ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Strength retrogression mechanisms of silica-enriched oil well cement under 240 °C curing conditions

Guodong Cheng, He Li, Haoya Liu, Haoguang Wei, Shiming Zhou, and Kuizhen Fang

SINOPEC Research Institute of Petroleum Engineering Co., Ltd., Beijing, China

E-mail: ggddcheng@sina.com

Received: 24 August 2025  Accepted: 24 October 2025

Abstract:

The long-term strength retrogression of silica-enriched oil well cement seriously threatens wellbore integrity in deep/ultra-deep wells. This study tested the performance evolution of silica-enriched oil well cement, initially set at 80 °C or 240 °C and then cured at 240 °C/20 MPa. Results showed: cement set at 80 °C showed strength growth during curing, while that set at 240 °C underwent strength loss within 28 days; neither increased silica sand dosage nor coal gangue powder addition inhibited this decline. SEM-XRD quantitative analysis revealed: for low-temperature-set cement, C-(A)-S-H content increased from 3 to 28d, and more xonotlite formed at 3d; though xonotlite impaired compressive strength, its structural stability ensured cement strength stability. In contrast, high-temperature-set cement had decreased C-(A)-S-H and continuously increased xonotlite during curing, causing microstructural coarsening and strength retrogression—this difference may stem from distinct C-(A)-S-H structures under the two setting temperatures. Notably, increasing silica sand dosage or adding coal gangue powder also failed to prevent such structural/compositional changes, and these microanalytical results explain the compressive strength of all systems.

Keywords: Silica-enriched oil well cement; Strength retrogression; Set temperature; High temperature; Quantitative X-ray diffraction (QXRD)

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-025-04478-7

Chemical Papers 80 (2) 1653–1663 (2026)