【Major Industrial Equipment in the Chemical Engineering Sector】002 – Domestic-made shallow-water subsea wellheads and production trees

The subsea tree system is a key piece of equipment in the production of offshore oil and gas fields; it connects the oil and gas coming from deep within the reservoirs to the external oil and gas transportation pipelines. It enables control over the rate of oil and gas extraction, as well as real-time monitoring and adjustment of production conditions. For a long time, China’s subsea Christmas tree systems have relied on imports.

It is understood that the underwater production tree that was successfully tested in these sea trials is part of a major project in Shandong Province as well as a key project under the province’s initiative for major technological innovation. It was developed and manufactured by Dongying Weifei Marine Equipment Manufacturing Co., Ltd. Compared to similar foreign products, this system has a 40% reduction in weight and a 30% reduction in cost. At the same time, the fully enclosed protective system used for the first time can effectively prevent the risks posed to underwater production systems by fishing nets getting entangled or ship anchors being lowered, and its design concept is at the international leading level. Mi Lijun, the project leader at CNOOC Research Institute, told reporters that the project overcame various technical challenges related to wellhead stability and flow safety, and completed the design, manufacturing, installation, and testing of more than 1,300 components, thereby creating an underwater production tree system with independent intellectual property rights in China.

Research on underwater tree technology began in the 1960s, with the American company FMC developing the world’s first underwater tree system, which was initially used at a water depth of 20 meters. Thereafter, as time passed, technology improved, and the focus of oil development shifted, subsea production trees experienced rapid development. There are various classification methods for subsea Christmas trees; for example, they can be classified into flowline Christmas trees and non-flowline Christmas trees based on the wellwork method ； Based on the installation method, they can be classified into diver-operated type, ROV/diver-assisted operation type, and fully ROV-operated type ； Based on the layout of main valves such as the production main valve and production wing valves, they can be divided into vertical production trees and horizontal production trees. Foreign countries have developed quite advanced technology in underwater production trees, and such equipment is widely used in oil and gas field development. At present, the technology for underwater production trees remains under complete foreign monopoly; a few multinational companies such as FMC and Vetco Gray control the majority of the global market share in this field, resulting in a high degree of market concentration in the underwater production tree industry.

In China, research on technology for marine subsea wellheads and oil production equipment started relatively late. In 2010, Jinshi Group, in collaboration with the American company Argus, introduced China’s first AZ-10 type of new central-hole subsea production tree in the Chinese market. Subsequently, Shanghai Shenkai Petroleum Chemical Equipment Co., Ltd. and Jianghan Petroleum Drilling Bit Co., Ltd. (now Sinopec Petroleum Machinery Co., Ltd.) carried out research in related fields one after another. In 2019, Avantgarde Company was given the opportunity to carry out a demonstration of subsea production trees at the Dongfang 1-1 gas field, which played a significant role in promoting the domestic use of such subsea production trees.