Foamed Cement Application In Canada

Abstract

Abstract With the development of cement slurries foamed with air or nitrogen, new methods of cementing wells are now available which will benefit operations in Canada*". Foamed cement has several physical properties which are very advantageous to some cementing operations. The most obvious advantage is its application as an economical, lightweight cement with relatively high strength. Formations which would normally break down when subjected to the hydrostatic pressures exerted by conventional lightweight slurries can now be cemented with foamed cement. The pseudoplastic properties of foamed cement slurries, combined with low density, make this cement ideal for curing lost circulation where conventional slurries containing lost circulation materials are ineffective. The air/nitrogen in the slurry provides compressibility, which will help maintain the hydrostatic pressure On the formation and improve zonal isolation by combatting annular gas channelling. Thermal cement slurries containing normal mix water ratios can also be foamed resulting in low density, set cements exhibiting good thermal stability along with greatly improved insulating qualities. This feature is attractive for cementing operations in Western Canada's thermal recovery projects. Foamed cementing operations can be conducted using conventional cementing equipment with the addition of an air or nitrogen source. This paper will review the physical properties of foamed cement and summarize the design and field operations of applications in Canadian operations. Introduction The use of compressed gases, notably nitrogen, to reduce hydrostatic pressure during primary cementing across severe lost circulation zones has been recognized for some time(1). Also, the use of low-density cement slurries has provided an alternate solution to slurry loss. In the past, these slurries fell into three classes. The first class includes slurries prepared by adding higher ratios of mix water and maintaining free water control (i.e. preventing cement separation) by incorporating clay-sized inorganic solids, or chemical extenders in the cement or mix water. The second class incorporates low-density solids notably organic material such as ground walnut hulls, coal, or gilsonite, into the slurries along with some additional mix water to achieve low density. The third class consists of slurries utilizing very fine glass or ceramic bubbles as the low-density solids(2,3). Both the first and second classes of slurries have been widely used and are still economical solutions to the cement requirements of most wells. Their use is limited however to cementing operations where slurry densities of greater than approximately 1450 kg/m3 are satisfactory as their compressive strength at lower densities are usually inadequate. The additives used in the second class of slurries also serve as bridging type lost circulation additives which are beneficial in cementing some wells. The third class of slurries has the advantage of higher strengths at lower densities, however, the collapse pressure of the additives (<50,000 kPa) and the relatively high cost has severely limited their use. Also, the need for dry blending the additive with the cement, causes complications in offshore applications. Not until recently(4,5) has the practicality of a fourth class of low-density slurry and cement been demonstrated.