In well cementing, Portland cement systems are
designed for temperatures ranges from below freezing in permafrost zones to
662°F (350°C) in thermal recovery and geothermal wells. They also encounter
pressures ranging from ambient to 30,000 psi (200 MPa) in deep wells.
Accommodation of such variations in conditions was only possible through the
development of cement additives. According to American Petroleum InstituteRecommended Practice 10B, additives are materials added to cement slurry to
modify or enhance desired property Anon. Cement additives selected for
cementing operations are an integral part of sound well design, construction
and well integrity.
Additives are available to enhance the properties of
oil well slurries and achieve successful placement between the casing and the
geological formation, rapid compressive strength development and adequate zonal
isolation during the lifetime of the well. According to Cowan and Eoff,
additives are commonly added to cement formulations to; disperse cement
particles, modify the setting time under temperature and pressure conditions in
the well, control filtration losses of the liquid from the cement slurry during
and after placement, compensate for shrinkage of the cement as it sets and
hardens, improve interfacial bonding between cement and casing, and control
influx and migration of formation fluids into the cement column during setting.
There are different types of cement additives that have been developed to allow
the use of Portland cement in many different oil and gas well applications Anon.
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