UNCONVENTIONAL GAS-WELL STIMULATION TECHNOLOGY. N. R. Warpinski Sandia National Labs

Transcription

1 UNCONVENTIONAL GAS-WELL STIMULATION TECHNOLOGY N. R. Warpinski Sandia National Labs

2 STIMULATING UNCONVENTIONAL GAS RESERVOIRS Resource Characteristics Low Permeability: Some Form Of Stimulation Required For Economic Production Of Unconventional Resources Fracturing Acidizing Cavity Completion Explosives & Propellants Injecting CO 2 In Coal Seams Other Complexity: Stimulation Effectiveness Dominated By Reservoir Characteristics Natural Fractures Compartmentalization Reservoir Anisotropy Fluid Compatibility Multiple Zones Others

3 STIMULATING UNCONVENTIONAL GAS RESERVOIRS Elements Of Formation Stimulation Pre-Stimulation Evaluation Formation Evaluation (The Reservoir?) Fracture/Acid Design Parameters (The Rock?) Well Construction & Completion Stimulation Modeling & Design Pre-Treatment Diagnostics Treatment Materials Fluids, Proppants, Additives Stimulation Operations Stimulation Evaluation Production, Pressure Analysis, & Diagnostics Production Operations Refracturing

4 STIMULATING UNCONVENTIONAL GAS RESERVOIRS Pre-Stimulation Evaluation Reservoir Assessment Well Testing Geophysics Logs & Core Reservoir Size (boundaries or infill distances) Rock Mechanics In Situ Stress, Modulus Fracture Azimuth, Height, & Complexity Stimulation Fluid Compatibility Rock And Reservoir Fluids Target Intervals Number, Separation, Characteristics

5 What Is The Reservoir? Size & Shape Water Saturation Porosity Permeability Vertical/Horizontal Permeability Anisotropy Dual Porosity Fracture Sets, Spacing, Continuity Evaluation Technology Well Testing Logs Core Geophysics (Seismic) Surface & Downhole Outcrop & Surface Studies RESERVOIR EVALUATION Fractures Isolated Zones Anisotropy Poor Vertical Perm Tight Gas Sands Amalgamated Lateral Accretion Point Bars Meander Belt System

6 RESERVOIR EVALUATION Permeability Matrix Extreme Water Saturation Effects Highly Stress Sensitive Clay Swelling & Mobilization High Capillary Pressures Fractures Stress Sensitive Highly Conductive During Injection Inject Gels Difficult To Clean Up Matrix Fractures PERMEABILITY (normalized) Permeability (MicroDarcys) ` Sw=0% 0.01 Sw=15% Sw=30% Sw=40% Sw=50% Production Net Stress (psi) Injection PORE PRESSURE (psi) Initial

7 Rock Mechanics Important Parameters Stress Field Fracture Height Azimuth & Re-Orientation Proppant Crushing & Embedment Deviated Initiation Elastic Parameters E, ν Toughness Measurement Technology Stress Direct Measurement From Sonic Velocity Elastic Calculation Elastic Parameters Core Analysis From Sonic Velocity Usually x2 Greater 2,000 psi Stress Contrasts 500 psi Stress Contrasts Depth (ft) Depth (ft) Stress (psi) Gamma Ray Stress (psi) Gamma Ray

8 Rock Mechanics Dynamic vs Static Young s Modulus Dynamic > Static Highly Variable Poisson s Ratio No Correlation Fracture Toughness Lab Measurement Scale Question

9 TARGET INTERVALS How Do You Stimulate Intervals Over 3000 ft A Series Of Thin Coals Gamma Ray Gamma Ray Depth (ft) 6000 Depth (ft)

10 STIMULATING UNCONVENTIONAL GAS RESERVOIRS Well Construction And Completion Strategy Well Placement Infill Location & Spacing Relationship To Fracture Azimuth Will Depletion Change Factors Well Configuration Vertical Well Deviated, Horizontal Or Multi-Lateral Liner or Open Hole, Cemented Perforation Placement Strategy Limited Entry Or Other Diversion Strategy Full Zonal Coverage Or Point Perforating Phase Angle Coverage Intersecting Natural Fractures Is Critical

11 PERFORATION STRATEGY Single Point Perforating Minimize Entrance Problems Tortuosity Multiple Fractures Is Water An Issue? Limited Entry Can This Really Be Designed Is There Enough Stress Information Are Moduli Known Are Other Complexities Accounted For Zero Degree Phasing Can Zero Phasing Reduce Entrance Problems Extreme Overbalanced Perforating How Does The Water Get Out If The Perforations Are Not At The Fracture Bottom? Do Multiple Perforation Sites Induce Multiple Fractures?

