Governed assumptions register

Every constant, correlation coefficient and design limit the calculation engine uses. Owned, versioned and identical for every engineer.

This is the register that replaces the constants buried in individual spreadsheet cells. A value here has an owner, a basis, an allowed range and a revision number. Changing one updates every design that depends on it, and every issued document records which revision it used, so a calculation from two years ago can still be reproduced exactly. Entries drawn directly from a published standard are locked.

Choke model13 entries

Assumption	Value	Unit	Allowed range	Rev	Owner	Basis
Gilbert coefficient A CHOKE_GILBERT_A	10	-	—	1	Testing Engineering	Gilbert (1954), API 14B practice rationale Baseline multiphase critical-flow correlation. Default for Middle East light/medium crude.	locked — published standard
Gilbert exponent B (GLR) CHOKE_GILBERT_B	0.546	-	—	1	Testing Engineering	Gilbert (1954) rationale Gas-liquid ratio exponent.	locked — published standard
Gilbert exponent C (bean) CHOKE_GILBERT_C	1.89	-	—	1	Testing Engineering	Gilbert (1954) rationale Choke diameter exponent, diameter in 1/64 in.	locked — published standard
Ros coefficient A CHOKE_ROS_A	17.4	-	—	1	Testing Engineering	Ros (1960) rationale Alternative correlation, tends to predict larger beans.	locked — published standard
Ros exponent B (GLR) CHOKE_ROS_B	0.5	-	—	1	Testing Engineering	Ros (1960)	locked — published standard
Ros exponent C (bean) CHOKE_ROS_C	2	-	—	1	Testing Engineering	Ros (1960)	locked — published standard
Baxendell coefficient A CHOKE_BAXENDELL_A	9.56	-	—	1	Testing Engineering	Baxendell (1957)	locked — published standard
Baxendell exponent B (GLR) CHOKE_BAXENDELL_B	0.546	-	—	1	Testing Engineering	Baxendell (1957)	locked — published standard
Baxendell exponent C (bean) CHOKE_BAXENDELL_C	1.93	-	—	1	Testing Engineering	Baxendell (1957)	locked — published standard
Achong coefficient A CHOKE_ACHONG_A	3.82	-	—	1	Testing Engineering	Achong (1961) rationale Derived from Lake Maracaibo wells; included for sensitivity comparison only.	locked — published standard
Achong exponent B (GLR) CHOKE_ACHONG_B	0.65	-	—	1	Testing Engineering	Achong (1961)	locked — published standard
Achong exponent C (bean) CHOKE_ACHONG_C	1.88	-	—	1	Testing Engineering	Achong (1961)	locked — published standard
Critical (sonic) pressure ratio CRITICAL_RATIO	0.55	Pdn/Pup	0.400 – 0.600	2	Testing Engineering	Isentropic choked flow, k~1.27 rationale Below this downstream/upstream ratio the bean is in critical flow and rate is independent of downstream pressure.

Assumption

Value

Unit

Allowed range

Rev

Owner

Basis

Gilbert coefficient A

CHOKE_GILBERT_A

—

Testing Engineering

Gilbert (1954), API 14B practice

rationale

Baseline multiphase critical-flow correlation. Default for Middle East light/medium crude.

locked — published standard

Gilbert exponent B (GLR)

CHOKE_GILBERT_B

0.546

—

Testing Engineering

Gilbert (1954)

rationale

Gas-liquid ratio exponent.

locked — published standard

Gilbert exponent C (bean)

CHOKE_GILBERT_C

1.89

—

Testing Engineering

Gilbert (1954)

rationale

Choke diameter exponent, diameter in 1/64 in.

locked — published standard

Ros coefficient A

CHOKE_ROS_A

17.4

—

Testing Engineering

Ros (1960)

rationale

Alternative correlation, tends to predict larger beans.

locked — published standard

Ros exponent B (GLR)

CHOKE_ROS_B

0.5

—

Testing Engineering

Ros (1960)

locked — published standard

Ros exponent C (bean)

