Tieback
Product · Tree

Tree pressure. From topside.

Subsea tree pressure estimated from topside choke pressure and temperature, choke opening and gas-lift rate, with an interval.

The demoThe numbers
1

Tree pressure with an interval

2

Identified per well from a normal window

3

Scored on a gauge it never sees

Hands on

Three steps.

2

The state you cannot see

Now showingSevere slugging The riser fills, then blows through.
Simulated well
TREE99 ± 22 barTOPSIDEdeepwater tieback
Riser-top pressure, bar54.1
Arrival temperature, °C35.8
Slug probability
What explains it
Slugging
47%
Instability
21%
Hydrate
0%
Choke restriction
16%
Gauge bias
8%
Tieback says

Tree pressure 99 ± 22 bar

Most likely: Slugging (47 %). Parameters not identified from the normal window: the band is wide on purpose.

How it turned out
3

One clear proposal

Proposal

Largest stable choke 100 % (band 100–100 %), now 74 %. Proposal: room to open up to 100 %.

Never writes to the chokeA person decides

What it needs

  • Topside choke pressure and temperature, choke opening, gas-lift rate
  • Well geometry, or a normal-operation window
  • Separator trip and choke logs

What it is not

  • Never writes to the choke
  • Not a transient multiphase simulator
  • Bands not calibrated on an unseen geometry; on real wells a soft sensor did better

Proven, in simulation

  • On an unseen well geometry, tree-pressure error 4.3 bar against 39–47 bar for soft sensors trained on the gauge of the other geometries (simulation, t001)
  • Never reads the tree gauge; a guard raises if an estimator tries
  • Catches 25 % of slugging wells at 0.28 false alarms a day; oscillation threshold 4 %, event classifier 20 % (simulation)

Not proven

  • In simulation, on the unseen geometry the 90 % band covers 47 % of the truth
  • On real wells: 315 instances on 9 wells of a public well-event dataset, 37.8 bar median error against 21.9 bar for a recurrent soft sensor trained on the other wells' gauge; band covers 39 %
  • On seen geometries the soft sensors win: 2.6–2.8 bar against 8.9 bar
  • Slug alarms come late: a median 44 minutes after onset
  • Largest stable choke: 98 % median error on the main families
  • No well identifiable from a quiet window: every band comes from priors
  • No real slugging instance usable: none starts with a labelled-normal hour; no well geometry in the public data
Works with

Slug

The slug, before the separator.

Open →

Choke

The largest stable opening.

Open →

Bank

Two observers, one answer.

Open →

Lift

What more gas-lift would do.

Open →
Tree — Tree pressure. From topside. · Tieback