Casing in a Well

There are several types of casing used in oil and gas wells, each serving specific purposes and placed at different depths within the wellbore.  The choice of casing type and its depth depends on the geological and reservoir characteristics of the well, as well as safety and regulatory considerations.

Common Types of Casing Used in Well Construction

Conductor Casing  -  This is the shallowest casing and is usually the first one set during well drilling.  Conductor casing provides stability to the upper part of the wellbore and prevents it from collapsing.  It also helps protect the environment by preventing the contamination of surface water and soil.
Surface Casing  -  Surface casing is set below the conductor casing and extends deeper into the well.  It is used to isolate shallow groundwater and other formations from deeper zones that may contain hydrocarbons or other fluids.  Surface casing also plays a role in preventing well blowouts.
Intermediate Casing  -  Intermediate casing is set at an intermediate depth in the wellbore.  Its primary purpose is to isolate and protect specific formations and zones that may pose drilling challenges or contain fluids that could interfere with drilling operations.
Production Casing  -  Also called production string or production casing, this is the final casing string set in the wellbore and extends to the deepest part of the well, typically into the hydrocarbon reservoir.  Production casing provides structural integrity to the well and ensures the safe and efficient production of hydrocarbons. It also isolates the reservoir from other formations.
Liner Casing  -  In some cases, liner casing is used instead of full length casing strings.  Liners are shorter sections of casing that are used to isolate specific zones or formations within the wellbore.  They are often used to save costs and reduce the environmental footprint of drilling operations.
Casing Accessories  -  Various accessories and tools, such as casing hangers, packers, and cementing equipment, are used in conjunction with casing to ensure proper well construction and integrity.

The specific design and arrangement of casing strings in a well can vary based on factors like well depth, reservoir characteristics, drilling challenges, and local regulations.  The primary goal is to ensure the safety, stability, and productivity of the well while minimizing environmental and safety risks.