- NOTE: may not be working correctly in Firefox -- this IS on Christine's 'to do' list, but in the meantime, it has been tested and works in IE.
Introduction
Goals of Stimulation in Tight-Gas Sands
McGuire-Sikora Folds-Of-Increase Curves for Pseudo Steady Flow
How Do We Benchmark Well Performance
Fractured Well Performance: 1
Fractured Well Performance: 2
Fractured Well Performance: 3
Performance of Well 1-8
Performance of Well 2-3
Business Case for Frac Improvement
Expected Well Performance for a 75 ft. Fracture Half-Length
Comparison of Well Performance with Different Xf
Business Case (cont'd)
What is Our Problem?
Dominant Physical Processes in Hydraulic Fracturing
Fracture Geometry
Which Fracture Geometry Is Important?
What Controls Created Fracture Geometry?
In-Situ Stresses
Definition of Stress
Effects of Stress Variation on Geometry
Calculating In-Situ Earth Stresses
Definition of Strain
Stress/Strain Relationship
Stress-Strain Slope Indicates Rock Stiffness
Deformation is Generally Non-Linear
Definition of Poisson's Ratio
Computing Stresses from Logs
Computing Poisson's Ratio for Log Data
Young's Modulus Related to Poisson's Ration
Other Moduli Defined
Uniaxial Strain: Deformation in One Direction
Tectonic Stresses Can Be Handled in Two Ways
Young's Modulus Can Affect In-Situ Stress
Horizontal Plane Strain Model
Estimated Stresses Depend on the Model Used
Stress Correction: Case History 1
Case 1: Conducted a Step-Rate Test
Stress Adjustments Through Tectonic Strain
Match of Main Frac: Borate/Guar @ 60 BPM
Poisson's Ratio Varies With Lithology
Young's Modulus Estimates Based on Velocity and Density
Plastic Deformation of Rocks Occurs Under Confining Stress
Rocks Behave Like Plastic Materials
Effects of Plasticity and Creep on Stress Estimates
Lithologies Susceptible to Plastic Creep
Effect of Pore Pressure on Stress
Net Effective Stress Causes Rock Deformation
Pore Pressure Variations Induce Closure Stress Contrasts
Change in Closure Stress Related to Change in Pore Pressure
Closure Stress Change Related to Pressure Depletion and PR
Effect of Reservoir Pressure Gradients
Final Proppant Distribution
Growth Asymmetry Related to Closure Stress Gradient
Causes of Asymmetric Fracture Growth
Fracture Geometry in Steeply Dipping Beds
Width and Containment
Height Containment Mechanisms Other Than Stress Contrast
The Plane-Strain Solution
The Plane-Strain Solution (cont.)
Elastically Coupled Displacement
Elastically Coupled Displacement (cont.)
Containment in a Coupled System
Composite Process Zone Modeled by Apparent Stress Concept
Variation in Tip-Zone Stress with Fluid-Lag Region Size
Actual Tip-Zone Mechanism Does Not Affect Overall Width Profile
Plane-Strain Width Solution Can be Inappropriate
Field Observations Suggest:
Displacement With Shear
Shear-Slip Model
Width Profiles for Various Shear-Dampening Radii
Shear Failure in Rock
Shear Failure in Rock (cont.)
Shear Failure in Rock (cont.)
Frac Extension with Bed Slip
Containment in a Decoupled System
Gel and Proppant Filled Fracture
Microseisms After Water Injection
Frac Geometry After Water Injection
Microseisms After X-L Gel Injection
Frac Geometry at End of Gel Injection
Observed and Predicted Treating Pressures
Other Possible Controls on Final Propped Frac Geometry
High Leakoff and "Permeability Barriers"
Fracture Geometry With High Leakoff Interval - No Proppant
Fracture Geometry With High Leakoff Interval With Proppant
Low Mobility Plugging Banks Can Be Used to Limit Growth
Problems with Artificial Barrier Placement
Closure Stress Distribution for Barrier Placement Study
Base Case: No Barriers Prop Concentration at Closure
Position of Artificially Placed Barriers
Partial Barriers: Prop Concentration at Closure
Duning versus Perfect Transport
Dynamic Barrier Placement: Prop Concentration at Closure
Multiple-Zone Fracturing
Methods for Multi-Zone Treatments
Conventional Multi-Stage Fracs
Fractured Well Performance: 3
Composite Flow-Through Frac Plugs
Flow-Through Frac Plug Example
Excape Completion System
Cross-sectional View
Example: EXCAPE Completion
Coiled Tubing Fracs
SurgiFrac
Expected Pressure Distribution in SurgiFrac
Wellhead/Platform Leg Removal (Lab Test)
Limited Entry Frac Designs
Perforation Restriction Causes a Large Pressure Drip
Crump/Conway Study
Crump/Conway Study (cont.)
