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SUMMARY Tar or bitumen deposits in the Canning Basin, Western Australia, indicate possible paths of petroleum migration. Neutron and X-ray tomography is applied to rocks containing biodegraded tar in order to investigate the distribution of petroleum within the pore system of the samples. Neutron tomography allows the imaging of hydrogen-rich components, such as tar and bitumen, within a sample, whereas X-ray tomography assists density analysis of the grains and pore space. The results indicate that the methodology discriminates excellently between tar and the other rock matrix and open void components. The images permit analysis of the connectivity of pore paths and enable conclusions to be drawn about petroleum migration. In the case history presented, the images demonstrate the injection of petroleum into a dilated fault zone, and the interaction of the petroleum with the fault gouge material. The images also demonstrate the nature of petroleum movement into sandstone beds, which were in communication with this fault zone.

SUMMARY Shallow anomalous high speed events, evident on the shot gathers, are observed to be associated with gas chimneys in the Central Perth Basin. Shot gathers in the vicinity of gas chimneys display these events, which have apparent speeds of around 3000 m/s in the uppermost 300 ms, and appear to localised around the gas chimneys. These high speed events have been investigated using existing seismic data from the region, with these high speed events modelled using wide aperture seismic (WAS) techniques. Understanding the effect of these shallow high speed layers is important for the following reasons 1. they may provide support for a petroleum prospect, 2. they may represent a possible geohazard during drilling, 3. these high speed layers can have a profound effect on the seismic imaging of the underlying strata.

Neutron radiography can provide images of the internal structure of rocks, through virtue of the differing neutron attenuation characteristics of hydrogen versus other elements commonly found in nature. Thus, pores filled with water, or oil, will attenuate neutrons to a greater extent than the surrounding rock matrix. Similarly, the internal structure of iron ore, which contains mixtures of limonite and goethite, which contain hydrogen in their crystalline lattice, and magnetite (no hydrogen), can also be imaged using neutrons. The ability of the technique to distinguish “effective porosity” versus “total porosity” is derived from the neutron radiographs. Images of two iron ore samples have also been analyzed to demonstrate how both different mineral assemblages and porosity can be determined.

Petrophysics, when applied to the fields of petroleum and groundwater resources, has the special connotation of fluid-rock interaction. Neutron radiography imaging techniques have been applied in the present study to evaluate fluid-rock behaviour for three specific experiments. The basic experimental set-up entails a beam of thermal neutrons intersecting a thin slice (5 mm thick) of fluid-filled porous rock, which is encased in aluminium to retain the fluid within the rock. Neutrons are attenuated by the fluid in the rock, and comparison of the neutron intensity in a dry and saturated state permits one to estimate the rock's porosity (ratio of pore volume to total volume) and relative fluid saturation, The three experiments are (I) Water inflitration into a porous rock, Displacement of heavy water by oil and 3 Water flooding of a clay-rich rock. Each experiment is analogous to a practical geological resource problem.

This paper reports experimental data relating the observed dry-bulk thermal conductivities of powdered minerals to the porosities of the powdered aggregates. The mineral samples were obtained by crushing quartz, calcite, and feldspar crystals. Experiments also were conducted on clays from various sources. The experimental data suggest an exponential relationship between the dry-bulk thermal conductivity and the aggregate porosity. The thermal conductivities of the original quartz, calcite, and feldspar crystals were determined in a dry state to estimate their matrix thermal conductivities. An empirical relationship was determined among dry-bulk thermal conductivity, aggregate porosity, and matrix thermal conductivity. This empirical relationship provided estimates of matrix thermal conductivity that were consistent with "theoretical mix" formulae for 50:50 mixtures of combinations of the minerals quartz, calcite, and feldspar, and also a sample of Flag Sandstone from the North West Shelf, Australia. The method was used to estimate heat flows at the sites of two Australian North West Shelf wells: Dampier 1 and Tryal Rocks 1, which are 47.4 mW/m2 and 79.7 mW/m2, respectively. These values are less than sea floor estimates of heat flow in the same region, and suggest nonconductive heat-transfer processes within the North West Shelf sedimentary section.