Murray J. Rogers

OSCILLATING RHEOMETER MEASUREMENTS ON OILFIELD CEMENT SLURRIES

Abstract Cement slurries which have their application in the oilfield industry have been evaluated on an oscillating rheometer. Viscoelastic properties were observed in four slurries; a neat slurry, a polymer modified, a polymer/sodium silicate modified slurry and a sodium silicate modified slurry. The viscoelastic properties may originate from dissolved polymers, electrostatic attraction between solids or from matrix structures associated with cement curing. The viscoelasticity was not restricted to gelled slurries. The viscoelastic properties were still observed after the gel structure has been broken. The polymer/sodium silicate containing slurry also exhibited a yield stress as observed with the oscillating rheometer.

The Effect of Cement Heat of Hydration on the Maximum Annular Temperature of Oil and Gas Wells

Recent advances in electronics technology have made it possible to monitor and record real-time annular temperatures in operational wells, both during and after primary cementing. The developments have allowed operators to record the entire annular-temperature history of their wells, including the critical period when cement hydration occurs. The ability to record these actual temperatures can significantly impact the oilfield cementing industry in several ways. Most significantly, currently accepted practice within the industry is to test certain critical aspects of set cement, such as compressive and tensile strength, at the bottomhole static temperature (BHST). If the short-term maximum annular temperature is significantly different from the later BHST of the well, laboratory tests run on cement at a steady BHST may prove to be inaccurate when based on the actual temperature encountered by a cement slurry downhole. Also of concern is the fact that the magnitude of any temperature change after the initial set may have profound effects on the induced stress in the cement sheath as well as on the casing and formation because the maximum temperature spike from hydrating cement may not occur until after the cement has achieved an initial set. On the basis of actual field measurements of annular temperatures, this paper details how the variable factors of individual heat of hydration (HOH), relative annular geometry, and final BHST interact to produce short-term maximum temperatures in the cement sheath. In some instances, these maximum temperatures can vary significantly from the stabilized BHST in a well. The actual annular-temperature data were recovered from wells in both North and South America and include shallow and deep well applications.