A study to determine the cement slurry behaviour to prevent fluid migration

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2010
Karakaya, Güray
Fluid migration behind the cased holes is an important problem for oil and gas industry both considering short terms and long terms after cementing operation. For many reasons like high formation pressures, high shrinkage rate of cement slurry while setting, lack of mechanical seal, channeling due to cement slurry setting profile, hydrocarbon migration may occur and lead expensive recompletion operations and sometimes abandonment. Solutions to this problem vary including high density-low fluid loss cement slurry or right angle cement setting profile. During this study, the effect of “free water” which is the basic quality property of API G class cement, on fluid migration potential has been tested for different samples and in combination with different physical conditions. For this study API G class cements have been used. In order to justify the quality of each cement sample standard API G class quality tests were conducted. Moreover, as a main instrument “Static Gel Strength Analyzer” is used to measure the static gel strength of cement slurry and how long it takes to complete transition time. Bolu cement, Nuh cement, and Mix G cement samples were tested according to their free fluid values which are %2.5, %5, %3.12 respectively, and it is found that the Bolu cement with lowest free fluid content has the lowest potential for fluid migration. As a conclusion, fluid migration through behind the cased hole is a major threat for the life of the well. Appropriate cement slurry system may easily defeat this threat and lead cost saving well plans. Key words: Fluid migration, fluid loss, transition time, channeling, right angle, API G class cement, free water, high formation pressure.