Full
Outline
In order to further study the mechanical properties and pore structure evolution of sandstone under the action of liquid nitrogen freezing and thawing cycles, the sandstone in natural water-bearing state and saturated state were taken as the research object. The compressive strength, elastic modulus, pore T2 map and nuclear magnetic porosity of sandstone after different liquid nitrogen freezing and thawing cycles were measured by nuclear magnetic resonance instrument and rock mechanics test system. The mechanical properties, porosity evolution and pore size distribution of sandstone under the action of liquid nitrogen were analyzed. Based on the SDR permeability model, the permeability change of sandstone after freezing and thawing cycles was calculated. The results show that the uniaxial compressive strength of sandstone decreases significantly after liquid nitrogen freezing treatment, and the decrease of strength increases with the increase of freezing and thawing cycles. When the number of cycles increases from 0 to 5, the decrease of compressive strength in natural state increases from 12.25% to 29.04%, while the maximum decrease of compressive strength of sandstone in saturated state is 55.50%. The results of nuclear magnetic resonance (NMR) test show that the freezing and thawing cycle of liquid nitrogen significantly increases the porosity and permeability of sandstone, especially for sandstone samples in saturated state. After five freezing and thawing cycles of liquid nitrogen, the porosity growth rate is 39.09%; and the permeability growth rate reaches 160%, which is 1.89 times that of natural water-bearing sandstone. The research results can provide a new idea for the efficient leaching of low permeability sandstone-type uranium deposits by liquid nitrogen fracturing technology.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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