Fracturing Basics

8/20/2019 Fracturing Basics

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Fracturing Basics

• Damage Bypass

• Stimulation

8/25/2015 1George E. King EngineeringGEKEngineering.com

Prod Improvement from Stimulations

1 10 100 1000 10000

Increased well radius/init well radius

J / J o

re/rw=625

re/rw=1250

re/rw=2500

re/rw=5,000

re/rw=10,000

Hydraulic

FracturingAcid Breakdowns

Optimizing Fracture Length by Reservoir Studies & Costs

Efficient fracture half lengths for various

permeabilities.

Fracture Gradient

• Ranges from about 0.5 psi/ft to over 1 psi/ft.

• Highly affected by regional and local stresses,

rock types, wellbore access to the reservoir,

deviation, plane of the perfs respective to the

frac direction, “tortuosity”, etc.

8/25/2015 George E. King EngineeringGEKEngineering.com

Usually a low

viscosity fluid

Usually a

viscosity frac

fluid.

Proppant Permeabilities

-12 / +20 mesh 450+ darcies

-20 / +40 mesh 120 darcies

-40/ +60 mesh 60 darcies-70/ +140 mesh 0.6 darcies

These perms are without stress and are for cleanproppant packs.

Proppant Conductivity

Conductivity

12/20 NW sand 4,500 md-ft

16/20 Naplite 15,000 md-ft

Resin coated 16/20 Naplite 15,000 md-ftResin coated 16/20 Carbolite 15,000 md-ft

Re-cycled 16/20 Naplite 3,500 md-ft

Conditions: Frac fluid is YF130LGD, Temp =

195 F, Closure Stress: 4000 psi (Valhall data)

Fracturing as a Means of Sand Control

• Frac and Pack

• Screenless Fracs

Perforating for Fracs

• Size - typically BH

• Orientation

– usually 60 degrees to 120 degrees

– 180 degree for screenless

• along frac direction?

Proppant

• Type -

– conductivity is most important

– strength is less important

– fines invasion?

– Other forms of damage

• paraffin

• asphaltenes

• scales

Fluids

• Non damaging

– look at clays

– look at water saturation

• Transport important

– must transport up to 16 ppga

• Efficiency critical

– building width is first step

Formation Permeability Ranges

• Low perm (<1 to 50), length is important

• High perm - conductivity critical

– get past the damage

– how long? - few meters

– how tall - ??

Maximizing Conductivity

• TSO Design (tip screen-out)

• maintaining conductivity

Application

• Pad - design from minifrac

• Slurry (1 to 12 ppga)

• Flush

Importance of Screenout

• Critical to make conductivity

– widths?

• normal frac = 0.1 to 0.3”

• TSO = 0.5 to >1”

• Screenout is usually seen as a pressure spike

near the end - can see it coming by watchingpressures

Tip Screen Out (TSO) FracturingScreen area open to flow =6% to >10%

Perf area open 6 to 10%

Skin = -3 to 10

Advantages

stimulation

links across layers and low vertical k

highest reliability sand control methodgood flow in moderate to higher kh

Disadvantages

usually most expensive

harder to design and apply

frac capacity vs. perm contrast critical

height growth uncertainty?

some proppant stability problem at depth

Step 1 - Sequence of Pumping a Tip-Screenout (TSO) Frac

Step 2- Start pad – no prop – breaks formation down & initiates fracture

What is happening? - fracture breakdown, width development, length growth, probably

height growth – AND – fluid loss from frac to the formation.

Step 3 End of the pad – prop is coming – fracture width is created

What is happening? - moderate frac width sufficient to admit proppant, sufficient length

and height to create width – AND – fluid loss from frac to formation with some fluid loss

control.

Step 4 – Start of first prop stage – usually about 2 lb/gal

What is happening? – Proppant is entering the

frac, and the pad, although diminished in

volume due to leakoff, is still increasing thefrac length and height (and width?). The

proppant is becoming more concentrated by

fluid leakoff as it travels down the fracture.

Fluid lost to the formation from the fracture steadily increases the proppant concentration of

the slurry in the fracture.

Step 5 – end of 2 lb/gal stage – start of 4 lb/gal stage

What is happening?

1 The small amount of pad remaining is at the

edges of the growing frac, but is being lost to fluid

leakoff;

2. The 2 lb/gal pad is losing liquid volume,

concentrating the proppant;

3. The 4 lb/gal pad has entered the fracture,

driving the other fluids in front of it and slowing

losing some of its volume to leakoff.

The proppant steadily concentrates in the remaining fracture fluid as leakoff into the walls of the

4 lb/gal Was 4 lb/gal,

now 6 lb/gal,Was 2, now 6

fracture continues.

Proppant concentration may begin as low as 1 to 2 lb/gal and increase to 12 or more lb/gal at

the very end of the fracture treatment.

Steps 6 and 7 – pumping stages of increased proppant concentration

What is happening?

1. Pumping sequential stages of 2, 4, 6,8, and 12 lb/gal.

2. The fluid leakoff is steadily increasing

the proppant concentration.

3. When the proppant concentration at

the tip of the fracture approaches 16

lb/gal, the slurry is no longer

pumpable.

Proppant concentration reaches a maximum at 16 lb/gal near the tip of at a highly permeably

i d h d h f l h i

section and the proppant screens out and the frac length stops growing.

Last stage of proppant – continues until the job screens out

Last Step – as pressure indicates that the tip screenout is forming, increase pressure at the

f d f h t ibl i t th f t Thi t t idth d

surface and force as much proppant as possible into the fracture. This creates extra width and

proppant loading at the wellbore – this means higher flow capacity.

Final proppant loading near the

wellbore may be 14 lb/ft2 or more.

Ob i DW F P k

Observations – DW Frac Pack• Frac Pack process very similar on every well

– Hard to evaluate ‘job quality’ from DIMS as data notreported

• Average sand placed is 84% of sand pumped

– Without 2 lowest jobs average is 89%

• Frac Screenout reported on 9 wells

• Annular Pack Processes Variable

– 6 wells with 8 BPM final rate

– 4 wells with less than 2 BPM final rate• 1 well reported 0.5 BPM to get annular pack

• Loss rate Post-Frac pack on 7 wells reported at less

than 25 BPH losses (13 reported losses, 7 did not)Dan

Gibson

8/25/201552

George E. King EngineeringGEKEngineering.com

Fracturing Disasters

• Too little proppant

• damaged or poor quality proppant

• reactive base fluids (formation damage)

• too few/too small perfs

• perf phasing way out of frac plane

over-flushing the treatment• fracturing out of zone

Minifracs

• Calibration Treatment

– 10 to 20% of frac volume

– same frac fluid at frac rate

• To Evaluate

– leakoff

– height growth

– frac geometry

• Procedure

Fracs in Horizontals and M-Ls

• Isolation is the key.

8/25/2015 55George E. King Engineering

GEKEngineering.com

Spacing on Fractures

• spacing related to drainage area

• permeability

• intersecting natural fractures

GEKEngineering.com

Concerns

Spacing

Frac directionIsolation

GEKEngineering.com

Fracturing Basics

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