Re-use of surfactant-containing fluids

A method for filtering a fluid comprising water, at least one surfactant and fine solids, the method comprising:

• contacting the fluid with a particle pack comprising substrate particles and comparatively smaller particulate additives, where the particulate additives:
• have a mean particle size from about 4 nm to about 500 nm, and
• are selected from the group consisting of alkaline earth metal oxides, alkaline earth metal hydroxides, alkali metal oxides, alkali metal hydroxides, transition metal oxides, transition metal hydroxides, post-transition metal oxides, post-transition metal hydroxides, piezoelectric crystals, pyroelectric crystals, and mixtures thereof;
• and
• removing at least a portion of the fine solids therefrom to give a filtered fluid containing the surfactant, where the particulate additives are present in the particle pack in an amount effective to remove at least a portion of the fine solids.

A method for filtering an aqueous fluid gelled with at least one viscoelastic surfactant in an amount effective to gel the aqueous fluid and further comprising fine solids, the method comprising:

• contacting the fluid with a particle pack comprising substrate particles and comparatively smaller particulate additives, where the particulate additives:
• have a mean particle size of 1000 nm or less, and
• are selected from the group consisting of alkaline earth metal oxides, alkaline earth metal hydroxides, alkali metal oxides, alkali metal hydroxides, transition metal oxides, transition metal hydroxides, post-transition metal oxides, post-transition metal hydroxides, piezoelectric crystals, pyroelectric crystals, and mixtures thereof;
• breaking the gel of the gelled fluid prior to or simultaneously with contacting the fluid with the particle pack;
• removing at least a portion of the fine solids therefrom to give a filtered fluid containing the surfactant, where the particulate additives are present in the particle pack in an amount effective to remove at least a portion of the fine solids;
• and
• reusing the filtered fluid containing the surfactants.