Feasibility of time-lapse VSP monitoring at the Aquistore CO2 storage site using a distributed acoustic sensing system

Abstract

The Aquistore carbon storage project, located near Estevan, Saskatchewan, Canada, aims to employ 3D time-lapse seismic techniques to monitor injected CO 2 at depths of 3100-3350 m. During early stages of the injection schedule, vertical seismic profiling (VSP) will primarily be utilized, given its inherent advantages in imaging close to the borehole. Distributed acoustic sensing (DAS) possesses the capability of providing a cost-efficient, high-resolution alternative to traditional geophone methods in VSP. In this study, an evaluation is made of baseline DAS and traditional geophone VSP data from an observation well located 150 m away from the injection well. Comparative images are analyzed for quantities of injected CO 2, ranging from 27 kt to 330 kt to determine the visibility of the CO 2 plume over time. The study demonstrated that DAS VSP is a feasible technique for reservoir monitoring at the Aquistore site. The CO 2 plume should be visible near the borehole after 90 days (27 kt of CO 2) of injection, with increasing clarity over a three-year duration.

The Use of Distributed Acoustic Sensing for 4D Monitoring Using Vertical Seismic Profiles: Results from the Aquistore CO2 Storage Project

“…No significant residuals were observed in the Black Island, as saturation levels have not exceeded seismic detectability thresholds. Based on the findings of Harris et al (2016), it is expected that a…”

“…In our case, the fiber is not functional below ~2800 m and the nearest-offset shot that is suitable for time-lapse analysis is ~150 m away from the observation well. The resulting specular blind-spot includes the entire location that the CO2 was expected to occupy at the time of the monitor survey (Harris et al, 2016). In order to image the reservoir in the immediate vicinity of the observation well with sufficient fold, the dip-limited migration aperture was set to ±15°.…”

“…Further shot selection resulted in a total of 50 shot gathers comprising 44 700 traces for migration. This subset included only shots located within 1000 m of the observation well, as predictions indicate the plume would be completely confined within a 500 m radius (Harris et al, 2016). Shot gathers were also omitted if their postprocessing difference gathers still exhibited strong upgoing energy, indicating poor repeatability.…”

“…Preliminary seismic modeling presented in Harris et al (2016) established the feasibility of using DAS VSP to monitor the injected CO2 plume at Aquistore for a minimum quantity of 27 kt. This conclusion was based on fluid flow simulations conducted in advance of any CO2 injection at the site and were based on hypothetical injection scenarios.…”

“…Direct comparisons have been made of VSP data recorded simultaneously at the Aquistore site using both downhole geophones and DAS (Harris et al, 2015;Harris et al, 2016;Miller et al, 2016). These comparisons have demonstrated that, although traditional three-component geophones recorded data with a higher S/N and a larger bandwidth, the DAS system provided an order of magnitude increase in spatial sampling (i.e., trace spacing) and a far larger recording aperture.…”