Experimental Study and Fractal Analysis of Heterogeneity in Naturally Fractured Rocks |
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Authors: | Kewen Li Roland N Horne |
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Institution: | (1) Department of Energy and Resources Engineering, College of Engineering, Peking University, Beijing, 100871, China;(2) Department of Energy Resources Engineering, Stanford University, Stanford, CA 94043, USA |
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Abstract: | Capillary pressure curves of six low porosity and low permeability core samples from The Geysers geothermal field were measured
using the mercury-intrusion approach to characterize the heterogeneity of rock. One high permeability Berea sandstone core
sample was analyzed similarly, for comparison. The maximum pressure of mercury intruded into the rock was about 200 MPa to
reach the extremely small pores. Experimental data showed that the capillary pressure curves of The Geysers rock are very
different from that of the Berea sandstone. It was found that the frequently used capillary pressure models could not be used
to represent the data from The Geysers rock samples. This might be because of the fractures in the rock. To this end, a fractal
technique was proposed to model the features of the capillary pressure curves and to characterize the difference in heterogeneity
between The Geysers rock and Berea sandstone. The results demonstrated that the rock from The Geysers geothermal field was
fractal over a scaling range of about five orders of magnitude. The values of the fractal dimension of all the core samples
(six from The Geysers and one Berea sandstone) calculated using the proposed approach were in the range from 2 to 3. The results
showed that The Geysers rock with a high density of fractures had a greater fractal dimension than Berea sandstone which is
almost without fractures. This shows that The Geysers rock has greater heterogeneity, as expected. |
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Keywords: | Fractal analysis Fractal dimension Heterogeneity of rock Fractures Capillary pressure The Geysers |
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