Assessment of the permanent seismic sources for borehole seismic monitoring applications: CO2CRC Otway Project

Abstract

Summary In the CO2CRC Otway Project, seismic monitoring has evolved from traditional campaign-based seismic acquisition using a large array of seismic receivers and mobile sources, towards the techniques using continuous borehole seismic acquisition based on permanently deployed sources and various receiver and DAS arrays deployed in the wells. Permanent borehole-based reservoir monitoring can minimize the cost and the environmental impact of geophysical surveillance. To this end, Surface Orbital Vibrators were deployed as permanent sources in late 2015 to two locations for real time and on-demand plume imaging. The sources include one large and one small motor. After optimisation of the SOV design in 2016, the existing buried geophone array was used to record continuously over several months. First, surface geophone array feasibility was performed and promising seismic repeatability was obtained that validates the borehole applicability of these vibrators. We then ran a series of VSP trials to test performance of DAS in combination of SOV sources. The objective was to test different fibre types and different sweep parameters. The results of the field trials show that the DAS/SOV combination presents good quality VSP datasets and, when using a more powerful motor with sweeps from 0 to 80 Hz, imaging beyond the injection interval. These results provided confidence in progressing further stages of the Otway Project which will focus on permanent borehole seismic monitoring.