Hydrothermal geothermal development method of multilateral well closed circulation

1. A hydrothermal geothermal development method of multilateral well closed circulation, comprises the steps of:

(1) dividing a geothermal reservoir into single layers of different geological conditions according to geothermal reservoir geological conditions, wherein an upper single layer with a lower water temperature and a higher permeability is taken as a recharge layer, and a lower single layer with a higher water temperature is taken as a production layer;

(2) determining a geothermal reservoir burial depth, designing a drilling engineering scheme, and drilling a vertical hole of a branch hole to reach a reservoir bottom;

(3) tripping a production casing into the vertical hole, and injecting cement for well cementation;

(4) performing casing lateral windowing in the vertical hole corresponding to the recharge layer, drilling at least one first branch radial horizontal hole into the recharge layer to form a recharge branch hole, and tripping a water filtering pipe of the recharge layer into the recharge branch hole for well completion;

(5) performing casing lateral windowing in the vertical hole corresponding to the production layer, drilling at least one second branch radial horizontal hole into the production layer to form a production branch hole, and tripping a water filtering pipe of the production layer into the production branch hole for well completion;

(6) tripping a guiding pipe into the production casing of the vertical hole, with a depth thereof reaching a well section between the recharge layer and the production layer;

(7) communicating the guiding pipe with the production branch hole, so that the guiding pipe is communicated with an annulus of the casing and the recharge branch hole to form a geothermal fluid circulation passageway;

(8) tripping a packer at a guiding shoe of the guiding pipe to isolate the guiding pipe and the annulus of the casing from each other, so as to prevent the recharge layer from being communicated with geothermal fluid of the production layer in the vertical hole;

(9) under a pressure difference between a stratum and the production branch hole, causing the geothermal fluid of the production layer to flow into the production branch hole, converge into the vertical hole and be exploited to the ground via the guiding pipe;

(10) utilizing heat of the exploited high-temperature geothermal fluid on the ground, so that the high-temperature geothermal fluid releases heat and is changed into low-temperature geothermal fluid, and re-injecting cooled low-temperature geothermal fluid into the recharge branch hole from the guiding pipe and the annulus of the casing using a high-pressure pump, so that the cooled low-temperature geothermal fluid flows into the recharge layer;

(11) under the gravity and an injection-production pressure difference, causing the low-temperature geothermal fluid entering the recharge layer to flow from the upper recharge layer to the lower production layer, then flow into the production branch hole after sufficiently exchanging heat with the geothermal reservoir during seepage, and exploited to the ground via the guiding pipe.

2. The hydrothermal geothermal development method of multilateral well closed circulation according to claim 1 , wherein a plurality of the first branch radial horizontal holes are drilled into the recharge reservoir, and a plurality of the second branch radial horizontal holes are drilled into the production layer.

3. The hydrothermal geothermal development method of multilateral well closed circulation according to claim 1 , wherein the number of the recharge layers is plural.

4. The hydrothermal geothermal development method of multilateral well closed circulation according to claim 3 , wherein the number of the production layers is plural.

5. The hydrothermal geothermal development method of multilateral well closed circulation according to claim 4 , wherein the number of the recharge layers is 2 to 4, and the number of the production layers is 2 to 4.

6. The hydrothermal geothermal development method of multilateral well closed circulation according to claim 1 , wherein both the water filtering pipe of the recharge layer and the water filtering pipe of the production layer both strainer-packing and wires-wrapping drilled water filtering pipes.

7. The hydrothermal geothermal development method of multilateral well closed circulation according to claim 2 , wherein each of the first branch radial branch holes has a length of 100 to 500 m.

8. The hydrothermal geothermal development method of multilateral well closed circulation according to claim 2 , wherein each of the second branch radial branch holes has a length of 100 to 500 m.

9. The hydrothermal geothermal development method of multilateral well closed circulation according to claim 1 , wherein well cementation for a well section of the production layer is performed using high-thermal conductivity cement paste with a thermal conductivity coefficient more than 30 W/m·K.

10. The hydrothermal geothermal development method of multilateral well closed circulation according to claim 4 , wherein 4 to 8 first branch radial branch holes can be drilled into each of the recharge layers, and 4 to 8 second branch radial branch holes can be drilled into each of the production layers.