Peter Hatherly

A simple approach to calculating refraction statics corrections

The higher the resolution demanded from the interpretation of seismic data, the more care required in the acquisition and processing of that data. Of the processing steps that directly influence resolution, the one that is having the most impact on land data is the statics correction. Geophysical conferences have devoted entire technical sessions to statics. Seismic crews frequently undertake specific refraction surveys just to obtain good statics data. Here we outline a very simple solution to the statics problem that produces remarkable results.

Kirchhoff diffraction mapping in media with large velocity contrasts

Finite‐difference methods for calculating traveltimes are superior to ray‐tracing methods in inhomogeneous media. However, when these techniques are applied to Kirchhoff migration, a severe problem occurs in the presence of large velocity contrasts. If finite‐difference traveltime methods are used to calculate first arrivals, an incomplete image is created because substantial subsurface information is often carried by direct body waves. We propose a solution to this problem by developing a new method of calculating later arrival times and applying both first and later arrival times to a Kirchhoff diffraction mapping algorithm. A comparison shows that the implementation of both first arrivals and later arrivals in Kirchhoff migration can substantially improve the images in media with large velocity contrasts.

Delineation of Geological Structures by 3D Seismic Surveys in Australian Coal Mining

Summary Successful underground coal mining requires certainty of geological conditions and knowledge of any geological structures which might disrupt the coal seams. Conventionally, such information has been sought through drilling programs. However, drilling is an expensive process and its relevance is limited to the immediate neighborhood of the borehole. The geological uncertainty remains. Seismic reflection surveying, especially 3D seismic, could provide much of the detailed information needed by coal mining, without resorting to excessive drilling. In recent years, 3D seismic reflection surveys have been undertaken at a number of coal mines in Australia in an attempt to provide a “no surprises” guarantee of seam conditions before mining. Superior seismic results were obtained. In this paper, the ability of seismic reflection methods to resolve localised geological features has been examined from a theoretical viewpoint and through using data obtained in recent 2D and 3D seismic surveys undertaken in Australia. The results show how subtle details in the coal seams are revealed. Techniques for computer aided interpretation are also demonstrated.

New Technique For Kirchhoff Diffraction Mapping Using Both First And Later Arrivals

Recently developed finite difference methods for traveltime calculations are superior to ray tracing methods in calculating first arrival times in inhomogeneous media. However, when these techniques are applied to Kirchhoff migration, a severe problem occurs where high velocity contrasts exist. An incomplete image is created because substantial subsurface information is often carried by ‘direct body waves’ rather than first arrivals. This paper looks into, and consequently gives a solution to this problem through developing a new method of calculating later arrival times and applying both first and later arrival times to Kirchhoff migration. A comparison shows that the implementation of both first arrivals and later arrivals in Kirchhoff migration can substantially improve the migration image.

New developments for coal exploration in Australia

During 1993, five experimental seismic surveys, in three different coal basins of Australia, were performed for a consortium of coal companies. The initial goal was to determine if seismic methods could be applied to support mining operations in these areas. Small charges of explosive were chosen as the major energy source. Three of the mines provided sonic and density logs prior to the field experiments. All seismic lines were processed using a novel surface consistent refraction static routine. To further analyze the potential of seismic methods in these areas, unconventional interpretation was performed. Pseudo 3-D map analysis in a combination with trace attributes were used in the two areas where the existence of low throw faults and fracture swarms were suspected. The major outcome of the study was that all areas had their optimum seismic parameters defined. This allowed the mining companies to interface future seismic exploration strategies into their mine planning activity with greater confidence than previously.