In order to determine the reasonable shape of the patching plate for the corrosion defects in the bottom of crude oil storage tank, this paper used finite element analysis to calculate the changes of the stress value in the corrosion defects after repairing different patching plate shapes, and then investigated the stress distribution and the safety factor value of the patching plate, and finally gave the best shape of the patching plate for the bottom of 20 000 m³ crude oil storage tank in Liaohe oil field. The results show that the best shape of the patching plate is a round patching plate. After repairing the corrosion defect, the stress value in the corrosion defect only decreases with the increase of the radius of the patching plate after the repair of the corrosion defect, and does not change with the change of the depth and radius of the defect. With the increase of the radius of the patch plate, the cost and safety of the patch plate will also increase, the specific size of the patch plate should be developed in accordance with the actual situation of the project. The results of the study can give theoretical guidance to the tank bottom repair from a scientific point of view.

The synthesis of gas hydrates with higher saturation under high pressure and low temperature conditions on the seabed was simulated, and use the multi?stage depressurization mode to extract the hydrate as the blank group, and the effects of multi?stage depressurization + alcohol injection, multi?stage depressurization + inorganic salts and chemical agents with different mass concentrations on the decomposition and recovery efficiency of natural gas hydrate were studied. At the same time, according to the experimental results, the chemical agent with the best decomposition efficiency was preferably evaluated. The results show that: the multi?stage depressurization + chemical injection to recover natural gas hydrate can effectively increase the instantaneous gas production rate and improve the overall decomposition efficiency compared with pure depressurization. Among them, the multi?stage depressurization + injection of 30% ethylene glycol has the best performance in alcohols, compared with the pure multi?stage depressurization mode, its decomposition efficiency is increased by 51.3%, and the recovery efficiency within 2 h is increased by 67.3%; the multi?stage depressurization + injection of 15% calcium chloride has the best performance in inorganic salts, compared with the pure multi?stage depressurization mode, its decomposition efficiency is increased by 47.3%, and the recovery efficiency within 2 h is increased by 60.4%. In the actual mining process, the appropriate chemical concentration should be used to avoid environmental pollution.