Casing is the major structural component of a well. Casing is needed to:
                       Maintain borehole stability
                        Prevent contamination of water sands
                        Isolate water from producing formations
                        Control well pressures during drilling, production, and workover operations
                        Casing provides locations for the installation of:                                                                                                                                                            Blowout preventers
                         Wellhead equipment
                         Production packers
                         Production tubing

The cost of casing is a major part of the overall well cost, so selection of casing size, grade, connectors, and setting depth is a primary engineering and economic consideration.