Seminar: Fibre-optic sensing DAS applied to seismic imaging and reservoir monitoring at the CO2CRC Otway Project

Ms. Julia Correa, PhD Candidate, Exploration Geophysics, Curtin University

Title: Fibre-optic sensing DAS applied to seismic imaging and reservoir monitoring at the CO2CRC Otway Project

Held: Thursday 22 November 2018, 2PM–3PM

ABSTRACT:

Seismic monitoring constitutes an essential step during the development of a CO2 geosequestration project, as it assures the injected fluid is safely stored in subsurface. However, seismic monitoring is often used restrictedly. Such surveys are highly expensive as an extensive amount of equipment needs to be deployed. Additionally, the access of large areas during the survey lead to high environmental and social impact.

In this work we test the applicability of Distributed Acoustic Sensing (DAS) technology for permanent and continues seismic monitoring in the context of CO2 geosequestration projects. DAS uses standard fibre-optic cables to form a series of distributed seismic receivers. Fibre-optic cables are relatively inexpensive, offer long durability and can operate in extreme conditions. Moreover, DAS is able to acquire seismic data instantaneously along the cable at fine spatial sampling intervals.

This research is set at the CO2CRC Otway project. The Otway project is located ~240 km away from Melbourne, Australia. The site has two wells instrumented with fibre-optic cables (one well on production tubing; the other well behind the casing). The wells contain a set of straight single-mode fibres, though, one of the cemented cables has a combination of conventional single-mode and specialty high-sensitive DAS fibres. Additional 40 km of fibre optic cable is deployed in 11 receiver line trenches along with 908 buried geophones.

Through the analysis of multiple datasets and different configurations, we demonstrate that DAS is the receiver of choice in many monitoring applications which would benefit from permanent receiver installation. DAS has a potential to outperform conventional geophones as a seismic sensor used to conduct imaging and monitoring of the subsurface. However, the nature of the measurement is different and must be taken into account, from survey design to data processing and interpretation