Abstract

AbstractWe have studied the impact of heterogeneity on relative permeability and residual trapping for rock samples from the Bunter sandstone of the UK Southern North Sea, the Ormskirk sandstone of the East Irish Sea, and the Captain sandstone of the UK Northern North Sea. Reservoir condition CO2‐brine relative permeability measurements were made while systematically varying the ratio of viscous to capillary flow potential, across a range of flow rates, fractional flow, and during drainage and imbibition displacement. This variation resulted in observations obtained across a range of core‐scale capillary number . Capillary pressure heterogeneity was quantitatively inferred from 3‐D observations of the fluid saturation distribution in the rocks. For each of the rock samples, a threshold capillary number, , was found, below which centimeter‐scale layering resulted in a heterogeneous distribution of the fluid phases and a commensurate impact on flow and trapping. The threshold was found to be dependent on the capillary number alone, irrespective of the displacement path (drainage or imbibition) and average fluid saturation in the rock. The impact of the heterogeneity on the relative permeability varied depending on the characteristics of the heterogeneity in the rock sample, whereas heterogeneity increased residual trapping in all samples above what would be expected from the pore‐scale capillary trapping mechanism alone. Models of subsurface CO2 injection should use properties that incorporate the impacts of heterogeneity at the flow regime of interest or risk significant errors in estimates of fluid flow and trapping.

Highlights

  • Predictions of the flow behaviour and storage capacity of CO2 in subsurface reservoirs are sensitive to the underlying multiphase flow properties of the system [Mathias et al, 2013; Yoshida et al, 2016; Szulczewski et al, 2012]

  • We have studied the impact of heterogeneity on relative permeability and residual trapping for rock samples from the Bunter sandstone of the UK Southern North Sea, the Ormskirk

  • Faults with the X-ray scanner affected three slices of the Captain sandstone sample, and those slices are absent in the figure

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Summary

Introduction

Predictions of the flow behaviour and storage capacity of CO2 in subsurface reservoirs are sensitive to the underlying multiphase flow properties of the system [Mathias et al, 2013; Yoshida et al, 2016; Szulczewski et al, 2012] These are primarily the capillary pressure, relative permeability, and residual trapping characteristics. We used an extension of the conventional core analysis protocol, characterising CO2-brine flow behaviour across a range of fluid flow velocities, fractional fluid flow, and during drainage and imbibition displacement This allowed for a characterisation of capillary heterogeneity within the framework of the capillary-viscous flow regimes and a direct link to the impacts on the macroscopic fluid mobility (relative permeability) and trapping

Sample locations
Routine petrophysical properties
Relative permeability and capillary trapping
Trapping
Characterising capillary pressure characteristic heterogeneity
Heterogeneity in the rock samples
The Bunter Sandstone
The Ormskirk Sandstone
The Captain sandstone
Discussion and Conclusions

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