Characterization of bedding crack evolution in mudstone under deterioration action of water saturation-dehydration circulation
In order to study the fracture evolution characteristics of expansive mudstone during water saturation-dehydration circulation,firstly,the prepared cylindrical mudstone samples were tested for five times of water saturation-dehydration circulation tests.Secondly,the original samples and the mudstone samples that went through 1 and 5 circulations were scanned by the CT scans.Finally,three-dimensional(3D)digital reconstruction of the internal stratified fracture network of mudstone was carried out by combining image analysis technology.The evolutionary characteristics of mudstone stratified fractures in qualitative and quantitative aspects were analyzed.The results show that the volume of the reconstructed 3D digital model is similar to that of the real mudstone samples,which can accurately characterize the sample volume characteristics and changes.As water saturation-dehydration circulation times increases,the mudstone represents different trends in different parts.The fractures grow faster in the upper part of mudstone and slower in the lower part of mudstone.As water saturation-dehydration circulation times increases,volumes for total fracture and the connected fracture steadily increase,while the volume for independent fissure is almost unchanged.As water saturation-dehydration circulation times increases,various parameters in the pore network model exhibit increasing tends.Meanwhile,the width and connectivity of fracture gradually increase with the increase of the number of cycles.During the water saturation-dehydration circulation,the connected laminar main fractures are induced by wedge pressure and the rectangular network of fractures forms with water loss and contraction action.
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