Abstract
The ability for oil-well cementing to guarantee well integrity is directly related to the preliminary
design of the setting slurry within the well. Prolonged storage of oil-well cement in non-airtight silos
can induce mineralogical changes on the cement surface. Once water is introduced and the cement
is converted into a slurry, changes in the powder surface will affect the preliminary slurry hydration
design, leading to catastrophic consequences.
Researchers have investigated how storage conditions affect the surface chemistry of cement and its
subsequent influence on the rheological and mechanical characteristics of the slurry. However, they
have not identified if a direct correlation exists between the storage induced evolution of the ageing
products on the surface and the hydration kinetics of the slurry. This work aims to investigate if a
correlation is present.
Oil-well cement powder is stored in multiple containers each for a month in a large air-tight storage
unit at sequential degrees of either relative humidity (RH) or temperature. The units are then subsampled
weekly. Upon subsampling, the chemical composition of the powder is probed using Diffuse Reflectance
Infrared Fourier Transform Spectroscopy (DRIFTS) with its results validated with Thermogravimetric
Analysis (TGA). Following the powder is turned into a slurry and the hydration is examined. Attenuated
Total Reflectance Fourier Transform Infrared Spectroscopy (FTIR-ATR, or commonly referred to as
ATR) is used to examine the chemical evolution, whereas 1H Nuclear Magnetic Resonance (NMR) is
used to explore the evolution of the water transport. Compressive strength testing of the cured slurry
is also explored.
The results reveal that elevating RH from 70% to 98% increases prehydration product buildup on the
cement surface, but saturation sets in after 14 days of storage at 70% and 85% RH. Beyond this point,
the slurry hydration kinetics and strength remain stable. However, at 98% RH, a prehydration induced
surface saturation is not observed, leading to a continual decline in hydration kinetics and strength.
Increasing the temperature from 20°C to 40°C at 75% RH minimally affects surface prehydration,
leaving hydration kinetics unaltered. These results indicate a correlation between the evolution of
prehydration on the surface and the hydration kinetics of the slurry.