Casing Classification And Function

The oil casing is a steel pipe that supports the oil and gas well walls. Each well requires several layers of casing based on different drilling depths and geology. After the casing is drilled, the cement is used to cement the well. Unlike the tubing and drill pipe, it cannot be reused and is a disposable material. Therefore, casing consumption accounts for more than 70% of all oil well pipes. Casing can be divided into use according to conditions: ducts, surface casing, technical casing and oil casing, their structure in the oil well shown in Figure 1.

1. Guide bush: It is mainly used for drilling in oceans and deserts to separate seawater and sand to ensure smooth drilling. The main specifications of this casing are:? 762mm (30in) × 25.4mm,? 762mm (30in) × 19.06mm.
2. Surface Casing: Mainly used for the first time drilling, drilling open surface soft ground to bedrock, in order to seal this part of the ground layer will not collapse, need to use surface casing for sealing. The main specifications of the surface casing: 508mm (20in), 406.4mm (16in), 339.73mm (13-3/8in), 273.05mm (10-3/4in), 244.48mm (9-5/9in) and so on. The depth of the lower tube depends on the depth of the soft formation, which is generally 80 to 1500m. Its external pressure and internal pressure are not large, generally use K55 steel grade or N80 steel grade.
3. Technical casingWhen the technical casing is used in the drilling process of complex formations, when it encounters complex parts such as collapsed layer, oil layer, gas layer, water layer, leakage layer, salt-gypsum layer, etc., it needs to be sealed by the lower technical casing, otherwise the drilling cannot be performed. get on. Some wells are deep and complex, and the depth of downhole is several kilometers. This kind of deep well requires several layers of technical casing. Its mechanical properties and sealing

performance are very high, and the steel grade used is also high, with the exception of J55 oil casing. More is the use of N80 and P110 grades, and some deep wells also use Q125 or even higher non-API grades such as V150. The main specifications of the technical casing are: 339.73mm (13-3/8in), 273.05mm (10-3/4in), 244.48mm (9-5/8in), 219.08mm (8-5/8in), 193.68mm ( 7- 5/8in), 177.8mm(7in), etc.

4 oil casingWhen the drilling reaches the target layer (including oil and gas layers), the oil and gas layers and the upper bare stratum must all be sealed by the oil reservoir casing.

The oil layer inside the oil reservoir casing is the oil layer. The reservoir casing is the deepest downhole in all types of casing, and its mechanical properties and sealing performance requirements are also the highest. Steel grades include K55, N80, P110, Q125, and V150. The main specifications of the reservoir casing are: 177.8mm (7in), 168.28mm (6-5/8in), 139.7mm (5-1/2in), 127mm (5in), and 114.3mm (4-1/2in).