praxair energized well fracturing
TRANSCRIPT
1 Upstream Overview – Business Confidential
December, 2011
Mark H. Holtz
Dan Dalton
Energized Well Fracturing
Reserve Growth for Higher Recovery Efficiency
2 Upstream Overview – Business Confidential
SPE 119626 Cawiezel and Gupta, 2009 ;Gupta et al. 2005
7,500 N2 and CO2 Foam Treatments Have
Been Successfully Applied
3,500 Visco-elastic Treatments in Canada
with N2 or CO2 for Energized Flow-Back
Assistance
Praxair Participated in 1,600 CO2 Frac
Applications in 2008
Fracing State of the Art
3 Upstream Overview – Business Confidential
Well Fracturing
Reasons for Hydraulic Fracturing
– Near wellbore damage mitigation
– Production enhancement
– Increases effective wellbore radius
Hydraulic Fracturing is a 3 Stage Process
– Pad stage, initiates and propagates fracture
– The slurry stage, moving proppent into fracture
– Flush stage, cleaning up fluid to perforations
4 Upstream Overview – Business Confidential
Controls On Well Fracturing
The Magnitude and Direction of Formation
Principal Stresses
Perforation Alignment with Principal Stresses
– Misalignment results in higher treating pressures
– Poor wellbore-fracture communication
Design of Hydraulic Fracing Process
– Fluids, pressures, proppents
5 Upstream Overview – Business Confidential
Fracturing Fluid Systems
Purpose: – Initiate and propagate fractures
– Transport proppant
– Aid in cleanup
Selection Criteria Includes: – Safety and environmental compatibility
– Compatibility with formation and additives
– Simple preparation and quality control
– Low pumping pressure
– Appropriate viscosity
– Low fluid loss
– Flowback and Cleanup (for higher fracture conductivity)
– Economics
( Modified from Jones and Britt, 2009
6 Upstream Overview – Business Confidential
Pad Stage CO2 and N2 Effects
Due to less Interfacial Tension and Fluid Density
CO2 Foam Fracturing Results in:
– Greater effective frac length
– Increase in pressure connected or drainable area
– Increase of pressure support available at the formation face
Hydrostatic Head Increase Due to CO2 Fluid
Density
Generates Two Phase Fluid with Excellent
Foaming Ability and Excellent Surface Tension
Reduction
7 Upstream Overview – Business Confidential
CO2 at certain fracturing pressure and temperatures can reach near water density
In many instances the density requires less hydrostatic pressures for hydraulic fracturing
Less horsepower for fracturing is required thus eliminating costs to the operator, from the service company
Allows use of normal fracturing equipment
Size of jobs are only limited by the storage equipment, supply, and size of location
Excellent proppant transporter because the CO2 properties remain relatively constant throughout the treatment
Effects of High Fluid Density
8 Upstream Overview – Business Confidential
Hydraulic Formation Damage
To Achieve a Conductive Fracture all
Fracturing Fluids Must be Removed From:
–The formation
–The induced and natural fractures
It Is Essential To Prevent Polymer From :
– Invading the formation
– Invading natural fractures (natural fractures can
be plugged by polymer)
9 Upstream Overview – Business Confidential
Categories of Fracturing Damage
1. Within the Fracture
1.Proppant crushing
2.Proppant embedment
2. Fracture Face Damage
1.Chemical and polymer fracture plugging (polymer residue)
3. Within the Formation
1.Excessive fluid leakoff
2.Clay swelling
3.Relative permeability damage
4.Capillary effects
10 Upstream Overview – Business Confidential
Fracture Damage
Fines
migration
Clay
Swelling
Polymer
Capillary water
blockage Fracture face
damage
Oil
- Sand Grains
• To achieve a conductive fracture
all fracturing fluids must be
removed from the formation and
fractures
• It is essential to prevent polymer
form invading the formation and
natural fractures (natural fractures
can be plugged by polymer)
11 Upstream Overview – Business Confidential
Hydraulic Formation Damage
Fracture Face Permeability Damage of 90% or
Higher can Cause:
– A major increase in water production
– Reduction in gas production (Gdanski et al. 2005)
CO2 is Relatively Soluble in Water
– Solution forms relatively noncorrosive carbolic acid
(ph 3.1- 4)
CO2 Reduces or Eliminates Clay Swelling
– Swelling reduction due to extra hydrogen ion
– Critical in many shaly formations
12 Upstream Overview – Business Confidential
