m. elgmati, h. zhang, m. zobaa, b. bai, and f. oboh ...web.mst.edu/~baib/shale...

M. Elgmati, H. Zhang,

M. Zobaa, B. Bai, and F. Oboh-Ikuenobe

June 15th, 2011

• Purposes • Palynofacies Analysis • Kerogen Type • Thermal Maturation • Estimated Key Geochemical Parameters • Total Organic Carbon • 3D Submicron Pore and 2D Organic Matter

Modeling • Conclusions • Acknowledgment

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• Conventional standalone analyses are inadequate and not suited for unconventional gas rock characterization

• Palynofacies analysis identifies intervals of exploratory interest in terms of hydrocarbon content

• The relatively inexpensive nature of palynofacies analysis makes it powerful in preliminary exploratory studies limited by tight budgets

• Pore imaging and modeling allows the evaluation of gas storage quantity and deliverability in shale-gas plays

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• The palynological study of depositional environments and hydrocarbon source rock potential based upon the total assemblage of particulate organic matter (Tyson, 1995)

• Palynofacies analysis was carried out on five samples • Three from the Utica Shale (two samples from Dolgeville

member and one sample from the Indian Castle Member)

• One sample from Haynesville shale

• One sample from Fayetteville shale

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• Conventional palynological processing technique: 1. Crush 10−15 grams of the sample in a mortar to the powder size

2. Treat the samples with concentrated HCl for 24 hours to remove their carbonate content

3. Dissolve the silicate fraction with HF treatment for 72 hours

4. Wash and sieve samples to remove clay particles and concentrated organic matter

5. Retain kerogen particles that range in size between 10−106 µm to make the final microscopic slides

6. Examine slides microscopically in transmitted light using variable magnification powers for analysis and photomicrography

7. Count 500 kerogen particles from each slide and classify them into four main categories namely, structured phytoclasts, degraded phytoclasts, opaques, and palynomorphs

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• Kerogen type IV was identified from all the studied samples, although they differ in the percentages of individual kerogen components

• Kerogen type IV was described (Peters and Cassa, 1994) as dead carbon, which has little or no hydrocarbon generating capability

• The examined samples (except sample #3 from Utica Shale) likely initially contained kerogen type III (gas prone material) that converted to type IV during the process of thermal over maturation

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Kerogen components identified from Haynesville Shale are dominantly phytoclasts and opaques

Palynomorph-like particles were observed, but could not be confirmed due to their high degree of degradation and very dark color

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Structured phytoclasts

49.2%

Degraded phytoclasts

14.8%

Opaques36%

Palynomorphs0%

Haynesville Shale at 12,000 ft

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Kerogen components identified are dominantly structured and degraded phytoclasts

Palynomorphs (essentially chitinozoans) were very rare and very dark brown to black in color, many of them were broken down.

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Structured phytoclasts

63.8%

Degraded phytoclasts

13.6%

Opaques22.6%

Palynomorphs0%

Utica Shale, Indian Castle Mb. at 4,649 ft

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An overwhelming abundance of black opaques with rare dark brown structured phytoclasts were found

The majority of opaque particles were equant in shape and smaller in size than those recovered from other samples

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Structured phytoclasts

3.8%Degraded

phytoclasts0%

Opaques96.2%

Palynomorphs0%

Utica Shale, Dolgeville mb. at 4,878 ft

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High abundance of very dark degraded phytoclasts along with black opaques and dark to very dark brown structured phytoclasts

Palynomorphs were very rare

Samples from the Dolgeville member of the Utica Shale at different depths were very different in their kerogen composition

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Structured phytoclasts

11.8%

Degraded phytoclasts

64.4%

Opaques23.6%

Palynomorphs0.2%

Utica Shale, Dolgeville mb. at 5,197 ft

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Very high abundance of black opaques in association with very little structured and degraded phytoclasts

No palynomorphs were observed during the counting process

Almost all of the kerogen particles in this sample were equant in shape 11

Structured phytoclasts

3%Degraded

phytoclasts3.8%

Opaques93.2%

Palynomorphs0%

Fayetteville Shale at 2,351 ft

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Total Organic Carbon (TOC)

Live Carbon Dead Carbon

Gas Oil Organic Matter

(Kerogen)

