CO2貯留研究グループ業績

Abstract

The Effect of Lamina on Super Critical CO2 Behavior in Porous Sandstone: Investigations from Elastic Wave Velocity
Journal of MMIJ, , Vol.128, 511-518 .
Keigo KITAMURA, Ziqiu XUE, Shun CHIYONOBU, Tatsuya YAMADA, Osamu NISHIZAWA

To better understand trapping mechanisms of CO2 in reservoir, we try to elucidate the effect of thin and low-porosity lamina in porous Tako sandstone on CO2 flow by experiments and numerical simulations. Tako sandstone is characterized by the well-developed and low porosity lamina, wherer the intergranular space is filled with precipitated iron-rich minerals. We measure P-wave velocities(Vp)in three channels which are crossing through high porosity zone(Ch.A), on a lamina(Ch.B), and beneath the lamina(Ch.C)during CO2 injection stage(drainage)and water re-injection stage(imbibition). In drainage, all channels show large Vp-reduction over 10%. In imbibition, they indicate Vp-increases but different recovery patterns with injecting CO2-saturated water. After 250 ml water injection, Vp of Ch.A and Ch.B almost recover from Vp-reduction in drainage. On the other hand, Vp of Ch.C still has a reduction about 4%. We then try 2D core-scale flow-simulations by using TOUGH-2 to confirm the effect of lamina on fluid flow and pattern of CO2 distribution. In drainage, CO2 has large mobility and moves upward vigorously to the top-end of core at 20ml CO2-injection. After reaching the top-end, CO2 invades lamina zone and raises CO2-saturation during drainage. In enhanced case of difference between porosity-permeability relation, the result of simulation indicates the strong heterpgeneity of CO2-distribution pattern, which shows clear low-CO2 saturation of the lamina zone and obvious high-CO2 saturation of the zone of direct beneath of lamina. In imbibition, CO2 saturation decreases rapidly after 40ml water injection. However, the zone of beneath the lamina keeps high CO2 saturation after 100ml water injection. These results suggest that the lamina in Tako sandstone behave as barriers of CO2 flow. This assumption is supported by results of Vp-measurement, because the channel of beneath a lamina still shows a Vp-reduction about 4% after 250ml water injection.