According to the function of petroleum casing pipe, it can be divided into surface casing, technical casing and oil layer casing.
1) Surface casing of petroleum casing:
1. It is used to block the unstable and soft, easily collapsed and leaking stratum and water layer in the upper part;
2. Install a wellhead device to control the blowout;
3. Partial weight of support technology casing and reservoir casing.
The depth of the surface casing depends on the specific situation, and is usually tens of meters to hundreds of meters or deeper (30 to 1500 meters). Extracorporeal cement is usually put back on the ground. When drilling high-pressure gas wells, if the upper rock layer is loose and fractured, in order to prevent high-pressure gas flow from the surface, the surface casing needs to be deeper. If the surface casing needs to be deeper, if the first drilling time is longer, the lower layer of the pipeline should be considered before the lower surface casing. Its function is to seal the surface, prevent the wellhead from collapsing, and form a drilling fluid circulation channel, which is convenient for long-term drilling. The depth of the catheter is generally 20-30 meters, and the cement outside the tube returns to the ground. The catheter is usually a spiral tube or a straight tube.
2) Oil casing technical casing:
1. It is used to close the complex strata, severe loss layers and oil, gas and water layers which are difficult to control by drilling fluid, and prevent the diameter from expanding.
2. In high-inclination directional wells, insert casing under the section to facilitate safe drilling of directional wells.
3. Provide conditions for the installation, blowout prevention, leakage prevention and suspension of well control equipment stern tube and protect oil casing.
3) Oil casing oil layer casing:
Used to separate the target layer from other layers; separate oil, gas and water layers under different pressures, and establish oil and gas channels in wells to ensure long-term production.
The depth of the oil layer casing depends on the depth of the target layer and the completion method. The cement slurry of the oil layer casing generally returns to the upper oil layer of more than 100 meters. For high-pressure wells, the cement slurry should be transported back to the surface, which is beneficial to strengthening the casing and strengthening the oil casing steel wire buckle, so that it can withstand larger Shut-off pressure.
