What is OCTG pipe? What are the main uses? Comprehensive analysis of petroleum special pipe
In the whole chain of oil and gas exploration and development, OCTG tubing is the core special equipment throughout, and it is known as the "underground lifeline" of oil and gas exploitation. Whether it is drilling to break rocks, completing and fixing walls, or transporting oil and gas, it is inseparable from the support of OCTG pipes. But for most people, the definition, characteristics and specific uses of OCTG pipe are still relatively unfamiliar. In fact, OCTG is not a single specification pipe, but a set of systematic products suitable for underground extreme working conditions, and its uses accurately correspond to the key links of oil and gas exploitation. This paper will systematically answer the core questions such as "What is OCTG pipe", "What is its core purpose" and "How to adapt to different scenarios" with the subtitle of question sentence, and combine with industry practice to build a comprehensive cognitive system for readers to help them understand this basic equipment of oil and gas industry in depth.
Definition of essence: What is OCTG pipe? How is it different from ordinary pipes?
OCTG is the abbreviation of Oil Country Tubular Goods, which literally translates as "special tubing for oil" in Chinese. Its essence is a tubular product system designed and manufactured for the whole process of oil and gas exploration and development, which can adapt to extreme working conditions such as underground high temperature, high pressure, strong corrosion and high wear, and support core operations such as drilling, completion, oil production and workover, rather than a single-form and single-function metal tubing. This definition defines the exclusive property of OCTG pipe, which makes it form a clear boundary with ordinary industrial pipe.
Compared with ordinary industrial pipes, OCTG pipes have three core differences: first, they are more adaptable to working conditions, and need to resist the high temperature above 150℃ and high pressure above 100MPa underground, as well as the corrosion of corrosive media such as hydrogen sulfide and carbon dioxide, so the performance of ordinary pipes is completely unattainable; Secondly, it is characterized by systematization, and it is composed of many kinds of products, such as drill pipes, steel casings, oil pipes, etc. All kinds of pipes perform their respective duties and cooperate with each other to form a complete equipment chain; Third, standards and accuracy requirements are more stringent, and authoritative standards such as API (api gravity) and GB need to be followed. The control accuracy of dimensional tolerance, mechanical properties, tightness and other indicators is much higher than that of ordinary pipes. It is these characteristics that make OCTG tubing an indispensable core equipment for oil and gas exploitation.
Core use: What links does OCTG pipe mainly serve for oil and gas exploitation?
The core application of OCTG tubing is centered on the whole process of oil and gas exploitation, which accurately corresponds to the three key links of drilling, completion and oil production, and also takes into account auxiliary operations such as workover and stimulation. With its exclusive function, all kinds of tubing can jointly ensure the continuous and efficient progress of oil and gas exploitation from "breaking the ground and forming holes" to "oil and gas production", which are indispensable.
Specifically, the drilling link depends on the drill pipe to transmit power and drilling fluid, which provides support for the drill bit to break the rock; In the completion process, the artificial shaft wall is formed by cementing steel casing, which realizes shaft wall support and stratum isolation and builds a safe defense line; In the oil production process, crude oil and natural gas in underground oil and gas reservoirs are efficiently transported to the surface through tubing, and at the same time, it is suitable for subsequent operations such as oil and gas lifting and separation. In addition, in workover operation, OCTG tubing can be used as a repair channel to deal with downhole plugging, tubing damage and other problems; In the fracturing stimulation operation, some high-strength OCTG pipes can also withstand the high pressure of fracturing fluid to ensure the safety of stimulation operation. It can be said that every key node of oil and gas exploitation is inseparable from the support of OCTG pipes.
Detailed classification: What are the specific uses of different types of OCTG pipes?
The uses of OCTG pipes are highly bound to their types. The core of OCTG pipes is divided into three categories: drill pipe, steel casing and tubing. The structures and properties of various pipes are different, and their specific uses are also emphasized. At the same time, OCTG pipes are matched with auxiliary pipes such as drill collars, couplings and sieve tubes to further expand the use boundary and adapt to more complicated operation requirements.
The core purpose of drill pipe is "power transmission+drilling fluid transportation", which is connected into a drill string through a threaded joint, and transmits the rotating power of the ground drilling equipment to the underground drill bit to drive the drill bit to break the rock stratum; At the same time, the drilling fluid is transported by means of the hollow structure, which cools the drill bit and carries cuttings out of the well to avoid borehole blockage and ensure continuous drilling. The purpose of steel casing focuses on "safety protection+stratum isolation", and it is divided into surface casing, technical casing and production casing according to the operation requirements: the surface casing isolates the surface soil from groundwater to prevent shallow borehole collapse; Technical casing should deal with complex formations such as deep high temperature, high pressure and fracture zone, strengthen borehole wall support and isolate harmful formation fluids; The production casing is in direct contact with the oil and gas reservoir, which protects the oil and gas reservoir from pollution and provides a stable channel for oil and gas transportation. The core use of tubing is "oil and gas transportation", which runs into the steel casing to accurately transport crude oil and natural gas produced by oil and gas reservoirs to the ground. Some special tubing can also be adapted to downhole throttling, heating and other functions to improve transportation efficiency. In the auxiliary tubing, the drill collar is used to increase the drilling weight and stabilize the drill string, the coupling strengthens the sealing performance of the tubing connection, and the sieve tube is used to filter sand particles and protect the tubing and subsequent equipment.
