According to the use, it can be divided into three types: surface casing, technical casing and oil casing.
The surface casing is used to drill through the soft and easy-to-collapse stratum on the surface, reinforce the shaft wall and make the drilling go smoothly.
Technical casing is used in the process of drilling to the target formation. In order to prevent well collapse, lost circulation and blowout, and high-pressure brine layer from soaking into the well, it is necessary to run technical casing to isolate and strengthen the well wall. When the formation conditions are not too complicated and the well depth is not large, it is generally unnecessary to run technical casing.
After the oil layer casing is drilled to the target layer, in order to prevent oil layers with different pressures from interfering with each other and other fluids from soaking into the well, it is necessary to run the oil layer casing to isolate oil, gas and water layers, so as to realize layered production and layered water injection.
The simple distinction is upper, middle and lower, top surface, intermediate technology and bottom oil layer. Is this easier to understand?