Effect of various testing parameters on the experimental evaluation of oil well cement cured under simulated downhole conditions

Abstract

It is well known that regular oil well cement systems experiences strength retrogression at curing temperatures above 110°C and silica sand is typically added to mitigate strength reduction. However, due to the complex experimental procedures associated with high temperature and high pressure curing of oil well cement specimens in the laboratory, historical test data tend to suffer significant uncertainties. A comprehensive study of the various influencing factors on the physical and mechanical property test results of oil well cement system cured under 200°C is conducted here. The specific influencing factors investigated include curing time (from 14d to 69d), depressurization rate, curing pressure (50MPa vs 150MPa), specimen size (diameter of 25mm vs 50mm) and curing autoclave design. The property of the set cement evaluated include strength and modulus, permeability, indentation modulus and hardness, etc. Test results suggest bigger specimen size and faster depressurization rate may lead to significant specimen damage, causing experimental artifact. Different autoclave design may also lead to significant differences in the mechanical property of the set cement even under the same curing temperature and pressure.