Completion and workover fluid

In the method for completion or workover of a well penetrating a subterranean reservoir wherein a completion or workover fluid is passed through the well into contact with the subterranean reservoir as part of the completion or workover method, the improvement which comprises (1) employing as the completion or workover fluid an aqueous composition comprising an admixture of:

• (a) a hydroxy containing aluminum component formed by mixing in an aqueous medium and under a high degree of agitation a water-soluble basic agent selected from the group consisting of an alkali metal aluminate, alkali metal hydroxide, ammonium hydroxide and mixtures thereof with a water-soluble acidic agent selected from an inorganic acid, aluminum chloride, aluminum sulfate, aluminum nitrate, their hydrates and mixtures thereof;
• at least one of said basic and acidic agents being an aluminum containing compound:
• said acidic and basic agents being reacted in a ratio such that the resultant product imparts to said aqueous medium a pH of from at least about 8 to about 10.3, said component being present in the aqueous composition in an amount of from about 0.5 to 10 weight percent;
• and
• (b) a fluid loss control agent selected from the group consisting of
• (i) a reaction product formed in an aqueous acidic medium having a pH of less than about 5.5 between polyvinyl alcohol having a weight average molecular weight of at least 20,000 with at least 0.01 percent of stoichiometry of a compound containing at least one aldehyde group therein or capable of generating in situ at least one aldehyde group;
• (ii) a cross-linked hydroxyalkyl cellulose reaction product, said reaction product formed by contacting in an aqueous medium a hydroxy C.sub.1 -C.sub.3 alkyl cellulose and from about 0.01 to 200 percent of stoichiometry based on the hydroxy groups of the cellulose of an agent capable of cross-linking said cellulose, said agent being epihalohydrin or said agent being a compound having a least one aldehyde group therein or a compound capable of generating an aldehyde group in situ;
• the reaction between said hydroxyalkyl cellulose and ephihalohydrin being carried out in an aqueous basic medium having a pH of about 9.5 or more and the reaction between said hydroxyalkyl cellulose and said compound having or capable of generating at least one aldehyde group therein being carried out in an aqueous acidic medium having a pH of about 5.5 or less;
• and
• (iii) mixtures therof;
• said fluid loss control agent being present in the aqueous composition in an amount of about 0.3 to 5 weight percent;
• and
• (2) displacing said completion or workover fluid and treating the well with acid to dissolve away any solid cake layer from the completion or workover fluid that has deposited on the walls of the well.