PRINCIPLES OF CASING DESIGN
The design of a casing program involves the selection of setting depths, casing sizes and grades of steel that will allow for the safe drilling and completion of a well to the desired producing configuration. Very often the selection of these design parameters is controlled by a number of factors, such as geological conditions, hole problems, number and sizes of production tubing, types of artificial lift equipment that may eventually be placed in the well, company policy, and in many cases, government regulations.
Of the many approaches to casing design that have been developed over the years, most are based on the concept of maximum load. In this method, a casing string is designed to withstand the parting of casing, burst, collapse, corrosion and other problems associated with the drilling conditions. To obtain the most economical design, casing strings often consist of multiple sections of different steel grades, wall thicknesses, and coupling types. Such a casing string is called a combination string. Cost savings can sometimes be achieved with the use of liner tie-back combination strings instead of full strings running from the surface to the bottom.
In this chapter, procedures for selecting setting depths, sizes, grades of steel and coupling types of different casing strings are presented.