Pore structure determination using Confocal Scanning Laser Microscopy

A methodology is presented that shows how Confocal Scanning Laser Microscopy (CSLM) can be used to measure the microscopic three dimensional distribution of pore bodies and pore throat size in sandstones with hydrocarbon reservoir potential. The technique involves injection of doped epoxy into the sample pore space, followed by non-destructive serial sectioning of the rock using laser light. Fluorescence imaging combined with image thresholding techniques allows the pore volume structure of the sample to be reconstructed to a depth of > 500 microns. The main problems encountered during experimentation were degraded depth resolution and laser attenuation, both of which contributed to inaccuracies in the sample image. Using a method of 'point-wise thresholding' these technical difficulties can be overcome, allowing a highly accurate volume reconstruction to be made. Accounting fully for laser attenuation will in principle allow a reduction in the amount of injected fluorochrome concentration, and thus deeper depth penetration and imaging of the sample. Euclidean distance maps are suggested as a means of addressing the shortcomings in classical medial axis transforms for application to connectivity investigations.