CHOKE_ROS_C

—

Testing Engineering

Ros (1960)

locked — published standard

Baxendell coefficient A

CHOKE_BAXENDELL_A

9.56

—

Testing Engineering

Baxendell (1957)

locked — published standard

Baxendell exponent B (GLR)

CHOKE_BAXENDELL_B

0.546

—

Testing Engineering

Baxendell (1957)

locked — published standard

Baxendell exponent C (bean)

CHOKE_BAXENDELL_C

1.93

—

Testing Engineering

Baxendell (1957)

locked — published standard

Achong coefficient A

CHOKE_ACHONG_A

3.82

—

Testing Engineering

Achong (1961)

rationale

Derived from Lake Maracaibo wells; included for sensitivity comparison only.

locked — published standard

Achong exponent B (GLR)

CHOKE_ACHONG_B

0.65

—

Testing Engineering

Achong (1961)

locked — published standard

Achong exponent C (bean)

CHOKE_ACHONG_C

1.88

—

Testing Engineering

Achong (1961)

locked — published standard

Critical (sonic) pressure ratio

CRITICAL_RATIO

0.55

Pdn/Pup

0.400 – 0.600

Testing Engineering

Isentropic choked flow, k~1.27

rationale

Below this downstream/upstream ratio the bean is in critical flow and rate is independent of downstream pressure.

Deliverability2 entries

Assumption	Value	Unit	Allowed range	Rev	Owner	Basis
Vogel IPR coefficient on (Pwf/Pr) VOGEL_A	0.2	-	—	1	Reservoir	Vogel (1968) rationale q/qmax = 1 - 0.2(Pwf/Pr) - 0.8(Pwf/Pr)^2	locked — published standard
Vogel IPR coefficient on (Pwf/Pr)^2 VOGEL_B	0.8	-	—	1	Reservoir	Vogel (1968)	locked — published standard

Assumption

Value

Unit

Allowed range

Rev

Owner

Basis

Vogel IPR coefficient on (Pwf/Pr)

VOGEL_A

0.2

—

Reservoir

Vogel (1968)

rationale

q/qmax = 1 - 0.2(Pwf/Pr) - 0.8(Pwf/Pr)^2

locked — published standard

Vogel IPR coefficient on (Pwf/Pr)^2

VOGEL_B

0.8

—

Reservoir

Vogel (1968)

locked — published standard

Erosion5 entries

Assumption	Value	Unit	Allowed range	Rev	Owner	Basis
API 14E C-factor, continuous service, solids-free EROS_C_CONTINUOUS	100	-	60.000 – 200.000	1	Flow Assurance	API RP 14E 2.5 rationale Conservative baseline for carbon steel continuous duty.
API 14E C-factor, intermittent service EROS_C_INTERMITTENT	125	-	60.000 – 250.000	1	Flow Assurance	API RP 14E 2.5 rationale Applicable to short-duration clean-up and flowback.
C-factor derating when sand is present EROS_C_SAND_DERATE	0.6	fraction	0.300 – 1.000	3	Flow Assurance	NESR internal ES-WT-011 rationale Applied when produced sand exceeds the trigger concentration.
Sand concentration triggering derate EROS_SAND_TRIGGER	1	pptb	0.100 – 10.000	2	Flow Assurance	NESR internal ES-WT-011 rationale Above 1 lb per 1000 bbl the solids-free C-factor is no longer valid.
Erosional velocity ratio caution threshold EVR_CAUTION	0.8	-	0.500 – 1.000	1	Flow Assurance	NESR internal ES-WT-011 rationale Design target is to stay at or below 80% of the erosional velocity.

Assumption

Value

Unit

Allowed range

Rev

Owner

Basis

API 14E C-factor, continuous service, solids-free

EROS_C_CONTINUOUS

100

60.000 – 200.000

Flow Assurance

API RP 14E 2.5

rationale

Conservative baseline for carbon steel continuous duty.

API 14E C-factor, intermittent service

EROS_C_INTERMITTENT

125

60.000 – 250.000

Flow Assurance

API RP 14E 2.5

rationale

Applicable to short-duration clean-up and flowback.

