Abstract
Tight gas sandstone samples are imaged at high resolution industrial X-ray computed tomography (ICT) systems to provide a three-dimensional quantitative characterization of the fracture geometries. Fracture networks are quantitatively analyzed using a combination of 2-D slice analysis and 3-D visualization and counting. The core samples are firstly scanned to produce grayscale slices, and the corresponding fracture area, length, aperture and fracture porosity as well as fracture density were measured. Then the 2-D slices were stacked to create a complete 3-D image using volume-rendering software. The open fractures (vug) are colored cyan whereas the calcite-filled fractures (high density objects) are colored magenta. The surface area and volume of both open fractures and high density fractures are calculated by 3-D counting. Then the fracture porosity and fracture aperture are estimated by 3-D counting. The fracture porosity and aperture from ICT analysis performed at atmospheric pressure are higher than those calculated from image logs at reservoir conditions. At last, the fracture connectivity is determined through comparison of fracture parameters with permeability. Distribution of fracture density and fracture aperture determines the permeability and producibility of tight gas sandstones. ICT has the advantage of performing three dimensional fracture imaging in a non-destructive way.
Highlights
Tight gas sandstone samples are imaged at high resolution industrial X-ray computed tomography (ICT) systems to provide a three-dimensional quantitative characterization of the fracture geometries
Quantification of fracture geometry remains essential for characterizing transport processes in fractured reservoirs[10,11]
High-resolution industrial X-ray computed tomography (ICT), based on the differential attenuation recording of an X-ray beam through a sample[11], is a nondestructive laboratory tool that provides in situ studies of the three-dimensional distribution of the interior structure of rocks[6,13,14]
Summary
Tight gas sandstone samples are imaged at high resolution industrial X-ray computed tomography (ICT) systems to provide a three-dimensional quantitative characterization of the fracture geometries. Distribution of fracture density and fracture aperture determines the permeability and producibility of tight gas sandstones. This study aims at the quantification of the fracture systems, and at providing a quantitative characterization of fracture attributes by 2-D slice analysis and 3-D volume-rendering. The surface area and volume of both open fractures and high density fractures are summarized by 3-D modeling The fracture parameters such as fracture porosity, aperture and density are calculated by a combination of 2-D slice analysis and 3-D visualization and counting, and these fracture parameters are correlated with those derived from the image logs. The fracture geometries of core samples using ICT in laboratory could be a beneficial complement to the traditional MS/AE (microseismic/acoustic emission) monitoring systems, which could provide real-time fracture information of rockmass[19,20,21,22]
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