Time Lapse Well Logging to Monitor the Injected CO₂ at the Nagaoka Pilot Site

Abstract

A pilot-scale sequestration of CO₂ into an onshore aquifer has been conducted by Research Institute of Innovative Technology for the Earth (RITE) in cooperation with Engineering Advancement Association of Japan (ENAA) . The CO₂ injection site is located at Minami-Nagaoka gas field, Nagaoka city, Niigata prefecture, Japan. One injection well (IW-1) and three observation wells (OB-2, OB-3, OB-4) were drilled. CO₂ was injected into a thin permeable zone of the reservoir at 20-40 tonnes per day. The CO₂ injection started on 7 July 2003, and ended on 11 January 2005 with the total CO₂ amount of 10,400 tonnes. The pilot-scale demonstration allowed an improved understanding of the CO₂ movement in a porous sandstone reservoir, by conducting time-lapse geophysical well logs at the three observation wells. CO₂ breakthrough was identified by induction, sonic, and neutron logs. The sonic P-wave velocity decreased up to 28% at OB-2, and 13% at OB-4. Small effects of CO₂ saturation on resistivity resulted in small changes in induction logs when the reservoir was partially saturated.