Classification by Material
- Carbon Steel Casings: They are cost-effective and possess certain strength and toughness, which can meet the basic requirements of conventional oil and gas wells. They are widely used in oil production. For example, casings with steel grades like J55 and K55 are often used in shallow and medium-depth wells.
- Alloy Steel Casings: With the addition of alloy elements, their strength, corrosion resistance, and high-temperature resistance are significantly improved. Alloy steel casings with steel grades such as C90 and T95 are suitable for high-temperature, high-pressure, and somewhat corrosive oil and gas production environments.
- Stainless Steel Casings: They have excellent corrosion resistance and high-temperature oxidation resistance and are commonly used in offshore oil and gas fields, high-sulfur oil and gas fields and other highly corrosive environments. Examples include casings made of stainless steel materials like 3Cr, 9Cr, and 13Cr.
- Titanium Alloy Casings: They feature high strength, low density, outstanding corrosion resistance, and anti-fatigue performance. They are especially suitable for extremely harsh oil and gas production conditions such as deep sea, ultra-high temperature and pressure. However, due to their high cost, their application is relatively limited.
Classification by Manufacturing Process
- Seamless Casings: Manufactured through processes like piercing, hot rolling, and cold drawing, seamless casings have no weld seams. They have the advantages of high strength, good pressure resistance, and reliable sealing performance. They are the main type of oil well casings and are widely used in various oil and gas wells.
- Welded Casings: They are formed by rolling and welding steel plates or steel strips. The manufacturing process is simple and the cost is low. However, the strength and corrosion resistance at the weld seams are relatively weak. They are generally used in shallow wells or low-pressure oil and gas wells where the performance requirements for casings are not particularly high.
Classification by Usage Environment and Function
- Surface Casings: Their main function is to fix the wellhead device, seal off the surface shallow water layer and shallow loose formations, and provide basic support for subsequent drilling and completion operations. Generally, they are set at relatively shallow depths.
- Intermediate Casings: They are used to seal off different pressure-bearing formation systems, prevent cross-flow of formation fluids, protect the stability of the wellbore, and provide channels for drilling fluid circulation. Depending on the well depth and geological conditions, multiple intermediate casings may need to be set.
- Production Casings: They are run into the oil and gas reservoir sections. Their main functions are to protect the oil and gas reservoirs, prevent the collapse of the wellbore, ensure that oil and gas can smoothly flow from the formations into the wellbore and then be transported to the ground. They have relatively high requirements for corrosion resistance, sealing performance, and strength.
- Special-Purpose Casings: For some special geological conditions or production requirements, such as horizontal wells, extended-reach wells, and thermal recovery wells, corresponding special-purpose casings have been developed. These casings have unique designs in terms of structure, material, or performance to meet specific production requirements.
Classification by Connection Method
- Threaded Connection Casings: This is the most common connection method. Threads are machined at both ends of the casings, and the casings are connected one by one through threads. According to the form and characteristics of the threads, they can be further divided into API standard threads, premium threads, etc. API standard threads are widely used, while premium threads have better sealing performance and connection strength and are suitable for some special working conditions.
- Welded Connection Casings: The ends of the casings are connected by welding. Welded connection casings have good integrity and high strength, but they are relatively difficult to install and disassemble. They are generally used in some specific well conditions or permanent installation occasions.
- Casings with Other Connection Methods: For example, casings with expansion joint connections or clamp connections. These connection methods have certain advantages in some special situations, such as quick installation and easy maintenance, but their application ranges are relatively narrow.