A method of water flow erosion for marine gas hydrate exploitation

Abstract

The present invention provides a method of water flow erosion for marine gas hydrate exploitation. Based on the characteristics of higher permeability around gas hydrate exploitation well, controlling the seawater flow process by the pressure difference between hydrate reservoir and gas hydrate exploitation well. And the chemical potential difference between hydrate phase and water phase is the main driving factor for promoting the hydrate decomposition. Meanwhile, the salinity will increase and then the phase equilibrium temperature of hydrate will increase during seawater flow process. The water flow erosion accelerates the heat and mass transfer in hydrate reservoir to promote the efficient and complete decomposition and collection of hydrate. And the method of water flow erosion can decrease the risk of the geographical destruction caused by the large pressure drop. The present invention also provides the combination modes of water flow erosion with depressurization, thermal injection and other methods.

We claims: 
     
         1 . A method of water flow erosion for marine gas hydrate exploitation, wherein it comprises the following steps:
 (1) drilling location selection: drilling multiple gas hydrate exploitation channels, there will be two pressure control channels and one gas collection channel for one set of gas hydrate exploitation channel; drilling multiple water storage channels between adjacent exploitation channels in gas hydrate reservoir to interlink the pressure control channel with gas collection channel, which is used to storage seawater;   (2) for each gas hydrate exploitation channels, a middle channel is chose to be the gas collection channel, which is used to control the pressure of gas hydrate reservoir and the difference pressure between different gas hydrate exploitation channels; the seawater flowing process is controlled by the difference pressure between different gas hydrate exploitation channels, and the hydrate decomposition is induced by chemical potential difference between hydrate phase and seawater phase, which is caused by seawater flow process; meanwhile, the salinity of gas hydrate reservoir will increase during the seawater flow process, then, further increase the phase equilibrium temperature to promote hydrate decomposition; what's more, the seawater flow process will increase the heat and mass transfer in gas hydrate reservoir, which can be efficient to prevent the hydrate regeneration and ice generation;   (3) changing the pressure of gas collection channel, increase the difference pressure between adjacent exploitation channels to increase the seawater We claims velocity in seawater storage channels, and then promoting parts of hydrate decomposition, increase the water and gas permeability in gas hydrate reservoir;   (4) adjusting the pressure of gas collection channel to stabile the difference pressure between adjacent exploitation channels and to promote the stability of seawater flow process; the best seawater velocity is chose to promote the hydrate exploitation; and then, achieving the efficient and safe hydrate exploitation in gas hydrate reservoir;   (5) the CH 4  is collected in the outlet of gas collection channel, and the pressure of gas hydrate reservoir is controlled by the gas collection process; then, the collected gas is stored and transported; the separated seawater from the gas collection channels is injected into the pressure control channel to be used to the secondary flow in gas hydrate reservoir.   
     
     
         2 . The method of water flow erosion for marine gas hydrate exploitation according to  claim 1 , is characterized in that the parts of gas hydrate is decomposed by the method of depressurization and thermal injection in the early stage to increase the local permeability of gas hydrate reservoir; and the method described in  claim 1  will be used in the later stage of hydrate exploitation; the combination of the method described in  claim 1  with depressurization and thermal injection is helpful to improve the permeability of the gas hydrate production channels, the periphery of seawater storage channels and the interior of gas hydrate reservoir; then, increase the flow ability of seawater in gas hydrate reservoir, and further achieve the efficient and safe hydrate exploitation by water flow erosion.