CO2 injection effect on physical properties of greensand from the North Sea

The objective of this study is to investigate CO2 injection effects on physical properties of greensand reservoir rocks from the North Sea. Greensands are sandstones composed of a mixture of clastic quartz grains and glauconite grains. A CO2 flooding experiments was carried to inject the CO2 into brine saturated samples and flush the CO2 saturated samples with brine at reservoir conditions.

Helium porosity, Klinkenberg permeability, and specific surface area (SSA) by BET were measured on dry greensand samples before and after the CO2 experiment. NMR T2 distribution and electrical resistivity were measured on brine saturated greensand samples before and after the CO2 experiment. Ultrasonic P-and Swave velocities were measured on brine saturated samples as well as on dry samples.

Our laboratory results show that CO2 injection has no major effect on porosity, electrical and elastic properties of greensand. The Klinkenberg permeability of greensand increased after CO2 injection. An NMR T2 distribution and NMR permeability modeling approach was tested to evaluate the effect on matrix permeability of CO2 injection.

It appears that permeability after CO2 injection increased due to the increase of macro-pores in the greensand. The increase of macro-pores size is probably due to migration of fine pore-filling minerals.