POROSITY AND PERMEABILITY ANALYSIS ON NANOSCALE FIB-SEM 3D IMAGING OF SHALE ROCK

摘要

As oil and gas production from conventional reservoirs is declining and oil price is going up,unconventional mudstone reservoirs(“shale-gas”) are becoming more important. However,while their characterization is of utmost importance for production planning, these low permeability rocks are very challenging to characterize due to their complex nano-scale pores and mineral structure.3D imaging is a critical tool in the visualization, analysis and modeling of these type of reservoirs. In this study,FIB-SEM(Focused Ion Beam - Scanning Electron Microscopy) 3D imaging at 5nm pixel resolution was used to study porosity,connectivity,and to model permeability of a mudstone core sample extracted from a production well in North America.With 3D reconstruction,extraordinary detail of the pore space in both the mineral and organic matter phases can be visualized and analyzed.Advanced image analysis algorithms were used to extract volumes of the different phases and to compare these with the physical laboratory experiments of porosity and permeability.Special focus was placed on the impact of pore space in the organic matter.These pores tend to be larger than the other pore types.The impact of segmentation procedure on porosity calculation was systematically studied. Segmented FIB-SEM images are used as the input to the Stokes flow solver to simulate viscous fluid flow through the rock.The simulation results can be compared with physical laboratory experiments. In addition to analysis of mudstone samples,the workflow proposed by this study is potentially applicable to a wide range of core sample and more general porous material analysis.