New Fast and Accurate 3D Micro Computed Tomography Technology for Digital Core Analysis

Abstract

Micro Computed Tomography (micro-CT) of cores is an emerging technology that yields vital information about key rock and fluid properties at pore-scale resolution. Micro-CT imaging results presented to date are encouraging and indicate that this technology has the potential to revolutionize petrophysical analysis and reservoir engineering. The application of micro-CT in petroleum engineering requires reconstructed scan data to be of high and uniform image quality to enable reliable analysis during subsequent segmentation and numerical modeling. This is achievable in existing micro-CT systems using standard circular scan trajectories with non-exact filtered backprojection (FBP) reconstruction, but requires small cone angles to keep cone beam artifacts below detectable limits. We describe the implementation and results of adapting an exact helical FBP reconstruction algorithm (the so-called “Katsevich Algorithm” or KFBP) and data acquisition scheme on a high-performance micro-CT system normally running in circular scan trajectory mode. Side-by-side comparisons of stitched circular scan trajectories with continuous helical scan trajectories on simulated and real rock core data show the throughput advantage of this modality for applications relevant for the petroleum industry keeping equivalent image quality to low cone angle circular scans. The analytical exact helical reconstruction can be performed in quasi-real time leading to instantaneous results. Simulated and experimental results indicate that an imaging throughput improvement of 2-5 times can be achieved employing KFBP-based exact helical reconstruction compared to the standard circle scan trajectory when imaging whole rock cores/plugs that are significantly longer than their diameter.