Pore-Scale Modelling Research at Imperial College , London

The aim of pore-scale modelling is to predict properties that are difficult to measure, such as relative permeability, from more readily available data, such as drainage capillary pressure. Martin Blunt (m.blunt@imperial.ac.uk), Professor of Petroleum Engineering, Centre for Petroleum Studies, Imperial College London presents some of the latest results obtained by his students (Per Valvatne, Mohammad Piri, Xavier Lopez, Mohammed Al-Gharbi and Hiroshi Okabe). For further information on the research together with recent papers and presentations see http://www.huxley.ic.ac.uk/research/PETENG/Perm/poreresearch.htm

An industrial consortium funded by BHP, Gaz de France, JNOC, PDVSA-Intevep, Schlumberger, Shell, Statoil, the DTI and the EPSRC has studied the use of pore-scale network modelling to predict single and multiphase transport properties. The pore space is represented by a topologically disordered lattice of pores connected by throats that have angular cross-sections - see Figure 1. This network represents a rock or sand pack of interest and is based on either a direct three-dimensional image of the pore space provided by micro CT scanning, or from reconstructing the geological processes by which the rock was formed.

By defining flow and displacement in each pore and throat of the network, we can simulate single and multiphase flow and from this predict macroscopic parameters, such as relative permeability and capillary pressure.

Figure1: (a) Reconstructed Pore Space at a Resolution of Three Microns, from Ø ren and co-workers at Statoil with (b) Its Topologically Equivalent Network Representation.

Figures 2 and 3 show our predicted relative permeabilities for a water-wet Berea core compared to experiments from Oak for primary drainage and waterflooding (imbibition). The predictions are excellent for this case, since we use a network based on a Berea sandstone and the wetting properties of the rock are easy to characterise.

Figure 2: Comparison of Network Model Predictions with the Steady-State Primary Drainage Experimental Data Measured on Berea Sandstone by Oak. In the Network Model it is assumed that the Oil/Water Contact Angle is Zero

Figure 3: Comparison of Network Model Predictions with the Steady-State Waterflood Experimental Data Measured on Berea Sandstone by Oak. In the Network Model it is Assumed that the Oil/Water Contact Angle is Randomly Distributed Between 62 and 82 Degrees

We can extend this approach to three-phase flow. Figure 4 shows the predicted oil relative permeability for gas injection into waterflood residual oil. The predictions are not so accurate, due to the uncertainty in determining the pore-scale physics in this case, but do better than current empirical three-phase models that require two-phase data as input.

Figure 4: Experimentally Measured Oil Relative Permeability for Gas Injection after Waterflooding (Crosses) from Oak Compared to Different Predictions: Network Modelling (line); and Empirical Three Phase Models that Extrapolate Two-Phase Data, Due to Baker (Dashed) and Stone (Squares)

Most reservoir rocks display mixed-wet or oil-wet characteristics. The network model presented in this paper can handle media of any wettability and has made accurate predictions of relative permeability and oil recovery for mixed-wet reservoir samples.

The aim of pore-scale modelling is to predict properties that are difficult to measure, such as relative permeability, from more readily available data, such as drainage capillary pressure. In addition, the model can readily be used to predict the changes in flow properties as the pore structure or wettability varies. As such it can be used to characterize multiphase properties in geological models. We have already shown that using pore-scale modelling to characterize variations in relative permeability leads to significantly different predictions of recovery at the field scale than traditional empirical modelling approaches.

Disclaimer: The material available on this website is designed to provide general information only. Whilst every effort has been made to ensure that the information provided is accurate, it does not constitute legal or other professional advice.
Please note: The Department of Trade and Industry cannot be held responsible for the contents of any pages referenced by an external link.