Evaluation of Highly Retarded Cement Systems Under Exposure to Radiation Sources for Oilfield Applications

Abstract

Cement slurries have been designed to remain liquid for extended periods of time (> weeks) until exposed to a radiation source to provide a triggered activation mechanism. The cement setting occurs in two stages. First, a triggered setting of an aqueous phase system forms a stiff gel; then, the gel hardens further and develops strength because of cement hydration. The initial set can be accomplished by means of the triggered mechanism, while final engineering properties are provided by the hardened cement. This paper describes the design and results of this initial work detailing the rheological behavior and mechanical properties of cement slurries on exposure to 14 MeV neutron radiation from an accelerator and ionizing sources currently used in wellbore logging, such as gamma radiation. Additionally, other radiation sources are described in terms of their potential for use in a wellbore environment. The triggered response of this system with relation to neutron energy and admixtures used in the cement design to impart direct response is discussed. Particular details are presented relative to usage of commercially available radiation sources and their efficacy in a wellbore environment. Correlations between energy output, calculated energy absorption, and cement response summarize the effects of this ionizing radiation on cement slurries containing admixtures designed to respond to such exposure. The discussed cement systems employ monomer and polymer chemistry specifically selected for use with radiation triggered systems. Use of these chemistries in cement as additives and in other systems, such as spacer fluids or drilling fluids, is demonstrated.