C-factor derating when sand is present

EROS_C_SAND_DERATE

0.6

fraction

0.300 – 1.000

Flow Assurance

NESR internal ES-WT-011

rationale

Applied when produced sand exceeds the trigger concentration.

Sand concentration triggering derate

EROS_SAND_TRIGGER

pptb

0.100 – 10.000

Flow Assurance

NESR internal ES-WT-011

rationale

Above 1 lb per 1000 bbl the solids-free C-factor is no longer valid.

Erosional velocity ratio caution threshold

EVR_CAUTION

0.8

0.500 – 1.000

Flow Assurance

NESR internal ES-WT-011

rationale

Design target is to stay at or below 80% of the erosional velocity.

Heating5 entries

Assumption	Value	Unit	Allowed range	Rev	Owner	Basis
Indirect heater thermal efficiency HEATER_EFFICIENCY	0.8	fraction	0.600 – 0.920	1	Equipment Engineering	Vendor data, glycol bath heaters rationale Applied to convert process duty to fired duty.
Specific heat of gas CP_GAS	0.55	Btu/lb-degF	0.400 – 0.800	1	Process	GPSA Data Book Fig. 24-7 rationale Average over the heating range for 0.65-0.85 SG gas.
Specific heat of crude oil CP_OIL	0.48	Btu/lb-degF	0.400 – 0.600	1	Process	GPSA Data Book Sec. 23
Specific heat of produced water CP_WATER	1	Btu/lb-degF	0.900 – 1.050	1	Process	Standard
Heater duty design factor HEATER_DESIGN_FACTOR	1.2	-	1.000 – 1.500	2	Equipment Engineering	NESR internal ES-WT-006 rationale Contingency applied to calculated duty before heater selection.

Assumption

Value

Unit

Allowed range

Rev

Owner

Basis

Indirect heater thermal efficiency

HEATER_EFFICIENCY

0.8

fraction

0.600 – 0.920

Equipment Engineering

Vendor data, glycol bath heaters

rationale

Applied to convert process duty to fired duty.

Specific heat of gas

CP_GAS

0.55

Btu/lb-degF

0.400 – 0.800

Process

GPSA Data Book Fig. 24-7

rationale

Average over the heating range for 0.65-0.85 SG gas.

Specific heat of crude oil

CP_OIL

0.48

Btu/lb-degF

0.400 – 0.600

Process

GPSA Data Book Sec. 23

Specific heat of produced water

CP_WATER

Btu/lb-degF

0.900 – 1.050

Process

Standard

Heater duty design factor

HEATER_DESIGN_FACTOR

1.2

1.000 – 1.500

Equipment Engineering

NESR internal ES-WT-006

rationale

Contingency applied to calculated duty before heater selection.

Hydrates2 entries

Assumption	Value	Unit	Allowed range	Rev	Owner	Basis
Joule-Thomson cooling coefficient, gas phase JT_COEFF	0.045	degF/psi	0.020 – 0.080	4	Flow Assurance	Field-calibrated, MENA gas 0.6-0.75 SG rationale Used to estimate temperature downstream of the choke. Replace with EOS flash when PVT is available.
Minimum margin above hydrate formation temperature HYDRATE_MARGIN_F	10	degF	5.000 – 25.000	2	Flow Assurance	NESR internal ES-WT-004 rationale Operating temperature must stay this far above the hydrate curve.

Assumption

Value

Unit

Allowed range

Rev

Owner

Basis

Joule-Thomson cooling coefficient, gas phase

JT_COEFF

0.045

degF/psi

0.020 – 0.080

Flow Assurance

Field-calibrated, MENA gas 0.6-0.75 SG

rationale

Used to estimate temperature downstream of the choke. Replace with EOS flash when PVT is available.

Minimum margin above hydrate formation temperature

HYDRATE_MARGIN_F

degF

5.000 – 25.000

Flow Assurance

NESR internal ES-WT-004

rationale

Operating temperature must stay this far above the hydrate curve.

