Eagle Ford Eagle Ford Relax-a-Frac
  • 26. 26 – Immediately post-frac • Relax-a-frac? SPE 136873 Eagle Ford Eagle Ford Relax-a-Frac Successful refracs have been performed in Barnett, Woodford, Eagle Ford, Bakken, Marcellus, Haynesville, Niobrara, Spraberry, Wolfcamp… What did we miss the first time?
  • 27. 27 – Standard models fail to predict refrac performance • Multiple mechanisms • Models fail to recognize compartmentalization, degradation, realistic conductivity, etc. – Artificial Intelligence, Neural Nets • Excellent success in some fields (Shelley, 1999) • Dismal failure at predicting success in others • Some refracs have worked when all diagnostics said they shouldn’t! – Reorientation • Beneficial when it occurs (except in some waterfloods) • Is not necessary for refrac success in many fields – Refracs have worked in most reservoir types • And there are examples of failures in most, also! – Well design • We need wells that can be cost-effectively isolated and restimulated Comments 65 – No “magic bullet” was apparent. However, most successful refracs have incorporated: • Larger proppant mass • Improved proppant quality • Higher proppant concentrations (if placed with crosslinked fluids) – Adding perfs (if pay was missed) is valuable. Diversion! – Proppant durability is an issue – Some refracs clearly touch new rock • Some refracs do not, yet are still economic – Good wells are often the most economic refrac candidates! • Refrac “dogs” if design or implementation failure on initial frac – Even the best wells can be improved! (corroborates SPE 119143) • Non-optimal initial fracs, proppant degradation, or reorientation “gift” – Refrac candidate selection takes effort • Not as “routine” as drill & complete • Outstanding economic opportunities available Some Interpretations 134330 & 136757 66
  • 28. 28 Human beings, who are almost unique in having the ability to learn from others, are also remarkable for their apparent disinclination to do so. Pertinent Quotation Douglas Adams (1952-2001) English writer