Glenn Pool project: Crosswell seismic data acquisition overview

Abstract

A two-day crosswell seismic field test survey was conducted in late August 1993. The test was successful in determining operational procedures and parameters for a (latter) full crosswell survey. This paper focuses on some of the deterministic field test results for the survey design. Various data acquisition parameters such as vertical stack, source spacing, sweep signal range are compared independently for improved data quality. The distance between the survey wells and data aperture controls the signal transmission range. Considering the pre-designed acquisition window and first arrival signal strength, a maximum interwell spacing is determined. A new well to be used in the full survey was spotted and drilled. The test survey was not intended for subsurface imaging. Ray coverage and ray density were insufficient for full velocity inversion. However, an initial attempt of processing the first arrival times resulted in an incomplete but promising tomographic reconstruction. Average velocities in the well-illuminated zone are in good agreement with sonic log data. The full crosswell survey was completed in early 1994. When processed, these will result in three P-wave tomograms two of which are oriented in the North-South direction and third extending approximately orthogonal to the other two.