oa Land VSP Seismic Sources Evaluation: CO2CRC Otway Project Case Study

It is widely accepted that, depending on acquisition technique, vertical seismic profiling (VSP) can provide us with extremely valuable information on seismic velocities (both P and S), attenuation and anisotropy of s eismic properties of the earth. Subsurface images, obtained with offset or 3D VSP could demonstrate superior resolution, signal-to-noise ratio and repeatability of surveys in comparison to standard surface seismic. These potential benefits are of great importance for both reservoir characterisation and time-lapse seismic monitoring. However in order to achieve them VSP surveys should be acquired with proper survey design and optimal source and receiver characteristics.

Modern 3C downhole VSP tools (such as VSI or similar array seismic equipment) are able to record seismic signal in wide frequency range (3-200 Hz) and provide high sensitivity and vector fidelity. Thus the main hardware factor affecting quality of VSP data is the seismic source. It can have different power, stability of the wavelet, frequency content and variable pattern of emitted wavefield including coherent noises.

In this paper we analyse land VSP data acquired with various seismic sources in order to determine signal quality and its repeatability. The data were acquired within the scientific program of the CO2CRC Otway Pilot Project in 2007-2009 and includes zero offset and offs et VSP in two neighbouring wells (CRC-1 and Naylor-1, distance between boreholes is ~300 m) and 3D VSP data in CRC-1. A wide range of seismic sources was used to acquire these vertical profiles; they include weight drop sources, MV vibroseis (6000 lbs), IVI Mini-Buggy vibroseis (16000lbs) and a limited amount of explosive shots.

We evaluate each source from a seismic data quality perspective (i.e. S/N ratio, image resolution, etc.) as well as acquisition performance and environmental impact.

Technical Area: Geophysics role in increasing innovative engineering opportunities