From Nano-Gas
to Commercial
Oil and Gas
Mihai Vasilache
Special Core Analysis Laboratories, Inc.
SCAL, Inc.
Midland, Texas
www.scalinc.com
Hydrocarbon Generation, Storage & Production
Pressure
Volume
Temperature
Kerogen Type
Geological Time
Hydrocarbon Generation
Compaction
Expulsion
Molecular Sieving
Migration
Rock Properties
Fluid Properties
Rock-Fluid Interaction
The more factors we use to describe
the process the better the results.
The Primary Reservoir
Source and Reservoir Rocks are in Contact
Same Burial History – Reservoir Composition is likely a Mixture of the Generation
Reservoir to Source Rock Ratio is Very Small
Secondary Reservoirs/Series
Tertiary Migration
Secondary Migration
Remigration
Micro Reservoirs - Primary and Secondary
Source Rock
Reservoir Rock
Primary Migration
Primary Reservoir
Compaction and Molecular Sieving
(a very large chromatographic column)
Molecule
Diameter
nm
Water
Methane
Normal Paraffins
Aromatic
Benzene
Cyclohexane
Complexe Rings
Asphaltenes
Helium
.30
.38
.4-10
.8-20
.47
.54
1-3
5-40
.098
Mercury
.314
“Pore throats act as
molecular sieves, allowing
particles smaller than the
orifice to pass and retaining
larger particles.”
If a shale needs to be crushed to allow
He to penetrate the nD matrix (GRI
porosity measurement) then that shale
will NOT STORE AND FLOW OIL.
Exploring for Oil and Gas Traps,
Edward A. Beaumont and Norman H.
Foster, AAPG 1999, Page 7-9
Compaction Model for Hydrocarbon Generation
Assume Type 2 Kerogen (oil and gas), Type 1 and 3 also fits the model
I
Open – Very Fast – Secondary Reservoir: Black Oil
Slug Flow
Normal Pressurized Primary Reservoirs
II
Trapped – Slower – Secondary Reservoir: Condensate
Porous Flow – Generation Fractures
Over Pressurized Primary Reservoirs
III
Sealed – Very Slow – Secondary Reservoir: Gas
Diffusion
Highly Over Pressurized Primary Reservoirs
The primary reservoir composition is a mixture of the I, II and III generation.
The API increases with burial
Gas Diffusion (seal quality) will affect the final reservoir composition
Compaction Model Implications:
The shale source is gas saturated even in the oil window.
The oil is produced in a conventional mode from the reservoir rock.
The ratio “shale source” to “shale reservoir” is high. Hard to find the “shale mix” fluorescence.
This ratio indicate high gas reserves/production even in the “shale oil” prospects.
In conjunction with thermal maturity and basic migration principle the model can explain and
position in the right place all types of hydrocarbon accumulations from heavy oil to dry gas.
The model explains the overpressure associated with the primary shale reservoirs. It also
allows for current time gas generation.
Shale compaction --- organic “shale source” --- “shale mix reservoir” --- trapped by “shale seal”
The final generation outcome (quantity and quality of hydrocarbons) depends on how fast the
compaction occurred.
Shale Source Rock Fluorescence and Maturity
High Maturity – Shale Gas
Low Maturity – Shale Oil
Before the addition of a cutting solvent
After the addition of a cutting solvent, with empty
wells for comparison
The Generation Process was Slowed Down
Organic Pores
Matrix
S1
• Not Sufficient geologic time
• Cooling associated with lower
radioactivity
• Compaction (cracking the
liquids)
S2
• Closed System (molecular
diffusion)
Organic Matter
Converted and Unconverted
The Source Rock and The Nano-Gas
Organic Pores
Matrix
The hydrocarbon generation is
responsible for the large organic
pores found spread in the very tight
shale matrix.
The higher the maturity the higher
the pore size.
The Nano-Gas is stored in the
organic pores as free and adsorbed
gas. There is no significant gas in
the shale matrix.
Therefore the gas quantity is
proportional with the hydrocarbon
generation (oil and gas).
Organic Matter
Converted and Unconverted
Using automated techniques and appropriate sample
sizes SCAL, Inc. provides sweet zone identification in
real time for a horizontal placement decision (most of
the time in 24-48 hr).
