Chasing Australia's unconventional resources with point-source, point-receiver, full azimuth surface seismic

Abstract

Detection of so called 'sweet spots' can be crucial for efficient development of unconventional reservoirs. An example is the REM shale gas interval in Queensland. Adequately sampled surface seismic has the potential to decrease risk in well planning. Identifying areas of the reservoir which are already naturally fractured or where minimum effort is required for stimulation is the ideal objective. Seismic methods can be utilized in unconventional resources characterization studies to achieve an improved understanding of the entire reservoir heterogeneity, structure and stress orientation. This leads to identification of production sweet spots? and more efficient well placement. To enable this type of study with surface seismic, we need to analyze the data not only against offset (reflection angle) but also azimuth (compass direction). This requirement places a larger demand on the seismic than would be needed for a purely structural image. In this paper we will describe the use of best-practice solutions based on experience in Australia and elsewhere for the design and implementation of the high specification Winnie 3D seismic survey. This survey featured broad-band point-sources using a non-linear Maximum Displacement sweep of 1 to 100 Hz and broad-band point-receivers. The omni-directional symmetrical dense sampling, in combination with long offsets, resulted in uniform azimuthal coverage and extremely high trace density. This design makes the ideal 'antenna' for the azimuthal analysis and the broad-band approach enables prestack inversion and seismic attributes extraction. We will demonstrate how this 3D design, specifically tailored for unconventional targets, resulted in good signal-to-noise datasets. Early stage data processing was suitable for detecting velocity anomalies. These may correlate with overpressure zones, representing potential prospective areas and identify possible drilling hazards such as volcanic intrusions. We will also demonstrate how the coordinate driven noise attenuation approach produced good quality prestack gathers for AVO/AVAz analysis