Pore-Scale Analysis of Oil Shale: Planned Research Tarik Saif Supervisors: Prof. Martin Blunt & Dr Branko Bijeljic 13 January 2014

Presentation Outline Introduction Oil Shale Overview Literature Review Research Aims & Objectives Workflow Plan Summary References

What is Oil Shale? The term Oil Shale is a misnomer because it does not contain oil, and is not 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 Production Processes Traditional and current mining methods have been used to extract the oil shale before retorting. An alternative but currently experimental process referred to as in situ pyrolysis involves heating the oil shale while it is still underground, and then pumping the resulting liquid to the surface. Example: Shell In-Situ Conversion Process (Pilot Test (Colorado, USA) Source: US DOE, 2008

Oil Shale Pyrolysis Several complex physical changes occur during the thermal conversion of kerogen in oil shale to produce hydrocarbons. It is the formation of oil and gas resulting from kerogen decomposition, the creation of pore structure in the shale, 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 Compositional and kinetic studies of oil shale pyrolysis from Green River formation of Utah, Wyoming and Colarado (Le Doan, 2013), Chinese oil shale (Han et al., 2006), Estonian oil shale (Külaots et al., 2010) and Moroccan oil shale (Aboulkas and El Harfi, 2008). Many studies have reported the effects of pyrolysis conditions, including heating rate, final heat treatment temperature, time at final temperature and sweeping gas atmosphere on product yield and composition using both ground and core samples. The effect of heating rate has been studied in terms of its effects on yield and kinetic parameters (activation energy). At lower heating rates (<10°C/min), liquid product yield was found to be higher than at higher heating rates (Williams and Ahmad, 1999, Nazzal, 2002).

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 mm3 (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 more sophisticated modelling methods this research is intended to make a valuable contribution to the oil shale industry. Before Pyrolysis After Pyrolysis (500°C) 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 pressure and 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.

Workflow Plan Kimmeridge oil shale samples will be collected from the cliffs in Dorset in early 2014. The organic composition of the oil shale will vary within the oil shale bed. To address this variability in resource composition and its effect on the pyrolysis product distribution, a number of measured samples will be collected. Elemental analysis of the Kimmeridge oil shale samples will be performed.

Workflow Plan Dry images will be taken to identify rock and kerogen phases. This stage will allow the exploration of the capabilities of micro-CT (~µm), nano-CT (~50nm) and FIB-SEM (resolution ~5nm), in relation to the sample physical size and in terms of the number of image voxels. This is required for simulation by network modelling or directly on the voxels, if possible.

Workflow Plan The 3rd stage will focus on 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: Is the solid/fluid conversion occurring at the rock matrix walls, in the pore centres, or randomly? Does growth of the first pores take place at the rock matrix walls or from the centre of the throats/pores? What is the percolation threshold point at which the pores become connected? The network will then 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. 

Experimental Set-up Source: Lin and Miller (2011)

Summary

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), 426-443. 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, 2408-12. Kang Z., Yang D., Zhao Y., Hu Y., (2011). Thermal cracking and corresponding permeability of Fushun oil shale. Oil shale; 28, 273-83. Külaots, I., Goldfarb, JL., & Suuberg, EM., (2010). Characterization of Chinese, American and Estonian oil shale semicokes and their sorptive potential. Fuel, 89(11), 3300-3306. 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), 225-238. 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, 547-554. Williams PT., Ahmad, N., (1999). Influence of process conditions on the pyrolysis of Pakistani oil shales. Fuel, 78(6), 653-662.