1. Pore-Scale Imaging and Analysis of Oil Shale
Tarik Saif
Supervisors: Prof. Martin Blunt & Dr Branko Bijeljic
12 January 2015

2. Unconventionals: Oil Shale

3. What is Oil Shale?
The term Oil Shale is a misnomer because it does not contain oil, and is not always made of shale.
Instead, rock is actually marlstone (mixture of clay and calcium carbonate), and the main organic constituent is kerogen.
It is a potential petroleum source rock that would have generated hydrocarbons if it had been subjected to geological burial at the requisite temperatures and pressures for a sufficient time.

4. Where is Oil Shale found?
Russia
Canada
Estonia UK
France
Italy
United States
Israel
China
Morocco
Jordan
Egypt
Zaire
Brazil
Australia
Trillion Barrels of Shale Oil Worldwide 4

5. Oil Shale Pyrolysis
Several complex physical changes occur during the thermal conversion of kerogen in oil shale to produce hydrocarbons.
It is (1) the formation of oil and gas resulting from kerogen decomposition, (2) the creation of pore structure in the shale, (3) the fluid flow through the pore channels and the ultimate recovery which are of interest in this research.
The pore structure and the connectivity of the pore space are important characteristics which determine fluid flow. A study investigating the nature of the pores and subsequent permeability is essential.

6. Previous Literature
X-ray micro tomography has been applied to describe thermal cracking of Chinese Fushun oil shale at different temperatures for sample sizes of 7 mm (Kang et al., 2011).
A study on the characterisation of oil shale using X-ray tomography before and after pyrolysis has also been presented in recent literature (Tiwari et al., 2013, Mustafaoglu, 2010).
However, the exact mechanism of kerogen decomposition at the pore-scale and the flow behaviour of the produced oil and gas are unknown.
Therefore, with improved imaging techniques and advanced modelling methods this research is intended to make a valuable contribution to the oil shale industry.
Before Pyrolysis
After Pyrolysis (500°C, 100°C/min, 24 hours)
Source: Tiwari et al. (2012)

7. Research Aims & Objectives
The aim of this research is to describe how oil shale reacts at a given temperature where kerogen decomposes to produce oil and gas, and to understand the dynamics of the subsequent two-phase flow through the pore space created.
As well as temperature (300°C, 400°C, 500°C, 600°C), heating rate (1, 10, 100°C/min), this study will investigate the effects of stress state/lithostatic load.
The goal is to have a model based on experimental observation of the physico-chemical mechanisms that govern the process, which will be able to advise on how the recovery can be optimised.  
Emphasis on understanding changes in pore structure and fluid distribution.

8. Research Aims & Objectives

9. Primary sample – Kimmeridge Oil Shale
Kimmeridge oil shale samples collected from the cliffs in Dorset
This oil shale is from the Upper Jurassic and is the primary sample for this study
The Kimmeridge Clay Formation contains shales with some of the highest total organic carbon (TOC) contents 20%+
Bulk density ~ 1.7g/cm3

10. Kimmerdige Oil shale – mineral analysis
Chemical Formula
Mineral %
Quartz
SiO2
10.4
Pyrite
FeS2
1.3
Oligoclase
Na0.8Ca0.2Al1.2Si2.8O8
14.2
Microcline
KAlSi3O8
3.8
Illite
KAl2[AlSi3O8](OH)2
6.2
Calcite
CaCO3
22.8
Dolomite
CaMg(CO3)2
23.4
Total Organic Carbon (TOC)
24.2

11. Micro-CT: before and after pyrolisis
Pixel size of 1µm
Exposure time: 10 seconds
3200 projections in 11 hours
Sample size: 6mm
Xradia micro-CT scanner
Image size: voxels
After Pyrolysis (500°C, 10°C/min, 3 hours)
Before Pyrolysis

12. FIB – Focused Ion Beam Helios NanoLab 600
Uses Ga+ ion beam to mill a small amount of material from the surface
The generated secondary electrons (or ions) are collected to form an image of the surface of the sample
Sample size: 6mm

13. Nano-CT: dry image Photon Energy: Monochromatic beam, 11.8 keV
Voxel size: 60 nm
Exposure time: 15 s per projection
Total tomography time: 3 to 4 hours (800 projections)

14. Future work: Imaging

15. Heating Oil Shale - Furnace
Furnace has capability to reach ~ 1400°C.
Heating rates of 1, 10 and 100°C/min to be tested.
10mm holes on either side of the furnace to allow penetration of X-rays for imaging.
Two ceramic end caps placed on either end for a closed system.
Ex-situ experiments to be performed initially.
In-situ experiments to be performed at a later stage.

16. Future work: Modelling
Modelling the kerogen decomposition to produce oil and gas and the flow of the fluids through the created pore structure using pore network modelling and also a Finite Volume method.
The research questions to be answered include:
Does the solid-fluid conversion occur at the rock matrix-kerogen interface, at the centre of the organic matter, or randomly?
What is the percolation threshold point at which the pores become connected?
What are the changes in fluid distribution as pyrolysis progresses?
The network will be periodically updated by extracting it over selected times. Initially, the parameters studied will include pore size distribution, connectivity (topological), and the rate of fluid formation as a temperature dependence. 

17. Pore-Scale Imaging and Analysis of Oil Shale
Thank You!
Tarik M. A. Saif
PhD Student (Petroleum Engineering)
Earth Science and Engineering Department
Imperial College London

18. References
Aboulkas, A., & El Harfi, K. (2008). Study of the kinetics and mechanisms of thermal decomposition of Moroccan Tarfaya oil shale and its kerogen. Oil shale, 25(4),
Doan VL., (2011). Oil Shale Pyrolysis Laboratory & Technique. Oil Shale Symposium.
Han X., Xiumin J., Lijun Y., Zhigang C., (2006). Change of pore structure of oil shale particles during combustion. Part 1. Evolution mechanism. Energy Fuels; 20,
Kang Z., Yang D., Zhao Y., Hu Y., (2011). Thermal cracking and corresponding permeability of Fushun oil shale. Oil shale; 28,
Külaots, I., Goldfarb, JL., & Suuberg, EM., (2010). Characterization of Chinese, American and Estonian oil shale semicokes and their sorptive potential. Fuel, 89(11),
Lin CL., Miller JD., (2011). Pore scale analysis of Oil Shale/Sands pyrolysis. Prepared for the United States Department of Energy and the National Energy Technology Laboratory. Oil & Natural Gas Technology.
Mustafaoglu O., (2010). Charactrization and pyrolysis of oil shale samples: An alternative energy option. LAP Lambert Academic Publishing.
Nazzal, JM., (2002). Influence of heating rate on the pyrolysis of Jordan oil shale. Journal of analytical and applied pyrolysis, 62(2),
Tiwari, P., Deo, M., Lin, CL. & Miller, JD., (2012). Characterization of Core Pore Structure Before and After Pyrolysis using X-ray Micro CT. Fuel, 2013, 107,
Williams PT., Ahmad, N., (1999). Influence of process conditions on the pyrolysis of Pakistani oil shales. Fuel, 78(6),