Fluid expulsion and microfracturing during the pyrolysis of an organic rich shale

Significance 

Demand and supply of oil and gas are set to change, but world oil and gas consumption are still increasing, and it is likely that consumption will continue to rise for some time, despite mounting environmental pressures to control the emission of greenhouse gases. One reason for the increase use of fossil fuel is due to underdeveloped alternative renewable energy sources. To this end, identification of the formation process and factors controlling the flow of hydrocarbons responsible for oil and gas formation has recently attracted significant attention of researchers. This will enable a better understating of the migration pathways for easy exploration and extraction.

The chemical composition of mature kerogen determines the amount of oil and gas. Generally, kerogen (fossilized organic matter) is categorized into type I, type II, type III and type IV with the highest to lowest hydrocarbon content respectively. However, type II kerogen is highly desirable as it produces oil and natural gas in large amount. Several approaches have been developed to explore the formation of hydrocarbons from kerogen and the factors affecting the primary oil and gas migration pathways.

Recently, University of Oslo researchers: Dr. Hamed Panahi, Dr. Maya Kobchenko, Professor Paul Meakin, Professor Dag Kristian and Professor François Renard assessed the primary migration of oil and gas and the factors affecting their transportation mechanisms. In particular, they designed a system based on an externally heated pressurized autoclave to measure the fluid pressure changes due to the maturation of the organic matter and expulsion of the hydrocarbon. They wanted to characterize the fluid expulsions at different temperatures and analyses their influence on the microfractures appearances. The study has been published in the research journal, Fuel.

Briefly, shale samples were confined under low pressure and heated at a varying temperature in the range of 210 °C-320 °C. Next, changes in static pressure, and dynamic fluid pressures at constant temperature were determined using pressure and piezoelectric sensors respectively. As the shale matured, the expulsion activities were analyzed at different temperatures based on the proposed model to determine the relationship between the temperatures and the amount of gases produced.

The authors observed that the fluid accumulated in the shale until a fairly large volume enough to start the expulsion was obtained. Expulsion of hydrocarbon occurred in bursts. Microfractures formed due to thermal decomposition of kerogen were noted to be parallel to the bedding plane with a few being perpendicular. It was found that an increase in the waiting time resulted in a corresponding decrease in the bursts frequencies, and that a range of burst amplitudes could be represented by a power law..

In summary, the study by University of Oslo researchers carefully analyzed four fluid expulsion stages including early stage, second stage, third stage and production of the fluid. High resolution synchrotron X-ray tomography was used to image the microfractures, and this confirmed that the primary migration of hydrocarbons is due to percolating microfracture networks. The paper, published in the journal Fuel, will advance exploration and extraction of oil and gas.

The work reported in this article, which focuses on static and dynamic pressure measurements, is part of a larger body of research on the mechanisms of primary migration. Time-resolved X-ray microtomography, enabled by a synchrotron X-ray photon source (beamline ID19 at the European Synchrotron Radiation Facility), and recent advances in the analysis of three-dimensional X-ray tomograms have played an important role in this work on primary migration.

Fluid expulsion and microfracturing during the pyrolysis of an organic rich shale - Advances in Engineering
A) Left: Steel sample holder that houses some of the samples, Center: A sample on top of a reinforced wave spring, Right: A sample after the experiment; B) Left: Hydrocarbon coating on the sample holder, Center: Hydrocarbon coating on the inner wall of the vessel at the end of one of the experiments, Right: A sample after one of the experiments with both vertical and horizontal fractures; C) X-ray micro-tomography image of a Green River Shale sample after heating at a temperature of 350 ⁰C for 6 days, which also shows horizontal and vertical fractures. Bed-parallel and bed-perpendicular fractures were produced during the expulsion of hydrocarbon. The voxel size was 17 micrometers. The 3D rendering shows the fracture network.

About the author

Paul Meakin is an Adjunct Professor in the Temple University Department of Physics. He received a BSc. In chemistry (first class honors) from Manchester University (UK) and a PhD in physical chemistry from the University of California, Santa Barbara. He is a member of the Norwegian Academy of Science and Letters and a Fellow of the American Physical Society. He is the sole author of a book titled Fractals, scaling and growth far from equilibrium (674 pages, Cambridge University Press, 1998).

He has published over 400 papers in refereed scientific journals and he has a Web of Science h-index of 82. He received the Gunnar Randers Research Prize from King Harald V of Norway in 2007 for “his pioneering research into complex materials and processes”.

About the author

Hamed Panahi received a PhD in physics from University of Oslo and Master’s degree in chemical and petroleum engineering from University of Tehran. In various capacities he was involved in many projects in the oil and gas, renewable resources and environment over the course of some 16 years. He started his career as a project engineer, process engineer and petroleum engineer and worked his way up to project coordination and project management at the Norwegian oil company Statoil (now Equinor). He also worked as an asset owner representative supervising multiple mega projects and worked with Exxonmobil, BP, Eni, Total and Petrobras in several projects.

About the author

François Renard is Professor of Geosciences at the Njord Centre, Department of Geosciences, University of Oslo in Norway, and Professor of Earth Sciences at Institute of Earth Sciences at the University Grenoble Alpes in France. He received two Master Degrees from the Ecole Normale Supérieure in Lyon and the University Pierre et Marie Curie in Paris and a PhD in geophysics from the University of Grenoble, France. He is a former member of the Institut Universitaire de France. He has published over 160 papers in refereed scientific journals and he has a Web of Science h-index of 42.

Reference

Panahi, H., Kobchenko, M., Meakin, P., Dysthe, D., & Renard, F. (2019). Fluid expulsion and microfracturing during the pyrolysis of an organic rich shale. Fuel, 235, 1-16.

Go To Fuel

Check Also

Propane Deresining – A Pilot Plant Study to Optimize Quality and Yield of Deresined Oil - Advances in Engineering

Propane Deresining – A Pilot Plant Study to Optimize Quality and Yield of Deresined Oil