Long-Term Effects Of High Temperature On Strength Retrogression Of Cements

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. 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 Neat Portland cement systems lose strength and become permeable at temperatures above 250 degrees F. This deterioration usually is more extreme over the first few days or month of heating but is usually not severe enough to cause disintegration of the neat cement. After this initial regression many neat Portland systems will regain a portion of Portland systems will regain a portion of their strength and reduce in permeability. This temperature regression of cement can largely be prevented by using about 35 per cent very fine silica sand. The strength can be maintained or increased but permeability will increase. Most additives for oil well cements can be included in such a silica stabilized system without extensive effect due to temperatures up to 600 degrees F. An exception to this is fly ashes and, to some degree, natural pozzolans. These are stable at 450 degrees but are losing strength and recrystalizing 600 degrees F. Introduction The deterioration of Neat Portland cement at temperatures above 250 degrees F (120 degrees C) has been known for many years. Menzel proved that fine silica added to a Portland cement paste would improve the strength of cements cured at elevated temperatures. An increasing number of wells are being subjected to these elevated temperatures each year. Deeper and hotter oil and gas wells are being drilled and other wells are being subjected to hot water, steam, or fire flood methods. High temperature geothermal wells are also increasing in number each year. The cement in these wells will be subjected to elevated temperatures from bottom to top. It is probable, therefore, that the surface and intermediate strings on many of these wells are not adequately protected from deterioration.