Optimizing Fracture Design and Injection with Microfracture Tests
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Microfracturing is an excellent method of obtaining direct stress measurements, not only in shales, but in conventional reservoirs as well. Recent advances have shown that microfracturing can help improve reservoir management by guiding well placement, completion design, and perforation strategy. Microfracturing consists of isolating small test intervals in a well between inflatable packers, increasing the pressure until a small fracture forms and then by conducting a few injection and shut-in cycles, extend the fracture beyond the influence of the wellbore. Results show that direct stress measurements can be successfully acquired at multiple intervals in a few hours and the vertical scale nearly corresponds to electric log resolution. Therefore, microfracture testing (generally performed in a pilot / vertical well) is an appropriate choice for calibrating log derived geomechanical models and obtaining a complete, accurate, and precise vertical stress profile. This talk describes the microfracturing process and presents several examples that led to increased hydrocarbon recovery by efficient stimulation and/or completion design. Case studies presented range from optimizing hydraulic fracturing in unconventionals, determining safe waterflood injection rates in brownfields, and improving perforation placement in ultra deepwater reservoirs. Mayank Malik is the Global Formation Testing Expert in Chevron's Energy Technology Company and is a champion for advancing research on microfracturing. He holds a B.S. in Mechanical Engineering from Delhi College of Engineering (India), MS in Mechanical Engineering from University of Toronto (Canada), and Ph.D. in Petroleum Engineering from The University of Texas at Austin (USA). Malik has authored numerous papers on petrophysics, formation testing, and microfracturing. He is currently serving on the SPE ATCE Formation Evaluation committee and is also the Chairman for SPWLA Formation Testing Special Interest Group.
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Optimizing Fracture Design and Injection with Microfracture Tests
- 1. Society of Petroleum Engineers Distinguished Lecturer Program www.spe.org/dl Mayank Malik Chevron Energy Technology Company
- 2. Common Fractures in the World! chanic
- 3. Why Microfracture? □ Industry relies too much on sonic/seismic models ! □ Microfracturing Advantages □ Direct measurement of rock stress □ Optimize injection pressure for EOR □ Robust fracture design
- 4. Outline □Why is Rock Stress Pertinent? □What is Microfracturing? □Microfracturing vs DFIT □Three Field Examples • Unconventional Shale • Offshore Ultra-Deepwater • Waterflood in Brownfield □Three Tips for Job Planning □Data Quality □Summary
- 5. Why is Rock Stress Pertinent? □ Applications in completion interval • Wellbore stability • Lost circulation • Mud weight optimization • Frac design and containment • Sanding Potential • Understand variability of stresses • Increase hydrocarbon recovery Limestone Shale Sandstone Barrier Containment Sh_sd= 5000 psi Sh_sh=4800psi Sh= Min Horizontal Stress FractureWidth Sh_sh=5100psi Sh_ls= 5200 psi Reservoir,Completions,Drilling
- 6. What is Microfracturing? □ Isolate a 1-m wellbore interval □ Inject a small volume (< 3 liters) of fluid with downhole injection pump □ Determine in-situ stresses Upper Element LowerElement Pressure Gauge Element spacing ~1m Desroches et al., SPE 58086 “Downhole Rock Mechanics Lab”
- 7. Microfracturing Technique Real-time monitoring and control (hours)
- 8. Different Methods to Interpret Fracture Closure □ Pressure declines in two flow regimes: linear and radialflow – Closure stress determined by identifying the end of the first linear flow regime □ Commonly used pressure decline analysis techniques to obtain closure stress : – Square-root time plot – G-function plot (most popular) – Log-log pressure vs time plot Closure TimePump Time Barree et al., SPE 107877 Martin and Rylance, SPE 127743
- 9. Breakout, or wellbore enlargements due to stress-induced failure, used to define minimum horizontal principle stress. Microfracture or drilling-induced fractures are vertical tensile cracks that occur orthogonal to breakout in the tensile quadrant of the wellbore. Stresses near the Wellbore Borehole max SH max SH min SH SH min Risnes et al., SPE 9650
- 10. Microfracturing vs DFIT Microfracturing □ Actual in-situ measurement □ Magnitude, orientation, known location and fracture height □ Up to 20 measurements/run □ Multiple attempts to identify fracture closure pressure □ Small volumes □ Slight risk of toolsticking □ Tool pressure limitationsreached below fracturing □ Problems with deflatingpacker □ Additional Image Iog required for induced fracture study Diagnostic Fracture Injection Testing (DFIT) □ Actual in-situ measurement □ Less risky than microfrac □ Large volumes □ Fracture fluid efficiency □ Fluid leak-off coefficient □ Reservoir perm measured □ Pressures measured at surface □ No fracture orientation information, location, or dimension of the fracture □ Single measurement per hole □ Single attempt to identify closure □ Long time to measure Cramer et al., SPE 163863
