Views:1 Author:Site Editor Publish Time: 2019-06-03 Origin:Site
Oil casing is divided into surface casing, technical casing and oil casing according to their functions.
Classification and application of oil casing
1, used to seal the upper unstable soft, easy to collapse, easy to leak formation and water layer;
2. Install wellhead device to control blowout;
3. Partial weight of technical casing and reservoir casing.
The depth of the surface casing depends on the specific situation, usually tens of meters to hundreds of meters or more (30 ~ 1500m). The cement on the outside of the pipe returns to the ground. When drilling high-pressure gas well, if the upper rock is loose and broken, in order to prevent high-pressure gas flowing out of the ground, it is necessary to lower the surface casing a little deeper. If the surface casing needs to be run deeper and the first spud time is long, the first layer of pipe should be considered before running the surface casing. Its purpose is to seal off the surface, prevent wellhead collapse, and form circulation channels for drilling fluid for a long time. The depth of the pipe is generally 20-30 meters, and the cement returns to the ground. The catheter is usually a spiral or straight slit tube.
1. Used to seal complex formations where drilling fluid is difficult to control, serious loss zones, and oil, gas and water layers with different pressures to prevent diameter expansion;
2. In directional Wells with large inclination, technical casing is inserted in the inclined section to facilitate safe drilling of directional Wells.
3. Provide conditions for the installation, blowout prevention, leakage prevention and hanging liner of well control equipment, and protect casing in oil layer.
Technical casing does not have to be run. We can control the complicated situation in the well by adopting high-quality drilling fluid, accelerating drilling speed, strengthening drilling and other measures, so that we can not run technical casing or less. The depth of technical casing is determined according to the complex formation to be packer, and the cement return height should reach more than 100 meters of the formation to be packer. For high-pressure gas Wells, cement return to the ground is often used to better prevent air leakage.
Oil layer casing
Used to seal off the destination layer from other layers; Seal off the oil, gas and water layers at different pressures, and establish an oil and gas passage in the well to ensure long-term production.
The depth of the casing depends on the depth of the target and the completion method. The cement slurry of oil layer casing generally returns to the top oil and gas layer more than 100 meters. For high pressure Wells, the cement slurry should return to the ground, which is conducive to strengthening the casing and enhancing the tightness of the casing screw, so that it can withstand large well shut-in pressure.