Methods for servicing subterranean wells

Abstract

Process fluids comprising more than 1 wt % polyacrylamide and a non-metallic crosslinker may be used to control lost circulation in subterranean wells. The process fluid is placed into a subterranean lost-circulation zone and allowed to crosslink, thereby forming a gel barrier that limits further flow of process fluid into the zone. The non-metallic crosslinker may preferably comprise one or more polylactams. A pH-adjusting agent may also be incorporated into the process fluid.

1 . A method for controlling lost circulation in a subterranean well, comprising:
 i. preparing a process fluid comprising more than 1 wt % polyacrylamide and a non-metallic crosslinker;   ii. placing the process fluid into a subterranean lost-circulation zone; and   iii. allowing the polyacrylamide to crosslink, thereby forming a gel barrier that limits further flow of process fluid into the zone.   
     
     
         2 . The method of  claim 1 , wherein the non-metallic crosslinker comprises a polylactam. 
     
     
         3 . The method of  claim 1 , wherein the non-metallic crosslinker comprises polyvinylpyrrolidone, polyvinylcaprolactam or a combination thereof. 
     
     
         4 . The method of  claim 3 , wherein the polyvinylpyrrolidone has a weight average molecular weight of greater than or equal to about 50,000 g/mol and less than or equal to about 2 million g/mol. 
     
     
         5 . The method of  claim 1 , wherein the non-metallic crosslinker has a weight average molecular weight greater than or equal to about 10,000 g/mol and less than or equal to about 2 million g/mol. 
     
     
         6 . The method of  claim 1 , wherein the polyacrylamide has a degree of hydrolysis less than or equal to about 40%. 
     
     
         7 . The method of  claim 1 , wherein the process fluid further comprises a pH-adjusting agent. 
     
     
         8 . The method of  claim 7 , wherein the polyacrylamide, non-metallic crosslinker, pH-adjusting agent or a combination thereof are encapsulated within a capsule or an emulsion or both. 
     
     
         9 . The method of  claim 8 , wherein the process fluid passes through a drill bit before entering the lost-circulation zone. 
     
     
         10 . The method of  claim 9 , wherein the encapsulated polyacrylamide, non-metallic crosslinker, pH-adjusting agent or a combination thereof are released upon passage through the drill bit, and the process-fluid pH is lower than or equal to about 3, or higher than or equal to about 9. 
     
     
         11 . A method for treating a subterranean well, comprising:
 i. preparing a process fluid comprising more than 1 wt % polyacrylamide and a non-metallic crosslinker;   ii. placing the process fluid into a subterranean lost-circulation zone; and   iii. allowing the polyacrylamide to crosslink, thereby forming a barrier that limits further flow of process fluid into the zone.   
     
     
         12 . The method of  claim 1 , wherein the non-metallic crosslinker comprises a polylactam. 
     
     
         13 . The method of  claim 1 , wherein the non-metallic crosslinker comprises polyvinylpyrrolidone, polyvinylcaprolactam or a combination thereof. 
     
     
         14 . The method of  claim 3 , wherein the polyvinylpyrrolidone has a weight average molecular weight of greater than or equal to about 50,000 g/mol and less than or equal to about 2 million g/mol. 
     
     
         15 . The method of  claim 1 , wherein the non-metallic crosslinker has a weight average molecular weight greater than or equal to about 10,000 g/mol and less than or equal to about 2 million g/mol. 
     
     
         16 . The method of  claim 1 , wherein the polyacrylamide has a degree of hydrolysis less than or equal to about 40%. 
     
     
         17 . The method of  claim 1 , wherein the process fluid further comprises a pH-adjusting agent. 
     
     
         18 . The method of  claim 17 , wherein the polyacrylamide, non-metallic crosslinker, pH-adjusting agent or a combination thereof are encapsulated within a capsule or an emulsion or both. 
     
     
         19 . The method of  claim 18 , wherein the process fluid passes through a drill bit before entering the lost-circulation zone. 
     
     
         20 . The method of  claim 19 , wherein the encapsulated polyacrylamide, non-metallic crosslinker, pH-adjusting agent or a combination thereof are released upon passage through the drill bit, and the process-fluid pH is lower than or equal to about 3, or higher than or equal to about 9.