Three-Dimensional Experimental Simulation Of Gas Hydrate Pressure Reduction Under Different Overlying Structures

Natural gas hydrate is extremely valuable for mining which is the new energy discovered in the early 20th century.It has a huge energy density which is about ten times as high as coal,it is rich in resources which are twice as the world's known fossil energy,and it is widely distributed in the sea bottom and permafrost.The further development and utilization of the gas hydrate in the seafloor can be used to deal with the worldwide energy crisis.The gas hydrate mining 3D simulation experiment equipments set up by the laboratory are applied to this project to prepare the CH4 hydrate sample in the reservoir condition,and on this basis the 3D simulation experiment of depressurizing production at different cladding structures.The main contents of this research are as follows:(1)The simulation experiment of depressurizing production with different sand layers above CH4 hydrate layer was carried out.Its purpose was to find out temperature and pressure variations of CH4 hydrate reservoir and sand layer,and explore the influence of sand layer thickness on the gas production,water production and gas-water ratio.The experimental results show that due to the increasing thickness and low permeability of the sand layer,a short-time low pressure area was formed near the production area which could promote the hydrate decomposition.Therefore,the gas production and gas rate increased while the water production and water rate reduced.After the sand layer thickness was increased,the permeability of hydrate in the depressurizing production increased and the production efficiency could be improved.(2)The simulation experiment of depressurizing production in the synthetic CO2 hydrate layer above sand layer was carried out.Its purpose was to find out temperature and pressure variations of CH4 hydrate reservoir and sand layer,explore the influence of sand layer thickness on the gas production,water production and gas-water ratio,and determine the seal and stability of the layer.The experimental results show that a short-time low pressure area was formed which could promote the hydrate decomposition and increase the permeability of hydrate in the depressurizing production.Therefore,the gas production and gas rate increased while the water production and water rate reduced.Finally,the production efficiency could be improved.