12 PERFORATION INITIATION MULTIPLE FRACTURES AT PERFS Several Distinct Fracture Planes NEVADA TEST SITE MINEBACK

13 STIMULATING UNCONVENTIONAL GAS RESERVOIRS Fracture Modeling & Design Type Of Fracture Or Acidization Model Buttons & Knobs Calibrated Model Input Data Requirements Most Significant Problem Type Of Fracture Gel Moderate to High Prop Load Foam Low to Moderate Prop Load WaterFrac Low Prop Load CO 2 Or Nitrogen Minimal Prop Design Requirements Required Effective Length Height Issues (e.g., Aquifers, Depleted Zones) Conductivity Clean-Up/De-Watering Diversion (Limited Entry, Ball Sealers, Other)

14 Design Mode Model Differ Greatly Height Growth Tip Effects Coupling Pressure Matching Similar Result Same Basic Input Modulus Viscosity Must Confine Fracture Similarly Stress Tip Effects Other Similar Efficiency FRACTURE MODELS Fracture Wing Length (ft) Model Comparison Study Constant Height Models Layers

15 FRACTURE COMPLEXITY M-SITE (4500 ft) Multiple Fractures Usually Observed In Core-Through Tests Largely Due To Process Zone Effects Similar Behavior In Volcanic Dikes Several Strands May Have Proppant These Have A Significant Effect Large Delta P Higher Leakoff Increased Storage How Do We Predict Or Account For These 4678 MWX (7100 ft) 4675 Fractures

16 FRACTURE HEIGHT Fracture Height Stress Contrasts Are Major Controlling Factor Diagnostic Imaging Often Indicates Less Height Growth Than Stress Contrasts Would Predict Are There Other Mechanisms Restricting Height Growth? FRACTURE OF STRENGTH MEMBER ORTHOGONAL SPLITTING YIELDING OF SOFT MATRIX Composite Height Growth Mechanism RESULT: DISSIPATION OF ENERGY AND MULTIPLE STRANDS OFFSETS AT LAYERS DISCONTINUOUS FRACTURES

17 FISSURE OPENING (ACCELERATED LEAKOFF) Natural Fractures Are A Key Element Of Most Unconventional Gas Reservoirs Intersect Produce Through Avoid Damaging Fissure Opening Is A Major Issue Inject Gel While Open Clean Up While Closed Can Leakoff Be Controlled 100 Mesh Sand Is This A Key Element Of WaterFracs? Fracture Injection: Fissures Opened By High Pressure Clean Up: Fissures Closed

18 STIMULATING UNCONVENTIONAL GAS RESERVOIRS Pre-Fracture Diagnostics Breakdown Procedure Diagnostic Tests Stress Tests Pore Pressure Evaluation Calibration Tests Step Rate Pump-In/Flow Back Step Down Permeability Injection Test Minifrac Why Bother With Calibration Tests Closure Stress Basis For All Modeling Difficult Meaurement Leakoff (Efficiency) Length/Width/Height Prop Placement ScreenOut Entrance Conditions

19 PORE PRESSURE CONSIDERATIONS Infill Drilling 5500 Gamma Ray Stress Lenticular Sands Depleted Zones Lower Stress 5600 Virgin Readily Fracture Virgin Zones Higher Stress 5700 Shales Less Fracturing Depleted Zones Depth (ft) 5800 Depeleted Reorientation Possible 5900 Virgin 6000

20 STIMULATING UNCONVENTIONAL GAS RESERVOIRS Treatment Materials Fluids Type (Gel, Foam, Water, Gas, CO 2 ) Reactive, Energized, Stability Crosslinkers, Stabilizers, Gel Breaker, Bactericides Proppant Type (Sand, Ceramic, Bauxite) Resin Coatings, Fibers Conductivity, Crushing, Embedment Additives Leakoff Control (Including Fissure Opening) Clay Stabilization Surfactants

21 STIMULATION MATERIALS Fluids Only Modest Gains Are Likely From Improved Fluids Low Residue Gels, Foams, CO 2, N 2, Water, Acid Systems Breakers, Stabilizers, Inhibitors, Clay Stabilizers There Is A Fluid System For Most Applications Proppants Adequate Variety Sand, Resin, Ceramics, Bauxite Possible Improvements in Resins & Fibers However, Often A Mismatch In Fluid Systems & Desired Prop Load Prop Transport Economics Is Probably The Key Driver

22 STIMULATING UNCONVENTIONAL GAS RESERVOIRS Treatment Operations Wellbore & Casing Considerations Fracturing Equipment Quality Control Diagnostic Equipment Pressure, Tracers, Production Logs Imaging Technology Flow Back Objective Method Clean Up Fracture Formation Effect Of Liquids In Low Permeability Reservoirs Net Pressure (psi) BHP (psi) Bottom-Hole Pressure Provides Critical Information Time (hrs) OVERBURDEN STRESS Time (hr) CHANGING CHARACTERISTICS Rate (bpm)

23 FLOW-BACK PROCEDURES Fracture Stimulation Timing & Rate Goal? Proppant Stabilization Fluid Cleanup Varieties Matrix Delayed, Stable Rate Immediate, Slow Rate Forced Closure Minimize Precipitates Get Rid Of Spent Acid As Soon As Possible Pressure Forced Closure Length

