Effects of ethylene diamine tetraacetic acid and calcium nitrate on high-temperature cementing slurry in a large temperature difference environment

Abstract

In wellhole environments with large temperature differences, high-temperature retarders can slow the strength development of the top of a cement slurry column, thus affecting construction progress and safety of cementing projects. Herein, to address the problem of slow strength development of the top of a cement slurry caused by the addition of the high-temperature retarder GH-8L, the synergistic effect of the co-addition of ethylene diamine tetraacetic acid (EDTA) and calcium nitrate (CN) is considered. The experimental results show that the thickening time of the cement slurry system mixed with EDTA and CN exceeds 300 min at 150 °C and 75 MPa and its strength at 48 h is >14 MPa. As demonstrated by the hydration heat tests, EDTA and CN promote the hydration heat release rate of the GH-8L cement slurry at low temperature. The synergistic mechanism of EDTA and CN in the GH-8L doped cement slurry promotes the initial dissolution of cement particles, significantly increases the content of C-S-H and CH in the hydration products, and promotes the formation of needle-like NO3–AFt ettringite. The cementing slurry, with the co-addition of EDTA and CN, can not only meet the requirements of thickening time and cementing with a large temperature difference but also compressive strength.