The casing centralizer is a core auxiliary tool in the cementing operation of oil and gas wells. It ensures the casing is centered in the wellbore, improves cementing quality, and its performance is directly related to the efficiency of oil well operations.
In terms of materials, there are two mainstream types: metal and composite materials. Metal materials are mainly carbon steel and alloy steel, which can withstand high pressure and high temperature, making them suitable for deep wells and ultra-deep wells. Composite materials are mostly glass fiber-reinforced resins, which are lightweight and corrosion-resistant, ideal for medium-shallow wells and corrosive formations.
The core performance indicators are centralizing force and passability. The centralizing force must match the casing weight and wellbore conditions to prevent casing deviation. Passability requires smooth passage through casing collars and wellbore diameter reduction sections to avoid jamming. In addition, it must have wear resistance and anti-aging properties, and be adaptable to different well temperature (-40℃ to 150℃) and pressure environments.
According to the structure, it can be divided into three types:
- Rigid centralizers (such as spiral type and blade type): They have strong centralizing force and are used in vertical wells and directional wells.
- Elastic centralizers (such as spring type): They have good compressibility and are suitable for wells with irregular wellbores.
- Automatic centralizers: They can automatically adjust the centralizing force according to the change of the wellbore, and are suitable for horizontal wells and extended-reach wells.
The model and size of the casing centralizer must match the casing specifications. Common models are classified by casing outer diameter. For example, a 139.7mm (5½ inch) casing is matched with a centralizer with an outer diameter of 165mm, and a 177.8mm (7 inch) casing is matched with a centralizer with an outer diameter of 203mm. Specifically, it is necessary to refer to API standards or manufacturer specifications to ensure a reasonable gap with the wellbore (usually 20-50mm).
In terms of application:
- Rigid centralizers are mostly used for cementing in the oil layer section of vertical wells and deep wells.
- Elastic centralizers are suitable for medium-shallow wells and easily leaky formations.
- Automatic centralizers are the first choice for horizontal wells and shale gas wells, as they can ensure the casing is centered in the horizontal section, improve the cementing bonding quality, and reduce the risk of oil and gas channeling in the later stage.
