Natural Fractures, Pore Pressure & Variable Formation Stresses: Linkages to Effective Gas & Oil Recovery Improvements?

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1 Importance of Geomechanics in Unconventionals Natural Fractures, Pore Pressure & Variable Formation Stresses: Linkages to Effective Gas & Oil Recovery Improvements? George E. King, P.E., Apache Corporation ARMA Unconventionals Workshop June 25, 2016 Westin Galleria, Houston

2 Rocks, Stresses & Production Intimately Related? Discussion Starters Where are the recoverable oil and gas reserves? Stress effects on stability of flow paths in low perm rock. Generating and maintaining access to flow paths.

3 Is shale porosity important? Three Porosities: Interstitial (between the grains) Natural fractures, fissures & micro-cracks Solution/modification porosity organic material shrinkage during maturation. Interconnected porosity? Size of pore throats limits the type of flow. Saturation of liquids generates capillary blocking problems. Learning hydrocarbon generation is from some organic carbons often deposited in TOC-rich layers in the shale. Low permeability may keep much of the hydrocarbon in this layer.

4 Crack (Fracture) Development in Shales Often Following the Natural Fracture System or Other Weak Points in the Rock The development of network fracturing, i.e., opening small cracks in the very low permeability shales, enables gas to flow. Propping these cracks with conventional methods, e.g. sand proppants, is virtually impossible, but the development of even the smallest crack delivers 100 s of times more flow capacity than the interstitial porosity offered by the matrix of the shale. The enormous number of these cracks, plus the potential propping action, delivered by trapping of water (capillary blocking effects) as the hydraulically opened fractures close, delivers flow capacity where none existed before. The water in the wider parts of these cracks will be displaced by gas, leaving trapped water to prop open the narrower parts of the crack.

5 Where is Hydrocarbon Generated, Stored & How Does it Flow? Shale Structure (URtec )

6 Transgressive Regressive Shore lines and impacts in shale deposition. Organic carbon is in layers within low permeability rock. Relative Hydrocarbon Potential (RHP) Access to the TOC layers is controlled by natural fissures. Some weak zones will preferentially fracture. Stable flow access is critical.

7 How Does Oil Move Through Shale?

8 There are Sweet Spots in the Barnett shale (based on highest production rates). Some reasons behind this are: Presence of mature TOC, Natural fractures, Operator knowledge, Remaining recoverable resources. Note that the greener areas (higher production) are somewhat colocated with stress modifying features 8 R. Gonzales

9 Effect of Regional Fractures? Best month production over 4 years of development two different fields what is happening?

10 What is the Permeability Range for Conventional and Unconventional Rocks? Conventional 1 md (10-3 D) to Darcies (D). Unconventional: varies from <1 nanodarcy, nd (10-9 D) to 1 microdarcy, md (10-6 D) for granites, shales & clays that form cap-rocks or compartmentalize a reservoir, Typical Productive Shales

11 Do All Perf Clusters or Fracs Produce?

12 Net Stresses Depend on Frac Growth and Where it Grows. 300 ft heigth 100 ft heigth Induced Stress vs. Distance from Center of Fracture

13 What happens to the stress as multiple fractures are added?

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15 Water molecule ~ 0.3 nm CH4 molecule ~ 0.4 nm C20 oil molecule ~ 1.7 nm 15

16 Is a quiet well path the best approach for well design? Locating a Wellbore Position An Integrated Workflow for Selecting Optimal Drilling Locations, E&P Magazine, June 2010, by Gerald Kidd and Fred Jensen.

17 Natural fractures are prevalent in productive shales. Flow through these fractures may be 10x to 10,000x higher than through the matrix. Fractures open at ~60% of pressure needed to fracture the rock.

18 Fracture Azimuth vs. Distance from Fault Average Frac Spacing Background Frac spacing = 24 ft. Stress Relaxed (?) Zone frac spacing = 4.3 ft.

19 EVALUATION OF HORIZONTAL WELLS IN THE EAGLE FORD USING OIL-BASED CHEMICAL TRACER TECHNOLOGY TO OPTIMIZE STIMULATION DESIGN SPE Overview: Tracking Frac Stage performance with Oil-Based Tracers Objective: Optimize Well and Frac Design Conclusion: Uncertain, but oil-based tracers may help define frac performance and optimized stage # s 2 wells first ten days 19

20 Effects of Geologic Occurrences Estimated gas in place (MMcfg/sq mi); modified from Marcellus Shale in New York, 2009.

21 Productivity Index Along the Lateral

22 Look for the Gas Shows Gas Show Quantity Ratio of gasses Corresponding GR Other logs (CNL, Density) to help assess TOC Density for Brittleness Resistivity for water saturation and salinity ROP (rate of penetration) Is it a hot shale or a natural fracture? The objective is to align the perf clusters with natural fractures.

23 The Curious Effect of ISIP. Why do pressures vary so much?

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25 Is it possible that stress changes will create a repeating frac pattern?

26 Stress Changes Along the Wellbore 3D seismic interpretation by Rich and Ammerman, illustrating significant differences in seismic attributes between toe and heel of the lateral. In their analysis, the natural fractures are parallel to fracture propagation in the toe. In the heel, the natural fractures are oriented perpendicular to hydraulic fracture direction. An alternate interpretation is that the differences between smin and smax are decreasing in the heel and are in the range that both fracture sets could grow and complexity is developed.

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28 No Conclusions that s up to you. Questions?

29 Mineralogy - Where do the UC Reservoirs fit?

30 Technology Made Shale Gas Production Possible Can understanding of stress increase recovery? Gas Oil