Carbonate outcrops were taken from Ma 51 sub-member in the Lower Paleozoic in the Yan’an gas field to conduct true tri-axial hydraulic fracturing experiments with water, liquid CO_(2) and supercritical CO_(2). CT sca...Carbonate outcrops were taken from Ma 51 sub-member in the Lower Paleozoic in the Yan’an gas field to conduct true tri-axial hydraulic fracturing experiments with water, liquid CO_(2) and supercritical CO_(2). CT scan was applied to analyze initiation and propagation laws of hydraulic fractures in carbonate rocks. The experiments show that supercritical CO_(2) has low viscosity, strong diffusivity and large filtration during fracturing, which is more liable to increase pore pressure of rocks around wellbore and decrease breakdown pressure of carbonate rocks. However, it would cost much more volume of supercritical CO_(2) than water to fracture rocks since the former increases the wellbore pressure more slowly during fracturing. For carbonate rocks with few natural fractures, tensional fractures are generated by fracturing with water and liquid CO_(2), and these fractures propagate along the maximum horizontal principal stress direction;while fracturing with supercritical CO_(2) can form shear fractures, whose morphology is rarely influenced by horizontal stress difference. Besides, the angle between propagation direction of these shear fractures near the wellbore and the maximum horizontal principal stress is 45°, and the fractures would gradually turn to propagate along the maximum horizontal principal stress when they extend to a certain distance from the wellbore, leading to an increase of fracture tortuosity compared with the former. For carbonate rocks with well-developed natural fractures, fracturing with fresh water is conducive to connect natural fractures with low approaching angle and form stepped fractures with simple morphology. The key to forming complex fractures after fracturing carbonate rocks is to connect the natural fractures with high approaching angle. It is easier for liquid CO_(2) with low viscosity to realize such connection. Multi-directional fractures with relatively complex morphology would be formed after fracturing with liquid CO_(2).展开更多
The menstrual cycle is always considered as a big nightmare by many women. This research aims to make this process smooth and safe by developing natural sanitary pads which are used to absorb and retain menstrual bloo...The menstrual cycle is always considered as a big nightmare by many women. This research aims to make this process smooth and safe by developing natural sanitary pads which are used to absorb and retain menstrual blood from the body. Some existing sanitary pads contain 90% plastics made of non-woven polypropylene/polyethylene sheets, super absorbent polymers, and polyethylene back sheets that will take up to 600 - 800 years to decompose. So, biodegradable sanitary pads using natural fibers are the best alternative to eliminate the pads which contain non-biodegradable materials. In this research, nonwoven bamboo will be used as the top layer, nonwoven cotton will be used as the second layer, the absorbent core is to be made by the combination of kenaf and chitosan fibers as the third layer, cotton as the fourth layer, and cornstarch-based bioplastic sheets as the bottom layer. These biodegradable natural materials will change the menstrual process into a healthy one as well as create a robust ecological community.展开更多
基金Supported by National Natural Science Foundation of China Project(51704249)The Open Fund Project of the State Key Laboratory Oil and Gas Reservoir Geology and Exploitation(PLN2020-1)。
文摘Carbonate outcrops were taken from Ma 51 sub-member in the Lower Paleozoic in the Yan’an gas field to conduct true tri-axial hydraulic fracturing experiments with water, liquid CO_(2) and supercritical CO_(2). CT scan was applied to analyze initiation and propagation laws of hydraulic fractures in carbonate rocks. The experiments show that supercritical CO_(2) has low viscosity, strong diffusivity and large filtration during fracturing, which is more liable to increase pore pressure of rocks around wellbore and decrease breakdown pressure of carbonate rocks. However, it would cost much more volume of supercritical CO_(2) than water to fracture rocks since the former increases the wellbore pressure more slowly during fracturing. For carbonate rocks with few natural fractures, tensional fractures are generated by fracturing with water and liquid CO_(2), and these fractures propagate along the maximum horizontal principal stress direction;while fracturing with supercritical CO_(2) can form shear fractures, whose morphology is rarely influenced by horizontal stress difference. Besides, the angle between propagation direction of these shear fractures near the wellbore and the maximum horizontal principal stress is 45°, and the fractures would gradually turn to propagate along the maximum horizontal principal stress when they extend to a certain distance from the wellbore, leading to an increase of fracture tortuosity compared with the former. For carbonate rocks with well-developed natural fractures, fracturing with fresh water is conducive to connect natural fractures with low approaching angle and form stepped fractures with simple morphology. The key to forming complex fractures after fracturing carbonate rocks is to connect the natural fractures with high approaching angle. It is easier for liquid CO_(2) with low viscosity to realize such connection. Multi-directional fractures with relatively complex morphology would be formed after fracturing with liquid CO_(2).
文摘The menstrual cycle is always considered as a big nightmare by many women. This research aims to make this process smooth and safe by developing natural sanitary pads which are used to absorb and retain menstrual blood from the body. Some existing sanitary pads contain 90% plastics made of non-woven polypropylene/polyethylene sheets, super absorbent polymers, and polyethylene back sheets that will take up to 600 - 800 years to decompose. So, biodegradable sanitary pads using natural fibers are the best alternative to eliminate the pads which contain non-biodegradable materials. In this research, nonwoven bamboo will be used as the top layer, nonwoven cotton will be used as the second layer, the absorbent core is to be made by the combination of kenaf and chitosan fibers as the third layer, cotton as the fourth layer, and cornstarch-based bioplastic sheets as the bottom layer. These biodegradable natural materials will change the menstrual process into a healthy one as well as create a robust ecological community.
