This publication presents the lessons learnt during an operation to remove a hydrate blockage and reinstate oil production from a deep water well offshore Nigeria. It also uses economics to justify facilities projects for hydrate prevention and flow assurance. Field D is a deep water field with sandstone reservoir formations, oil, and gas-cap gas at initial conditions. It has been developed with over 10 subsea production and injection wells tied back to a Floating, Production, Storage, and Offloading (FPSO) vessel.
Field D was shut down for turnaround maintenance during the summer of 2016. After the field was restarted, one of the production wells (D2) failed to flow. An evaluation of the pressure and temperature data suggested that the well had a tubing restriction. This was attributed to hydrate formation and blockage caused by limited methanol injection capacity.
A number of attempts were made to restart the well with no success. A subsea intervention vessel was then hired to execute a clean out intervention operation, which restored oil production from the D2 well. The intervention operation added 26 000 barrels of oil per day production to the asset.
To minimise hydrate blockage and oil production losses, the asset team completed feasibility studies to evaluate the viability of installing a second methanol umbilical and a test/service pipeline. These studied indicated that installing both facilities enhancement projects are economically attractive.
This publication presents the lessons learnt during hydrate formation in a producing oil field, and outlines practical methods that can be used to justify facilities enhancement projects.