Effects of Cable Deployment Method on Das VSP Data Quality: Study at CO2CRC Otway in-situ Laboratory

Summary Distributed acoustic sensing provides a unique opportunity to deploy massive seismic receiver arrays on the surface and in downhole environments. For downhole installation several options including temporary wireline deployment or more permanent setups such as cementing behind the casing, strapping to production tubing or cementing inside the casing during the abandonment operations. CO2CRC Otway project was the first Australian demonstration of CO2 geosequestration commenced in 2006. Stage 3 of the project is focused on the downhole monitoring of a small scale (15,000 t) CO2-rich gas injection utilising a borehole array. This array comprises of existing and several new 1.5-1.7 km deep wells drilled within approximately 1 km2 area and all instrumented with optical fibres. The wells have a combination of fibre optic cables deployed using different approaches, in some cases – one well can have several cables deployed differently. Prior to completion of the wells, we acquired a set of zero-offset VSP surveys using conventional 3C geophones in the four new wells drilled in 2019. A series of DAS tests focusing on the effects of deployment methods on DAS VSP data quality were also performed. In this presentation, we share findings from these experiments.