Early's Results Tabulated
Perforation dP in Limited Entry Treatments
Post Frac Logs - LE Frac in OK
Prop Concentration After LE Frac Compared to Model
Fracture Geometry in Multi-Zone Treatments
Is Crossflow Significant?
Two-Layer Case with Stress Contrast
Model Results for Two Layer Case: Prop Distribution at EOJ
Two-Layer Case: Prop Distance at Closure
Two-Layer Case: Fluid Velocity During Closure
Concerns with LE Design
Perforating for Stimulation
Tortuosity Caused by Poor Perf Orientation and Poor Cement
Poor Perf Orientation with Good Cement Bond
Typical Shaped Charge
Approximate Jet Velocities and Pressure
Ported Hollow Carriers
Jet Perforator
"Stress Cage" Formation in Sandia Mine-Back Experiment
Poor Perforation Breakdown Caused by "Stress Cage"
Typical Perforation Damage
Typical Perforation Configurations
Proper Perforating Techniques Can Minimize Damage
E-Gun (Bullet) Perforator
Bullet Perforator
Perforation Entrance Characteristics
Perforation Wall Characteristics
Perforation Diameter Characteristics
Fractures Radiate from Bullet-Formed Perforation
Formation Properties Affect Bullet and Jet-Perforator Performance
Minimum Perforation Sizes for Sand Bridging
Minimum Required Perf Diameter Depends on Concentration
Recommendations for Perforating
Aggressive Perforation Cleanup Techniques Should Be Used
Effect of Acid on Sandstone
High Treating Pressures in Deviated Wells
Fracture Re-Orientation Can Cause High Tortuosity
Multiple Fracture Strands Endanger Treatment Efficiency
Proppant Migration
Proppant Movement During Closure
High Leakoff Case: Prop Distribution at EOJ
High Leakoff Case: Prop Distribution at Closure
Final Prop Concentration for Isolated Permeable Sands
Effects of Flowback Procedures
Symmetric Height Growth: Prop Distribution at EOJ
Symmetric Height Growth: Prop Distribution at Closure
Symmetric Height Growth: Prop Distribution at Closure (cont.)
Upward Height Growth: Prop Distribution at EOJ
Upward Height Growth: Prop Distribution at Closure
Upward Height Growth: Prop Distribution at Closure (cont.)
Fluid Leakoff
Typical Fracturing Fluid Loss
Filtration Process
Classical Filtration Modeling
Effect of Shear Rate HPG at 2000 psi, 1 md
Effect of Shear Rate HPG+B, 2000 psi, 1 md
Forces Acting on Polymer Molecule
Effect of Permeability and Shear HPG+B, 1000 psi
Effect of Filtration Pressure HPG+B
Effect of Breaker
Influence of Fluid Properties and Temperature on Spurt Loss
Influence of Fluid Props and Temp on Filter Cake Growth
Formulation of FLIC
FLIC Modeling of Invaded Region
FLIC Modeling of Invaded Region (cont.)
FLIC Modeling of Filter Cake
Classical vs. FLIC
Classical vs. FLIC (cont.)
Classical vs. FLIC (cont.)
Pre-Frac Injection/Falloff Tests
Sample Injection Test Procedure
Pre-Frac Step-Rate Injection Test
Traditional SRT Analysis
Wellbore Pressure Calculations
G-Function Pressure Falloff Analysis
Analysis of Pressure Dependent Leakoff Using the G-Function
Fluid Efficiency and Leakoff Coefficient During Closure
Calculated Efficiency With No Pressure Dependent Leakoff
Effects of Natural Fractures
Natural Fracture System in Hard-Rock
Fissures Opened By Tensile Stress Field
Fissure Opening Conditions Depend on Stress Ratio
Fissure Opening Conditions
Pressure Dependent Leakoff and Effective Modulus
Pressure Dependent Leakoff with Constant Compliance
Calculated Efficiency With Pressure Dependent Leakoff
Field Example of Pressure Dependent Leakoff
Determination of Pressure Dependent Leakoff Coefficient
Height Recession form High Stress Layers
Field Example of Height Recession
Permeability Estimate from G at Closure
Observed Gas Flow versus G at Closure
Fracturing Fluid Rheology
Fracturing Fluid Rheology
Power Law Rheology Model
Service Company Data Does Not Tell the Whole Story
Definition of Carreau Parameters
Carreau Rheology Model
Shear Rate vs. Viscosity
Correlations for Observed Slurry Viscosity Increase
Actual Frac Fluid Rheology: 40 #/Mgal Linear Guar
Effect of Sand Addition on Frac Fluid Rheology
Proppant Transport
Traditional Prop Transport
Proppant Transport has Been Estimated using Simple Models
Factors Affecting Proppant Transport
