Abstract: A method for determining the success of a multiple perforation operation by determining whether all perforations are open comprising providing a fluid loss control composition which carries one or more materials designed to form a filter cake on the wellbore wall, at least one of the filter cake forming materials being radioactively tagged, injecting the fluid loss control composition into the wellbore and into the perforations to build up a filter cake on the wellbore wall behind the perforations and running a nuclear log survey in the wellbore to determine which of the perforations were sufficiently open to the wellbore wall to establish a filter cake buildup thereon.

Abstract: A method for determining the vertical extent of a fracture in a wellbore wall wherein a fluid loss control composition is employed which contains at least at one filter cake forming material which has been radioactively tagged so that upon injection of the fluid control composition into the wellbore in the vicinity of the fracture, the filter cake is built up along the fracture and thereafter, upon running a nuclear log survey in the wellbore to determine the vertical extent of the filter cake, the vertical extent of the fracture is also thereby determined.