Evaluation of wellbore cement integrity in contact with high temperature brine

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Conference Proceeding

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Strength retrogression occurs in cements at high temperatures when calcium silicate hydrate phase in hydrated cement converts to alpha dicalcium silicate hydrate phase. The higher the temperature, the quicker the rate of transformation of calcium silicate hydrates. This conversion changes the structure of the hydrated cement leading to increased porosity, permeability and lowered compressive strength. The real problem lies in the great increase of permeability which makes the cement conductive to corrosive formation fluids and therefore impairs the primary fiinction of cement as hydraulic barrier material. Class H cement cores (water to cement ratio: 0.38) with slurry density of 1.97 g/cc (16.40 ppg) were cured at constant temperatures of 90 °C and 100% relative humidity over a period of 28 days. In addition, cores with same slurry design were cured in water bath at ambient conditions for 28 days as control samples. Higher permeability values in cement cores cured at high temperature shows the onset of strength retrogression. Lower Vickers hardness measured in the cement sample cured confirms the onset of strength retrogression. This is as a result of packing of large, coarse calcium silicate hydrate crystals observed using scanning electron microscopic imaging technique.

Publication Source (Journal or Book title)

48th US Rock Mechanics / Geomechanics Symposium 2014

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