What is OCTG Casing?

What is OCTG Casing?

Introduction to OCTG

OCTG, full name Oil Country Tubular Goods, oil special pipe. Refers to a type of steel pipe specially used for oil and gas extraction, most of which are seamless pipes, but welded pipes also account for a considerable proportion.

(1) Standard: API-5CT standard drill pipe is the pipe connecting the drilling motor and the drill bit during the drilling process. The outer diameter is generally 2-6.5 inches (50-165mm), and the length is generally between 5-14m. Casing serves as the structural wall or lining of oil/gas wells to prevent contamination of the well or surrounding groundwater and can be up to 26 inches in diameter. Casing accounts for more than three-quarters of oil-specific pipe shipments.
(2) Working principle: Drilling fluid flows to the drill bit through the drill string to cool the drill bit, and at the same time, the drilled soil and rock debris and drilling fluid form mud, which is transported to the ground surface through the annular space (the gap between the casing and the drill string). Due to the harsh working environment, most drill strings are seamless pipes.

Definition of OCTG casing

Oil pipes are mainly used for oil and gas well drilling and oil and gas transportation. It includes oil drilling pipe, oil casing, oil extraction pipe. Oil drill pipe is mainly used to connect drill collars and drill bits and transmit drilling power. The oil casing is mainly used to support the well wall during the drilling process and after the well completion, so as to ensure the drilling process and the normal operation of the entire oil well after the well completion. The oil suction pipe mainly transports the oil and gas at the bottom of the oil well to the surface.

Oil casing is the lifeline to keep oil well running. Due to the different geological conditions, the downhole stress state is complex, and the combined effects of tension, compression, bending and torsional stress act on the pipe body, which puts forward higher requirements on the quality of the casing itself. Once the casing itself is damaged for some reason, it may lead to a reduction in production of the entire well, or even scrap it. According to the strength of the steel itself, the casing can be divided into different steel grades, namely J55, K55, N80, L80, C90, T95, P110, Q125, V150, etc. Different well conditions and well depths require different steel grades. In a corrosive environment, the casing itself is also required to have corrosion resistance. In places with complex geological conditions, the casing is also required to have anti-collapse performance.

How to prepare OCTG casing?

27MnCrV is a new type of steel for the production of TP110T steel grade oil pipe sleeves. The conventional steel grades for TP110T steel grade oil pipe sleeves are 29CrMo44 and 26CrMo4. Compared with the latter two, 27MnCrV contains less Mo element, which can greatly reduce the production cost. However, 27MnCrV produced by normal austenitizing and quenching process has obvious high temperature temper brittleness, resulting in low and unstable impact toughness. Two methods are usually used to solve such problems: one is to adopt the method of rapid cooling after tempering to avoid high temperature brittleness and obtain toughness. The second is that the sub-temperature quenching method can effectively improve harmful elements and impurities and improve toughness through incomplete austenitization of steel grades. The first method has relatively strict requirements on heat treatment equipment and requires additional costs.

AC1=736°C and AC3=810°C of 27MnCrV steel, the heating temperature is selected between 740-810°C during sub-temperature quenching. The heating temperature for sub-temperature quenching is 780°C, and the holding time for quenching heating is 15 minutes; the temperature for tempering after quenching is 630°C, and the holding time for tempering heating is 50 minutes. Since the sub-temperature quenching is heated in the α+γ two-phase region, the quenching is carried out in the state of retaining part of the undissolved ferrite, and the toughness is improved while maintaining high strength. At the same time, low-temperature quenching is lower than the conventional temperature, which reduces the stress of quenching, thereby reducing the deformation of quenching, which ensures the smooth operation of heat treatment production and provides good raw materials for subsequent wire processing.

This process has been applied in the processing plant. The quality assurance data shows that the yield strength Rt0.6 of the steel pipe after heat treatment is 820-860MPa, the tensile strength Rm is 910-940MPa, the impact toughness Akv is between 65-85J, and the anti-destruction performance is 100%. qualified. The data shows that 27MnCrV steel pipe is already a very high-quality high-grade steel oil casing. On the other hand, it also shows that the sub-temperature quenching process is a method to avoid high-temperature brittleness in the production of steel products.

Uses of OCTG casing

Oil casing is a large-diameter pipe that fixes the walls or holes of oil and natural gas wells. The casing is inserted into the wellbore and fixed with cement to help the wellbore separate the rock formation and prevent the wellbore from collapsing, while ensuring the circulation of the drilling mud to facilitate drilling and production.
Steel grades of oil casing: H40, J55, K55, N80, L80, C90, T95, P110, Q125, V150, etc. Processing form of casing end: short round thread, long round thread, partial trapezoidal thread, special buckle, etc. Used in oil well drilling, it is mainly used to support the well wall during the drilling process and after the well completion, so as to ensure the drilling process and the normal operation of the entire oil well after the well completion.

The importance of oil pipelines

The petroleum industry is an industry that uses petroleum pipes in large quantities, and petroleum pipes play an important role in the petroleum industry:
1. Petroleum pipes are used in a large amount and cost a lot, so there is great potential for saving expenses and reducing costs. The consumption of oil well pipes can be calculated according to the annual drilling feet. According to the specific conditions of our country, generally 62kg of oil well pipes are required for every 1m of drilling, including 48kg of casing and 10kg of oil pipe. Drill pipe 3kg, drill collar 0.5kg;
2. The mechanical and environmental behavior of the oil pipe has an important influence on the adoption of advanced technology and the increase of production and efficiency in the oil industry;

3. Oil pipes cause huge losses due to failure, and their safety, reliability and service life are of great importance to the oil industry.