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Methods of cementing in a subterranean formation include passing a swelling agent to a permeable zone in a subterranean formation. The swelling agent is combined with a carrier fluid before being passed to the permeable zone. Upon contacting an aqueous fluid, the swelling agent swells in the permea

Methods of cementing in a subterranean formation include passing a swelling agent to a permeable zone in a subterranean formation. The swelling agent is combined with a carrier fluid before being passed to the permeable zone. Upon contacting an aqueous fluid, the swelling agent swells in the permeable zone. The aqueous fluid may already be present in the subterranean formation, or alternatively, it may be introduced to the subterranean formation after passing the swelling agent into the subterranean formation. The swelling agent substantially inhibits a cement slurry subsequently pumped into the subterranean formation from passing through the permeable zone. The cement slurry therefore continues flowing down through the casing and up through the annulus where it sets and forms a strong cement column.

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What is claimed is: 1. A method of cementing a wellbore in a subterranean formation, comprising: completing drilling of the wellbore; subsequently passing a swelling agent to a permeable zone in the subterranean formation, wherein the swelling agent contacts an aqueous fluid, causing the swelling a

What is claimed is: 1. A method of cementing a wellbore in a subterranean formation, comprising: completing drilling of the wellbore; subsequently passing a swelling agent to a permeable zone in the subterranean formation, wherein the swelling agent contacts an aqueous fluid, causing the swelling agent to swell in the permeable zone; and pumping a cement slurry into the subterranean formation, wherein the swelling agent substantially inhibits the cement slurry from passing through the permeable zone. 2. The method of claim 1 wherein the swelling agent is selected from the group consisting of crosslinked polyacrylamide, crosslinked polyacrylate, copolymers of acrylamide and acrylate monomers, a starch backbone grafted with acrylonitrile and acrylate, polymers of two or more of allylsulfonate, 2-acrylamido-2-methyl-1-propanesulfonic acid, 3-allyloxy-2-hydroxy-1-propane-sulfonic acid, acrylamide, and acrylic acid monomers, and combinations thereof. 3. The method of claim 1 wherein the swelling agent is selected from the group consisting of hydrolyzed polyacrylonitrile, carboxyalkyl cellulose, carboxyalkyl starch, salts of carboxyalkyl cellulose, carboxyalkyl polysaccharide, and combinations thereof. 4. The method of claim 1 wherein the swelling agent comprises a blend of two or more materials having different rates of water absorption. 5. The method of claim 1 wherein the swelling agent comprises particles having different sizes. 6. The method of claim 1 wherein the aqueous fluid is fresh water produced by the subterranean formation. 7. The method of claim 1, further comprising combining the swelling agent with a carrier fluid prior to said passing the swelling agent to the permeable zone. 8. The method of claim 7 wherein the aqueous fluid is pumped into the subterranean formation subsequent to said passing the swelling agent and the carrier fluid into the subterranean formation. 9. The method of claim 8 wherein the aqueous fluid is fresh water. 10. The method of claim 9 wherein the carrier fluid comprises at least one of a non-aqueous solution and a metal salt aqueous solution. 11. The method of claim 10 wherein a metal salt is present in the aqueous solution in an amount greater than about 1 weight % per total weight of the aqueous solution. 12. The method of claim 11 wherein the metal salt aqueous solution is saturated. 13. The method of claim 10 wherein the metal salt aqueous solution comprises at least one of an alkaline earth metal salt and an alkali metal salt. 14. The method of claim 10 wherein the metal salt aqueous solution comprises at least one of a NaCl aqueous solution, a KCl aqueous solution, and a CaCl2 aqueous solution. 15. The method of claim 7 wherein the swelling agent is present a composition comprising the swelling agent and the carrier fluid in an amount ranging from about 0.5% to about 25% by weight of the composition. 16. The method of claim 7 wherein the swelling agent is present a composition comprising the swelling agent and the carrier fluid in an amount ranging from about 1% to about 10% by weight of the composition. 17. The method of claim 1 wherein the cement slurry is pumped into the subterranean formation during a primary cementing process. 18. The method of claim 7, further comprising combining a silicate solution with the swelling agent prior to said passing the swelling agent to the permeable zone, the silicate solution comprising sodium silicate, potassium silicate, or both, and wherein the silicate solution is the in carrier fluid or is in addition to the carrier fluid. 19. The method of claim 18, further comprising combining the silicate solution with a gelling agent to cause it to gel. 20. The method of claim 18, further comprising contacting the silicate solution with an aqueous calcium salt solution subsequent to placing the silicate solution containing the swelling agent in the permeable zone, thereby forming an insoluble calcium silicate barrier in the permeable zone. 21. The method of claim 18 wherein the cement slurry, which comprises calcium, contacts the silicate solution subsequent to placing the silicate solution containing the swelling agent in the permeable zone, thereby forming an insoluble calcium silicate barrier in the permeable zone. 22. The method of claim 19 wherein the gelling agent comprises at least one of an acid, an acid producing chemical, and a hydrogen ion producing chemical. 23. The method of claim 19 wherein the gelling agent comprises at least one of (a) esters and lactones capable of undergoing hydrolysis in the presence of the silicate solution, (b) amides, and (c) a mixture of a reducing agent and an oxidizing agent capable of undergoing an oxidation-reduction reaction in the presence of the sodium silicate solution. 24. The method of claim 18 wherein the silicate solution is produced from a silicate powder comprising a mixture of sodium silicate and potassium silicate. 25. The method of claim 24 wherein the molar ratio of silicon dioxide to sodium oxide in the sodium silicate is in the range of from about 1.5:1 to about 3.3:1. 26. The method of claim 25 wherein the molar ratio of silicon dioxide to potassium oxide in the potassium silicate is in the range of from about 1.5:1 to about 3.3:1. 27. The method of claim 26 wherein the silicate powder has a water content in the range of from about 14% to about 16% by weight of hydrated silicate.