A New Method For Sub-resolution Porosity Modelling On Rock Samples Using X-ray Microtomography And Pore Network Modelling Techniques

Resumo

The heterogeneity of carbonate rocks at multiple scales presents challenges in terms of estimating their
petrophysical properties and predicting the full capacity of oil and gas reservoirs. Digital analyses are increasingly
used to study the complex pore structure of carbonate rocks by means of such techniques as X-ray tomography.
With this approach, one usually needs to find a compromise between the field of view (i.e., the volume dimension)
and the resolution (i.e. the smallest size of distinguishable structures). For large volumes, this usually means that
a fraction of the pore space, whose size is below the resolution, is not visible (i.e., the sub-resolution porosity or
unresolved porosity). In this work, X-ray microtomography images of a carbonate rock with a significant fraction
of porosity below the image resolution will be used to estimate flow properties. The presence of unresolved
porosity is supported by mercury intrusion capillary pressure (MICP) and nuclear magnetic resonance (NMR)
data. A new method is proposed for modeling the sub-resolution porosity of the images in which the topology of
unresolved pores bodies/throats is correlated with the CT values of regions below the imaging resolution. Within
these regions, preferential paths between visible pores will be determined using the minimal distance weighted by
a probability function. Connections between visible pores are then created by assigning pore bodies and throats
along these paths, whose dimensions are compatible with MICP measurements. Finally, results of numerical flow
simulation with obtained pore network model are shown, demonstrating the improvement in the permeability and
the potential of the proposed methodology.