Day 2 4 carbonate acid fracturing stimulations

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Geology ME 

slide 2


! Enormous permeability contrast matrix - fracture system
! Short flush production of oil/gas
! Unwanted inflow of water through fracture system
! Large variation in reservoir types

Breakthroughs required É.
Reduction of water production
! Substantial

increase in production
reduction in well cost
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Well Type Conclusions
Vertical

Slanted

!  Least Expensive

!  Would require 85¡ penetration

!  Straight-forward to frac

of reservoir for significant benefit
!  Would exit area before reaching
base of reservoir

"  Selected for Phase 1

#  Not Suitable

Horizontal

Multi-Lateral

!  Expensive to drill at this depth

!  Complex & costly (at this depth)

!  More difficult to frac
!  Limited productivity improvement
due to low / no vertical permeability

!  More difficult to frac
!  Technology constantly developing
but not yet sufficiently mature

#  Not Suitable

#  Potential for Longer-Term
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! Enormous permeability contrast matrix - fracture system
! Short flush production of oil/gas
! Unwanted inflow of water through fracture system
! Large variation in reservoir types

Breakthroughs required É.
Reduction of water production
! Substantial

increase in production
reduction in well cost
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Chemical Fracture Shut‐off 


NEED to KNOW………. 

flow into the well bore 

●     How does water 

●     How do I stop it???? 

slide 7

Oil or Water ???? 

slide 8


Coiled tubing

Gelant in sea water

Water flooded Zone

Oil bearing Zone
Re-perforation target

Calcium Chloride/Bromide Fill
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IN-DEPTH FLOW DIVERSION
Injector

Producer

Low k
zone
High k zone
Low k zone

1. Water injection flushing mainly the high k zone
2. Injection of system to block flow through high k layer

3. Injected water diverted to low k layers resulting in improved oil production

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SELF-SELECTIVE SYSTEMS MICRO SCALE

Oil Path

water Path

Polymer
Oil
Oil
@ Srw

Water
Polymer
@ Sor

Polymer Injected

Polymer Injected

Oil/gas flows through the middle
of the pore channel. Slight effect by
adsorbed polymer on oil/gas flow

Water flows mainly along the sand.
Water mobility reduced because

water flow path partly occupied
by adsorbed polymer.


New technology to Stop Inflow of Water  
¥  Controlled chemical release
Ð  Intelligent gels
Ð  Controlled fracture shut-off
Ð  Super absorbents
Ð  Self-Selective shut-off
water diffusion

Slow nutrient
release

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Current Applications

☛  Carbonless copy paper
☛  Pharmaceutical chemicals
➢ slow release enables drugs to be administered less
frequently and impart some target selectivity

☛ Agrochemicals
➢ controlled release of chemicals i.e.. the insecticides
PenncapM (methylparathion) and KNOX OUT
2FM (diazinon)

☛  Cosmetics
➢ liposomes which allow skin penetration but prevent
adsorption into the blood stream.
➢ Clearasil


! Enormous permeability contrast matrix - fracture system
! Short flush production of oil/gas
! Unwanted inflow of water through fracture system
! Large variation in reservoir types

Breakthroughs required É.
Reduction of water production
! Substantial

increase in production
reduction in well cost


Or in Low permeability 
Carbonates  
Hydraulic (acid)    

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Carbonates 
!  Limestone 
!  Chalk 
!  Dolomite 

Calcium
or
Calcium/magnesium
Carbonate

slide 16


Dissolves in: 

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Types of Acid 
!  Plain HCL + viscous Pad 
!  Gelled HCl 
!  Chemically  retarded HCL 
!  Emulsified acid 
!  Self diverting acid 

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ReacΚon‐Rate Modeling 
2HCL + CaCO3

CaCl2 + CO2 + H2O

4HCL + CaMg(CO3)2

CaCl2 + 2CO2 + 2H2O + MgCl2

Reaction rate:

m

rHCl = kjA CHCl

m= reaction order 
CHCl= concentration 
kj= reaction rate constant 
A= surface area 

kj= k0 exp ( -Ea/RT)

Ea= activation Energy 
R= Arrhenius constant (8.3) 

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Exercise 
!  Limestone:  
!  1 gram of pure HCl dissolves 1.372 gram of rock 
!  Dissolving Power Xc is volume of rock 

dissolved by volume unit of acid 
ρcC 1.372
Xc =

ρCaCO3

Calcite: 
ρ28% = 1.14 $ X28= 0.161 
ρ15% = 1.07 $ X15= 0.082 
Dolomite: 
ρ28% = 1.14 $ X28= 0.141 
ρ15% = 1.07 $ X15= 0.071 
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Exercise 
!  For an acid etched fracture of 50 m long by 

30 m high and 4 mm wide in Limestone 
!  How much (m3) 28% acid do I need 
!  How much 15% acid do I need 

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Exercise 
!  For an acid etched fracture of 50 m long by 

30 m high and 4 mm wide in Limestone 
!  How much (m3) 28% acid do I need 
!  How much 15% acid do I need 

Rock volume to dissolve: 
 2x 50x30x0.004= 12 m3 

X28= 0.161 m3/m3  

75 m3 28% HCL 

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ReacΚon Rate Modeling 
!  Acid transport to and reaction at the rock 
!  Acid depletes towards the fracture tip 
!  Heat transfer, as reaction is temperature 

sensitive 
!  Leak‐off of acid into formation (reactive!) 

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Temperature profile 

hot

cool
Wall layer

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Temperature profile in Limestone frac 

20 min 
10 min 
30 min 

Blue is aer cease pumping 

Source: spe26185
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