Abstract: A drilling mud, or other drilling fluid containing particulate expanded aggregates is effective to seal the fractures and openings and prevent lost circulation of the mud or fluid in a well. The expanded aggregates used are inorganic clays, shales and slates which are heat treated at temperatures up to about 3000.degree. F. to produce an expanded lattice structure having a series of interconnecting passages. The expanded aggregates are added to any conventional drilling mud, or other drilling fluids, either water-based or oil-based, in an amount sufficient to stop the fractures and openings in the formation. The proportion of the aggregates in the drilling mud, or other drilling fluid, will be varied as needed and will usually range from 1-33 parts by weight per 100 parts by weight of drilling mud. Water-based and oil-based drilling muds containing expanded aggregates are novel compositions.

Abstract: A method of sealing fractures and openings in an earth formation traversed by a well bore comprises adding particulate expanded aggregates to a drilling mud, or other drilling fluid, circulating through the well bore, which aggregates seal the fractures and openings and prevent lost circulation of the drilling mud, or other drilling fluid. The expanded aggregates used are inorganic clays, shales and slates which are heat treated at temperatures up to about 3000.degree. F. to produce an expanded lattice structure having a series of interconnecting passages. The expanded aggregates are added to any conventional drilling mud, or other drilling fluids, either water-based or oil-based, in an amount sufficient to stop the fractures and openings in the formation. The proportion of the aggregates in the drilling mud, or other drilling fluid, will be varied as needed and will usually range from 1-33 parts by weight per 100 parts by weight of drilling mud.