High-efficiency yield-increasing exploitation method for natural gas hydrates

A high-efficiency yield-increasing exploitation method for natural gas hydrates, comprising the following steps:

• (i) drilling of natural gas hydrate reservoirs along horizontal wells
• as for the natural gas hydrate reservoirs, drilling well arrays in an exploratory trench drilling manner along the horizontal wells, each of which comprising three horizontal wells:
• a first horizontal well, and a second horizontal well and a third horizontal well positioned on two sides of the first horizontal well, and each of the horizontal wells comprising a vertical well section, an inclined well section, and a horizontal well section;
• (ii) seepage increasing by fracturing for fracture forming and stability improvement by grouting in the natural gas hydrate reservoirs
• after completing a drilling operation, implementing fracturing for fracture forming at the horizontal well section of the first horizontal well, injecting a seawater fracturing fluid into the first horizontal well, and allowing the seawater fracturing fluid to flow into the natural gas hydrate reservoirs along the horizontal well section, so that fractures are formed in the hydrate reservoirs between the first horizontal well and the second horizontal well, and between the first horizontal well and the third horizontal well,
• then, injecting foam cement slurry into the horizontal well section of the first horizontal well, allowing the foam cement slurry to be distributed all over the natural gas hydrate reservoirs, and curing for forming, and
• finally, injecting a resin or oligomer chemical sand control agent into a periphery of the well to reduce or avoid a sand production rate during an exploitation of the natural gas hydrates at a later period;
• and
• (iii) yield improvement by combined exploitation of depressurization of the horizontal wells and heat injection
• injecting seawater into the natural gas hydrate reservoirs along the first horizontal well at a temperature of above 60° C., and meanwhile, reducing a bottom pore pressure of the second horizontal well and the third horizontal well, so as to improve a decomposition rate of the natural gas hydrates in the reservoirs under a collaborative action of the two operations.