Fracture Initiation from Perforations

Transcription

1 Fracture Initiation from Perforations Andy Martin & Harvey Williams IPS 14-02

2 Agenda Perforating objectives for fracture stimulation Modelling Fracture Initiation Penetration Clean Perforations Direction Conclusions 12 May 2014, 2

3 Perforating Objectives for Fracturing Make frac jobs more effective Lower breakdown pressures Lower treatment pressures with better treatment rates Controlled frac placement All of this leads to better production Also helps avoid disasters like aborted jobs 12 May 2014, 3

4 Perforating Objectives Perforations should minimize: Near wellbore pressure drop Perforation friction Tortuosity Micro-annulus pinch points Multiple competing fractures 12 May 2014, 4

5 Well Direction and Gun Phasing Gun phasing and interval perforated should be based on well direction compared to the preferred fracture plane 12 May 2014, 5

6 Hydraulic Fractures in Horizontal Wells Longitudinal fracs Transverse fracs 12 May 2014, 6

7 What can we control? Size and type of gun Penetration (type of charge) Casing entrance hole Shot density Shot phasing Interval length Gun orientation Focus has been casing entrance hole 12 May 2014, 7

8 Casing Entrance Hole EH size about 8 to 10 times proppant diameter to prevent bridging Consistent EH for accurate limited entry designs 40% variation in EH results in 120% increase in pressure drop EH variation 50% 40% 30% 20% 10% EH variation vs Error in Pressure Calculation 0% 0% 20% 40% 60% 80% 100% 120% 140% Error in pressure (from SPE 83950) 12 May 2014, 8

9 Minimizing Casing Entrance Hole Variation Use largest gun possible to reduce water clearance Centralize gun Design shaped charge for minimum variation even across large water clearances Best Frac Charge Std Frac charge New Frac charge 12 May 2014, 9

10 What do the models say? 12 May 2014, 10

11 Modelling Fracture Initiation 12 May 2014, 11 Modeling of fracture initiation from cemented perforated wellbore provides insight into direction and penetration

12 Modelling Fracture Initiation Models of cased and cemented perforations can help determine well direction and perforation direction to minimize fracture initiation pressure. 12 May 2014, 12 As pressure increases, transverse fractures propagate from perforations

13 Hoop Stress & Cement Simple calculations of hoop stress for horizontal well with various casing/cement conditions Simulation shows that there can be a large stress difference between top and bottom Stress estimation around casing vs variation cement/casing situations 12 May 2014, 13

14 Model Limitations So far single perforations are modelled Detail geomechanics required Detailed cement quality required Need perforation shape Assumes clean perforations 12 May 2014, 14

15 What about penetration? 12 May 2014, 15

16 Penetration is Not Important. All We Need is 6 to 8 in. All DP shaped charges shoot more than 8 in. Just look at the API data. We know that we need to get beyond near-wellbore stress, formation damage and break outs. But all we need is about 1 BH diameter. It is amazing how many Frac Engineers do not know that penetration is affected by UCS and Stress 12 May 2014, 16 Up to 5-inch damage (SPE )

17 I want >6 penetration in 20,000 psi UCS rock. Which shaped charge should I use? API concrete data misleading Rock model important Importance of Knowing Penetration in Rock Rock model 12 May 2014, 17

18 What about clean perforations? 12 May 2014, 18

19 What about Clean Perforations? Plugged perforations NO fracture Clean Perforations with fracture passing through perforations (from SPE 20661) Enable injection to start deeper in formation, avoids near wellbore damaged zone Fractures may not initiate from plugged perforations (see big block tests left) Clean perforations allow fluid leak-off, increasing nearwellbore pressure prior to fracture initiation (from SPE ) 12 May 2014, 19

20 Plugged perfs NO fracture (from SPE 20661) 12 May 2014, 20

21 Clean Perfs Fracture (from SPE 20661) 12 May 2014, 21

22 What about direction? 12 May 2014, 22

23 Gun Phasing and Direction Fractures initiate from perforations aligned with maximum stress direction Best gun phasing is in max stress direction Near-vertical wells Perforations aligned with maximum horizontal stress 12 May 2014, 23 (from SPE 20661)

24 Gun Phasing and Direction Fractures initiate from perforations aligned with maximum stress direction Best gun phasing is in max stress direction Near-vertical wells Perforations aligned with maximum horizontal stress 12 May 2014, 24 (from SPE 20661)

25 Perforations aligned with maximum horizontal stress (from SPE 20661) 12 May 2014, 25

26 Gun Phasing and Direction Near-vertical wells Fractures initiate from sand-face when perforations are misaligned Other gun phasings: 120 (at 1 ½ times spf); 60 (at 3 times spf) Perforations misaligned with maximum horizontal stress (from SPE 20661) 12 May 2014, 26

27 Perforations not aligned with maximum horizontal stress (from SPE 20661) 12 May 2014, 27

28 What We Get with 60 Phasing Longitudinal fractures initiate first Terminate about 2 wellbore diameters in vertical direction Extend along wellbore Initial pumped volumes dominated by longitudinal fracs Transverse fractures initiate after Perpendicular to longitudinal Do not rotate from longitudinal 12 May 2014, 28

29 What we get with 60 Phasing 12 May 2014, 29

30 Can We Do Better? Several experiments done in large blocks in a tri-axial stress frame to simulate horizontal well Both DP and BH charges used Directional perforations aimed at the same transverse plane Transverse fracture from directed perforations Result: Transverse fractures created 12 May 2014, 30

31 Directional perforations in the same transverse plane transverse fractures are created 12 May 2014, 31

32 Conclusion Models of fraction initiation from perforations show importance of direction Models supported by practical experiments Data acquired from wells will help validate both experimental data and models 12 May 2014, 32

33 Questions? 12 May 2014, 33