Cementing Materials for Cold Environments

Abstract

A frozen consolidated formation that is. unharmed by thawing probably can be cemented with any slurry that will adequately set at the existing curing temperature. In area where the frozen formations contain ice lenses and are incompetentwhere the formation must not be allowed to thawspecialized slurries must be called upon to do the job. Introduction Increasing oil industry activity in the nothern areas of Canada, the Arctic Islands, and the State of Alaska has focused attention on the special problems of cementing conductor and surface casing in cold and frozen formations. With an understanding and proper application of the relationships among the performance of available materials formation and well fluid temperatures, mixing water and cement slurry temperatures, and the cement heat of hydration, the present-day practice of adhering to a 24-hour present-day practice of adhering to a 24-hour waiting on-cement (WOC) time can be modified so that the WOC is as short as 8 hours. Cementing through the permafrost of the more northern regions presents a new set of difficulties. Cementing techniques and materials depend mainly upon the type of permafrost. A frozen consolidated formation that is unharmed by thawing probably can be cemented with any slurry that will adequately set at the existing curing temperature. In areas where the frozen formations contain ice lenses and are incompetent - where the formation must not be allowed to thaw - specialized slurries must be used. Cementing Through Nonfrozen Formations Strength of Cement Accepted practice of the industry in cold formations has been to place cement behind conductor or surface pipe and wait 24 hours. Investigators recognized pipe and wait 24 hours. Investigators recognized many years ago that very little strength was needed to support casing and drillpipe in the borehole (Table 1). Because of variations in procedures, materials, and curing temperatures, conditions cannot be sufficiently known in the field to establish the curing time required to obtain this minimum strength, thus a safety factor should be applied. A compressive strength of 500 psi is generally accepted as adequate for most operations, and with diligent practice an operator should be able to drill out safely practice an operator should be able to drill out safely using an established minimum strength of 250 psi. The curing time (WOC) for cement to develop the minimum required strength can be shortened by reducing the volume of mixing water (densification), by adding an accelerator, or by combining densification and acceleration. This is illustrated in Figs. 1 and 2, which show that curing temperature is a significant factor in strength development. To establish a sensible WOC time some knowledge of curing temperature must be gained. Static bottom-hole temperatures in western Canada 5 and other areas have been reasonably well defined by application of surface isotherm data coupled with depth-temperature gradients. However, the curing temperature of the cement will not equal the formation temperature and it does not even have a constant value. It is governed by a complex set of variables that includes the temperature of the drilling mud, cement slurry, and displacement fluid, as well as the heat of hydration of the cement. JPT P. 1215

Novel Chemically-Bonded Phosphate Ceramic Borehole Sealants (Ceramicretes) for Arctic Environments

“…Permafrost is a permanently frozen subsurface formation which exists in arctic regions such as the Canadian Northwest, the Arctic Islands, and the ANS (Maier et al, 1971); permafrost forms where annual temperatures remain at the freezing point or colder all year. Permafrost depth may vary from 500 ft. to 2000 ft. on the ANS (Morris, 1970).…”

“…Drilling a well and cementing the surface casing in permafrost requires the prevention of wellbore enlargement due to thawing as well as cement that sets with low heat of hydration. Thus, in order to maintain well integrity, it is necessary to develop cement which sets with low heat of hydration and does not cause thawing of permafrost (Maier et al, 1971). …”

“…In the 40 years since that time, the burgeoning oil industry in areas such as northern Canada, Russia, the Arctic Islands, and Alaska has led to significant research into proper oilfield practices for these environments. However, the techniques appropriate for a cold formation vary widely depending on the geological and physical properties of the cold formation (Maier, 1971).…”

“…There is no particular need for specialty material use as the primary problem of freezing can be controlled through numerous measures, limited only by the environmental laws of the area. Table 2 summarizes various methods of slurry protection that are appropriate for a consolidated cold formation (Maier, 1971).…”

“…A frozen consolidated formation that is unharmed by thawing can likely be cemented with any slurry that will adequately set at the existing curing temperature. However, in areas where the frozen formation contains ice lenses and is incompetent in the material sense, where the formation must not be allowed to thaw, specialized slurries must be called upon to do the job (Maier, 1971). …”