Casing Design This  section will introduce you to casing and will help you to understand the function and the reasons that casing design is so important. For people wishing to use this site to continue their education I have made up a one week on-line casing and cementing course suitable for Derrick men and above. find out more by contacting me using the link provided   The main functions of the casing in any well are: maintain hole integrity, isolate abnormally pressured zones, protect shallow weak formations from heavier mud weights required in the deeper portions of the hole, and to isolate fresh water, salt and coal seams.  Choosing the correct size, type, and amount of casing that is used in well construction is of utmost importance to the success of the well. The casing must be of sufficient size and strength to allow the target formations to be reached and produced.  The design of the integrated casing, cementing, mud, and blowout prevention control program must take into account. The depths at which freshwater, hydrocarbon, salt, coal seams and other mineral-bearing formations are expected to be penetrated, the formation fracture gradients and pressures expected to be encountered, and other pertinent geologic and engineering data and information about the area. The main functions of the casing in any well are: Maintain hole integrity, Isolate abnormally pressured zones, Protect shallow weak formations from heavier mud weights required in the deeper portions of the hole, Prevent release of fluids from any stratum through the well bore (directly or indirectly) into the waters; Prevent communication between separate hydrocarbon-bearing strata (except such strata approved for commingling) and between hydrocarbon and water-bearing strata; Prevent contamination of freshwater-bearing strata; Support unconsolidated sediments;  Provide a means of controlling formation pressures and fluids. Casing being install should conform with American Petroleum Institute (API) standards and cement should meet API standards and when mixed with water of adequate quality does not degrade the setting properties.   The diameter, weight and strength must be calculated with respect to realistic load conditions during the lifetime of the well. If an exploration or appraisal well is planned  the casing design must also take into account temperature expansion causing an increased collapse force on the production casing.   When preparing the casing design, information from offset wells and  well drilled within the area along  with the geological and pressure related conditions in the well must be taken into account and the casing strings set at such depth that full control of the well can be maintained at all times.  Installation should be in such a way that they anchored and can withstand the pressures and loads from fluids and gases that can be expected in the well.  Casings must  also be of such quality that it  can withstand particularly corrosive media in the well (H2S, CO2 etc.), if exposed to such formations. There are primary four types of casings that are commonly used in well construction.