Choke Bean Sizing Calculator (5 Correlations) - Rapid Global

Choke Bean Sizing — Calculation Sheet

Choke Bean Sizing

Required surface choke size from target liquid rate, GLR, and wellhead pressure

Method	Gilbert-type critical-flow correlation
Reference	Gilbert (1954) et al.

Inputs

Correlation These are independently fitted empirical correlations, not variations of a single standard — they can disagree by 30% or more on the same well. Gilbert is the most widely cited baseline; a study of 155 well tests found it gave the best overall match to measured rates. Prefer whichever correlation your field data show is the best local fit, if you have one. Liquid rate, q (STB/d) Producing gas-liquid ratio, GLR (scf/STB) Correlations were fitted over roughly 300–50,000 scf/STB. Outside that range, treat the result with extra caution. Target upstream (wellhead) pressure, P1 (psia) Downstream / flowline pressure, P2 (psia) Used only to check the critical-flow assumption the correlation depends on (P2/P1 roughly ≤ 0.55–0.7). Not used in the sizing formula itself — these correlations are independent of downstream pressure by design.

Units

Result

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Nearby standard choke sizesResulting P1

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P1 = C × GLR^m × q ÷ Sⁿ

S = (C × GLR^m × q ÷ P1)^1/n

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Correlation	—
Liquid rate, q	—
GLR	—
Target P1	—
Downstream P2	—
Result — exact required choke	—
Nearest standard choke & actual P1	—
Critical flow check	—

Reference & methodology

Method: Gilbert-type empirical correlations for two-phase critical (sonic) flow through a surface wellhead choke, of the general form P1 = C·GLR^m·q/Sⁿ, where P1 is upstream (wellhead) pressure in psia, q is gross liquid rate in STB/d, GLR is producing gas-liquid ratio in scf/STB, and S is choke size in 64ths of an inch. The calculator solves this for S given a target P1.

Coefficients: C, m, and n are independently fitted constants from field production data, not derivations of a single physical model — Gilbert (1954, Ten Section Field, California), Baxendell (1957) and Ros (1960) (Lake Maracaibo), Achong (1961) (Lake Maracaibo), and Pilehvari (1980). Values used here (C, m, n): Gilbert (10, 0.546, 1.89), Ros (17.4, 0.5, 2.0), Baxendell (9.56, 0.546, 1.93), Achong (3.82, 0.65, 1.88), Pilehvari (46.67, 0.313, 2.11) — per Guo, B., Petroleum Production Engineering, A Computer-Assisted Approach, Table 5.3, cross-checked against an independent secondary source.

Critical flow requirement: these correlations assume sonic (critical) flow, where the downstream pressure has no effect on the upstream pressure or rate. This requires the downstream-to-upstream pressure ratio to stay below a critical value — commonly cited in the 0.5–0.7 range for oil/gas mixtures. If your actual P2/P1 exceeds that, flow is subcritical and none of these correlations apply; a subcritical two-phase model (e.g., Ashford, Sachdeva) is needed instead.

Scope and limitations: These are empirical curve fits to specific fields (California, Lake Maracaibo) and can disagree with each other, and with your well, by 30% or more — there is no single authoritative standard for multiphase choke flow. Validity is generally cited for GLR of roughly 300–50,000 scf/STB and choke sizes of 8/64–64/64 in. Actual choke beans come in discrete standard sizes (commonly in 2/64 in. steps), so the calculator also shows the nearest standard sizes and their actual resulting pressure. Always confirm against field-calibrated choke performance data for your specific well and separator system where available.

For preliminary screening only. Not a substitute for a certified engineering assessment or field-calibrated choke performance data.

Read why the correlations disagree, and a worked example →

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