C6 - Perforating for Stimulation

(1)

Perforation

Design

for

Well

Stimulation

R. R. D.

D. Barree

Barree

(2)

Detonating

cord groove ¾

Main

explosive

charge

Case or

container

Liner

Primer

charge

Typical

(3)

Detonating

cord groove ¾

point of

initiation

Main

explosive

charge

Case or

container

Liner

Primer

charge

Typical

(4)

Approximate

Jet

Velocities

(5)

Typical Perforation Damage

Reduced Permeability Zone

Perforation Tunnel

Plastically Compacted Zone

(6)

“Stress Cage” Formation

(7)

Poor Perforation Breakdown

_‐

(8)

Compaction Damage is

Related to Charge Design

•

“Big Hole” charges are focused to create large

diameter entry holes

– More radial deformation – More stress

_‐

cage effect – Less penetration

•

“Deep Penetrating” charges are focused for maximum

depth of penetration

– Usually less radial deformation – Smaller stress

_‐

cage effect

(9)

Proper Perforating Techniques Can

Minimize Damage

0 100 200 300 400 500 600 0 20 40 Perforation Charge, gm N e t B r e a k d o w n P r e s s u r e , p s i 4 perfs Open

In soft rocks perforation charge size can affect

breakdown pressure. Perforation diameter is more important than penetration.

More holes are better

(10)

Step

_‐

rate Analysis for Conventional

Perfs

(11)

Impact of Poor Perforations

on Job Performance

00:00 00:20 00:40 01:00 01:20 01:40 02:00 02:20 02:40 03:00 03:20 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 A 0 10 20 30 40 50 B 0 1 2 3 4 5 C

(12)

Avoiding Plastic Compaction and

Stress Cage in Perforating

•

Bullet

_‐

guns avoid plastic compaction and may

generate fracturing and perm enhancement

•

Hydrojetting (abrasive sand

_‐

jetting) can cut

deep, efficient holes with minimal mechanical

damage

–

Avoid jetting for long times as this can generate

fines and emulsions

–

Hydrojetting can provide penetration up to 12

(13)

Fractures Radiate from

(14)

Wellhead/Platform Leg

Removal (Lab Test)

successful cut

(15)

Step

_‐

Rate Analysis for Hydro

_‐

Jet Holes:

No measurable DP

(16)

Case 1: 100% of Perfs Open for Low

Density Perforating

(17)

Minimum Perforation Sizes

for Sand Bridging

•

Perforation diameters of 6x the prop diameter

assure no bridging.

Proppant Size Recommended Perf Diameter

(mesh) (inches) 6/12 0.80 8/16 0.56 12/20 0.40 16/30 0.28 20/40 0.20 30/50 0.14 40/70 0.10

(18)

Minimum Required Perf Diameter

Depends on Concentration

M i n i m u m P e r f D i a m e t e r , i n 0 0.1 0.2 0.3 0.4 0.5 0.6 8/12 mesh 10/20 mesh 20/40 mesh 40/60 mesh 8/12 10/20 20/40 40/60

(19)

Fractures Rarely Initiate at Perf

Tunnels

(20)

Tortuosity Caused by Poor Perf

Orientation and Poor Cement

Perforation Orientation

Restricted Cement Annulus

Fluid Flows through

(21)

Near

_‐

Wellbore Pressure Loss

• Stress halo around perf

• Flow around cement micro

_‐

annulus

• Perforation interference

• Narrow fracture width

• Fracture turning and

branching (multiples) • Off

_‐

vertical fractures

• Pulverized cement debris

• Charge debris

• Leakoff into drilling and perf induced fracs

(22)

Recommendations for Successful

Perforating for Stimulation

•

Perf underbalanced, flow back and clean up perfs

•

Use aggressive cleanup procedures

•

Large enough diameter to accept proppant

•

Sufficient number and diameter to allow fluid entry

at desired pressure

•

Determine optimum phasing to minimize entry

friction

•

Don’t shoot more holes than you need

•

If a screenout occurs consider reperforating

(23)

Aggressive Perforation Cleanup

Techniques Should Be Used

• Perforation Breakdowns

– Injection of non

_‐

damaging fluids – May not open all perforations

• Acid or Brine Ballouts

– Small perforated intervals – May not contact all perfs

• Perforation Surging and Washing

• Perforation Isolation Tools

• Acid Soaks

– Maintain drawdown over a long time period

• Extreme Overbalance Perforating

(24)

Conventional Perfs After Ballout:

Does it help?

(25)

Underbalance Perforating

Removes Perforation Damage

•

Underbalance provides surge of fluid into the

wellbore for cleanup.

•

Excess underbalance may cause collapsed casing,

formation breakdown and damage from fines

movement.

•

Underbalance requirement is indicated by field data:

– No improvement from acidizing indicates clean perforations

– Underbalance is determined by reservoir permeability – At low permeability, may be associated with insufficient

(26)

Underbalance

Perforating in Oil Wells

0.1 1 10 100 1000 P e r m , m d ? Recommended Underbalance

(27)

Underbalance Perforating

in Gas Wells

0.1 1 10 100 1000 100 1000 10000

Total Underbalance, psi

P e r m , m d Recommended Underbalance Casing collapse Stuck Packer

(28)

(29)

Summary of Perforating

Recommendations

• One size does NOT fit all

– What works GREAT! In one area may not work in another

– Find the optimum strategy for your reservoir and stress state

• In general fewer holes shot means higher perf efficiency and less near

_‐

well damage

– I do not favor cluster perforating

– I do like low shot density to avoid overlapping stress cages

• If you don’t know the stress field orientation, phasing can be inconclusive

• In deviated holes and highly anisotropic stresses, try to shoot in the direction of minimum near

_‐

well compression

– For highly deviated and horizontal holes, that is top and bottom

• Depth of penetration is meaningless in a well that must be fractured to produce commercially

• Get a hole through the pipe that is big enough for the proppant

(30)

Limited Entry Frac Designs

•

Force fluid into more than one zone

–

use perf restriction as flow orifice

–

high shear and treating pressure

–

possible fluid damage

–

perforation erosion concerns

(31)

Perforation Restriction Causes

a Large Pressure Drop

P

q

C N d

psi

pf

f

D

p p

=

1975

2 2 2 4

.

;

ρ

where

q = the total pump rate, bpm

f = the slurry density, g/cc

C_D = the perforation coefficient

N_p= the number of open perforations

(32)

(33)

6 lb/gal 2.5 lb/gal

Crump & Conway, SPE 15474

(34)

Final Perf Geometry in

Crump/ Conway Study

(35)

Perforation

_Δ

P in

(36)

Post Frac Logs

_‐

LE Frac in OK

(37)