This identification approach is
faster than any other techniques
and is not subject to sample
contamination.
Pore Size Distribution as a Thermal Maturity Scale
Pore Size Distribution
40crushed
A sidewall sample 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”.
40plug
Pore Throat Entry Radius [microns]
100
10
The pore sizes measured on the crushed
sample are similar to the ones showed in
the SEM picture.
Crushed Sample
1
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 range, therefore the
connectivity is limited at best.
0.1
0.01
In 2005 SCAL, Inc. introduced:
Seal - Plug Sample
0.001
0
10
20
30
40
50
60
70
Mercury Saturation [%]
80
90
100
The pore network connectivity can be
described using the Diffusion Parameter
Ratio for the plug and crushed sample.
Nano Gas Measurements are:
Fast (real time directional decisions)
Accurate (eliminated all the temperature corrections)
Direct method performed on
Native state
Uncrushed
Un-extracted samples
Minimal invasion
Cost effective (an automated desorption isotherm costs $350/sample)
Used to identify the sweet zones … for both oil and gas.
Not measuring the native Nano Gas is like not using Mud Logging in an oil
well just because “you are looking for oil”.
Quick-Desorption™ Shale Portable Laboratory
The equipment is installed in an SUV
and consists of 2 accurate
mechanical convection laboratory
ovens (0.3 oC uniformity), stainless
steel canisters and a very accurate
gas measuring system operating
isothermal at reservoir temperature.
The measuring system includes an
industrial computer interfaced with a
laptop computer. The equipment is
powered by digital invertergenerators and in-line digital UPS
systems. A backup generator is also
included in the system.
Full Diameter Quick-Desorption™
Using a portable diamond drill, 1 inch
diameter plugs are drilled vertically into
the center of the full diameter sample at
the well site. These smaller samples
are loaded into our standard desorption
canister.
Desorption Canisters
The sidewall cores are cut top to bottom to minimize the lost gas. After
retrieval the samples are sealed in canisters at the well site. We collect
desorption data at reservoir temperature as we drive back to our
laboratory facility where the testing is continued.
Quick-Desorption™ Equipment and Software
Quick-Desorption™ and Shale Evaluation
Quick-Desorption™ Gas Composite Plots
Used for real time horizontal placement decisions
17
Residual+ Analysis
Eagle Ford Shale
Restored State Shale Analysis System
“Can I have a good shale oil well if my core
does not have any matrix fluorescence?”
A multistage hydraulic fracturing job fracture opens areas greater
than one can see in 1,000,000 rotary sidewall jobs at 45 samples
each.
The sampling needs to include potential reservoir rock … not only
the source rock.
It has happened quite a few times before!
Where is the Oil and Gas produced from?
1.
Source rock (gas producing). Diffusion and Desorption. Unconventional .
2.
Primary reservoir rock or “shale mix” (oil and gas). This has better
permeability than the compacted shale. Probably a multitude of primary
reservoirs joined by hydraulic fracturing. Conventional.
3.
Secondary and tertiary migration paths (oil, gas and water). Is it possible
to back produce a multitude of small secondary reservoirs with higher
porosity and permeability. Conventional.
4.
Kerogen current generation will likely be gas (molecular sieving). Very
Unconventional … deserves some serious research.
Conclusions
The gas desorption is the best direct native state technique available (fast,
accurate and economic) to evaluate the shale source in both oil and gas shale
plays:
1. it identifies the high maturity/generation zones
2. it provides accurate data for gas reserve calculations
3. is not subject to contamination (pipe dope, diesel, etc.)
The sorption isotherms are used:
1. to predict reservoir performance
2. determine free gas (helium) and calculate average reservoir porosity
(use it to calibrate the log response).
3. check and verify lost gas calculations
4. increase the data confidence (sorption/desorption check)
The “shale mix” needs to be sampled and analyzed using conventional core
analysis techniques.
References
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Mercury Injection Capillary Pressure (MICP) A Useful Tool for Improved Understanding of Porosity and Matrix Permeability
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Thank you
for your time!
www.scalinc.com