Methods for Servicing Subterranean Wells

Abstract

Pumpable process-fluid compositions comprise polyacrylamide, a non-metallic crosslinker and a pH-adjustment material. Such compositions have utility in the context of controlling lost circulation in subterranean wells. Upon entering at least one lost circulation zone, the compositions crosslink, thereby forming a barrier that minimizes or stops fluid flow from the wellbore into the lost circulation zone.

1 . A method for controlling lost circulation in a subterranean well, comprising:
 i. preparing a process fluid composition comprising water, less than 1 wt % polyacrylamide, a non-metallic crosslinker and a pH adjustment agent;   ii. pumping the composition down the wellbore and into at least one lost circulation zone, thereby establishing a filtration process between the wellbore and the lost circulation zone;   iii. allowing the water to flow into the lost circulation zone, thereby forming a filter cake in which the polyacrylamide concentration rises above 1 wt %;   iv. allowing the polyacrylamide to crosslink and convert the filter cake into a barrier that blocks the lost circulation 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 higher than or equal to about 0% and lower than or equal to about 40%, and the molecular weight of the polyacrylamide is between about 10,000 g/mol and 20 million g/mol. 
     
     
         7 . The method of  claim 1 , wherein the process fluid composition further comprises fibers. 
     
     
         8 . The method of  claim 1 , wherein the fiber concentration in the process fluid is between about 28.5 kg/m 3  and about 171 kb/m 3 . 
     
     
         9 . The method of  claim 1 , wherein the fiber length is between about 1 mm and about 15 MM. 
     
     
         10 . The method of  claim 1 , wherein the pH of the process fluid is higher than or equal to 11 or lower than or equal to 1 when the fluid is adjacent to or inside the lost circulation zone.