Gas migration represents 25% of the primary cement jobs failures. For this reason, studies have been done in order to evaluate several properties of cement slurry like fluid loss, permeability, static gel strength, and others. However, the study of these variables has not shown separately a method to prevent the gas migration and which of these properties of cement slurry have to be controlled to avoid such problem. This paper describes a methodology to control the gas migration. The results of this study were validated with field experiences. The methodology consists of the next three steps: the first one is the evaluation of the Flow Potential Factor (FPF) which predicts severity of the problem. Then, the static gel strength is measured as a function of time, obtaining the transition time of the cement slurry. Finally, pressure reduction due to static gel strength versus time is simulated with the Fluid Migration Analyzer (FMA), validating gas migration through cement slurry. Three wells were study in Santa Barbara and San Joaquín fields located in Eastern Venezuela. In each well, pore pressure of the gas zone, temperature, gas zone depth and the annular space across the gas zone were used to determine the FPF. The results of this study agree with field experiences, based on quantitative measurements like transition time and FPF. This methodology allows selecting the optimum cement slurry design in a way that prevents industrial accidents and assuring the well life.
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