Scene adaptation: How to adjust the use of OCTG pipes under different oil and gas conditions?
Oil and gas exploitation scenarios are complex and diverse, ranging from shallow conventional oil fields to deep high-temperature and high-pressure oil fields, high-sulfur gas fields and deep-sea oil fields, and the working conditions are significantly different. Although the core of the use of OCTG pipes remains unchanged, it is necessary to adjust the types, materials and processes to meet the special needs of different scenarios to ensure the safety and reliability of the application.
The working conditions of shallow conventional oil fields are mild, and the use of OCTG tubing is mainly based on basic operations. Grade J55 and K55 carbon-manganese steel casing and tubing and grade E75 drill pipe are selected to meet the requirements of conventional drilling and transportation. In deep high-temperature and high-pressure oil fields (temperature > 150℃, pressure > ＞100MPa), it is necessary to choose P110 and Q125 grade high-strength alloy pipes to strengthen the creep resistance of drill pipe and the supporting strength of casing, so as to ensure stable use under extreme pressure and temperature. The core risk of high-sulfur gas field is hydrogen sulfide corrosion, so it is necessary to choose corrosion-resistant OCTG pipes such as 13Cr and 22Cr dual-phase steel to avoid corrosion failure of pipes and ensure the normal performance of casing isolation function and tubing transportation function. Deep-sea oil fields need to cope with high pressure, seawater corrosion and low temperature impact at the same time. Super 13Cr alloy or titanium alloy pipes are selected with cathodic protection technology to ensure the long-term service of drill pipes, casings and tubing in the marine environment, which is suitable for deep-sea drilling and oil and gas transportation. In broken formation, it is necessary to strengthen the supporting use of casing, select thick-walled casing and optimize cementing technology to prevent borehole wall collapse from affecting operation.
Value extension: What is the significance of the use of OCTG pipes to the oil and gas industry?
The use of OCTG pipe is not only limited to the specific operation links of oil and gas exploitation, but also has irreplaceable significance to the safety, efficiency, cost and industrial upgrading of oil and gas industry. The effective application of OCTG pipe directly determines the success or failure of oil and gas exploitation and the quality of industry development.
From the safety point of view, the protection and isolation of OCTG pipes can effectively avoid major safety accidents such as borehole wall collapse, oil and gas leakage, pipe fracture, etc. A high-sulfur gas field has achieved stable operation for 15 years due to the selection of suitable corrosion-resistant OCTG pipes, without any safety hazards; On the other hand, if the use and working conditions of tubing are mismatched, it may lead to shutdown and workover, and the loss of single well exceeds tens of millions of yuan. From the perspective of efficiency and cost, the OCTG tubing with suitable working conditions can shorten the drilling cycle and prolong the operation and maintenance life. After selecting high-strength drill pipe in a deep oil field, the drilling efficiency is improved by 30% and the operation and maintenance cost is reduced by 25%. From the perspective of industrial upgrading, the expansion and upgrading of the use of OCTG pipes has promoted oil and gas development to more complex scenes. The application of super alloys and intelligent OCTG pipes has made it possible to develop oil and gas resources that are difficult to produce, such as deep sea, ultra-deep layer and high sulfur content, and supported the high-quality development of the oil and gas industry. At the same time, the localization adaptation of OCTG pipe use is of strategic significance for ensuring national energy security and reducing dependence on foreign equipment.
To sum up, OCTG tubing is a systematic special equipment specially designed for oil and gas exploration and development. Its core use covers the whole process of drilling, completion and oil production. Different types of tubing have their own functions, and at the same time, it can meet the operational requirements of different extreme working conditions through scene adaptation. Its effective application not only ensures the continuous and efficient oil and gas exploitation, but also supports the oil and gas industry to expand to complex scenes and upgrade to high quality. With the continuous progress of oil and gas development technology, the use of OCTG pipe will be further extended. With intelligent and green technology, it will help the oil and gas industry achieve sustainable development while improving operation efficiency and ensuring safety. In the future, OCTG pipes will continue to provide solid support for global energy supply with the core positioning of "underground lifeline".
From the development trend, the use of OCTG pipes will be more precise and multifunctional, such as intelligent tubing with transmission and monitoring functions, composite casing adapted to multi-extreme working conditions, etc., which will further expand its application boundary in oil and gas exploitation and inject new impetus into the technological innovation of oil and gas industry.
