Mandatory Project Assignment MEK4450

First 3 modules H2013

Due date: 18. October 2013, 4:00 pm by email to

Flow Assurance – A System Perspective

Magnus Nordsveen and Birgitte Nordheim Tveter (Statoil) [

Ketil Firing Hanssen (DnV) [

Tine Bauck Irmann-Jacobsen and Brian Gyles (FMCTechnologies) [

Exercise

Figure 1: Schematics of system (both friction and gravity in well and flow line –change figure)

Design basis

Two identical vertical wells

One flow line

Distance from reservoir to subsea wellhead 4000m

Water depth 1000m

Assume multiphase flow and GOR>40000

Distance from wellhead to onshore 50km

Inner Diameter of well 5”

Inner Diameter of flow line 12"

U value well 9 W/m²K

U value flow line 20W/m²K

Topside receiving pressure (Psep) 50bara

Production profile

Pres / Psep / Tres / Tsea / Qg pr well / Qg total
Year / bar / bar / oC / oC / Kg/s / Kg/s
1 / 360 / 50 / 150 / 7 / 45 / 90
5 / 300 / 50 / 150 / 7 / 40 / 80
10 / 240 / 50 / 150 / 7 / 33 / 66
15 / 180 / 50 / 150 / 7 / 26 / 52
20 / 120 / 50 / 150 / 7 / 20 / 40

Density vs pressure for the multiphase fluid

Pressure [Bar] / Density [kg/m³]
223 / 163
178 / 130
139 / 102
100 / 73
56 / 41

Figure 2: Phase envelope

Figure 3: Hydrate envelope

Figure 4: Wax appearance curve

Answer the following:

  1. Calculate approximate pressure drop in wells and flow line with help of the exercises in compendium
    (tips: Use reservoir conditions in well, Use well head pressure and seabed temperature for density in flow line, Assume molecular weight (M) of gas equal to 17 g/mol)
  2. Discuss the results vs. the proposed production profile
  3. At which year will it be necessary to install pressure support?
  4. Choose a compressor which can give up to 50 bar pressure boosting with a mass flow rate of 60 kg/s.
  5. If subsea compression is chosen, what prerequisites (auxiliary systems) are necessary for our field development and what are the main challenges?

e.  Evaluate field development impacts of installing topside vs. subsea compression. Base the discussion in both a project execution and field operation aspect and the assumption that topside compression will be at field location.

f.  Discuss field development impacts of installing a subsea compressor initially (from day 1) vs. as a phased development as indicated in 1b.

  1. Set up an overview of the flow assurance issues you are going to evaluate.
  2. Calculate approximate temperatures for the system with help from the exercises
    (tip: Use average temperature of Tres and Tsea for T surrounding in the well)
  3. Will the system be above hydrate temperatures?
  4. Will the system be above WAT?
  5. Describe a hydrate management philosophy for the system
  6. Describe a Wax management for the system
  7. Do a sensitivity of temperatures in the system if the Uvalue is 1.
  8. Which implications will that have on the hydrate and wax management?
  9. Mark operational points into the phase envelope
  10. Do you think flow induced vibrations will be a problem in the X-mas tree?
  11. Discuss important parameters required to select and design a subsea development, and describe how these parameters affect the field layout and the equipment design.
  12. What are the main functions of a subsea flow tree (Christmas tree), and how are these functions accommodated for in the design?

You can make your own assumptions if necessary as long as you are clear about it.

Use the compendium.