an essay concerning subsea pipelines flexible api 17j 20150809

the knowledge, expertise and knowledge are generated in dongfang 1-1 gasfield, phase 1 development/adjustment wells project, water depth 70 meters around, the flexible pipelines were fabricated in a yard near the coastline in wudi, binzhou, shandong, china and the pipelay vessel alongside the coastline as well.

to understand subsea flexible pipelines, the following points are to be addressed:
  • fabrication
  • composition
  • functionality/application
  • installation
  • commissioning
  • operation (workflow, or the service process) , start-up
  • maintenance (rov/cctv, or as george orwell called ‘big bother’ whatever you name it)
  • after-sales service (spare parts, facility statues inspection and that sort of things)
subsea flexible pipelines (API 17J &B) generally consist of these layers, each may or may not be subdivided:
  • carcass
  • inner sheath/liner
  • pressure armour
  • tensile armour
  • external sheath/liner

interlocked carcass

it is metal and the wellstream is supposed to travel within the carcass

inner sheath/liner
it is extruded from unbonded polymer, it seals the liquid leakage in the annular betwixt the two armors, and prevents the carcass from the corrosion caused by liquid leakage in the annular in the two armors

pressure armour

it is supposed to be pressure-resistant, but i have no idea whether it is the inner pressure of the wellstream in the carcass or the external pressure from the currents or waves in the waters… it has 4/6 sublayers. it serves with the function of preventing the carcass from the collapse caused by pressure.
tensile armour
it is resistant to tensions despite the flexible pipelines are burial, but if the pipelines are not buried beneath the mudline, it flows on the sea floor, then it screws, and thus the torques/tensions (clockwise and anticlockwise) are created, the tensile armor that consists two sublayers is resistant to the each direction of tensions
outer sheath/liner
extruded from unbonded polymer as well, it is fabricated from the same machine that the inner liner comes out from. the function of this layer is to seal the liquid leakage in the annular in the armors together with the inner liner, and seals the pipelines from sea water.
hydrostatic testing was performed, i didn’t come close because i might be hurt due to the high pressure, the testing lasted for a long time.
with the pipelines were fabricated and tests performed, they were transported from the yard to a pipelaying vessel, i saw a tensioner was used. the pipelines were placed in a basket on that vessel rather than a reel – i assume it is not reel lay – because it was in a basket.
Flexlay
an anti-wear tap layer was included sometimes. i believe a sensor is supposed to be attached to one layer to detect the fatique, durability and leakage things, but we didnt have it as we just started to develop it year ago. we have to bridge the gap with whatever the effort we must make, and with each feature of the innovation gathered and united in a product, we must penetrate inch by inch alongside the predesigned course to meet the target.
the experience was fruitful and worthwhile despite it was near the shore/shine/coastline and 40 miles far from the county.
with composition and the functionality of each layer and sublayer explained. we now come to the the flexible pipelines applications.
subsea pipelines serve in the production phase and midsteam (gathering, transportation and storage).
generally the offshore wells are drilled as satellite or cluster wells.
as for the cluster wells, a template is installed on the seabed with some holes in it – 6, 8, it depends. and the drilling is conducted through the holes. the wells are close to each other, but beneath the mudline they are deviated. but satellite wells are individually drilled and connected with flowlines(flowlines can also be rigid) to manifolds, and manifolds connected with riser base so that the production, injection and export become a possibility. the flexible pipelines applications are:
  • production pipelines, transporting the wellstream to an offshore platform or onshore facility
  • injection pipelines (of chemicals, additives, water and gas) to lift the oil from the payzone for recovery
  • export pipelines, after the wellstream treated and processed on the platform with three phase separator that separates oil, water and gas, then the oil, if not exported to shuttle tanks though floating hoses, is sent back through an export riser back to the seabed, and the subsea export/sales pipelines shall transport oil to an onshore facility to be treated and processed.
flexible pipe can also serve as a riser – not as a drill riser but production riser, or a riser system that stands on a riser base to connect with turrent and swivel on a fpso.
marginal field development:
there are two sorts of development for marginal fields
  • bee mode and
  • 3-1 mode
bee style is designed for satellite wells, it looks like a been that drains one well and then another, a mopu- mobile offshore production unit is needed, they told me the mopu dairy rate for chartering was 150 thousand.
3-1 mode: 1 production platform, 1 subsea cable(control system) and 1 pipeline.
i shall write in anoter essay concerning marginal field development.
Jun Wang