Oil Prone Gas Prone

Total Organic Carbon (TOC) Dead

Carbon Gas Oil Organic Matter

Total Organic Carbon (TOC) Dead Carbon Gas Oil OM

Total Organic Carbon (TOC) Dead CarbonGas Oil OM

Total Organic Carbon (TOC) Dead Carbon

Incre

ased

Matu

ratio

n

Modified after Jarvie, 2004

• The wall color in photomicrographs of the chitinozoan specimens identified from Utica and Haynesville shale samples ranges from dark brown to nearly black indicating post-mature thermal phase

• Shale sample from Dolgeville member at the depth of 4,878ft has generated little dry gas, or nothing

• Other samples (with initial kerogen type III content) have generated wet gas and condensate

• All the samples currently contain thermally post-mature type IV kerogen, their source potential is limited to minor amounts of dry gas, or barren, at the present time

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1 2 3 4

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%Ro=0.55

Modified after Jarvie, 2004

Producible gas may be found at ~ 1.0% Ro

Adopted form Traverse, 2007

%Ro=0.70

%Ro=0.90

%Ro=1.10

%Ro=1.40

• Qualitatively estimate some key organic geochemical parameters such as vitrinite reflectance (Ro %) and thermal alteration index (TAI)

• The dark to very dark brown colors of palynomorph walls in the studied samples(excluding Fayetteville Shale sample), which are typical post-mature source rocks, correspond to -4 to 4 TAI and 1.5−2.5% vitrinite reflectance (Traverse, 2007).

• This further suggests these source rocks are mainly in the metagenesis thermal alteration stage indicative of about 150−200° C temperature range (Peters and Cassa, 1994).

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• The studied samples were quantitatively investigated in the laboratory for TOC analysis

• The analyzed samples have TOC contents of 0.81−4.04 wt%

• It is likely that most of the TOC, at present, is dead carbon

• Inorganic carbon content was also observed in Utica Shale samples, which is likely resulted from high concentrations of calcite (CaCO3) in this shale-gas play (Elgmati et al., 2011)

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#1 #2 #3 #4 #5

Inorganic C 1.16 5.21 9.69 8.71 1.09

Organic C 0.81 1.31 0.31 1.12 4.04

0

2

4

6

8

10

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To

tal C

arb

on

(w

t. %

)

Sample #1 : Haynesville Shale at 12,000 ft

Sample #2 : Utica Shale, Indian Castle Mb. at 4,649 ft

Sample #3 : Utica Shale, Dolgeville mb. at 4,878 ft

Sample #4 : Utica Shale, Dolgeville mb. at 5,197 ft

Sample #5 : Fayetteville Shale at 2,351 ft

• Submicron pore imaging and modeling provide insights into the petrophysical properties of shale-gas source rocks such as pore size histogram, porosity, and TOC.

• A dual beam system (SEM/FIB) was utilized to reconstruct the 2D kerogen model and the 3D pore model of shale-gas plays.

• A successful example of reconstructed submicron pore model from Fayetteville shale-gas sample is presented.

• 200 2D SEM images were used to reconstruct the original 3D submicron-pore structure.

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SEM image showing the organic matter

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Converted 2D binary image of 0 and 1 pixel values

The extracted TOC value is 3.91% (vs. 4.04 wt.% in TOC test).

• Dark porous spots represent kerogen materials which contain high organic carbon contents

• The solid part is believed to represent aluminum silicate class mineral (possibly illite)

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Elements Atomic%C 37 %O 63 %

Elements Atomic%O 83 %Al 16 %Si 1 %

Elements Atomic%C 42 %O 58 %Spectrum 3

Spectrum 2

Spectrum 1

Spectrum 1 Spectrum 2 Spectrum 3

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3D model after alignment and stacking

Binary model of 0 and 1 voxel value

Element boundaries determined

• Major kerogen pore size is 30nm

• Few micron-sized pores exist in this 3D model

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Kerogen type IV was identified from all the studied samples with different percentages of individual kerogen components.

The observed palynomorphs implied high level of maturation.

Measured TOC content ranged from 0.81−4.04 wt% in the studied samples.

Pores of organic matters were found in nano size and occupied 40−50% of the kerogen body.

Petrophysical properties of the original pore structures can be effectively extracted from reconstructed three-dimensional models.

Good agreement between the computed TOC from the SEM image and the measured TOC in the laboratory.

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Financial support for this work from the Research Parternership to Secure Energy for America (RPSEA) and the United States Department of Energy.

American Chemistry Society Petroleum Research Funding

Baker-Hughes

Southwestern Energy

Thank You!

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