On June 25, CNOOC’s first set of shallow-water underwater Christmas trees was independently developed by CNOOC Energy Development Co., Ltd.
(hereinafter referred to as “CNOOC Development”) rolled off the production line in Hainan, and its key technologies have reached the leading level in the industry.
This set of subsea oil trees has achieved the world’s first dual-channel safe transmission of temperature and pressure sensor signals of subsea equipment.
Compared with conventional subsea trees, the structure is more compact,
the operation is more convenient, and the weight is reduced by 40%. Compared with similar international products,
the production and delivery cycle has been shortened from at least 18 months to less than 8 months,
and the manufacturing cost has been reduced by 40%. After being put into use,
it can leverage the efficient development of hundreds of millions of tons of restricted crude oil reserves in the Bohai Oilfield.
1. Tailor-made shallow water underwater Christmas tree
The underwater Christmas tree is one of the core equipment for offshore oil and gas development.
It is an important hub connecting thousands of meters of oil and gas production strings below the seabed with tens of kilometers of submarine oil and gas transportation pipelines.
They are like an intelligent “faucet” at the wellhead, controlling the exploitation of oil and gas.
speed, and conduct real-time monitoring and adjustment of production conditions.
It can monitor important data in the oil and gas production process such as oil and gas well production temperature,
pressure, water content, sand production, and gas-oil ratio in real-time through highly integrated precision instruments,
and guide technicians to reasonably control single well production,
Take timely measures to increase and stabilize production to maximize the production life and oil and gas recovery of oil and gas fields.
In the past, subsea trees were often used in deep-water oil and gas development.
For a long time, only a few companies in the world have mastered the design and manufacture of subsea trees, and foreign technology monopolizes them. This poses a severe challenge to increasing reserves and production in Bohai oilfields. For this reason,
CNOOC has innovatively proposed to change the development of oil and gas fields in restricted areas from jacket platforms to underwater production models,
which means that shallow-water underwater Christmas trees and their supporting service capabilities will become a lever for hundreds of millions of tons of restricted crude oil reserves in the Bohai Sea. key.
CNOOC Development directly faces the oil and gas development needs of Bohai Oilfields and actively implements the development model of CNOOC’s shallow-water underwater Christmas trees.
After several months of research and development day and night,
the project team has completed the arduous research and development process of domestic underwater equipment research and development for at least three years.
In June 2023, the shallow water subsea oil tree changed from an initial idea to a stack of graphics,
from a drawing to a product. The project has just started, and everyone is quickly getting into top shape. Basic design, scheme optimization,
detailed design, expert argumentation, drawing, etc. are closely linked, and the project members have never slacked off.
At the beginning of the overall plan design, the project team fully investigated the actual production needs,
closely following the actual background of the Bohai Oilfield jacket platform switching to underwater production,
and the Bohai Sea shallow water oilfield mainly uses electric submersible pumps for lifting. The shallow oil reservoir is loose and prone to sand production. In the later stage,
Since well workovers may be relatively frequent, the optimization plan design was repeatedly adjusted and finally the idea of the structural design of dual electric submersible pumps was finalized.
“The dual-electric pump design can significantly reduce the frequency of workovers,
and can effectively solve the problem of high frequency of pump inspections and workovers caused by single electric submersible pumps in the Bohai area due to sand production and other factors,
effectively extending the production cycle of oil wells and increasing the annual production of oil wells. “Said Ju Shaodong, the technical director of the project. Underwater valves are key components of underwater trees.
If the underwater tree production channel is compared to a highway for oil and gas production,
then the underwater valves on the channel are like traffic police on the highway, directing the oil flow to advance or stop.
In order to meet the Bohai Oil and Gas Field’s development needs for lightweight and miniaturized underwater equipment,
the project team innovatively replaced the traditional cylindrical spring with a strong elastic disc spring and applied it to the valve hydraulic actuator.
After 200 temperature cycle tests, the high-pressure chamber Cycle testing and endurance cycle testing verify the reliability of the design.
“We are not afraid of repeated optimization and repeated testing. Our design is to make products that are usable, easy to use, and durable.”
The design of the underwater Christmas tree project always adheres to this concept.
“Another challenge in the development of shallow-water underwater trees is the design and selection of many parts of the underwater trees,”
said Wang Xing, the person in charge of the major project implementation of shallow-water underwater trees. The underwater Christmas tree is a system engineering product that involves the collaboration of materials engineering,
heat treatment technology, underwater anti-corrosion technology, marine life control, and other professional disciplines,
as well as the design, processing, assembly, and testing of more than 1,200 parts. “The stability of the quality of components can ensure the stability of the overall equipment performance to a greater extent.
” In order to solve this problem, the project team followed the standard that “the entire shallow water subsea tree system can operate normally on the seabed for 20 years” in the early stages of product development.
