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From Nano-Gas to Commercial Oil and Gas
Mihai VasilacheSpecial Core Analysis Laboratories, Inc.SCAL, Inc.
Midland, Texaswww.scalinc.com
PressureVolume
TemperatureKerogen Type
Geological TimeHydrocarbon Generation
CompactionExpulsion
Molecular SievingMigration
Rock PropertiesFluid Properties
Rock-Fluid Interaction
Hydrocarbon Generation, Storage & Production
The more factors we use to describe the process the better the results.
Primary Reservoir
Secondary Reservoirs/Series
Tertiary MigrationRemigration
Source Rock
Reservoir Rock
Primary Migration
Secondary Migration
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
Micro Reservoirs - Primary and Secondary
MoleculeDiameter nm
Water .30Methane .38Normal Paraffins .4-10Aromatic .8-20 Benzene .47Cyclohexane .54Complexe Rings 1-3Asphaltenes 5-40Helium .098Mercury .314
“Pore throats act as molecular sieves, allowing particles smaller than the
orifice to pass and retaining larger particles.”
Compaction and Molecular Sieving(a very large chromatographic column)
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 GenerationAssume Type 2 Kerogen (oil and gas), Type 1 and 3 also fits the model
I Open – Very Fast – Secondary Reservoir: Black OilSlug FlowNormal Pressurized Primary Reservoirs
II Trapped – Slower – Secondary Reservoir: CondensatePorous Flow – Generation FracturesOver Pressurized Primary Reservoirs
III Sealed – Very Slow – Secondary Reservoir: GasDiffusionHighly Over Pressurized Primary Reservoirs
The primary reservoir composition is a mixture of the I, II and III generation.The API increases with burialGas Diffusion (seal quality) will affect the final reservoir composition
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.
Compaction Model Implications:
Shale Source Rock Fluorescence and Maturity
Before the addition of a cutting solvent After the addition of a cutting solvent, with empty wells for comparison
High Maturity – Shale Gas
Low Maturity – Shale Oil
The Generation Process was Slowed Down
• Not Sufficient geologic time
• Cooling associated with lower radioactivity
• Compaction (cracking the liquids)
• Closed System (molecular diffusion)
Organic Pores
Organic MatterConverted and Unconverted
Matrix
S1
S2
The Source Rock and The Nano-Gas
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).
This identification approach is faster than any other techniques and is not subject to sample contamination.
Organic Pores
Organic MatterConverted and Unconverted
Matrix
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).
Pore Size Distribution as a Thermal Maturity Scale
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”.
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 range, therefore the connectivity is limited at best.
In 2005 SCAL, Inc. introduced:
The pore network connectivity can be described using the Diffusion Parameter Ratio for the plug and crushed sample.
Crushed Sample
Seal - Plug Sample
Fast (real time directional decisions)Accurate (eliminated all the temperature corrections)
Direct method performed onNative stateUncrushed
Un-extracted samplesMinimal 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”.
Nano Gas Measurements are:
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 inverter-generators and in-line digital UPS systems. A backup generator is also included in the system.
Quick-Desorption™ Shale Portable Laboratory
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.
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.
Desorption Canisters
Quick-Desorption™ Equipment and Software
Quick-Desorption™ and Shale Evaluation
Quick-Desorption™ Gas Composite PlotsUsed for real time horizontal placement decisions
17
Residual+ AnalysisEagle Ford Shale
Restored State Shale Analysis System
“Can I have a good shale oil well if my coredoes 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 zones2. it provides accurate data for gas reserve calculations3. is not subject to contamination (pipe dope, diesel, etc.)
The sorption isotherms are used:
1. to predict reservoir performance2. determine free gas (helium) and calculate average
reservoir porosity (use it to calibrate the log response).3. check and verify lost gas calculations4. increase the data confidence (sorption/desorption
check)
The “shale mix” needs to be sampled and analyzed using conventional core analysis techniques.
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