3D vertical seismic profile acquired with distributed acoustic sensing on tubing installation: A case study from the CO2CRC Otway Project

Distributed acoustic sensing (DAS) can revolutionize the seismic industry by using fiber-optic cables installed permanently to acquire on-demand vertical seismic profile (VSP) data at fine spatial sampling. With this, DAS can solve some of the issues associated with conventional seismic sensors. Studies have successfully demonstrated the use of DAS on cemented fibers for monitoring applications; however, such applications on tubing-deployed fibers are relatively uncommon. Application of tubing-deployed fibers is especially useful for preexisting wells, where there is no opportunity to install a fiber behind the casing. In the CO2CRC Otway Project, we acquired a 3D DAS VSP using a standard fiber-optic cable installed on the production tubing of the injector well. We aim to analyze the quality of the 3D DAS VSP on tubing, as well as discuss lessons learned from the current DAS deployment. We find the limitations associated with the DAS on tubing, as well as ways to improve the quality of the data sets for future surveys at Otway. Due to the reduced coupling and the long fiber length (approximately 20 km), the raw DAS records indicate a high level of noise relative to the signal. Despite the limitations, the migrated 3D DAS VSP data recorded by cable installed on tubing are able to image interfaces beyond the injection depth. Furthermore, we determine that the signal-To-noise ratio might be improved by reducing the fiber length

Time-lapse seismic data inversion for CO2 sequestration CO2CRC Otway Project

The second stage of the CO2CRC Otway Project aims to explore the capabilities of various technologies - including time-lapse seismic - for the monitoring of small amounts of supercritical CO2/CH4 mixture. To this end, 15 kt of CO2/CH4 mixture was injected at the depth of 1.5 km into the saline sandstone reservoir in 2015-2016. A part of the monitoring program completed to date consists of a baseline survey followed by three monitor surveys after the injection of 5 kt, 10 kt and 15kt. Time-lapse seismic paired with simultaneous 4D inversion is a proven tool in reservoir monitoring because of its effectiveness in tracking the movement of CO2 and providing quantitative estimation of the changes in reservoir acoustic impedances. Here we demonstrate our workflow and the results of post stack model-based 4D seismic data inversion. The workflow was first tested and calibrated on the 4D synthetic time-lapse data. The calibrated workflow was then applied to the field seismic data

Offset VSP for monitoring of the injection of small quantities of CO2 - CO2CRC otway case study

Time-lapse seismic methods have become an essential part of monitoring and verification operations for carbon capture and storage (CCS) projects. Within the range of seismic methods, lapse borehole seismic methods have a potential to become the leading technology in on-shore CO2 monitoring due to quiet and stable sensor conditions, and minimal land access issues. In this paper we demonstrate the results of 4D offset vertical seismic profiling (VSP) surveys for detection of small amount of injected carbon dioxide. VSP datasets were acquired as a part of the monitoring program of Stage 2C of the CO2CRC Otway Geosequestration Project (Victoria, Australia). Borehole seismic program included recording data from four VSP offsets before commencement of injection and after injection of 5kt, 10 kt and 15 kt of CO2. The time-lapse analysis of the results shows capabilities of the VSP methodology to detect a small CO2 plume and track its evolution within a geological formation. The results demonstrate the potential of borehole seismic for permanent reservoir monitoring

Model-guided processing of time-lapse seismic for realtime monitoring of CO2 geosequestration - CO2CRC Otway Project case study

Carbon capture and storage is gaining acceptance around the world as one of the means for CO2 emission reduction. As the technology is just emerging, there is a necessity to address arising issues from technical details to geological hazards to public liaison. Otway Project is the first Australian attempt to address these issues. Stage 2C of the Otway Project is designed to identify the lower limit of CO2 detectable by seismic monitoring in saline aquifers. In this paper, we show that designing seismic processing workflows using a combination of baseline field data and a synthetic finite-difference 4D dataset speeds up time-lapse seismic processing to provide express time-lapse images of the plume with excellent signal-to-noise ratio and repeatability in less than a week upon completion of the monitor acquisition. Obtained time-lapse seismic images allow detection and tracking of the evolution of a small CO2-rich plume injected into a saline aquifer at 1500 m depth

3D vertical seismic profile acquired with distributed acoustic sensing on tubing installation: A case study from the CO2CRC Otway Project

Distributed acoustic sensing (DAS) can revolutionize the seismic industry by using fiber-optic cables installed permanently to acquire on-demand vertical seismic profile (VSP) data at fine spatial sampling. With this, DAS can solve some of the issues associated with conventional seismic sensors. Studies have successfully demonstrated the use of DAS on cemented fibers for monitoring applications; however, such applications on tubing-deployed fibers are relatively uncommon. Application of tubing-deployed fibers is especially useful for preexisting wells, where there is no opportunity to install a fiber behind the casing. In the CO2CRC Otway Project, we acquired a 3D DAS VSP using a standard fiber-optic cable installed on the production tubing of the injector well. We aim to analyze the quality of the 3D DAS VSP on tubing, as well as discuss lessons learned from the current DAS deployment. We find the limitations associated with the DAS on tubing, as well as ways to improve the quality of the data sets for future surveys at Otway. Due to the reduced coupling and the long fiber length (approximately 20 km), the raw DAS records indicate a high level of noise relative to the signal. Despite the limitations, the migrated 3D DAS VSP data recorded by cable installed on tubing are able to image interfaces beyond the injection depth. Furthermore, we determine that the signal-To-noise ratio might be improved by reducing the fiber length

