Enzymes for removing sulfurous compounds in downhole fluids

Abstract

Cysteine synthase or O-Acetyl-L-Serine Sulfhydrylase enzymes, such as those derived from the Aeropyrum pernix bacterium, may be used in additive compositions, fluid compositions, and methods for decreasing or removing hydrogen sulfide from recovered downhole fluids and/or the subterranean reservoir wellbore from which the downhole fluid was recovered. The fluid composition may include at least one cysteine synthase enzyme and a base fluid, such as a drilling fluid, a servicing fluid, a production fluid, a completion fluid, an injection fluid, a refinery fluids, and combinations thereof.

What is claimed is: 
     
         1 . An additive composition for a base fluid selected from the group consisting of a drilling fluid, a completion fluid, a production fluid, a servicing fluid, an injection fluid, a refinery fluid, and combinations thereof; wherein the additive composition comprises at least one cysteine synthase enzyme that is at least 75% homologous to the cDNA sequence of SEQ ID NO:1. 
     
     
         2 . The additive composition of  claim 1 , wherein the concentration of the at least one cysteine synthase enzyme within the additive composition ranges from about 1 nanomolar (nM) independently to about 5 millimolar (mm). 
     
     
         3 . The additive composition of  claim 1 , further comprising an additional component selected from the group consisting of a pyridoxal phosphate, O-acetyl-serine, dithiothreitol (DTT), and combinations thereof. 
     
     
         4 . The additive composition of  claim 1 , wherein the at least one cysteine synthase enzyme forms cysteine in the absence of pyridoxal phosphate. 
     
     
         5 . The additive composition of  claim 1 , further comprising O-acetyl-L-serine in a concentration ranging from about 1 mM to about 20 mM. 
     
     
         6 . The additive composition of  claim 1  further comprising dithiothreitol (DTT) in a concentration ranging from about 0.25 mM to about 5 mM. 
     
     
         7 . A fluid composition comprising:
 a base fluid selected from the group consisting of drilling fluids, servicing fluids, production fluids, completion fluids, injection fluids, refinery fluids, and combinations thereof; and   at least one cysteine synthase enzyme that is at least 75% homologous to the cDNA sequence of SEQ ID NO:1.   
     
     
         8 . The fluid composition of  claim 7 , wherein the concentration of the at least one cysteine synthase enzyme within the additive composition ranges from about 1 nanomolar (nM) independently to about 5 millimolar (mm) as compared to the total base fluid. 
     
     
         9 . The fluid composition of  claim 7 , wherein the fluid composition further comprises an additional component selected from the group consisting of a pyridoxal phosphate, O-acetyl-serine, dithiothreitol (DTT), and combinations thereof. 
     
     
         10 . The fluid composition of  claim 7 , wherein the fluid composition further comprises at least one sulfur-containing compound; and wherein the fluid composition comprises the sulfur-containing compound in a reduced amount as compared to an identical fluid composition absent the at least one cysteine synthase enzyme. 
     
     
         11 . The fluid composition of  claim 7 , further comprising O-acetyl-L-serine in a concentration ranging from about 1 mM to about 20 mM. 
     
     
         12 . The fluid composition of  claim 7  further comprising DTT in a concentration ranging from about 0.25 mM to about 5 mM.