Pore structure evolution and strength development of G-type elastic oil well cement. A combined 1H NMR and ultrasonic study

Cement sheath integrity is very critical in drilling and completion of oil wells. Oil well cements include special additives in order to develop required functionalities. Until now efforts to develop such additives are based on empirical rules, because it was impossible to correlate microscopic properties of cement pastes with bulk elastic properties. Here, we show that mechanical strength of hardened oil well cement pastes can be analyzed at molecular scale, by revealing a power law sigma proportional to(1/T-1)(nu) between the H-1 NMR relaxation rate (1/T-1) of water molecules in cement paste pores, with ultrasonic measurements of compressive strength a Accordingly, the effect of a multifunctional additive comprised of latex and micronized silica on the hydration of class G cement at borehole conditions is presented. Remarkably, NMR and ultrasonic hydration curves at different temperatures and pressures are excellently matched by applying scaling arguments, indicating a linear relation between sigma and 1/T-1, i.e. nu approximate to 1. (C) 2015 Elsevier Ltd. All rights reserved.