Self-generating heat process for in-situ conversion of medium-low mature and organic-rich shale

A self-generating heat process for in-situ converting medium-low mature and organic-rich shale, the process comprises following steps:

• Step 1:
• determining a target area of self-generating heat in-situ conversion of medium-low mature and organic-rich shale, formation conditions of the target area being that:
• vitrinite reflectance of the medium-low mature and organic-rich shale formation is from 0 to less than 1%, oil content of the medium-low mature and organic-rich shale formation is more than 5%, thickness of the medium-low mature and organic-rich shale formation is more than 15m, water content of the medium-low mature and organic-rich shale formation is from 0 to less than 5% and burial depth of the medium-low mature and organic-rich shale formation is from 0 to less than 3000m;
• Step 2:
• arranging a well pattern in the target area as described in step 1, which adopts an inverse nine-point well pattern, wherein a ratio of an injection well pattern to a production well pattern being 3:1;
• Step 3:
• reconstructing reservoir on the medium-low mature and organic-rich shale formation by volume fracturing and shock wave fracturing in turn to form a fracture network, and a ratio of permeability of fractures to permeability of matrix is less than 10000, the fracture spacing being from 0.1 meters to less than 0.5 meters;
• Step 4:
• after reservoir reconstruction, preheating vicinity of the injection well of the medium-low mature and organic-rich shale formation, with preheating temperature reaching 300° C. and a preheating radius around the injection well reaching 2 m;
• Step 5:
• after preheating, injecting ambient temperature air into the injection well, controlling a pressure at the bottom of the injection well to be from 5 MPa to less than 20 MPa, and ensuring that the pressure at the bottom of the production well is same with formation fluid pressure, with an injection of ambient temperature air, an autogenous heat reaction being triggered, and along a direction of displacement, a chemical reaction zone consisting of a residue zone, an autogenous heat zone, a cracking zone and a preheating zone in sequence is formed in the medium-low mature and organic-rich shale formation between the injection well and the production well, heat being released by oxidation reaction of residues generated after kerogen thermal cracking so as to realize convection heating the medium-low mature and organic-rich shale formation, oil and gas products from pyrolysis of kerogen entering the production wells through fractures, and being lifted to ground,
• wherein the reverse nine-point well pattern includes at least one well unit, each of which includes a production well located at the center of a rectangle, and an injection well located at four vertex positions of the rectangle and four center positions of four edges of the rectangle,
• wherein in Step 5, an air injection amount is from greater than 140 m3/(h·m) to 560 m3/(h·m), and an air injection time is until the temperature of the production well reaches ambient temperature,
• wherein in Step 5, when a volume fraction of CO2 in the production well is from 0 to less than 5%, it is necessary to increase the amount of air injected to 560 m3/(h·m).