2. “One-stop, one-room” helps underwater tree testing pass
“As an important part of the underwater production system, the underwater tree must ensure that the entire system can operate normally on the seabed for 20 years.
Dozens of rigorous tests must be conducted on the underwater tree and its connecting equipment.”
Hainan Province Deep Sea Tong Wujun, the subject leader of the research direction of underwater wellhead and underwater Christmas tree testing technology in the key engineering laboratory,
said. Foreign companies once sold underwater Christmas tree products at high prices while bundling expensive technical services. Technology monopoly and restrictions became a major obstacle to the development of the underwater industry.
In May 2020, in order to fully support the construction of the “Deep Sea No. 1” gas field development project and solve the problem of receiving and testing the project’s 11 underwater trees,
CNOOC Development Engineering Technology Company established CNOOC’s first team of underwater tree testing engineers.
Multi-party docking, and actively prepare for relevant testing technical support services.
“If the first hurdle is not broken, the second hurdle is difficult to overcome. The test team started from scratch,
and after nearly three months of exploration, the SRT (system reception) test of the first underwater tree in the ‘Deep Sea No. 1’ gas field was completed.”
Underwater tree test Team leader Xiao Tan said. At that time, affected by the global epidemic,
it was difficult to coordinate personnel, equipment, and other resources, and underwater Christmas tree testing was not easy. Everyone explored step by step, summarized bit by bit,
continuously optimized the test procedures, repeatedly adjusted the test process, and finally completed the test of 11 1,500-meter underwater trees of “Deep Sea No. 1”,
ensuring that the project development was implemented as scheduled. With the accumulation of experience and technological updates,
the underwater tree testing team compiled and launched testing specifications, forming three testing guidelines, and its testing capabilities were gradually enhanced. With the precipitation of testing technology,
the underwater tree testing team has successively completed the pre-production system test of the 500-meter underwater tree independently developed by my country,
the test of three underwater trees in the Dongfang 1-1 gas field,
and the Ministry of Industry and Information Technology The first phase of the underwater tree testing and the testing of 16 underwater trees.
“We can solve all the tests of subsea trees by ourselves, and we are no longer subject to foreign companies.” Xiao Tan said, “
At present, the tests of all 12 subsea trees in the second phase of the ‘Deep Sea No. 1’ project have been handed over to our testing team responsibility.
“At the same time, strong support from national policies has accelerated the realization of independent controllability of underwater tree testing technology.
In order to realize independent innovation in the field of marine science and technology and build a high-level scientific research platform for key core technology research,
CNOOC South China Sea Oil and Gas Energy Academician Workstation and Hainan Provincial Key Laboratory of Deep Sea Deep Engineering were successively unveiled in Haikou.
Among them, the underwater production system test base of the academician workstation and the underwater production system test experiment center of the key laboratory are both located in the deep-water drilling and production Hainan base of CNOOC Development Engineering Technology Company.
“Relying on the technical support of ‘one station, one room’ and the previous technical precipitation, we have built a comprehensive subsea tree base with design,
assembly, final assembly, testing, maintenance, operation and maintenance, and service,
forming a subsea production system The three major testing technology systems and the four major testing platform systems provide sufficient guarantee for the customs clearance of underwater Christmas tree products,” said Tong Wujun.
3. Strive for excellence to build a “tree-planting” iron army
The underwater oil tree is firmly placed on the seabed, and the oil and gas production string and the submarine oil and gas transportation pipeline are normally connected,
so that the function of the intelligent “faucet” can be fully exerted. How to “plant” underwater oil trees weighing dozens of tons on the seabed in a marine environment hundreds of meters or even thousands of meters deep?
This problem will not be fully and independently solved by CNOOC people until 2022. 
The installation team adopted the “double insurance” strategy to seize the time window. On the one hand, the offshore team keeps track of the on-site operations,
on the other hand, in order to deal with emergencies, the land technical support team is on call 24 hours a day.
The operation team used the hemp rope to guide the high-pressure tree cap and the underwater oil tree. Due to the strong wind, it was difficult to maintain the attitude of the tree cap.
The operators brainstormed and temporarily processed the guide frame of the high-voltage tree cap to provide additional straightening and centering services for the high-voltage tree cap,
which greatly shortened the docking time and improved the operation efficiency. After a night of uninterrupted struggle,
with the end of a series of underwater operations such as placing steel rings,
disassembling and assembling rope anchors, and pressing and locking,
the installation of the underwater Christmas tree and underwater testing was fully completed within the scheduled time.
The outstanding achievement of “failure” has achieved the first breakthrough of CNOOC’s “planting trees” on the seabed.
In March this year, the team successively completed offshore maintenance services for three subsea trees in the Dongfang 1-1 gas field.
So far, the three subsea trees have been running smoothly, and the production of the gas field has exceeded expectations.