Okpoho-Okono 12″ and 6″ Subsea Flexible Pipelines Project

Project Details

Title: Okpoho-Okono 12″ and 6″ Subsea Flexible Pipelines Project

Client: NPDC

Location: Block OML 119 – Niger Delta

Date: 2019
 

DESCRIPTION

Okono and Okpoho fields are located offshore Nigeria in OML119 block. All Okono wellheads are subsea and directly connected to an FPSO (Mystra), while Okpoho wells are produced to dry tree positioned on Okpoho Wellhead Platform (WHP). Multi-phase Okpoho fluid is to be transported by a 16” pipeline to the FPSO (Mystra), where the separation takes place. The oil is stabilized for export, while the excess gas is flared. The current production is from four (4) Okono wells; Okono-2, Okono-5, Okono-6 & Okono7 and two (2) strings of Okpoho wells, due to failure of the 16” pipeline. Hence, crude from Okpoho wells is being transferred to the FPSO (Mystra) via an 8” pipeline originally designed for gas. To restore locked-in or differed production from Okpoho wells, NPDC is embarking upon a 12” & 6” pipelines replacement project.

Flow Assurance Analyses

A flow assurance analysis was carried out for a 6-inch subsea flexible gas lift pipeline from FPSO Mystra to Okpoho WHP.

The objectives of the flow assurance analysis were:

  • To carry out steady state simulations.
  • To perform shutdown simulation to understand the available flowline cooldown profile and to assess cooldown time of the system.
  • To perform the pipeline depressurization.
  • To report the required flowrate for a range of pig velocities
  • To evaluate the risk of hydrate formation in all simulated cases.

A flow assurance analysis was also carried out for a 12-inch subsea flexible multiphase flowline. The objectives of the flow assurance analysis were:

  • To carry out steady state simulations.
  • To perform shutdown simulation to understand the available flowline cooldown profile
  • To perform restart simulations, determine thermal and hydraulic performance and assess liquid surge tendency on restart.
  • To study turndown/ramp-up cases to assess thermal performance and slugging tendency.
  • To perform depressurization of pipeline and investigate risk of pipeline temperature excursion below pipeline design temperature and assess risk of hydrate formation during blowdown
  • To perform pigging analysis and determine the required flow during pigging operation and evaluate the slugging behavior.
  1. Flow assurance hydraulic analysis report for 6” gas lift pipeline.
  2. Flow assurance hydraulic analysis report for 12” multiphase pipeline.