Geophysical Monitoring for Geologic Carbon Storage. Группа авторов

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Geophysical Monitoring for Geologic Carbon Storage - Группа авторов


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higher permeability (Fig. 2.4). The correlation of this high permeability feature with a northwest trending break in seismic topography suggested that the carbon dioxide injected into well KB‐501 might flow preferentially along a fault zone on the flank of the anticline defining the field (Vasco et al., 2008).

Schematic illustration of (a) Onset time of the most rapid change in reservoir volume. (b) Logarithm of the permeability multiplier found by solving equation 2.20 along the trajectories. Schematic illustration of (a) Detailed view of range change above well KB-502 following 1,060 days of injection. (b) Seismic horizon displaying pushdown, most likely due to velocity decreases associated with the migration of injected carbon dioxide.

      A homogeneous elastic model of the overburden did not produce the correct range change estimates, and hence an inversion based upon a model with uniform properties led to erroneous depth estimates for a tensile source. Thus, elastic layering, derived from well logs, had to be included in the modeling. The total range change from 12 July 2003 through 19 March 2007 was used to infer the distribution of volume change within the reservoir and the distribution of aperture change over the fault/fracture zone. It was found that the range changes could be matched by a combination of reservoir volume change and cumulative tensile opening of a fault/fracture zone confined to lie at depths within 100 m of the reservoir (Vasco et al., 2010). The lateral extent of the fracture opening was much greater, extending over 3 km from the injection point. Aspects of the fault/fracture zone were subsequently supported in an analysis of three‐dimensional surface seismic data. In particular, Gibson‐Poole and Raikes (2010) noted that time shifts, thought to be due to the injection of carbon dioxide and the resulting seismic velocity change, followed a remarkably linear zone with near parallel boundaries located between the two lobes of range change (Fig. 2.5). The orientation of the seismic feature agreed rather well with the azimuth of 135 degrees required to fit the range‐change data. These conclusions were subsequently supported by the work of Zhang et al. (2015, 2016).

       X‐Band InSAR and Multicomponent Displacement Data

      The Envisat C‐band satellite was deorbited on October 2010 and was no longer available for monitoring the range changes over the injectors at In Salah. Fortunately, several other satellite systems were functional as replacements before this date. In particular, the COSMO‐SkyMed (CSK) X‐band satellite pair were launched and operational before the loss of the Envisat satellite. Similarly, the TerraSAR X‐band satellite was also put in orbit, with a repeat cycle of 11 days. Thus, three X‐band satellites were accessible for estimating range changes at the In Salah site due to the injection of carbon dioxide. The repeat time attainable for these three satellites was 8 to 11 days, much better than the best possible Envisat return time of 35 days. The down side of this transition to X‐band data was the increased cost of data acquisition because the satellites have to be tasked to gather data at a particular site. However, with the help of British Petroleum, we were able to acquire X‐band SAR scenes from both ascending and descending acquisition geometries from 2009 until 2012.

      2.4.2. Aquistore, Canada


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