Damage Bypass Stimulation - • Damage Bypass • Stimulation ... Increased well radius/init...

Fracturing Basics

• Damage Bypass

• Stimulation

3/14/2009 1George E. King Engineering

GEKEngineering.com


GEKEngineering.com

Prod Improvement from Stimulations

012345678

1 10 100 1000 10000

Increased well radius/init well radius

J/Jo

re/rw=625re/rw=1250re/rw=2500re/rw=5,000re/rw=10,000

Hydraulic FracturingAcid Breakdowns


GEKEngineering.com


GEKEngineering.com

Optimizing Fracture Length by Reservoir Studies & Costs


GEKEngineering.com

Efficient fracture half lengths for various permeabilities.


GEKEngineering.com


GEKEngineering.com

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.

3/14/2009George E. King Engineering

GEKEngineering.com17


GEKEngineering.com

Usually a low viscosity fluid

Usually a high viscosity fracfluid.


GEKEngineering.com

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 clean proppant packs.


GEKEngineering.com

Proppant Conductivity

Conductivity12/20 NW sand 4,500 md-ft16/20 Naplite 15,000 md-ftResin coated 16/20 Naplite 15,000 md-ftResin coated 16/20 Carbolite 15,000 md-ftRe-cycled 16/20 Naplite 3,500 md-ft

Conditions: Frac fluid is YF130LGD, Temp = 195 F, Closure Stress: 4000 psi (Valhall data)


GEKEngineering.com


GEKEngineering.com

Fracturing as a Means of Sand Control

• Frac and Pack

• Screenless Fracs


GEKEngineering.com

Perforating for Fracs

• Size - typically BH

• Orientation– usually 60 degrees to 120 degrees

– 180 degree for screenless• along frac direction?


GEKEngineering.com

Proppant

• Type -– conductivity is most important

– strength is less important

– fines invasion?

– Other forms of damage• paraffin

• asphaltenes

• scales


GEKEngineering.com

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


GEKEngineering.com

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 - ??


GEKEngineering.com

Maximizing Conductivity

• TSO Design (tip screen-out)

• maintaining conductivity


GEKEngineering.com

Application

• Pad - design from minifrac

• Slurry (1 to 12 ppga)

• Flush


GEKEngineering.com

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 watching pressures


GEKEngineering.com

Tip Screen Out (TSO) FracturingScreen area open to flow =6% to >10%Perf area open 6 to 10%Skin = -3 to 10

Advantages

stimulationlinks across layers and low vertical khighest reliability sand control methodgood flow in moderate to higher kh

Disadvantages

usually most expensiveharder to design and applyfrac capacity vs. perm contrast criticalheight growth uncertainty?some proppant stability problem at depth


GEKEngineering.com

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


GEKEngineering.com

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.


GEKEngineering.com

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.


GEKEngineering.com

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 the frac length and height (and width?). The proppant is becoming more concentrated by fluid leakoff as it travels down the fracture.


GEKEngineering.com

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


GEKEngineering.com

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.


GEKEngineering.com

4 lb/gal Was 4 lb/gal, now 6 lb/gal,

Was 2, now 6

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


GEKEngineering.com

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.

Steps 6 and 7 – pumping stages of increased proppant concentration


GEKEngineering.com

Proppant concentration reaches a maximum at 16 lb/gal near the tip of at a highly permeably section and the proppant screens out and the frac length stops growing.


GEKEngineering.com

Last stage of proppant – continues until the job screens out


GEKEngineering.com

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


GEKEngineering.com

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

– Hard to evaluate ‘job quality’ from DIMS as data not reported

• 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

3/14/200952

George E. King Engineering GEKEngineering.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


GEKEngineering.com

Minifracs

• Calibration Treatment– 10 to 20% of frac volume

– same frac fluid at frac rate

• To Evaluate– leakoff

– height growth

– frac geometry

• Procedure


GEKEngineering.com

Fracs in Horizontals and M-Ls

• Isolation is the key.


GEKEngineering.com

Spacing on Fractures

• spacing related to drainage area

• permeability

• intersecting natural fractures


GEKEngineering.com

Concerns

Spacing

Frac direction

Isolation


GEKEngineering.com


GEKEngineering.com

Damage Bypass Stimulation - • Damage Bypass • Stimulation ... Increased well radius/init...

Documents

Transcript of Damage Bypass Stimulation - • Damage Bypass • Stimulation ... Increased well radius/init...