The process of foaming cement to make lightweight slurries is well known and documented in the literature. However, the technology for applying this process to oil and gas-well cementing has been lacking. New techniques and treatment designs have now been developed which show that the use of lightweight foamed cements in oil field operations can solve many problems. Treatments can be performed with the current equipment and personnel operating in the field. When compared to other processes for making ultra-lightweight slurries, foamed cements are very economical.
There are many reasons for using lightweight slurries in oil-well cementing. Probably, the foremost of these are problems of lost circulation or where long lifts of cement are required. The use of lightweight foamed cement slurries for these problems offers several advantages over the more common lightweight slurries. Some of the advantages are given below.
Lower density slurries, which will develop adequate strengths for filler-type cements, can be obtained. A density as low as eight pounds per gallon can be achieved with foamed cement while approximately 10.5 lb/gal is the lowest which can be achieved when using materials such as bentonite, perlite or sodium silicates.
Hollow spheres have been used to achieve slurry densities in the eight pounds per gallon range. Foamed cements are considerably more economical and are not subject to the pressure limitations of ceramic spheres.
A series of field trials using foamed cement has been performed in the Rocky Mountain area. Descriptions of these field trials, including the techniques being used, are presented along with supporting laboratory data showing typical compressive strengths and permeabilities for foamed cement systems.