In a typical well cementing operation, a cement slurry is pumped into the annulus between the well casing and the bore hole. As the cement slurry hydrates, it undergoes a volume change which translates into bulk expansion or shrinkage. Knowing the amount of expansion or shrinkage allows users to design cement systems which can achieve optimal bonding with the borehole and well casing without sacrificing the integrity of the cement matrix. The Circular Cement Expansion Mold is designed to measure the expansion or shrinkage of well cement slurries according to the guidelines in API Recommended Practice 10B-5.
The Circular Cement Expansion Mold has an external ring with a vertical slit on one side to allow it to expand. Before testing begins, the width of the gap is measured with the included micrometer. The expansion mold is filled with a cement slurry and cured in a water bath or curing chamber. As the cement cures, the external ring will expand or contract with the cement slurry. At the end of the test, the gap is measured again to determine the expansion factor.
When wet cement begins to set, the crystals that form the set cement matrix take up less volume than the initial reactants that make up the base cement blend mixture. As a result of the chemical reaction, the cement undergoes a net reduction in volume. This phenomenon is called bulk shrinkage. When the cement is in contact with water during the setting process, cement hydration consumes the water as a part of the chemical reaction. The influx of water, chemical shrinkage, into the cement matrix offsets the bulk shrinkage. The result is hardened cement that experiences significantly less volumetric shrinkage.
For cement that is placed in an oil well, the phenomenon of shrinkage is problematic. Volumetric shrinkage causes the cement to pull away from both the formation and the steel casing. The result is a loss of zonal isolation, which is one of the most basic functions of oil well cement. To overcome situations where shrinkage is a potential issue, cement service companies add certain additives to promote expansion of the set cement. The expansion of the cement promotes bond integrity between the cement and the formation and maintains zonal isolation throughout the life of the well.
The OFITE Circular Cement Expansion Mold measures the expansion or shrinkage of a well cement. It has an external ring with a vertical slit on one side to allow it to expand. Before testing begins, the width of the gap is measured with a micrometer. Then, after curing, the gap is measured again.
The complete kit includes the mold, micrometer, micrometer stand, and carrying case. Click here to learn more.