Hydraulically Fractured Gas Wells Can Experience
Water Blocking Due To:
– Capillary pressure character
– Capillary pressure hysteresis
– Relative permeability
“The most important factor that reduces fracture fluid cleanup and gas
recovery is the gel strength of the fluid that remains in the fracture at the
end of the treatment.” Wang, Holditch and McVay, 2009 SPE # 119624
Energized Fluid Fracing Reduces Gel Usage
Water Based Hydraulic Fracing
13 Upstream Overview – Business Confidential
Flush Stage Energized Fluids Assistance
Increased Fluid Recoveries Cause by Gas Expansion
CO2 Dissolves or Mixes with Hydrocarbon Fluids
– Solution causes hydrocarbon swelling decreasing viscosity and increasing fluid mobility on flow back
CO2 Solubility Reduces Interfacial Tension
– Results in less force in the capillaries causing increased fluid recovery
– This type of interfacial tension is not seen in a water based frac, without the use of surfactants
Faster Wellbore Cleanup to Start Producing Sooner
14 Upstream Overview – Business Confidential
From Gupta, 2003
CO2 Phase During Fracing Pressure – Temperature of CO2 Thru Frac Cycle
Pre
ssu
re (
MP
a)
Temperature (C) 1 – Trailer
2 – Boost Pump
3 – High Pressure Pump
4 – Mixed with Treatment Fluid
5 – Bottom Hole Pressure
6 – Bottom Hole Temperature After Job
7 – Return to Surface
-100 -80 -60 -40 -20 0 20 40 60
.1
VAPOUR
SOLID LIQUID
2
1
.2
.3
.4
.5
.6
.8 1.0
2
3
7
3 4 5
6
4 5 6
8 10
20
30
40 50 60
80
100
Critical
Point
Triple
Point
15 Upstream Overview – Business Confidential
N2 and CO2 Foams, The Surfactant Gel System
Logistically Simple – 2 surfactant based system
– Provides exceptional low-shear viscosity and
cleanup characteristics Fluids are not Wall-Building on Fractures
Very Good Retained Permeability Both in the
Formation and the Proppant Pack
Foaming Provides: – Significant increases in viscosity
– Superior leak-off control
Nearly 100% Propped Fracture Clean-up
16 Upstream Overview – Business Confidential
Time Savings to Bring on Production
Improved Placement of Proppant
Benefits of Energized Fluid Foam Fracs
Time from completion of fracturing treatment to sales, h
ThermaFOAM CO2
system
Conventional
Fluid systems
Source: South Texas operator
0 5 10 15 20 25 30 35
Schulmberger’s web site
17 Upstream Overview – Business Confidential
Obtain Greater Well Productivity
Benefits of Energized Fluid Foam Fracs
SPE paper # 119265
Rati
o p
ost
frac/p
er
frac w
ell p
rod
ucti
vit
y
Gas in all stages Gas only on
Proppant Stages
(Base Design)
Gas in only pad
stages No gas
0
0.5
1
1.5
J/J
°
2
2.5
3
3.5
4
4.5
18 Upstream Overview – Business Confidential
Supply liquid CO2 and N2 to Site
Portable CO2 Storage Containers
– (33 Ton, 50, 60 and 80 Ton)
Boost Pumps
– Takes the product from the storage tanks (275 psig)
and boosts the pressure to a constant 350 psig
CO2 Expansion Skids
Ensure that the Customer gets a Consistent Flow
of Pressurized Product
Praxair Capabilities
19 Upstream Overview – Business Confidential
Main Control System
Praxair Capabilities
Remote Booster Pump Control for Added Safety
Automatically Records Suction Pressure,
Discharge Pressure, and CO2 Flow Rate
20 Upstream Overview – Business Confidential
Praxair N2 /
CO2 Vessels
Praxair Pump
Trailer
Water
Tanks
Well
Head
Proppant
Truck
Pump
Trucks
N2 / CO2
Vessels
Well Stimulation Services
Gas Supply and Service Provider
21 Upstream Overview – Business Confidential
CO2 and Booster Pumping Services
22 Upstream Overview – Business Confidential
Technicians and Engineers Experienced in
Fracing
Energized Fluid Frac Modeling
– Equation of state (EOS) fluid calculations
– Models capillary and relative permeability effects
Praxair Capabilities
( Picture form SPE 119265)
23 Upstream Overview – Business Confidential
Summary Water Fracturing Challenges
Damage to Fracture Face, Formation, and
Natural Fractures
Undesirable By-Products Reduce
Fracture Conductivity
Wasted Fracture Volume
Less Than Optimal Production
24 Upstream Overview – Business Confidential
Summary CO2 & N2 Well Stimulation Services
Benefit of Using Gas
Solubility and viscosity
Less damaging
Easier cleanup
Greater effective frac length
Foaming ability
Excellent surface tension
reduction
Praxair Services
Supply liquid CO2 & N2
Logistic and consulting services
Dedicated primary pressure pumping
Strategically located supply plants