Cement compositions with improved corrosion resistance and methods of cementing in subterranean formations

Abstract

The present invention relates to subterranean well cementing operations, and more particularly, to cement compositions having improved corrosion resistance and methods of using such compositions in subterranean formations. The cement compositions generally include an unhydrated cement that includes a high alumina cement, a silica source, and a soluble phosphate; and a set retarder that includes a water soluble carboxylic acid. Optionally, other additives may be included, such as accelerants, dispersants, weighting agents, and the like.

1 . A cement composition comprising: 
 an unhydrated cement comprising: 
 a high alumina cement,  
 a silica source, and  
 a soluble phosphate; and  
   a set retarder comprising a water soluble carboxylic acid.    
   
   
       2 . The cement composition of  claim 1  wherein the high alumina cement has an alumina concentration in the range of from about 40% to about 80% of the weight of the high alumina cement.  
   
   
       3 . The cement composition of  claim 1  wherein the high alumina cement is present in the cement composition in an amount in the range of from about 20% to about 80% by weight of the unhydrated cement.  
   
   
       4 . The cement composition of  claim 1  wherein the silica source is present in the cement composition in an amount sufficient to provide a desired level of corrosion resistance.  
   
   
       5 . The cement composition of  claim 1  wherein the silica source comprises vitrified shale.  
   
   
       6 . The cement composition of  claim 4  wherein the silica source further comprises fly ash.  
   
   
       7 . The cement composition of  claim 1  wherein the silica source is present in the cement composition in an amount in the range of from about 20% to about 80% by weight of the unhydrated cement.  
   
   
       8 . The cement composition of  claim 1  wherein the soluble phosphate is present in the cement composition in an amount sufficient to provide a desired level of corrosion resistance.  
   
   
       9 . The cement composition of  claim 1  wherein the soluble phosphate is present in the cement composition in an amount in the range of from about 1% to about 10% by weight of the unhydrated cement.  
   
   
       10 . The cement composition of  claim 1  wherein the soluble phosphate is selected from the group consisting of sodium hexametaphosphate, sodium polyphosphate, vitreous sodium phosphate, and mixtures thereof.  
   
   
       11 . The cement composition of  claim 1  wherein the set retarder is present in the cement composition in an amount sufficient to prevent the cement from setting until a desired time after the cement has been placed in a subterranean formation.  
   
   
       12 . The cement composition of  claim 1  wherein the set retarder is present in the cement composition in an amount in the range of from about 0.1% to about 5% by weight of the unhydrated cement.  
   
   
       13 . The cement composition of  claim 1  further comprising a fluid loss control additive, a weighting agent, a defoamer, a surfactant, mica, fumed silica, a salt, a dispersant, a formation conditioning agent, an expanding additive, microspheres, or an accelerant.  
   
   
       14 . The cement composition of  claim 1  further comprising water in an amount sufficient to form a pumpable slurry.  
   
   
       15 . The cement composition of  claim 14  wherein the water is present in the cement composition in an amount in the range of from about 30% to about 50% by weight of the unhydrated cement.  
   
   
       16 . The cement composition of  claim 14  wherein the water is fresh water, salt water, brine, sea water, or a mixture thereof.  
   
   
       17 . The cement composition of  claim 1  wherein the cement composition further comprises carbon fibers, present in the cement composition in an amount sufficient to achieve a desired tensile strength for the set cement.  
   
   
       18 . The cement composition of  claim 17  wherein the carbon fibers have a mean length of 150 microns.  
   
   
       19 . The cement composition of  claim 17  wherein the carbon fibers are present in the cement composition in an amount in the range of from about 1% to about 15% by weight of the unhydrated cement.  
   
   
       20 . The cement composition of  claim 1  wherein the cement composition further comprises inert ground rubber particles, present in an amount sufficient to achieve a desired degree of ductility for the set cement.  
   
   
       21 . The cement composition of  claim 20  wherein the rubber particles have a mean length of less than about ¼″.  
   
   
       22 . The cement composition of  claim 20  wherein the rubber particles are present in the cement composition in an amount in the range of from about 10% to about 30% by weight of the unhydrated cement.  
   
   
       23 . The cement composition of  claim 1  wherein the density of the cement composition is in the range of from about 6 to about 23 pounds per gallon.  
   
   
       24 . The cement composition of  claim 24  wherein the cement composition is a low-density cement composition.  
   
   
       25 . The cement composition of  claim 1  wherein the high alumina cement has an alumina concentration in the range of from about 40% to about 80% of the weight of the high alumina cement; wherein the high alumina cement is present in the cement composition in an amount in the range of from about 20% to about 80% by weight of the unhydrated cement; wherein the silica source comprises vitrified shale; wherein the silica source is present in the cement composition in an amount in the range of from about 20% to about 80% by weight of the unhydrated cement; wherein the soluble phosphate is sodium hexametaphosphate present in the cement composition in an amount in the range of from about 1% to about 10% by weight of the unhydrated cement; and wherein the set retarder is present in an amount in the range of from about 0.1% to about 5% by weight of the unhydrated cement.