2. Lower Shale Porosities Are Better
Mihai Vasilache, Chris Daily, Paul Vasilache and David Gordon
Special Core Analysis Laboratories, Inc. SCAL, Inc.
Midland, Texas

3. Commercial Oil and Gas Essentials Primary Reservoir
Deposition, Burial and Compaction of Mineral and Organic Material
Hydrocarbon Generation and Migration
High Generation Pressures (higher than hydrostatic plus capillary pressure)
Open system (fast slug then slower relative permeability flow).
Closed system (slow diffusion). Eventually only gas can be generated.
Trapping (the shale source rock under continuous compaction due to the small grain size transforms into a seal providing):
structural trap for the oil
molecular trapping for the gas in the shale source
Storage – Porosity, Oil Fluorescence. This is the oil reservoir rock.
Transport – Combination of Matrix and Fracture Permeability
Horizontal Drilling and Multi Stage Fracturing (connect the reservoir rock)

4. Primary Reservoir (Self Sourced) Fluorescence
Natural Fluorescence Indicates Storage Reservoir Rock
Cut Fluorescence Alone Indicates Hydrocarbon Generation
Source Rock
Reasonable assumption:
Organic material was deposited in both shale and silt
Primary Reservoir Definition:
The source and the reservoir rocks are in contact

5. Wettability Measurements (µm DSA) Molecular and Stratigraphic Trap
The Gary Silt has Porosity and Permeability (open generation system)
The organic material was completely converted to hydrocarbons
The Black Shale is Tight (closed generation system)
The organic material was partially converted (S1 and S2 and black color)
Oil %
Water %
Silt
Reservoir Rock
Oil %
Water 9%
Shale
Molecular and Stratigraphic Trap
Oil %
Water %
Shale-Silt Mix
Primary Reservoir

6. Converted and Unconverted
Incomplete Closed System Generation
Gas Window
Matrix
Organic Pores
Organic Matter
Converted and Unconverted

7. Source Rock and Gas Reservoir Rock
Oil Window
Gas Window
Reservoir Rock Oil and Gas
Oil
Gas
Before the addition of a cutting solvent
After the addition of a cutting solvent
Before the addition of a cutting solvent
After the addition of a cutting solvent
Exploring for Oil and Gas Traps, Edward A. Beaumont and Norman H. Foster, AAPG 1999, Page 9-70

8. Introducing:
The Organic Shale
Porosity -Temperature Diagram

14. Shale Color (Color Change)

16. Shale Permeability
The laboratory permeability will also be drastically affected by the organic content changes due to laboratory temperature exposure
The sample grinding level also affects permeability values
Liquid hydrocarbons will not flow in rocks that have pores sizes
smaller than the molecular size of the liquid hydrocarbons
Diffusion parameters describing the transport capacity of the shale are determined from the slope of the desorption isotherms

17. Effective Oil Permeability Test (UV Pictures)
This is the reason for stage fracturing
DST Oil
Confining Pressure : 5,600 psi
Pore Pressure : 2,500 psi
Differential Pressure: 2,500 psi
Temperature : 151 °F
Oil viscosity : cP 12
Kk (He) =.0031 mD
Zero Matrix Permeability to Oil
Open Fracture Fluorescence
Fracture Permeability 31 31 31
Kk(He) = mD

18. Laboratory Hydrocarbon Generation (due to stress removal) Frac Fluid with Catalyst?

19. Current Gas Generation (after the reservoir confining stress is removed)
Reservoir Pressure 3,900 psi, Temperature 200 oF

20. Current Oil Generation and Associated Fracturing (after the reservoir stress is removed)

21. Shale Porosity and Log Response
This is a mercury injection porosity study conducted by Kerogen Resources, Inc. on 19 different potential shale plays and a total of 614 samples.
Mercury Injection Capillary Pressure (MICP) A Useful Tool for Improved Understanding of Porosity and Matrix Permeability Distributions in Shale Reservoirs* by Robert K. Olson and Murray W. Grigg,
Kerogen Resources, Inc.

22. attempts to calibrate laboratory data using log data
“The blind is leading the blind”
In finding the highly desired large shale porosities
In the absence of an API Standard
Questionable shale porosity data is used to “calibrate” questionable log data
and even worst
attempts to calibrate laboratory data using log data

23. Desorption Isotherms to the Rescue
Non fluorescent shale (oil or gas window) will produce ONLY gas
Sweet zone identification
Fast, independent based on hydrocarbon generation and
not subject to contamination
Difficult to measure porosity
We can accurately and independently measure gas reserves/storage using the CBM approach by measuring
the total gas content (scf/ton) instead
4. Difficult to measure permeability
The matrix shale gas production is controlled by diffusion and the diffusion parameters are determined from the slope of the Desorption Isotherms.
Fresh, fast, uncontaminated, native state, uncrushed measurements

24. Sweet Zone Identification
The hydrocarbon generation is responsible for the large organic pores found spread in the tight shale matrix. The higher the maturity the higher the pore size.
The gas is stored in the organic pores as free and adsorbed gas. There is no significant gas in the unconverted kerogen or the shale matrix.
Therefore the gas quantity is proportional with the kerogen to hydrocarbon conversion.
This identification approach is faster than any other techniques and is not subject to sample contamination.
Organic Pores
Matrix
Organic Matter
Converted and Unconverted
Using automated techniques and appropriate sample sizes SCAL, Inc. can provide positive sweet zone identification in real time for a horizontal placement decision (24-48 hr).

