The well pipe casing is a large-diameter tubing used primarily to secure the walls or boreholes of oil and natural gas wells. Once inserted into the borehole, the casing is cemented in place to prevent well wall collapse, isolate rock formations, and ensure circulation of drilling mud, thereby ensuring smooth drilling and extraction operations. Due to its importance and practicality, well pipe casing is commonly used, with external diameters typically ranging from millimeters to 508 millimeters. The critical importance of well pipe casing in drilling operations is evident, as its quality directly impacts the safety and efficiency of drilling operations. One of the key factors determining the performance and reliability of well pipe casing is its material. Below, we will provide a detailed introduction to the main materials used for well pipe casing.
Carbon steel is one of the most common materials for well pipe casing. It offers good mechanical properties and corrosion resistance, suitable for most oil and gas wells. Carbon steel well pipe casing typically uses grades like J55, N80, L80 as per API 5CT specifications. These materials provide high strength and corrosion resistance, meeting the requirements of general oil and gas wells. Lower grades like J55 and N80 are used for welded pipes. Oil pipes transport petroleum from reservoirs to the surface through couplings or integral connections.
Alloy steel offers higher strength and excellent corrosion resistance, suitable for harsh conditions such as high temperature and pressure. Alloy steel well pipe casing typically uses grades like C95, P110 as per API specifications. These materials provide higher strength and better corrosion resistance, suitable for drilling operations in deep and complex well types.
Stainless steel well pipe casing offers excellent corrosion resistance and high temperature performance, suitable for drilling operations in acidic or alkaline environments. Stainless steel well pipe casing typically uses materials like 316, 316L, known for their high corrosion resistance and high temperature performance, effectively preventing corrosion and deformation of the casing.
Plastic well pipe casing is a new type of casing material, known for its lightweight, corrosion resistance, and good insulation properties, suitable for specific operational conditions. Plastic well pipe casing is typically made from materials like polyvinyl chloride (PVC) or high-density polyethylene (HDPE), offering excellent corrosion resistance and high temperature performance to meet the demands of certain well types.
Production and Inspection of well pipe casing
The production and inspection of well pipe casing must adhere to strict standards and specifications to ensure its quality and reliability.
Chemical Composition Testing:In claim cases, external defects such as black threads, thread damage, pipe folding, thread breaks, tight thread spacing, and coupling size discrepancies have been noted. Internal quality issues include casing brittleness and low yield strength.
Well casing applications and specifications
The application of well pipe casing in the petroleum industry is crucial for drilling and transporting oil and gas from wells. It includes drill pipes, well pipe casing, and production tubing. Drill pipes connect the drill bit and drilling rig, transmitting drilling power. Well pipe casing supports the wellbore during drilling and after completion, ensuring smooth operations and normal functioning of the entire well. Production tubing transports oil and gas from the well bottom to the surface.27MnCrV is a new type of steel used to produce TP110T grade well pipe casing. Conventional steels used for TP110T grade casing include 29CrMo44 and 26CrMo4. Compared to the latter two, 27MnCrV contains fewer rare elements, significantly reducing production costs. However, normal austenitizing and quenching processes for 27MnCrV may result in high-temperature temper brittleness, leading to lower and unstable impact toughness.
For 27MnCrV steel, AC1=736°C, AC3=810°C. Subcritical quenching involves heating between 740-810°C, with a selected heating temperature of 780°C and a soaking time of 15 minutes; subsequent tempering is conducted at 630°C for 50 minutes. Subcritical quenching heats in the α+γ phase region, preserving some undissolved ferrite during quenching to maintain higher strength while improving toughness. Additionally, lower quenching temperatures reduce quenching stress compared to conventional methods, minimizing deformation. This ensures smooth operation of heat treatment and provides excellent raw material for subsequent thread machining and other processes.
These categorizations ensure efficient and safe drilling operations across various geological conditions.
Standards and specifications for oil well pipe casing
The surface of the casing and thread connections must be smooth, without burrs, tears, or defects that could interrupt threading or compromise strength and tight connections.
According to SY/T6194-96, lengths of domestic casing can vary from 8 to 13 meters. Casing lengths shorter than 6 meters can be provided, but should not exceed 20% of total casing.
Both internal and external surfaces of the casing must be free from folds, stripes, delamination, cracks, rolling, and scars. These defects must be completely removed, with depths not exceeding 12.5% of the nominal wall thickness.