A cement which expands (or at least does not contract) under down-hole conditions can prevent microannular flow and can make bond log interpretation easier.

A comprehensive laboratory investigation of cement expansion using the most common cement expansion additives, calcium sulfate and sodium sulfate, was performed. Four API classes of cement were investigated from 75° to 200°F at pressures from atmospheric to 5000 psi. The slurries were cured in air, water, oil, and 100 percent humidity environments. The cements were mixed with three water contents. The expansion measurements were taken for ten days. The expansion measurements were of the type which measure the exterior dimensions of a cement sample as it cures.

The various curing environments are meant to simulate the curing environments experienced downhole. For instance, wells drilled with oil base mud would leave the wellbore area inundated with oil and thus the cement would be exposed to oil and not water during the curing period.

Several new additives for cement expansion have recently been introduced from the cementing service companies. Now that a thorough background study on existing materials has been completed, new materials can be more easily evaluated.

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