Arctic Cements And Cementing
Authors: Cunningham W.C. , Fehrenbach J.R. , Maier L.F. 
Published: March 2010

Cementing operations in Arctic environments continue to require research on many unanswered problems. Laboratory studies and observation of field practices helped answer some of these questions. Areas of laboratory study were:electrical resistivities of neat and drilling mud contaminated cement.stability of cement to freeze-thaw cycles,effect of variations in concentration of freeze temperature depressant andthe volumetric expansion of neat and drilling mud contaminated slurry when frozen under hydraulic pressure.

Recent developments in cementing practices and techniques will also be discussed.

Introduction

MORE THAN THREE YEARS have now lapsed since the Prudhoe Bay discovery well focused attention on the Arctic oil potential. At the time of the Prudhoe Bay discovery, only a few wells had been drilled and cemented in Arctic regions - about 6 on the Naval Petroleum Reserve No. 4 in northwestern Alaska and approximately 12 in northern Canada. Only one laboratory Study(1,2) of cements specifically designed for the Aretic environment had been made at the time and it was made 20 years prior to the Prudhoe Bay discovery. Several studies of the properties of cements under low and freezing temperature conditions were made and published following the Prudhoe discovery.(3,4,5) however many questions and problems have arisen since the appearance of these publications. It is the purpose of this paper to present more recent laboratory test data with on-site cementing practice so the oil industry may keep abreast of the latest developments in cements for Arctic environments.

Freeze Temperature Depressants

One of the initial requirements for a cementing material for permafrost use was that the material be placed at low temperatures and allowed to hydrate properly without freezing, which could best be accomplished by the addition of a freeze-point depressant such as sodium chloride. Three cementing compositions have been used as the primary formulations for cementing through the Arctic permafrost. These are Ciment Fondu, Ciment Fondu blended with fly ash and a formulation sold under the tradename "Permafrost" cement. Some work has also been performed with Class G cement accelerated with calcium chloride. The Ciment Fondu and Fondu - fly ash blend have been used both with and without small quantities of sodium chloride. Permafrost cement, which has emerged as the most commonly used material, normally has sodium chloride as a dry blended constituent although it could be omitted if so desired.

Permafrost cement is a blend of controlled set gypsum cement, Class G cement, salt, a dispersant and chemical additives to control thickening time. For its relatively high early strength, i.e. over 500 psi. Permafrost cement utilizes the ability of gypsum cement to set and gain strength rapidly, even at low temperatures. The later strength gain depends on the hydration of conventional API Class G cement. As shown in Figure 1, should initial set take place with a nonfreezing- point depressed slurry and the slurry temperature then drops below the freezing temperature of the mixing water, the hydration reaction essentially stops.