Video cathodoluminescence microscopy of diagenetic cements and its applications

Diagenetic studies of sedimentary rocks using cold cathodoluminescence (CL) microscopy have been severely limited because of the very low intensity of visible luminescent emissions, which required long photographic exposure times, and because of the difficulty in obtaining quantitative data from CL observations. The solution to this problem is to fit the microscope with a high-sensitivity digital colour video camera linked to a computer with image enhancement and image analysis software. The new technique described in this paper: produces digital CL images of consistent high quality, both quickly and cheaply; controls the capture and editing of CL images, to reveal detailed textural information even from minerals exhibiting low level luminescence such as quartz; acquires quantitative information on pore systems and the abundance of cement zones from CL images. Examples are presented to demonstrate the high quality of images produced in this way and the range of uses to which the new technique can be applied. The ability to image exactly the same field of view in both plane polarised Light and CL is a particular advantage. Image analysis techniques have been developed to give a statistical characterisation of both pore systems and cement phases that infill them. The abundance of contrasting cement zones seen in CL can be measured and the abundance of cement phases can be mapped across a reservoir. The history of porosity occlusion can be reconstructed quantitatively and integrated with burial history and hydrocarbon migration. Porosity can be measured accurately and, since the technique obtains data on pore geometry as well as abundance, the pore system can be characterised by pore size distributions and pseudo-capillary pressure curves. This also opens the possibility of estimating permeability from thin sections. (C) 2001 Elsevier Science Ltd. All rights reserved.