3D visualization of a rock sample, Rotliegend sandstone, Southern Permian Basin: applications for core analysis and petrophysics

Abstract

A methodology has been developed to visualize and interpret the texture and pore system of rock samples using a virtual reality application. This technique is illustrated using an aeolian sandstone core sample of the Rotliegendes Dethlingen Formation from the Southern Permian basin of northwest Germany. The methodology involves digitizing a series of densely spaced microfocus computer tomography (μCT) images with an appropriate sampling and processing the individual images, which are based on density contrasts, into a volume definition similar to seismic data. Once the volume file has been created the data can be visualized and analysed using virtual reality software. Visualization of scanned core samples has benefits with regards to both the qualitative interpretation of the rock as well as to the quantitative evaluation of the intergranular volumes, cements and pore space. Further advantages exist in terms of the effective communication and collaboration within relevant communities in exploration and production. A key requirement for this technology to be beneficial is calibration of the input slices with rock properties. In terms of the qualitative analysis of the rock, visualization offers the possibility to view slices of the rock samples in any direction. Consequently, bedding planes and fracture planes can be viewed orthogonally even if the physical sample has been cut oblique to these planes. Both slice and transparent volume views are possible, readily revealing the sedimentary and structural features of the rock. Provided that the scanning process has taken place with sufficient resolution, the views can separate grains from cement, matrix and pore space. In addition to the qualitative aspect of visualization, the 3D interpretation capabilities of the software are very valuable. Voxel-based technology allows measurement of grain sizes, cement, matrix and pore space, both in terms of volume as well as geometry. This provides important information in addition, and complementary, to conventional core analysis. In most cases the volume measurements can be expected to be more precise than traditional 2D methods, such as point counting, because they account for the three-dimensional anisotropy of the rock. Stereo-viewing allows pore space to be ‘experienced’ in 3D, offering a better perception and analysis with a view towards hydrocarbon recovery and production strategies. Finally, visualization offers an optimal means to communicate and collaborate, creating a better shared understanding of the relevance of the rock properties within the overall exploration and production evaluation process. Supplementary material: The movie referred to in the article is available at https://doi.org/10.6084/m9.figshare.c.4812969