The problems due to lost circulation events may represent a major source of expenses for drilling operators, even if their consequences do not have all the same level of gravity. Probably the most problematic situations are the naturally fractured formations where the operator may face total loss with no mud return in the annular.

The voids or large fractures encountered in this case are often far too large to be plugged with conventional Lost Circulation Material. For these severe losses, the failure of extreme solutions as cement injection may even lead to loss of the well. Recently, treatments based on cross-linked pills have shown their effectiveness to plug large fractures under downhole conditions of pressure and temperature.

This paper describes the research and development process to formulate a new cross-linked pill usable to control severe losses: this new pill is a nanocomposite organic/inorganic gel. Formulation strategy, laboratory procedures and experimental results will be described. The gelation time, the viscosity before setting, the gel strength formed and the dependence of these parameters with pressure, temperature and physico-chemical environment are characterized with specific experimental devices. Particular components of the formulation give excellent visco-elastic properties to the nanocomposite gel, enhancing the ability to sustain pressures peaks.

The typical final formulation, which is easily prepared on site (dry blend formulation) gives remarkable properties regarding pumping through drill pipes, adjustment of setting time and especially strength of the lost zone sealing.

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