Physics of Geological Processes (PGP) is a Norwegian Center of Excellence with the mission to obtain a fundamental and quantitative understanding of the complex patterns and processes of the Earth. PGP has a major initiative to understand the deformation of and transport in tight rocks. This has applications to hydrocarbon source rocks, gas and oil extraction from shales and CO2 sequestration.
PGP has chosen Avizo as its main 3D analysis and visualization software. Avizo offers a broad spectrum of 3D image analysis tools, intuitive and sophisticated algorithms for segmentation, as well as many options for 3D visualization.
Recovery of oil from oil shales and the natural primary migration of hydrocarbons are closely related processes that have received renewed interests in recent years because of the ever tightening supply of conventional hydrocarbons. However, better understanding how hydrocarbons escape the source rocks (primary migration) is needed.
This study shows how insight into hydrocarbon migration in source rocks can be obtained by using sequential high-resolution synchrotron X-ray tomography. An immature shale sample from Green River Basin was heated in situ up to 400°C as 3D images were recorded. Tomography resolution was 5 micrometer, which is sufficient to resolve the rock structure down to the grain level. During the heating phase, the organic matter was decomposed, and gas was released. Generated hydrocarbons caused internal pressure build up and led to fracturing of the rock. Time resolution was 15 minutes per 3D scan, which enabled monitoring the crack development.
The main technical difficulty was numerical extraction of microcracks that have apertures in the 5 to 30 micrometer range (within the size range of individual grains) from a large 3D volume of X-ray data. With the Avizo software we developed a methodology to process these 3D data and image the cracks. This methodology is based on several levels of spatial filtering and automatic recognition of connected domains.
The advanced image processing tools in Avizo enabled us to segment the 3D data. Powerful quantitative analysis was applied to obtain information about porosity evolution and geometrical characteristics of formed cracks. As one application of the 4D micro-tomography and the developed workflow we show that fluid generation was accompanied by crack formation in the shales, which might provide paths for primary migration.