Casing design_rahmanHigh pressure zones, weak and fractured formations, unconsolidated formations an sloughing shales (Drilling problems)conductor pipe is fitted with the diverter equipment to water and gas flow encountered.The conducor pipe is not shut in as seat may not sustain with well force.Generally 16" conductor pipe is use for shallow wells & 20" in deep wells.Onshore conductor pipe is usually 20".The length of conducotr pipe may be up to 500 ft onshore and may be up to 1000 ft offshore.Surface casing is generaly set in competant formations such as hard limestone or dolomite. setting depth of suface casing may be up to as deep as 5000 ft. sizes varies from 7 to 16". whereas 10 3/4" & 13 3/8" are among most common sizes. surface casing usually cemented up to surface. In offshore wells may be up to kick off point.Intermediate casing depth varies from 7000 ft to 15000 ft. sizes varies from 7" to 11 3/4" OD.It is commonly cemented up to 1000 ft from shoe.Production casing varies from 4 1/2" to 9 5/8". Cemented above the producing formations. Geneally cemented 1000 ft above the shallow Hydrocarbon zone.Tie-back liner is a section of casing extending upwards from the top of the existing liner to the surface. Casing (Upper completion) is stabbed into existing liner (Lower completion) via polished bore receptle (PBR)Scab liner is section of casing used to repair existing damaged casing. it may be cemented or sealed with packers at top & bottom.Casing manufacturing processseamless pipewelded pipecasing is cold-worked during manufacturing to increase its collapse resistance.casing joint lengthsRange Length Average lengthRange I 16-25 22Range II 25-34 31Range III over 34 42R3 l3ngth are more common as it reduces number of joints which reduces rig time and probablity of joint failures.Makeup losswhen casing joints are joined together, overall length of string is less than sum of the individual joints.makeup loss per jointMake up loss= (length of the coupling/2)-(distance between end of casing in power tight position and center of the coupling)steel gradethe steel grade of casing relates to tensile strength of the steel from which casing is made. L grade has similar yield strength as N grade, but N grade has rockwell hardness greater than 22 which makes it unsuitable for H2S service. L grade has rockwell hardness of 22 or less.casing coupling and threadscoupling is short piece of pipe used to connect the two ends of the casing.In general, casing couplings are specified by the types of threads cut on the pipe ends and coupling. Design of thread form is obvious way of increasing load bearing capacity of casing connection.two most common thread froms are squared and V-shape. The API uses round and butress which are special forms of squared and V-shape threads.