Oil country tubular goods, also known as oil country tubular goods, are the foundation of the oil industry. Casing, tubular goods, and drill string components (drill pipe, drill collar, square drill pipe, etc.) are collectively referred to as oil country tubular goods (OCTG).
Oil country tubular goods (OCTG: Oil Country Tubular Goods) and oil and gas pipelines (Line Pipe) are collectively referred to as oil country tubular goods. Oil country tubular goods are deep-processed products of steel pipes, including oil country tubular goods and oil and gas pipelines. Drill pipes, casing, tubular goods, drill collars, square drill pipes, etc. are collectively referred to as oil country tubular goods.
1. What are the production and inspection standards widely used for oil country tubular goods at home and abroad?
The service conditions of oil-country tubular goods are quite harsh, and their quality requirements are much stricter than those of general seamless pipes. They must be produced and inspected by special standards or technical conditions. At present, the production and inspection standards widely used for oil country tubular goods at home and abroad are mainly based on the American Petroleum Institute or API standards. Casing and tubing adopt the API SPEC5 CT standard, drill pipe adopts the API SPEC5 standard, and drill pipe joint adopts the API SPEC7 standard.
2. To meet the special geological working environment of oil fields, what types of non-API tubing and casing currently used at home and abroad can be divided into?
In addition to API standard casing, domestic and foreign countries have also researched and developed non-API casing that meets the special geological working environment of oil fields, including:
Ultra-high strength tubing and casing for deep wells;
High resistance to collapse casing;
Hydrogen sulfide stress corrosion-resistant tubing and casing used in hydrogen sulfide oil and gas wells;
High-strength tubing and casing for low-temperature oil and gas wells;
Tubing and casing are used in corrosive environments with only carbon dioxide and chloride ions and almost no hydrogen sulfide;
Tubing and casing are used in highly corrosive environments where hydrogen sulfide, carbon dioxide, and chloride ions coexist.
3. What are the functions of tubing and casing in oil wells? What are the different types of casing according to their functions?
In oilfield drilling and production operations, “casing” refers to the steel pipe used as a borehole lining to prevent the wellbore from flowing or collapsing. It is a permanent part downhole, and the bottom of the casing is fixed with cement. The cement sometimes returns to the surface. Most casings have an outer diameter of 114.3mm or larger. The innermost steel pipe in the well is called tubing. Downhole fluid is sent to the surface through the tubing, which can be separated from the casing by a production separator. The tubing is often pumped out of the well and sometimes needs to be replaced. Most tubing has an outer diameter of 114.3mm or smaller. The drilling environment often requires several layers of casing to reach the expected total well depth. Each layer of casing can be divided into the following according to its function:
(1) Conduit. The outermost layer of the well, its main function is to reinforce the wellbore wall and prevent the surface gravel layer and unbonded rock from falling into the well.
(2) Structural pipe. Located between the guide tube and the surface pipe, the purpose of this layer of casing includes solving the problem of recurring leakage or well collapse and avoiding the problem of shallow gas well kick as much as possible.
(3) Surface casing. The purpose of the lower surface casing is multiple, including isolating the freshwater layer, preventing collapse and leakage, isolating the weak layer that cannot withstand the back pressure applied by controlling the well kick, providing conditions for installing blowout preventers, and supporting the weight of all layers of casing that are smaller than the surface casing.
(4) Intermediate casing. The main purpose is that high-pressure layers will be encountered during drilling, and high-density drilling fluid is required to control abnormally high pressure. Shallow and weak formations must be protected to prevent leakage or stuck drill. In some special cases, intermediate casing is also used to isolate salt layers or expansive and easily collapsed shale layers.
(5) Liner. The liner has the same function as the intermediate casing. The liner extends from the bottom of the well upward into the intermediate casing but does not extend to the ground. To save money, the liner does not need to extend the pipe string to the ground but can still achieve the purpose of controlling pressure and fracture gradient.
(6) Production casing. Also known as oil layer casing. The function of this pipe string is to separate the production layer from other formations, form a working wellbore with a given diameter that can reach the production layer, and protect the production oil pipe and equipment.
(7) Back-up pipe string. The liner is also often used as part of the production casing, instead of running another pipe string from the ground to the production layer. The liner can be returned to the ground from the top of the liner with an appropriate amount of steel pipe.
4. What is the steel grade of the oil pipe and casing, and what is the specific meaning?
In the API SPEC5CT standard, the steel grade of the casing and oil pipe indicates its yield strength and some special characteristics. The steel grade is usually indicated by 1 letter and 2 or 3 numbers, such as N80. In most cases, according to the order of the letters in the alphabet, the later the letters are the greater the yield strength of the steel pipe. For example, the yield strength of N80-grade steel is greater than that of J55. The numerical symbol is determined by the minimum yield strength of the pipe expressed in thousands of pounds per square inch. For example, The minimum yield strength of N80 grade steel is 550Mpa. The casing steel grades listed in API SPEC5 CT standard are: H40, J55, K55, N80, M65, L80, C90, C95, T59, P110, Q125; casing steel grades are: H40, J55, N80, L80, C90, T59, P110.
Post time: Oct-29-2024