Common Assumptions on Fluid Loss/Transport/Screenout
Remedies for Early Screenout
Velocity Distribution of Particles Between Parallel Plates
Particle Velocity Profiles Normalized to Fluid Velocity
Proppant is Not Homogeneously Distributed
Relative Particle Velocity Changes With Concentration
Single Particle Setting Velocity Predictions
Single Particle Terminal Settling Velocities
Single Particle Settling Rates in a 1.0 cp Newtonian Fluid
Single Particle Settling Rates in a 55.0 cp Newtonian Fluid
Single Particle Settling Rates in a 155.0 cp Newtonian Fluid
Slurry Settling Experiments in a Vertical Slot Model
Slurry Settling Rates Controlled by Bulk Density Gradients
Observed Slurry Settling Rates Are Affected by Viscosity
Proppant Movement by Bulk Flow or "Convection"
Slurry Distribution in Large Scale Slot Model
Slurry Distribution With No Density Gradients
Channeling of Overflush Fluid in Large Scale Slot Model
Other Factors Affect Final Propped Geometry
Proppant Bridging and Screenouts
Variable-Width Slot Apparatus
Slot Bridging Video (Under construction)
Video (Under construction)
Summary of Bridging Studies
Annular Flow Apparatus
Proppant Transport in the Presence of Fluid Leakoff
Particles Held Dynamically at the Fracture Wall
Video (Under construction)
Sand Accumulation: Low Cv
Sand "Node" Formation
Video (Under construction)
Video (Under construction)
Sand Deposition and Erosion at High Rate
Video (Under construction)
Stable Channel Flow
General Observations on Sand Accumulation
Summary of Experimental Results
Sand Accumulation for All Data
Proppant Holdup in Fractured Systems - Early Injection
Proppant Holdup in Fractured Systems - Continued Injection
Proppant Holdup in Fractured Systems - Incipient Screenout
Effects of Proppant Holdup
Effects of Holdup (cont)
Proppant Holdup: Qpin/Qpout
Example of Proppant Induced Pressure Increase Modeling
Mitigating Proppant Holdup
Video (Under construction)
100 Mesh Sand in Coal Cleats
Proppant Holdup in Matrix Leakoff
Video (Under construction)
Fracture Conductivity Estimates
Traditional Conductivity Estimates
Polymer Concentrates During Leakoff and Closure
Persulfate Degradation in Cores at 150 F
Oxidizer Consumption
Half Life of Various Breakers
Zero Shear Viscosity of Guar at 250 F
Dehydrated Gel is Difficult to Move
Retained Perm Determined by Gel Residue
Polymer Residue at Closure: Uniform Leakoff
Polymer Residue at Closure: Local Leakoff
Fluid Rheology Changes Frac Shape and Prop Distribution
Useful Conductivity May be Localized
Proppant Crushing by Uneven Loading
Proppant Crushing Under "Uniform" Stress - 5000 psi
Proppant Crushing (cont.)
Comparison of Viscous and Inertial Flow Effects
Impact of Multiphase Non-Darcy Flow
Forcheimer "Turbulence" Factor
Non-Darcy Flow Affects Performance
Effects of Multi-phase Flow
Hypothetical Rel-Perm Curve
Effects of Rel-Perm on Flow
Performance of Well 1-8
Pressure Buildup Analysis for Well 1-8
Performance of Well 2-3
Pressure Buildup Analysis for Well 2-3
Unresolved Questions
Frac Pressure Drop Estimates
Addressing the Conductivity Issues: "New" Frac Fluids
New Fluids: General Observations
When to Consider Foams
Downsides with Foams
Quality Assurance and Quality Control
Small Problems Can be Catastrophic
Goals of Quality Assurance Program
Quality Control Form is Key to Implementation of Program
People do what you inspect, not what you expect!
Three Phases of Preventive Quality Control
Vendor Guidelines
Pre-Treatment Quality Assurance
Three Phases of Preventive Quality Control
Key Vendor Personnel
Pre-Treatment Assessment
Self-Education Opportunity
Three Phases of Preventive Quality Control
Q-C Form Summarizes Conformance to Guidelines
Quality Assurance Summary
Development of On-site Testing Program
On-Site Quality Control Tests
Base Fluid Properties
Example of Buffer Effect
Crosslink Time Testing
Static Break Tests
Break Profiles of 80# Guar + 2# SP @ 120F
Water Quality - Pre Job Testing
Water Quality - Pre Job Testing (cont.)
Water Quality - Pre Frac Testing
Fluid Quality During Treatment
API Proppant Quality
General Proppant Quality
In Summary
Summary
Summary (cont.)
Where do we go from here?
Where do we go (cont.)
