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

Unconventionals: Oil Shale

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.

Where is Oil Shale found? Russia Canada Estonia UK France Italy United States Israel China Morocco Jordan Egypt Zaire Brazil Australia 2.8-3.3 Trillion Barrels of Shale Oil Worldwide 4

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.

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)

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.

Research Aims & Objectives

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

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

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: 10003 voxels After Pyrolysis (500°C, 10°C/min, 3 hours) Before Pyrolysis

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

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)

Future work: Imaging

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.

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. 

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 Email: t.saif13@imperial.ac.uk

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