Method for creating branch seam with temporary plugging and pressure buildup using super absorbent resin

Abstract

A method for creating a branch fracture with temporary plugging and pressure buildup using super absorbent resin, comprising: setting a fracturing packer to fracture a target layer by pad fluid to form a main fracture; injecting into the main fracture pad fluid mixed with salt-intolerant super absorbent resin and performing replacement till depth of the main fracture, and then injecting pad fluid mixed with strong salt-tolerant super absorbent resin; after the strong salt-tolerant super absorbent resin absorbs water and expands to form a temporary plugging layer, re-injecting the pad fluid to create a branch fracture with pressure buildup; and lifting injection pressure to break up the temporary plugging layer formed by the strong salt-tolerant super absorbent resin to form residue, transporting the residue to the depth of the main fracture to bridge the temporary plugging layer formed, and re-building up pressure to create a branch fracture.

1 . A method for creating a branch fracture by temporary plugging and pressure buildup using absorbent resin, comprising the following steps:
 Step 1: setting a fracturing packer and using pad fluid to fracture a target layer to form a main fracture;   Step 2: injecting into the main fracture pad fluid mixed with a first absorbent resin and adding a pad fluid free of absorbent resin to displace the pad fluid mixed with the first absorbent resin until the pad fluid mixed with the first absorbent resin reaches a position which is 67%-90% of the depth of the main fracture, and then injecting pad fluid mixed with a second absorbent resin;   Step 3: after the second absorbent resin absorbs water and expands and forms a temporary plugging layer at a position which is 50-80 m away from an opening of the main fracture, injecting the pad fluid free of absorbent resin to create a branch fracture by building up the pressure;   Step 4: lifting injection pressure of the pad fluid to break up the temporary plugging layer formed by the second absorbent resin, forming broken second absorbent resin residue, transporting the broken second absorbent resin residue to the the temporary plugging layer formed by the first absorbent resin to be bridged to the temporary plugging layer formed by the first absorbent resin in the main fracture, and re-building up pressure to create a branch fracture;   Step 5: injecting pad fluid containing ammonium sulfate and hydrochloric acid to dissolve the first absorbent resin and the broken second absorbent resin residue; wherein the pad fluid containing ammonium sulfate and hydrochloric acid facilitates an increase in the length of the main fracture and of the branch fracture; and   Step 6: injecting sand carrying liquid to fill the main fracture and the branch fracture, subjecting all the injected liquid, adding the pad fluid free of absorbent resin for displacement and stopping the pump;   wherein in the fifth step, the ammonium persulfate is 15%-25% by weight of the pad fluid, and the hydrochloric acid is 5%-10% by weight of the pad fluid.   
     
     
         2 . The method according to  claim 1 , wherein the first absorbent resin in the second step is starch grafted polyacrylamide or cellulose grafted polyacrylamide, wherein the starch grafted polyacrylamide has a water absorption ratio of 1:30-80 by weight, a particle size range of 0.5 mm-2 mm, a compression strength of 0.05 MPa-1 MPa after per cubic centimeter of the starch grafted polyacrylamide is saturated with a brine, and the cellulose grafted polyacrylamide has a water absorption ratio of 1:40-85 by weight, a particle size range of 0.5 mm-2 mm, and a compression strength of 0.04 MPa-1.2 MPa after per cubic centimeter of the cellulose grafted polyacrylamide is saturated with the brine, and the second absorbent resin is a ternary copolymerized acrylic acid absorbent resin with a water absorption ratio of 1:150-270 by weight, a particle size range of 0.5 mm-1.5 mm, and a compression strength of 0.01 MPa-0.05 MPa after per cubic centimeter of the ternary copolymerized acrylic acid is saturated with the brine. 
     
     
         3 . The method according to  claim 2 , wherein the brine is normal saline of 0.9% NaCl. 
     
     
         4 . The method according to  claim 1 , wherein the the second step comprises the following steps: continuously injecting 5 m 3 -10 m 3  of the pad fluid mixed with the first absorbent resin into the main fracture at a speed of 3 m 3 /min-10 m 3 /min, and then injecting 5 m 3 -10 m 3  of the pad fluid containing no absorbent resin as displacement liquid to displace the first absorbent resin until the first absorbent resin reaches the position which is 67%-90% of the depth of the main fracture, and finally continuously injecting 8 m 3 -10 m 3  of the pad fluid mixed with the second absorbent resin into the main fracture at a speed of 1 m 3 /min-3 m 3 /min, wherein the first absorbent resin is 2%-8% by weight of the pad fluid, and the second absorbent resin is 10%-15% by weight of the pad fluid. 
     
     
         5 . The method according to  claim 1 , wherein the the third step comprises the following steps: after the second absorbent resin fully absorbs water and expands to form a temporary plugging layer, beginning to inject pad fluid into the main fracture at a speed of 5 m 3 /min-15 m 3 /min to build up pressure; during the injection process, finding that bottom hole pressure continuously increased until breakthrough pressure began to decrease, indicating that temporary plugging pressure has reached formation fracture pressure and began to form a branch fracture, then injecting 25 m 3  of the pad fluid at a speed of 2 m 3 /min-5 m 3 /min to increase the length of the branch fracture. 
     
     
         6 . The method according to  claim 5 , wherein if after pad fluid is injected in the third step, bottom hole pressure cannot be lifted, indicating that the amount of the second absorbent resin is insufficient to form a temporary plugging layer, mixing the second absorbent resin having a particle size of more than 1 mm and a mass fraction of 3%-5% into pad fluid which is then continuously injected into the main fracture until the pressure starts to continuously rise, stopping the addition, beginning to build up pressure to create a branch fracture. 
     
     
         7 . The method according to  claim 1 , wherein the the fourth step comprises the following steps: after the formation of the branch fracture at the front end of the main fracture is finished, beginning to continuously inject pad fluid; gradually increasing pumping pressure at a speed of 0.2 MPa/s; if it is found during the injection process that bottom hole pressure begins to greatly drop at a speed of not less than 0.5 MPa/s during increasing, indicating that the temporary plugging layer formed by the second absorbent resin has broken and collapsed, then stopping increasing pumping pressure and continuously injecting pad fluid at a speed of 2 m 3 /min-5 m 3 /min to transport the second absorbent resin residue to the depth of the main fracture; if bottom hole pressure starts to increase again at a speed of not less than 5 MPa/min during transportation, indicating that the broken second absorbent resin residue has been bridged to the temporary plugging layer formed by the first absorbent resin, and beginning to form temporary plugging, and performing pressure buildup to create a branch fracture for the second time in the same manner as in the third step. 
     
     
         8 . The method according to  claim 7 , wherein in the fourth step, pumping pressure is gradually increased at a speed of 0.2 MPa/s, and if bottom hole pressure is still not lowered after rising to 65 MPa, adding 0.05%-1% NaCl into pad liquid, and lifting osmotic pressure of pad fluid so that the second absorbent resin loses water and begins to shrink or adding 10%-15% ammonium persulfate into pad fluid to dissolve the second absorbent resin to help it break up and collapse. 
     
     
         9 . (canceled)