Role of micro-cracks on fluid flow and mechanical response of chalk formations

Carlos Augusto Soares Ferreira: How modelling fractured porous media might help us in the energy transition.

Porous media is a concept almost everyone is familiar with and it is present in our everyday lives, for example in the sponges we use for washing and in water filters. In fact, the phenomenon of fluid flow through deformable porous media is important in many areas of science and engineering, such as soil mechanics, geomechanics, geosciences, tissue mechanics (biomechanics), etc. In addition, this phenomenon is especially important for the future planning of carbon capture and storage (CCS) practices and geothermal applications, as Denmark moves towards becoming one of the green energy leaders in the world. But how is fluid flow through deformable porous media related to fluid production from hydrocarbon and geothermal reservoirs as well as fluid injection for CCS practices?

First, subsurface reservoirs, such as the chalk formations in the Danish part of the North Sea, are deformable porous media and “fluid production/injection” translates into “fluid flow”. Second, chalks are filled with these so called "micro-cracks", which basically are tiny fractures that may not be visible without magnification. They may be too small to the naked eye, but on the other hand they are large compared to the chalk pores’ size. This means that there is a significant difference between fluid transmission through the micro-cracks and through the pore network, because of course the fluid would flow preferentially through a large crack space rather than through a very restricted small pore space.

And despite being subject of study and research for a long time, the proper mathematical description of deformable porous media still poses a challenge in terms of accuracy. Add "fractured" before "porous media” in "deformable porous media" and the challenge becomes substantially greater, which is the case for chalk formations. Even though the micro-cracks are one the most influential and common traits in chalks, their role in the fluid flow phenomenon is often neglected or underestimated due to their complexity.

But why do we want to describe fluid flow in chalk formations accurately? Because it affects deeply the production performance of subsurface reservoirs, and everything associated with it. And in the decades to come, we will need the subsurface fluid to supply the energy demand, during the ongoing energy transition. Having that in mind, we need the production from hydrocarbon and geothermal reservoirs to impact minimally the environment, which is only possible if, among other things, we understand profoundly what is happening in the subsurface. And to understand, we build mathematical and numerical models and we run simulations using these models to check the possible outcomes of each decision we make.

For that effort, the CT-scanners from DHRTC can be used for dynamical imaging of fluid flow through rock samples. The quantitative information extracted from this process will be used to validate our mathematical and numerical models of the phenomenon. And with accurate models, our understanding of the subsurface processes can be applied to practical cases to predict (and prevent) unwanted outcomes of the production strategy. In other words, this knowledge will help us supply the energy demand with minimum impact to the environment while planning and carrying out the energy transition towards a sustainable future.

PhD project

By: Carlos Augusto Soares Ferreira

Section: Danish Hydrocarbon Research and Technology Centre (DHRTC)

Principal supervisor: Hamidreza Maghami Nick

Co-supervisor: Mohammad Reza Hajiabadi

Project title: Role of micro-cracks on fluid flow and mechanical response of chalk formations

Term: 01/10/2020 → 30/09/2023


Carlos Augusto Soares Ferreira
Research Assistant
DTU Offshore
+45 81 94 38 63


Hamid Nick
Senior Researcher
DTU Offshore
+45 93 51 14 97


Mohammad Reza Hajiabadi
DTU Offshore