Properties of Cementing Compositions at Elevated Temperatures and Pressure

Abstract

Published in Petroleum Transactions, AIME, Volume 213, 1958, pages 20–27. Abstract Studies have been conducted on the properties of many deep well cementing compositions to determine their strength behavior over curing periods to 180 days at elevated temperatures and 3,000 psi pressure. This pressure results in essentially the same compressive strength as that obtained with much higher pressures in accordance with the findings of an API subcommittee. These different compositions include API Classes A, E, and F cements containing additives such as retarders, bentonite, heavy weight materials and pozzolans. All compositions except mixtures of pozzolans and hydrated lime show from mild to severe degrees of strength loss over a temperature range from 230 to 320°F after setting. Pozzolan-lime compositions actually gain in strength with time at these high temperatures. Other chemical and physical properties evaluated to observe their interrelationship with strength loss show very little correlation except in permeability. As retrogression in strength Increases, the permeability of set cement increases. X-ray diffraction patterns on the set products indicate the formation of certain compounds having little or no strength value in those cementing compositions where strength loss was more severe. Introduction As a result of the growing trend toward deep well completions, a study has been made on the properties of the various cementing slurries presently in use at elevated temperatures and pressure. The strength of these compositions is of prime importance in selecting the most suitable material for use at high temperatures, to determine WOC time and the proper time to perforate with a minimum of shattering. Of primary interest in this investigation was the strength behavior of various compositions currently in use, and the effect of additives on cement after long periods of curing under severe conditions. Earlier investigators have pointed out that the strength of some cements will increase with increasing curing temperature to about 220 to 240°F, but at higher temperatures a loss in strength occurs at extended time intervals. Studies by the API Mid-Continent District Study Committee on Oil Well Cements outlined a testing procedure whereby field conditions of temperature and pressure could be simulated in the laboratory. It was observed that retarded cements undergo changes at elevated temperatures and some lose as much as 50 per cent of their early strength when cured at high temperatures. The scope of these tests was limited to curing periods of 1 to 28 days; additives were not covered in this study.