Long-Term Effects of High Temperature on Strength Retrogression of Cements
Authors: Eilers L.H. , Root R.L. 
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
This paper was prepared for the Improved Oil Recovery Symposium of the Society of Petroleum Engineers of AIME, to be held in Tulsa, Okla., March 22–24, 1976. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and with the paper, may be considered for publication in one of the two SPE magazines.

Abstract
There is very little information available as to the long-term effects of high temperatures on the strength and permeability of cements, especially with additives. permeability of cements, especially with additives. Most strength tests are run for short periods of time, possibly 30 to 90 days and these extrapolated to long-term effects. There are few short-term permeability results and very few attempts extrapolate these results. This report presents the results of study of cement systems at 450 deg. F for two years and 600 deg. F for one year under steam pressure. At these conditions we found that most changes did occur within the first week to one month and that extrapolation to longer periods was usually valid. Certain pozzolan (fly ash) systems, however, showed signs of deterioration only after several months at 600 deg. F and one year at 450 deg. F. There was also some variation in results between various sizes of silica, especially as to the effect on permeability.

Introduction
The deterioration of neat Portland cement (cement + water) at temperatures above 250 deg. F has been known for many years. The use of fine silica to reduce such deterioration has been practiced in oil and gas well cementing for about the last 20 years. Today there are numerous wells in which the cements bonding the steel casing to the formation are subjected to temperatures above 400 deg. F. These are deep petroleum wells drilled in the Gulf Coast area, geothermal wells, or wells being subjected to various thermal recovery methods. There is very little information available as to what effects these high temperatures have on Portland cements over extended periods of Portland cements over extended periods of time. There are results on systems for up to 30 days and a few for up to 3 and 6 months. These have been used to extrapolate to longer time. Recently there have been indications that deterioration was occurring over extended periods of time with certain cements being periods of time with certain cements being used in geothermal steam wells.
Tests were therefore conducted at 450 deg. F in sealed tubes under steam pressure for two years and at 600 deg. F for up to one year to determine whether the previous extrapolations were valid. Strengths, permeabilities, specimen weights and specimen dimensions were determined.