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PETE 629 ADVANCED

HYDRAULIC FRACTURING Dr. Peter P. Valk

professorTexas A&M University

RICH 709 862-2757p-valko@tamu.edu

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Source:Reservoir

Stimulation

3 rd Ed.

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Well or Reservoir Stimulation? Near wellbore region and/or bulk reservoir? Acceleration versus increasing reserve?

Explosives

Huff and puff stimulation (steam, CO 2, electric) Acidizing Acid fracturing Propped fracturing Water frac

Coupling of goals Frac&pack

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Principle of least resistance

Horizontal fracture Vertical fracture

Least Principal Stress Least Principal Stress

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h

R f

w

An Early Paradigm

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Vertical Fracture - Vertical well Bypass damage

Original skin disappears Change streamlines

Radial flow disappears

Wellbore radius is not a

factor any more Increased PI can be utilized

p or q

p J q post D

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Transverse Vertical Fractures - HorizontalWell

H,max

Hydraulic Fracture

H,max

D

x f

H,min

Radial

convergingflow in frac

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Fracture Morphology(source: Petroleum Well Construction)

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Fracture Propagation Elasticity Fluid Friction Material balance Fracture Mechanics

(Propagation)

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Goals first

Which wellbore-fracture orientation isfavorable? Which can be done? How large should the treatment be? What part of the proppant will reach the

pay? Width and length (optimum dimensions)? How can it be realized?

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Materials and Equipment

Fracturing fluids Proppants Equipment

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Fluid type

Oil-based (phasing out) Water based (polimer)

Linear Cross linked

Containing Nitrogen or Carbon dioxidegas

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Crosslinked fluid systemsCrosslinker Gelling Agent pH range Temperature range oF

B, non-delayed guar, HPG 8-12 70-300

B, delayed guar, HPG 8-12 70-300

Zr, delayed guar 7-10 150-300

Zr, delayed guar 5-8 70-250

Zr, delayed CMHPG, HPG 9-11 200-400

Zr-a, delayed CMHPG 3-6 70-275

Ti, non-delayed guar, HPG,CMHPG

7-9 100-325

Ti, delayed guar, HPG,CMHPG

7-9 100-325

Al, delayed CMHPG 4-6 70-175

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Fluid additives

Additive Concentration, gal or lb m added to 1000 gal clean fluid

purpose

biocide 0.1-1.0 gal prevent guar polymer decomposition by bacteria

fluid loss 10-50 lb decrease leak off of fluid during fracturing breakers 0.1-10 lb provide controlled fluid viscosity reduction

frictionreducers

0.1-1.0 gal reduce wellbore frictional pressure loss while pumping

surfactants 0.05-10 reduce surface tension, prevent emulsions,and wetting

foamingagents

1-10 gal provide stable foam with nitrogen and carbondioxide

clay control ----- provide temporary or permanent clay -watercompatibility

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Breakers

Breaker Applicationtemp, deg F

Comments

Enzyme 60-200 Efficient breaker. Limit to below pH 10.

Encapsulated Enzyme 60-200 Allows higher concentrations for faster breaks.

Persulfates(Sodium,Ammonium)

120-200 Economical. Very fast et higher temp.

Activated persulfates 70-120 Low temperature and high pH

Encapsulated persulfates

120-200 Allows higher concentrations for faster breaks.

High temperatureoxidixers

200-325 Used where persulfates are too quick.

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Fluid testing

Compatibility (Precipitation of solids)Rheology (effect of temp, pH, shear)

Fluid LossBreakingProppant carrying capacity

Residue in the proppant packFilter-cake residue

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Permeability vs. Closure Stress20/40 Brady Sand

1

10

100

1000

0 2000 4000 6000 8000 10000

Closure Stress, psi

P e r m e a

b i l i t y ,

D a r c y

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Primary proppant selection

(stress affected pack permeability)

6

8

10

15

20

0 5 10 15 20 25

Sand

Resin Coated Sand

Inter.-Strength Ceramic

Inter.-Strength Bauxite

High-Strength Bauxite

Closure Stress (kpsi) Secure

Considerable lossof pack perm

kpsi is 1000 psi, not Mpsi

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Laboratory-Determined Permeability ofSelected Proppants at 6000 psi(Highly optimistic, KCl water )

Proppant (API st) Proppant

permeability (md)

20/40 Ottawa Sand 150,00012/20 Texas Brown 200,00020/40 ISP, Ceramic 310,00020/40 HS, Bauxite 370,000

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Main Concerns

Proppant crush

Proppant fine migration Gel remaining Non-Darcy flow

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Procedure Decide if to fracture or not Determine size of treatment Determine main dimensions

Understand role of rock properties andstress states Make decisions on fluids, proppants Carry out a simple design

Provide reasonable data for designsoftware Generate pics Evaluate job, make strategic suggestions