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Representing a fast growing area in oil and gas exploration, digital rock physics allows researchers to analyse the properties of rock samples, including permeability and pore characteristics. The creation of 3D models from different scan modalities (such as micro-CT and FIB-SEM), can complement experimental testing and generate valuable data for analysis of rock types. At Simpleware we¡¯ve developed solutions for doing more with 3D image data for digital rock physics, with a particular focus on streamlining multiple stages of image visualisation, analysis and model generation for simulation.

When working with geological samples, it is possible to create volume images that contain different material phases, enabling comprehensive analysis of grain structure, porous networks and other characteristics. Quantifying these features and using finite element simulation (FEA) and computational fluid dynamics (CFD) allows for a deeper understanding of the potential behaviour of samples; this has applications to reservoir characterization, oil recovery and hydrocarbon production potential, among many other areas. Analyzing samples at different length scales means being able to better understand flow and transport properties for even very small pore connections.

Our solution for digital rock physics starts with visualizing image data, acquired as a stack of images that can be converted from 2D pixels into 3D pixels (voxels) in ScanIP. From this image data, different material phases can be segmented into regions of interest (ROIs) using semi-automatic and manual tools, for example to create solid and fluid masks. In addition, filters can be applied to reduce scan noise and better visualize image data, making it easier to view different features.

Options are also available for obtaining quantified data on the properties of samples, including porosity analysis. Mask and model statistics can be quickly obtained for the volume and surface area of data, as well as on tortuosity, connectivity and pore sizes. We have also developed image processing and measurement features that are useful for analysing multi-phase and porous materials, including watershed segmentation for analysing particles, and centerlines. With this approach, it is possible to quickly visualize, segment and obtain statistics from samples taken from 3D scans.

We have developed image-based meshing techniques that allow robust FE and CFD models to be generated directly from image data with conforming interfaces and shared nodes; models are suitable for digital rock physics simulation. There are several meshing approaches available when working with rock physics data, including a grid-based mesher (+FE Grid), and an adaptive meshing algorithm (+FE Free). The grid-based algorithm developed by Simpleware generates mixed hexahedral and tetrahedral meshes ¨C voxels are effectively converted directly to hex elements and then converted to tet elements at the interfaces for a smooth surface. This image-based approach takes into account partial volume effects, and preserves topology and volume from the original scan. It is also possible to use +FE Free to adaptively re-mesh data.

+FE Free re-meshes multi-part surfaces while preserving the original geometry generated using a grid-based approach. Mesh inspection tools are also available to ensure that the model exported to FE and CFD solvers is robust. For digital rock physics, models can be created that support multiple phases and enable FEA/CFD of stress and permeability, among other physical stimuli. Being able to mesh multiple segmented parts solves the problem of working with very complex scans when generating models.