Rheology drilling fluid and method

Abstract

Drilling fluids having improved rheology under downhole temperature and pressure. The improved rheology (IR) drilling fluids are particularly suited for use in deepwater drilling operations. The IR drilling fluids are invert emulsion fluids with viscosifier to rheology modifier weight ratios between about 6 and about 14. The IR drilling fluids exhibit low shear yield point variance and/or yield point variance of below 60 percent based on high-temperature, high-pressure viscometer measurements.

We claim: 
     
         1 . A drilling fluid with improved rheology under downhole conditions, comprising:
 a continuous phase consisting of a paraffin, an olefin, a mineral oil, an ester, or a mixture of any combination thereof;   an internal phase consisting of an aqueous solution having one or more solutes in a concentration of about 10 to about 40 weight percent of the aqueous solution;   an emulsifier;   a polymeric rheology modifier;   a viscosifier comprising an organophilic clay;   wherein a weight ratio of the amount of the viscosifier to the amount of the polymeric rheology modifier is about 6 to about 14.   
     
     
         2 . The drilling fluid of  claim 1 , wherein the weight ratio of the amount of the viscosifier to the amount of the polymeric rheology modifier is about 8 to about 12. 
     
     
         3 . The drilling fluid of  claim 1 , wherein the weight ratio of the amount of the viscosifier to the amount of the polymeric rheology modifier is about 10. 
     
     
         4 . The drilling fluid of  claim 1 , wherein the amount of the viscosifier in the drilling fluid is about 0.3 to about 20 pounds per barrel. 
     
     
         5 . The drilling fluid of  claim 1 , wherein the amount of the polymeric rheology modifier in the drilling fluid is about 0.05 to about 2 pounds per barrel. 
     
     
         6 . The drilling fluid of  claim 1 , wherein the polymeric rheology modifier comprises a reaction product of a fatty acid and a polyamine. 
     
     
         7 . The drilling fluid of  claim 1 , wherein the amount of the continuous phase in the drilling fluid is about 40 to about 90 volume percent. 
     
     
         8 . The drilling fluid of  claim 1 , wherein the amount of the internal phase in the drilling fluid is about 5 to about 40 volume percent. 
     
     
         9 . The drilling fluid of  claim 1 , wherein the one or more solutes in the internal phase consists of calcium chloride, sodium chloride, calcium bromide, or a combination thereof. 
     
     
         10 . The drilling fluid of  claim 1 , wherein the one or more solutes in the internal phase consists of a glycol, a polyglycerine, or a combination thereof. 
     
     
         11 . The drilling fluid of  claim 1 , wherein the amount of the emulsifier in the drilling fluid is about 5 to about 20 pounds per barrel. 
     
     
         12 . The drilling fluid of  claim 1 , further comprising a weighting agent in an amount of up to 600 pounds per barrel, and wherein the weighting agent consists of barite. 
     
     
         13 . The drilling fluid of  claim 1 , further comprising a fluid loss control agent in an amount of about 0.5 to about 2 pounds per barrel, and wherein the fluid loss control agent consists of a polymeric fluid loss control additive or a styrene/acrylate copolymer. 
     
     
         14 . The drilling fluid of  claim 1 , further comprising an alkalinity control agent in an amount of about 1 to about 12 pounds per barrel, and wherein the alkalinity control agent consists of lime.