- 11. Example 1 : Avalon Shale (Delaware Basin) □ Multiple-stacked sequences comprised of naturally-fractured, low-porosity interbedded carbonates, clastic sands, and shales □Bone Spring is deposited throughout the basin and is divided into four sequences: nd • Avalon Shale • 1st Bone Spring • 2 Bone Spring • 3rd Bone Spring New Mexico Delaware Basin Texas UUppppeerrAAvvaalloonn MMiiddddlleeAAvvaalloonn LLoowweerrAAvvaalloonn 11sstt BBoonneeSSpprriinnggSSaanndd 22nnddBBoonnee SSpprriinnggSSaanndd 33rrddBBoonneeSSpprriinngg SSaanndd WWoollffccaammppSShhaallee MiddleAvalon UpperAvalon 1st Bone Spring Sand 2nd Bone Spring Sand 3rd BoneSpring Sand Wolfcamp Shale Lower Avalon Non-prospective cemented carbonate zones (possible frac barriers) shown in blue Malik et al., SPE 166264
- 12. Completion Evaluation Program □Answer key questions regarding economic potential of Delaware Basin and Avalon shale in particular o Are stresses variable across prospectiveintervals? o Energy required to initiate a new frac in targetzone? o Contrast between frac/pore pressure? o Are fracture barriers/seals effective? o Suitable location for casing shoe? o Calibrate log-derived stress values
- 13. Microfracturing in Reservoir Eight intervals targeted for microfracturing, Fracture closure identified from pressure decline plots 14
- 14. Comparing Microfracture with DFIT &Sonic Logs Close agreement between Microfracture test and DFIT acquired at same depth Default Sonic log derived model overestimated stresses
- 15. Fracture Closure Stress vs First Yr Production (BCF) Seismic 3D closure stress volume can be used to optimize landing depth, well path, and frac design 0.5 0 Production 1 First Year 1.5 2 2.5 0 0.1 0.2 0.3 0.4 0.5 Closure Stress Attribute (seismic calibrated with microfrac) Strong relationship observed across 7 wells Close et al., The Leading Edge, May 2012
- 16. Example 2 : Offshore Ultra- Deepwater Deeper, less forgiving targets Difficult to map with seismic Narrow window between formation vs fracture pressure Risk of seal breach with Frac Pack completions
- 17. Consequence of Stress Reversal on Completions Risk: Perforations must be placed 120 ft below shale seal to minimize fracture height growth, leads to loss of net pay 25000 26000 28000 29000 19000 23000 Rock Stress (psi) 20000 21000 22000 Depth (ft) 27000 ShalePaySand Microfrac test directly measures rock stress in shale Stress from Geomechanics Model
- 18. Example 3 : Waterflood in Brownfield Risk 1: Production decreases by limiting injection pressure Risk 2: Chemical EOR project not viable
- 19. New stress map generated for entire field to increase injector pressures and rates 6300 4000 7000 Depth (ft) Rock Stress (psi) 5000 6000 OverburdenSh_min from Microfrac Microfracture Test Gives Confidence in Optimizing Injection Safely 6400 Sh_min from Sonic logs 6500
- 20. Incremental re-injection rate 24,000 bwpdIncremental re-injection rate 24,000 bwpd Incremental Oil rate 1,500-2,000 bopd 2014 2015 Business Impact in Brownfield Increasing injection pressure by 320 psi enhances field production by 2000 bopd
- 21. Tip #1: Minimize Solids in Mud (Ideally < 5% volume) Filter Screens can get clogged O-rings/Mud Check valves may not seal Mud particles can enter flowline Solids can block hydraulic pump
- 22. Tip #2: Use Image/Wireline Logs to Select Intervals Elastomer extension caused by vug Avoid zones with vugs But try testing all lithofacies in completion interval
- 23. Tip #3: Design Test with Packer Specs from Vendor and Borehole Size Differential pressure limit chart vary for tools Ask your vendor for packer specs Have info on expected fracture gradient Can sleeve frac prior to microfracturing iffrac gradient is too high Use caliper log to confirm hole is in-gauge
- 24. A Note on Data Quality □ Wrong Data leads to Wrong Answer □ Pump enough volume to overcome hoop stress □ Spend more time on the last falloff cycle with naturalleakoff □ Check repeatability of measurements □ Plot stresses with depth to identify outliers □ Compare results with sonic models □ Analyze pressure transient plots to pick closure inreal-time □ Integrate information from microfracture test, image logs, core analysis, and injectiontests □ When in doubt, phone-a-friend!
- 25. Job Execution – Remote Microfracture Monitoring Cannot “reprocess” or “normalize” MF data ifnot acquired correctly the firsttime Field Engineers Wellsite Geologists Ops Petrophysicists Vendor Experts Asset Teams Completions Experts Real-time decisions enabled through cloud
- 26. Summary □ Reliable stresses in Avalon shale to assess economics □ Direct stresses for optimal perforations in Ultra Deepwater □ Increase oil recovery by enhancing safe waterflood re-injection rate in Brownfield □ Microfrac = Downhole Rock Mechanics Lab
- 27. Society of Petroleum Engineers Distinguished Lecturer Program www.spe.org/dl 28 Your Feedback is Important Enter your section in the DL Evaluation Contest by completing the evaluation form for this presentation Visit SPE.org/dl