Method for stimulating oil and gas reservoir volume by forming branch fractures in main fracture

Abstract

The present invention provides a method for further forming a plurality of small fractures in a main fracture. If a radial main fracture is further fractured axially to form a plurality of branch fractures, the stimulated volume of the oil and gas reservoir will be achieved to greatly increase the yield of dense oil and gas. The main contribution of the present invention is to form three-dimensional fracture networks for any low-permeability oil reservoirs to achieve stimulated reservoir volume. The concept is that an original main fracture is further fractured to form a plurality of branch fractures (the branch fractures form included angles with the original main fracture), and the locations for forming the branch fractures in the main fracture and even the size and length of the branch fractures can be controlled artificially, so that the branch fractures can be formed by fracturing where needed.

What is claimed is: 
     
         1 . A method for stimulating oil and gas reservoir volume by forming branch fractures in a main fracture, wherein
 explosives are detonated in the main fracture by pressurizing to form a plurality of branch fractures, which comprises a step of forming a plurality of branch fractures in the main fracture in stages and/or forming a plurality of branch fractures in the main fracture at once so that the main fracture is changed into a fracture network to improve the seepage of low-permeability oil and gas reservoirs.   
     
     
         2 . The method for stimulating oil and gas reservoir volume by forming branch fractures in a main fracture according to  claim 1 , wherein
 forming a plurality of branch fractures in the main fracture in stages comprises steps of:   adding fracturing fluid to the main fracture in stages after the completion of perforation;   adding fracturing fluid containing pressure-controlled explosives in the first stage, wherein the pressure-controlled explosives are located on the top of the main fracture after the completion of the fracturing fluid leak-off, injecting conventional fracturing fluid at high pressure and detonating the explosives to form the branch fractures in the main fracture;   adding the conventional fracturing fluid in the second stage to increase the length of the main fracture and the branch fractures formed in the first stage;   in the third stage, repeating the operations of the first stage, and in the fourth stage, repeating the operations of the second stage, during which the location, number and length of the branch fractures are controlled according to the leak-off amount of the fracturing fluid into the formation and the amount of the pressure-controlled explosives.   
     
     
         3 . The method for stimulating oil and gas reservoir volume by forming branch fractures in a main fracture according to  claim 2 , wherein
 forming a plurality of branch fractures in the main fracture in stages comprises:   a first step of fracturing the main fracture: running a pipe string for perforation and fracturing operations, and lifting the pipe string out after the completion of the operations;   a second step of injecting the fracturing fluid containing pressure-controlled explosives into the main fracture by a low-pressure pump; and running a dual-packer single-stick pipe string which comprises a top packer, a pressure guide sleeve and a bottom packer, wherein the fracturing fluid containing pressure-controlled explosives is injected after the top packer and the bottom packer are set, and the pressure-controlled explosives are located on the top of the main fracture after the completion of the fracturing fluid leak-off;   a third step of injecting spacer fluid into the main fracture by a high-pressure pump and detonating the pressure-controlled explosives: injecting the spacer fluid into the main fracture by a high-pressure pump; and perforating the main fracture when the pressure in the main fracture reaches a detonating point of the pressure-controlled explosives and detonating the pressure-controlled explosives to form the branch fractures in the main fracture;   a fourth step of continuing injecting the fracturing fluid into the main fracture by the high-pressure pump to further increase the length of the main fracture; after the completion of perforation in the branch fracture, injecting the fracturing fluid by the high-pressure pump to increase the length of the branch fractures;   a fifth step of repeating the second step to the fourth step as needed, and determining how many branch fractures need to be formed in the main fracture according to the requirements of fracturing design, and repeating the second step to the fourth step; and   a sixth step of discharging the explosives from the main fracture and the branch fractures.   
     
     
         4 . The method for stimulating oil and gas reservoir volume by forming branch fractures in a main fracture according to  claim 1 , wherein
 forming a plurality of branch fractures in the main fracture at once comprises: after the completion of perforation, increasing the length of the main fracture by injecting fracturing fluid,   then placing the explosives in the main fracture in advance,   igniting the explosives in the main fracture by an igniter to form the branch fractures,   injecting the fracturing fluid into the main fracture again after the initiation of detonation to increase the length of the branch fractures, and   controlling the location and the length of the branch fractures according to the amount or concentration of the explosives injected.   
     
     
         5 . The method for stimulating oil and gas reservoir volume by forming branch fractures in a main fracture according to  claim 4 , wherein
 forming a plurality of branch fractures in the main fracture at once comprises:   a first step of fracturing the main fracture: running a pipe string for perforation and fracturing operations, and adding the fracturing fluid to increase the length of the main fracture after the completion of the operations;   a second step of adding fracturing fluid containing pressure-controlled explosives: in this step, a method for adding pressure-controlled explosives in stages is used, when there is fracturing fluid containing pressure-controlled explosives at different depths of the main fracture, alternately injecting the fracturing fluid and the fracturing fluid containing pressure-controlled explosives by pumps at time intervals by calculating leak-off amount and discharge amount, and placing the explosives at destination locations;   a third step of detonating the explosives by an electronic igniter: detonating explosives by an igniter after the explosives have been completely injected by the pumps, and re-perforating the main fracture to form the branch fractures; and   a fourth step of fracturing the branch fractures: adding the fracturing fluid to the main fracture again, where, at this moment, the fracturing fluid permeates into the branch fractures to increase the length of the branch fractures, so that the main fracture and the branch fractures form a fracture network to improve the seepage of the oil and gas reservoir.