Overview
Wells are rarely controlled on bottomhole pressure directly. In practice the
constraint is the tubinghead pressure (THP) at surface, and the relationship
between THP and the flowing BHP depends on the multiphase flow up the tubing — a
relationship tabulated as a vertical flow performance (VFP) table. BirSim reads
VFPPROD and VFPINJ tables and controls wells on THP by solving for the BHP that
is consistent with both the reservoir inflow and the tubing table.
It also supports history-mode producers (WCONHIST), which reproduce observed
surface rates — the workhorse of a history match.
VFP tables & THP control
| Table | Dimensions | Lookup |
|---|---|---|
VFPPROD | 5-D | BHP = f(FLOW, THP, WFR, GFR, ALQ) |
VFPINJ | 2-D | BHP = f(FLOW, THP) — single injected phase |
VFPPROD supports the full Eclipse axis set: RATE ∈ {LIQ, OIL, GAS, WG},
WFR ∈ {WCT, WOR, WGR}, and GFR ∈ {GOR, GLR, OGR}.
How THP control converges. A THP-controlled well has two constraints that must
agree — the reservoir inflow (BHP → rate) and the VFP table (rate, THP → BHP).
BirSim solves this as a BHP↔rate fixed point via bisection, with a
VFP-datum ρg correction so the table’s reference depth and the well’s BHP
datum are reconciled. The result is the operating point where both curves meet.
History matching: WCONHIST
WCONHIST runs a producer on observed rates rather than a control target:
ORAT/WRAT/GRAT/LRAT→ rate-control at the observed surface rate.RESV→ control the reservoir voidageq_o·B_o + q_w·B_w + (q_g − R_s·q_o)·B_g, computed each step from the observed surface rates and the current formation volume factors.
Validation
Custom decks were run against OPM Flow for both the THP-control and history-mode paths.
| Path | Quantity | BirSim vs OPM |
|---|---|---|
| VFPPROD, THP-controlled producer | WBHP, field pressure (FPR) | within ~1% |
| VFPINJ, THP-controlled injector | IBHP, field pressure | within ~1% |
WCONHIST ORAT | Oil surface rate | exact (matches observed) |
WCONHIST RESV | Water rate (voidage) | exact |
The THP-controlled cases match OPM’s bottomhole pressures and field pressure to
~1%, confirming the BHP↔rate fixed point lands on the same operating point OPM
finds. The WCONHIST rates are exact by construction — BirSim honors the observed
ORAT and reproduces the RESV voidage rate that OPM computes from the same
surface data.
Why it matters
THP control and history-mode producers are what make a deck resemble a real field study rather than a textbook problem: surface-constrained wells and a history match against observed production. Matching OPM Flow on both — table lookup, THP fixed point, and voidage bookkeeping — closes the gap between a benchmark simulator and one that runs an operator’s actual deck.
Reference
VFP tables and THP control follow the Eclipse VFPPROD/VFPINJ/WCONHIST
semantics; BirSim is validated against OPM Flow on the same decks. Deck paths and
command lines are available on request.