Pressure integrity3 entries

Assumption	Value	Unit	Allowed range	Rev	Owner	Basis
Minimum margin of equipment MAWP over MASP DESIGN_MARGIN_PCT	10	%	5.000 – 25.000	3	Well Integrity	NESR internal ES-WT-002 rationale MAWP of the weakest spread component must exceed MASP by this margin.
Site pressure test factor on MOP TEST_PRESSURE_FACTOR	1.1	-	1.000 – 1.500	1	Well Integrity	ASME B31.3 / client procedure
Fallback static gas gradient GAS_GRAD_PSI_FT	0.08	psi/ft	0.030 – 0.150	1	Well Integrity	Used only if composition is unavailable rationale The engine prefers the compressible column calculation.

Assumption

Value

Unit

Allowed range

Rev

Owner

Basis

Minimum margin of equipment MAWP over MASP

DESIGN_MARGIN_PCT

5.000 – 25.000

Well Integrity

NESR internal ES-WT-002

rationale

MAWP of the weakest spread component must exceed MASP by this margin.

Site pressure test factor on MOP

TEST_PRESSURE_FACTOR

1.1

1.000 – 1.500

Well Integrity

ASME B31.3 / client procedure

Fallback static gas gradient

GAS_GRAD_PSI_FT

0.08

psi/ft

0.030 – 0.150

Well Integrity

Used only if composition is unavailable

rationale

The engine prefers the compressible column calculation.

Radiation10 entries

Assumption	Value	Unit	Allowed range	Rev	Owner	Basis
Fraction of heat radiated, oil burner RAD_F_OIL	0.2	-	0.100 – 0.400	1	HSE Engineering	API STD 521 Annex C rationale Typical for atomised crude burners with air assist.
Fraction of heat radiated, gas flare RAD_F_GAS	0.15	-	0.100 – 0.350	1	HSE Engineering	API STD 521 Annex C rationale Function of gas composition and tip design.
Atmospheric transmissivity TAU_ATM	1	-	0.700 – 1.000	1	HSE Engineering	API STD 521 6.4.2 rationale Conservative value of 1.0 used unless humidity correction is agreed with client.
Lower heating value of crude LHV_OIL	18,300	Btu/lb	16,000.000 – 20,000.000	1	Process	GPSA Data Book Sec. 23
Lower heating value of associated gas LHV_GAS_SCF	1,050	Btu/scf	900.000 – 1,400.000	2	Process	GPSA Data Book Sec. 23 rationale Rich associated gas. Reduce for lean or N2-bearing streams.
Radiation limit, continuously manned area K_PERSONNEL	500	Btu/hr-ft2	440.000 – 600.000	1	HSE Engineering	API STD 521 Table 8 (1.58 kW/m2) rationale Continuous exposure with appropriate clothing.	locked — published standard
Radiation limit, escape route, few seconds exposure K_ESCAPE	1,500	Btu/hr-ft2	1,200.000 – 1,800.000	1	HSE Engineering	API STD 521 Table 8 (4.73 kW/m2)	locked — published standard
Radiation limit, equipment and unmanned areas K_EQUIPMENT	2,000	Btu/hr-ft2	1,500.000 – 3,000.000	1	HSE Engineering	API STD 521 Table 8 (6.31 kW/m2)	locked — published standard
Flame length correlation coefficient FLAME_LEN_A	0.006	-	—	1	HSE Engineering	API STD 521 Annex C rationale L = A * Q^B, Q in Btu/hr, L in ft.	locked — published standard
Flame length correlation exponent FLAME_LEN_B	0.478	-	—	1	HSE Engineering	API STD 521 Annex C	locked — published standard

Assumption

Value

Unit

Allowed range

Rev

Owner

Basis

Fraction of heat radiated, oil burner

RAD_F_OIL

0.2

0.100 – 0.400

HSE Engineering

API STD 521 Annex C

rationale

Typical for atomised crude burners with air assist.

Fraction of heat radiated, gas flare

RAD_F_GAS

0.15

0.100 – 0.350

HSE Engineering

API STD 521 Annex C

rationale

Function of gas composition and tip design.

