Assessing the repeatability of reflection seismic data in the presence of complex near-surface conditions CO2CRC Otway Project, Victoria, Australia

Abstract

A depleted Gas Field (Naylor) located in the onshore Otway Basin of Australia (Figure 1) is situated in a tilted fault block structure. After some years of gas production from Naylor-1, the field was abandoned. Subsequently, the field is being used for CO2 sequestration as a demonstration project, and will be used for monitoring the migration of CO2 during the injection process into a sandstone reservoir 300 m down-dip from the monitoring well. Optimum seismic repeatability is critical to the monitoring of the field. In order to assess the relative influences of source types and environmental conditions, a series of repeated 2D seismic test surveys were performed before injection commenced. It was discovered that the absorption of energy in the near surface had much greater effect than anticipated.