Full waveform inversion of time-lapse offset VSP data - CO2CRC Otway project case study

Vertical Seismic Profile (VSP) is a useful tool for time-lapse monitoring. We conduct elastic 2D Full Waveform Inversion (FWI) on offset Vertical Seismic Profile (VSP) data to detect and quantify the time-lapse anomaly introduced by the CO2 geosequestration. Two datasets are being studied: a 2D synthetic dataset and the field dataset acquired during the Stage 2C of the CO2CRC Otway project. FWI proves capable of detecting the timelapse anomaly on both datasets, however, the strength of the anomaly in the field data inversion results is lower than expected from theoretical predictions. We attribute this to 3D effects, which are not taken into account. In the end, FWI proves to be an instrument that fits the monitoring problem well. The inversion of the monitor dataset is significantly quicker than the baseline inversion, which enables the time-lapse anomaly identification shortly after the data acquisition

CO2 Storage Site Characterisation using Combined Regional and Detailed Seismic Data: Harvey, Western Australia

Some 115 km 2 of regional 3D seismic data were acquired in the first quarter of 2014 near Harvey, Western Australia, for the needs of the South West CO2 Hub project. The survey proved to be of great importance for a regional characterisation of the reservoir, identification of the large structures and key geological interfaces. However, small to medium size structures of interest for the development of the static and dynamic models were poorly imaged in this survey as the recording geometry was adjusted for the greater depths, which was between 2 km and 3 km. To improve the imaging of the shallow structures, a high-resolution (nested) 3D survey centered at Harvey 4 well was undertaken in 2015 (Urosevic et al., 2015). This survey utilised a single geophone and single, 24 s long, broadband (6-150 Hz) sweep combined with high data density to improve signal to noise ratio that was initially lowered by not employing high-power sources and geophone arrays. The results of this high-resolution 3D survey demonstrate that high-density surveys are important even at the characterisation stage and are crucial for development of a detailed static model. For that purpose, both post and pre-stack inversions of these data were utilised to model distribution of paleosols, lenses of high clay content, which are assumed to serve as baffles for CO 2 upward migration. A good correlation was established between very low impedance values and increased percentage of paleosols and on the other end of the scale very high impedance values and low porosity sandstones. A pre-stack migrated high-resolution cube and the attribute derived from it, such as coherency and impedance, enabled improved structural and stratigraphic analysis around Harvey 4 well. The results shown were of a crucial importance for the containment studies, development of the dynamic model and establishment of the injection intervals

Distributed Acoustic Sensing Applied to 4D Seismic: Preliminary Results From the CO2CRC Otway Site Field Trials.

Carbon geosequestration requires the mapping and monitoring of the injected CO2 to assure the gas is safely stored in the formation. In this context, Distributed Acoustic Sensing (DAS) has the potential to reduce the costs of seismic operations and increase equipment survivability. Field demonstrations show that DAS can be used for reservoir monitoring in geosequestration applications but most of its studies are limited to borehole seismic surveys, while very little has been published towards DAS for surface seismic. To bridge this gap, capability for seismic monitoring using a 3D DAS array was tested during a test CO2 injection of the CO2CRC Otway Project (Victoria, Australia). DAS was deployed together with geophones along eleven receiver lines and data were acquired before and after the injection of 5kt, 10kt and 15kt of supercritical CO2. Processing of DAS data is very challenging due to strong angle dependence of its sensitivity and very large volumes of recorded data. Preliminary processing results show that we can identify the main reflectors but noise is still strong. The results also show strong azimuth dependence of DAS sensitivity

Surface orbital vibrator (SOV) and fiber-optic DAS: Field demonstration of economical, continuous land seismic time-lapse monitoring from the Australian CO2CRC Otway site

© 2016 SEG.We present an analysis of a field dataset demonstrating the combined use of a permanent surface orbital vibrator source (SOV) and a trenched fiber-optic cable sampled using distributed acoustic sensing (DAS). We examine SOV signal characteristics, repeatability, and wavefield decomposition for a short duration test. We show the SOV source to have excellent spectral repeatability but asymmetric response depending on spin direction. Wavefield decomposition tests demonstrate that the rotating source can effectively be decomposed into equivalent horizontal and vertical forces, well-suited to isolation of wavefield components. Finally, quantitative analysis of repeatability metrics normalized rms difference (NRMS) and predictability (PRED) show that wavefield phases with sufficient signal-to-noise ratio (S and surface waves) have high repeatability. The combination of SOV & DAS appears to be a promising approach for high temporal resolution time-lapse monitoring efforts in a variety of contexts