24 FRACTURE & RESERVOIR CLEAN UP Hydraulic Fracture Gel Break Sufficient Energy Energized Systems Fracture Conductivity Matrix Capillary Pressure Relative Permeability Reservoir Pressure Gel In Fissures Fluid Damage Clay Swelling Pressure (psi) High Speed Centrifuge Test Por=5.2%; Dry Perm=0.01md Por=7.2%; Dry Perm=0.04 md Por=6.9%; Dry Perm=0.02 md Water Saturation (%) Mesaverde Sandstones, CO

25 LOW PERMEABILITY CARBONATES Many Reservoirs Deep High Temperature Horizontal/Multi-Lateral Wells Common Operational Difficulties Effective High Temperature Acid System Technology For Accessing Multi-Laterals Workover, Re-Stimulation Optimum Stimulation Methodology Acid, Fracturing, Other, Hybrid

26 STIMULATING UNCONVENTIONAL GAS RESERVOIRS Stimulation Evaluation Pressure Behavior Nolte Approach & Derivatives Pressure History Matching (Model) Fracture Diagnostics Wellbore Tracers, Temperature Logs, Production Logs Far Field Microseismic, Surface & Downhole Tiltmeters Well Testing Operational Considerations (e.g., Commingled Production) Pre-Frac Reservoir Understanding Production Ultimate Assessment

27 FRACTURE DIAGNOSTICS - MICROSEISMIC 1500 Well A WaterFracs Activate Natural Fractures Large Amount Of Shear Movement Water Dispersed Throughout Fracture System Prop? South-North (ft) Well D Monitor Well Well E Well C Frac Well Well B Courtesy of Devon West-East (ft)

28 WATERFRACS IN SHALES Effective Method Of Connecting Fracture System Shear Displacement Microseismic Activity Tiltmeter Residual Deformation Elimination Of Gel In Fissures Elimination Of Fissure- Opening Clean-Up Problem Penetrating Fluid Water Penetration Opening of Nearly Sealed Natural Fractures Wide Dispersal Microseisms TILT (microradians) M-SITE APRIL KCl INJECTIONS (1B - 4B) 1B 3B 2B 4B Shear Movement Within The Reservoir RESIDUAL DEFORMATION AFTER UNPROPPED INJECTIONS AS MEASURED BY DOWNHOLE TILTMETERS TIME (days) 20%

29 FRACTURE CONDUCTIVITY DEGRADATION 100 Limited Data On Shale Fracture Behavior Cyclic Loading Of Unpropped Fractures Reduced Conductivity Permanent Damage Minimize Pressure Variations Conductivity (microdarcy-ft) Fracture Permeability(Darcys) Shale Unpropped Fracture Time (days) Austin Chalk Fracture Net Stress (psi)

30 FRACTURE DIAGNOSTICS - MICROSEISMIC Multi-Zone Stimulation Unequal Fracturing Activity Some Sands Unstimulated Depleted Sands May Fracture Most Depth (ft) Gamma Log Unequal Distribution of Fracturing Activity Side View Distance Along Fracture (ft) Lenticular Sandstone Case

31 EFFECTIVE FRACTURE GEOMETRY Fracture Diagnostics Provide Fracture Length & Height Fracture Azimuth Fracture Complexity Secondary or T Fractures Need Effective Fracture Length Propped Length Cleaned-Up Area Fracture Length Propped Length Effective Length Poor Clean UP

32 STIMULATING UNCONVENTIONAL GAS RESERVOIRS Production Operations Dealing With Water Natural Lift Artificial Lift Wellbore Configuration De-Watering Of Coal Seams Optimizing Production Pressure Threshold For Damage Rate Threshold For Damage Gas Proppant Natural Fractures Water Crush Embed Fines

33 STIMULATING UNCONVENTIONAL GAS RESERVOIRS Refracturing When Is It Advantageous How Should It Be Done Why Is It Necessary What Actually Happens Extend Old Fracture Better Height Containment In Depleted Zones Start New Fracture Reorientation Of Fracture Direction Intercept New Compartments Surface Tiltmeter Measurement

34 UNCONVENTIONAL GAS RESERVOIR STIMULATION Summary Of Research Needs Reservoir Size & Shape Compartmentalization Permeability Matrix, Fractures, Anisotropy Natural Fractures Sets, Azimuth, Spacing, Properties In Situ Stresses Elastic Parameters Completion Method For Multi-Zones Large Interval Large Number Of Reservoirs Effects Of Depletion Perforation Strategy Spacing, Phasing, Limited Entry Closure Stress Pore Pressure Fractures Fractures Fractures

35 UNCONVENTIONAL GAS RESERVOIR STIMULATION Summary Of Research Needs (Continued) Model Improvements Complexity Height Effect Of Natural Fractures (Fissure Opening) Accurate Input Data Bottom-Hole Pressure During Treatments Waterfracs Mechanism That Make This Approach Effective Understanding Of Flow Back Process Improved Fracture Imaging Capabilities Less Expensive Longer Distances Effective Fracture Length Improved/Enhanced Artificial Lift Improved Production Strategy Refracturing Mechanisms That Make Refracturing Effective