FUNDAMENTAL ASPECTS OF CASING DESIGN
When drilling wells, hostile environments, such as high-pressured zones, weak and fractured formations, unconsolidated formations and sloughing shales, are often encountered. Consequently, wells are drilled and cased in several steps to seal off these troublesome zones and to allow drilling to the total depth. Different casing sizes are required for different depths, the five general casings used to complete a well are: conductor pipe, surface casing, intermediate casing, production casing and liner. As shown in Fig. 1.1, these pipes are run to different depths and one or two of them may be omitted depending on the drilling conditions: they may also be run as liners or in combination with liners. In offshore platform operations, it is also necessary to run a cassion pipe.
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Fig. 1.1: Typical casing program showing different casing sizes and their setting depths. |
