June 15 th , 2011 Purposes Palynofacies Analysis Kerogen Type - - PowerPoint PPT Presentation

• 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

• rganic 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,

• paques, 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% Opaques 36% Palynomorphs 0%

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% Opaques 22.6% Palynomorphs 0%

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 phytoclasts 0% Opaques 96.2% Palynomorphs 0%

Utica Shale, Dolgeville mb. at 4,878 ft

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 High abundance of very dark degraded phytoclasts along with black

• paques 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% Opaques 23.6% Palynomorphs 0.2%

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

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Structured phytoclasts 3% Degraded phytoclasts 3.8% Opaques 93.2% Palynomorphs 0%

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 Carbon Gas Oil

OM

Total Organic Carbon (TOC)

Dead Carbon

Increased Maturation

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,
• r 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 13

1 2 3 4

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%Ro=0.55

Modified after Jarvie, 2004 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
• bserved 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 2 4 6 8 10 12 Total Carbon (wt. %) 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!

Questions?