Porosity of oil well cement slurries during setting

Abstract

The phenomenon of ‘gas migration’ during oil well cementing is believed to occur during the transition state between initial and final set of the cement. In order to evaluate the importance of pore openings and total porosity in the critical time gap, a suitable experimental technique was tested on some neat oil well cement slurries. The hydration was effectively stopped every 30 min at 20°C and every 20 min at 60°C by dropping plastic tubes containing the cement slurry into liquid nitrogen (i.e. quenching), cracking the tubes open and letting the frozen bits of paste thaw in ethanol. The change in porosity and pore size distribution was determined by helium pycnometry and mercury intrusion porosimetry as a function of time in the setting period for a plain API class G cement slurry (w/c = 0·50) at both 20°C and 60°C. These data were compared with the amount of chemically hound water in the same samples, and used to predict the total porosity at a given degree of hydration. The excellent correspondance of experimental and theoretical porosities validates the experimental procedure, which can also be used in explaining the variation in gas migration between commercial oil well cement slurries.

Characterizing Curing Cement Slurries by Electrical Conductivity

“…where T=the temperature in °C, σT=the conductivity at that tem- This paper and Justnes et al 33,34 This paper, initial slurry data Least squares fit, F=0.126/φ^5.77 perature, and σ25=the corrected conductivity at 25°C. This correction is based on sodium chloride solutions at temperatures of between 0 and 156°C and is reasonably accurate.…”

“…Our conductivity data were compared to the porosity data of Justnes et al, 33,34 one at an ambient condition and four at 150°C in the time interval of 100 to 270 minutes. In addition, the initial porosity of all the 33 tested slurries (25 to 195°C) was calculated from the cement recipes and compared to the conductivity at the onset of the induction period of hydration.…”

Modeling Pore Continuity and Durability of Cementitious Sealing Material

“…From there, the temperature is kept constant. (17)) <£max = < l> 0 exP (17) This formula is used for the results of the 0.44 wcr slurry, and tak ing a pore structure constant a = 0.1 and a minimum pore diame ter of (/)(, = 2 nm [36,37], The calculated results show the maximum pore diameter of the continuous pores to range from 0.93 pm at the beginning of hydration until 6.5 nm, 7.8 nm-9.0 nm at a degree of hydration of ac = 0.8, for ambient temperatures of T = 20 °C 7'= 4 0 °C, and T= 60 °C, respectively. The rate of this process is depending on the ambient temperature conditions and complies with the Arrhenius law [24].…”

Utilization of Agarwood Distillation Waste in Oilwell Cement and Its Effect on Free Water and Porosity

“…Gas leakage is one of the problems caused by the hydraulic pressure that falls below the formation pore pressure due to the unconsolidated cement slurry [8]. It is not only dependent on the mechanical strength of cement based materials, but also its durability is affected by the volume and size distribution of cement pores.…”