Monitoring and Quantification of Stored CO2 with Combined P-wave Velocity and Resistivity

al., 2008, Xue et al., 2002, 2005; Xue & Ohsumi 2004a, 2004b, 2005; Onishi et al., 2006). In the most CO2 storage sites, seismic survey has been conducted to monitor the injected CO2. From the recent injection projects, seismic survey shows great results for monitoring the migration of the CO2 in the reservoirs such as Sleipner or Nagaoka site (Arts et al., 2002, 2004; Bunge et al., 2000; Davis et al., 2002; Xue et al., 2006). In Nagaoka project, studies have attempted to estimate the CO2 saturation around the observation wells by using the results of well logging and laboratory studies (Kim et al., 2009b, Nakatsuka et al., 2009, Xue et al., 2006). When estimating CO2 saturation from seismic survey, Gassmann’s theory which consisted of bulk modulus of the saturated porous rock has been often used (Gassmann, 1951). When the saturation was less than 20%, P wave velocity shows good response but when the saturation was more than 20%, P-wave velocity became less sensitive to CO2 saturation. P-velocity is not sensitive to gas saturation in high gas saturation regime (Sg>20%) for either homogenous saturation or patchy saturation with patchy size << wavelength (Xue & Lei 2006, Lei & Xue 2006). To overtake this weak point of seismic monitoring for the estimation of CO2 saturation, there is a need for estimating accurate CO2 saturation using resistivity. In this paper, laboratory experiments have been conducted to monitor combined P-wave velocity and resistivity simultaneously in porous sandstone during CO2 injection process.