Imaging the Aquistore reservoir after 36 kilotonnes of CO₂ injection using distributed acoustic sensing

Abstract

Aquistore is a geologic [Formula: see text] storage project that is using a deep saline formation as a storage reservoir. From April 2015 to February 2016, approximately 36 kilotonnes of [Formula: see text] were injected into the reservoir at a depth of 3130–3350 m. We have developed an analysis of distributed acoustic sensing (DAS) 3D vertical seismic profiling data acquired in February 2016, marking the first seismic survey since injection began. The VSP data were processed in parallel with baseline preinjection data from a November 2013 survey, with the objective of detecting and characterizing the subsurface [Formula: see text] plume and evaluating the repeatability of DAS in a reservoir monitoring project. A single processing sequence was devised that (1) accurately imaged the reservoir for the baseline and monitor data and (2) attained adequate repeatability to observe time-lapse differences related to the presence of [Formula: see text]. Repeatability was somewhat compromised by the less advanced noise cancellation methodology of the DAS system used for the baseline survey. In the final cross-equalized migrated data volumes, normalized root-mean-square ([Formula: see text]rms) difference values of [Formula: see text] were attained at the reservoir level indicating good repeatability compared with most surface seismic studies. An injection-related amplitude anomaly with maximum [Formula: see text]rms values of approximately 0.7 is apparent in the Deadwood Formation of the reservoir, whereas no significant [Formula: see text]rms anomalies were observed near the injection and monitoring wells in the Black Island Member or above the reservoir.

Seismic monitoring of a small CO2 injection using a multi-well DAS array: Operations and initial results of Stage 3 of the CO2CRC Otway project

“…There are added benefits of placing seismic receivers all the way to, or even below, the injection interval. Proximity to the injection interval eliminates blind spots in illumination, which, for instance, has affected 4D VSP at Aquistore (Harris et al, 2017). By monitoring reflectivity changes above the storage interval as well as travel time delays within and below the injection interval can help to constrain velocity-saturation relations (Al Hosni et al, 2016).…”

A Review of Distributed Fiber–Optic Sensing in the Oil and Gas Industry

“…A limitation of the VSP survey produced by the fiber-optic DAS is that it provides an estimate of the subsurface properties in the proximity of the optical fiber, which is a drawback of the geophone arrays as well. However, the use of fiber-optic DAS for time-lapse (also known as 4-D) VSP can monitor the movement of fluids on a reservoir scale [57].…”

Seismic Applications of Downhole DAS

“…In the Gulf of Mexico, deepwater DAS measurements reached a 7% discrepancy between surveys, measured through the normalized root mean square (NRMS) method [84], a figure which is considered excellent [53]. Therefore, 4-D surveys can also be reliably conducted in wells that are Time-lapse DAS VSP has been used to track CO 2 in the Aquistore project in Canada [86,87] and South West Hub in Australia [88]. The reflectivity of the target reservoir varies due to the injection of CO 2 , and these changes can be detected by a time-lapse of DAS records.…”

“…Time-lapse DAS VSP has been used to track CO 2 in the Aquistore project in Canada [ 86 , 87 ] and South West Hub in Australia [ 88 ]. The reflectivity of the target reservoir varies due to the injection of CO 2 , and these changes can be detected by a time-lapse of DAS records.…”