25. Field Quick-Desorption™ System
SCAL, Inc. SPECIAL CORE ANALYSIS LABORATORIES, INC.

26. Quick-Desorption™ Gas Composite Plots Used for real time horizontal placement decisions

27. Residual+ Analysis Eagle Ford Shale
There is more gas in the Eagle Ford Shale (oil window) than in the Barnett Shale (gas window)

28. Accurate Shale Gas Reserves
Without Porosity Measurements
The gas is a significant part of the reservoir material balance
G = Gas-in-Place, scf
A = Reservoir Area, acres
G = A h ρc Gc h = Thickness, feet
ρc = Average In-Situ Shale Density, g/cm3
GC = Average In-Situ Gas Content, scf/ton
Example Calculation:
$/acre-ft = x 1acre x 1ft x 2.55g/cc x 100scf/ton / 1000scf x 4.35$/mscf
= $1,508/acre-ft
SCAL, Inc. SPECIAL CORE ANALYSIS LABORATORIES, INC.

29. How do I explain the Oil Production?
The high ratio of source to reservoir rock ratio make it very difficult to explain where the oil is being produced from.
A multitude of micro reservoirs located along the “Migration Road” (path of least resistance). Once connected by fracturing they act like a large reservoir.
The hydraulic fracturing will propagate along the same ”Migration Road”.
The low load recovery after hydraulic fracturing in an oil wet nD matrix permeability shale suggests that the fractures might travel a lot longer distances along the “Migration Road”(contradicting the “perfect geometry” fracturing simulators).
We might be able to drill the “Migration Road” and get even better productions as long as we find porous and permeable rocks with mechanical properties that will hold the proppant from embedding.

30. Conclusions:
Low porosity (compacted) organic shale source rock is desirable:
The compaction is very important in hydrocarbon generation, expulsion, migration and trapping (oil stratigraphic while the shale gas is molecular).
The compaction will decrease the porosity but will generate lighter oils with high GOR (reservoir energy) and in many cases abnormal pressures (highly desirable in a low permeability environment).
High porosity (partially compacted) oil saturated shale is difficult to produce:
Low hydrocarbon generation, heavier oil, lower gas, lower reservoir energy, low expulsion, low migration, heavier oils with lover GOR.
High adsorption of the liquid hydrocarbons combined with a high surface area will result in very high residual oil saturations … and probably no commercial production at all.
The only proven process capable to produce the oil out of the shale is
the geologic time compaction

31. What other USEFUL things can be measured?
Sweet zones identification via desorption isotherms – fast, independent method based on hydrocarbon generation
The pore size distribution (MCIP) and Wettability (DSA) are related to thermal maturity. Both very important
Extended rock gas composition – O2, N2, He, H2, H2S, CH4, CO2, ethane, propane,
i-butane, n-butane, i-ethane, n-pentane, hexanes, C7 plus grouping and C8+.
Gas Reserves (the gas is part of the reservoir material balance)
Optimize completion fluids (DSA, CST, roller oven), hi-tech surfactants
Optimize proppant (size, embedding, crushing)
Measure rock mechanics (hydraulic fracturing)
Geochemistry (understanding local generation and migration)

32. The Pore Size Distribution and Thermal Maturity
A core plug was divided in 2 parts. One part was crushed to approx. 45 mesh. High pressure mercury injection test (60,000 psia) was performed on each part (plug and crushed). The plug sample pore size distribution looks like a “seal” while the crushed sample looks more like a “reservoir rock”.
The pore sizes measured on the crushed sample are similar to the ones showed in the SEM picture.
These pores observed in the crushed sample are large enough for a mD range permeability. However, the measured shale matrix permeability is often nano to micro Darcy, therefore the connectivity is limited at best.
2005 SCAL, Inc. introduced:
The pore network connectivity can be described using the Diffusion Parameter Ratio for the plug and crushed sample.
The area between the 2 curves is proportional to the thermal maturity of the sample.
Crushed
Plug

33. Drop Shape Analysis (DSA)

34. Contact Angle
Interfacial Tension

35. Dual Drop Wettability Measurement
Formation Water Drop
Crude Oil Drop

39. We use DSA to optimize fluids for:
We use DSA to optimize fluids for: • Drilling (well bore stability problems) • Completion • Stimulation (surfactant optimization) • Water Flooding (low salinity flooding) • EOR

40. Black tight shale is actually good for oil production!
Thank you for your time!
Black tight shale is actually good for oil production!

41. Rock Evaluation Pyrolysis
Temperature oC
Time 15 minutes
S1: free hydrocarbons or (gas and oil) past generation.
S2: hydrocarbons cracked or future generation potential.
Tmax: maturation of the organic matter.