Vietsovpetro JV, the leading oil company in Vietnam, has been producing hydrocarbons on the shelf of the South China Sea for more than 40 years. The oil produced at the Vietsovpetro fields is mainly highly paraffinic with a paraffin content of up to 25% and a pour point of up to 34 °С. Subsea pipelines are laid on the seabed at a depth of about 50 m and are constantly in operation. As of 2022, the number of oil pipelines at the fields is 69 lines with a total length of 313.3 km. The total length of gas and gas lift pipelines is 312 km, pipelines of water injection system - 167 km. Most oil pipelines have a long service life and are not thermally insulated. This circumstance creates the preconditions for paraffin deposits formation. There are several types of deposits that form in pipeline systems: solid deposits of wax, gradually formed in non-thermal insulated pipelines during the transportation of hot oil; soft deposits and stagnant zones formed during the transport of low-performance oil with a temperature close to the pour point; inorganic deposits formed in oil and gas pipelines (iron oxides, salt deposits, clay and rocks). In addition, due to a decrease in production, the speed of products transport has decreased, and the water cut has increased, which leads to precipitation of free water and the intensification of corrosion. There is an urgent need for periodic cleaning and in-line diagnostics of pipelines, which is complicated by the fact that most pipelines are not equipped with cleaning and diagnostic tools. The article covers various methods of cleaning pipelines used in Vietsovpetro JV, including alternative methods, which, although do not guarantee complete removal of deposits, allow restoring the productivity of the pipeline and ensuring safe transportation of products. This is the application of solvents - condensate and compressate, flushing with water and purging with gas, as well as combined methods. The greatest effect is achieved when cleaning using mechanical and gel pigs. Specifics of offshore oil and gas production and transport (difficulty in installing pumps, sharp turn angles of pipelines, the presence of large vertical risers up to 70 m high, etc.) do not allow completely copying the mechanical cleaning technologies used onshore. The adaptation and implementation of these technologies in relation to the conditions of offshore fields is being successfully carried out.
References
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