Low pH fracturing compositions

A process for fracturing a subterranean formation which comprises:

• introducing into said formation an aqueous gel at a flow rate and pressure sufficient to produce a fracture in said formation, said aqueous gel comprising:
• an aqueous fluid comprising water and up to about 80 percent alcohol by volume of the aqueous fluid;
• a gelling agent comprising a solvatable polysaccharide having a molecular weight in excess of about 100,000 selected from the group consisting of glucomannans, galactomannans, said gelling agent being present in an amount of from about 0.2 to about 1.25 percent by weight of said aqueous fluid;
• a buffer which can maintain the pH of the gel in the range of about 2.0 to about 4.5;
• an aluminum-based crosslinking composition comprising water, aluminum carboxylates, acetic acid and an agent capable of chelating aluminum, wherein said aluminum carboxylates are selected from the group consisting of salts of the homologous series comprising formic, acetic, propionic, and butyric acids, oxalic, malonic, and succinic acids, citric acid, glyoxylic acid, glycolic acid, o-, m- or p-phthalic acids and glucuronic acid;
• and
• a crosslinking retardant composition selected from the group consisting of xanthan gum and a slurry of xanthan gum in water.

A process for treating a subterranean formation penetrated by a well bore which comprises:

• preparing a base gel by mixing an aqueous fluid with a gelling agent selected from solvatable polysaccharides having molecular weight of at least about 100,000, said gelling agent being present in an amount of from about 0.2 to about 1.25 percent by weight of said aqueous fluid;
• admixing a buffer which can maintain the pH of the base gel and the range of about 2.0 to about 4.5;
• admixing xanthan gum wherein the ratio of xanthan gum to crosslinking composition is between about 0.00001:1 to about 10:1;
• admixing an aluminum-based crosslinking composition comprising water, alcohol, aluminum carboxylates, acetic acid and an agent capable of chelating aluminum;
• introducing said base gel containing said buffer, said crosslinking composition and said xanthan gum into said well bore;
• permitting said base gel and said crosslinking composition to react to form a crosslinked aqueous gel, wherein the crosslinking reaction time is increased by the presence of said xanthan gum;
• and
• introducing said crosslinked aqueous gel into said formation from said well bore at a flow rate and pressure sufficient to fracture said formation.