Atmospheric transmissivity

TAU_ATM

0.700 – 1.000

HSE Engineering

API STD 521 6.4.2

rationale

Conservative value of 1.0 used unless humidity correction is agreed with client.

Lower heating value of crude

LHV_OIL

18,300

Btu/lb

16,000.000 – 20,000.000

Process

GPSA Data Book Sec. 23

Lower heating value of associated gas

LHV_GAS_SCF

1,050

Btu/scf

900.000 – 1,400.000

Process

GPSA Data Book Sec. 23

rationale

Rich associated gas. Reduce for lean or N2-bearing streams.

Radiation limit, continuously manned area

K_PERSONNEL

500

Btu/hr-ft2

440.000 – 600.000

HSE Engineering

API STD 521 Table 8 (1.58 kW/m2)

rationale

Continuous exposure with appropriate clothing.

locked — published standard

Radiation limit, escape route, few seconds exposure

K_ESCAPE

1,500

Btu/hr-ft2

1,200.000 – 1,800.000

HSE Engineering

API STD 521 Table 8 (4.73 kW/m2)

locked — published standard

Radiation limit, equipment and unmanned areas

K_EQUIPMENT

2,000

Btu/hr-ft2

1,500.000 – 3,000.000

HSE Engineering

API STD 521 Table 8 (6.31 kW/m2)

locked — published standard

Flame length correlation coefficient

FLAME_LEN_A

0.006

—

HSE Engineering

API STD 521 Annex C

rationale

L = A * Q^B, Q in Btu/hr, L in ft.

locked — published standard

Flame length correlation exponent

FLAME_LEN_B

0.478

—

HSE Engineering

API STD 521 Annex C

locked — published standard

Separation5 entries

Assumption	Value	Unit	Allowed range	Rev	Owner	Basis
Souders-Brown K, horizontal vessel with mist extractor SB_K_HORIZONTAL	0.4	ft/s	0.200 – 0.600	1	Process	API 12J / Arnold & Stewart rationale Governs maximum gas velocity before liquid carryover.
Design liquid fill fraction of separator volume SEP_LIQUID_FILL	0.5	fraction	0.300 – 0.700	1	Process	API 12J rationale Half-full is the standard horizontal separator design case.
Oil retention time RETENTION_OIL_MIN	3	minutes	1.000 – 10.000	2	Process	API 12J Table 1, 30-40 API crude rationale Increase to 5-10 min for heavy or foaming crude.
Water retention time RETENTION_WATER_MIN	3	minutes	1.000 – 10.000	1	Process	API 12J Table 1
Separator utilisation caution threshold SEP_UTIL_CAUTION	0.85	fraction	0.600 – 1.000	1	Process	NESR internal ES-WT-008 rationale Flag when predicted load exceeds 85% of rated capacity.

Assumption

Value

Unit

Allowed range

Rev

Owner

Basis

Souders-Brown K, horizontal vessel with mist extractor

SB_K_HORIZONTAL

0.4

ft/s

0.200 – 0.600

Process

API 12J / Arnold & Stewart

rationale

Governs maximum gas velocity before liquid carryover.

Design liquid fill fraction of separator volume

SEP_LIQUID_FILL

0.5

fraction

0.300 – 0.700

Process

API 12J

rationale

Half-full is the standard horizontal separator design case.

Oil retention time

RETENTION_OIL_MIN

minutes

1.000 – 10.000

Process

API 12J Table 1, 30-40 API crude

rationale

Increase to 5-10 min for heavy or foaming crude.

Water retention time

RETENTION_WATER_MIN

minutes

1.000 – 10.000

Process

API 12J Table 1

Separator utilisation caution threshold

SEP_UTIL_CAUTION

0.85

fraction

0.600 – 1.000

Process

NESR internal ES-WT-008

rationale

Flag when predicted load exceeds 85% of rated capacity.

Sour service3 entries

Assumption	Value	Unit	Allowed range	Rev	Owner	Basis
H2S partial pressure threshold for sour service H2S_PARTIAL_LIMIT	0.05	psia	0.050 – 0.050	1	Materials	NACE MR0175 / ISO 15156-1 rationale At or above this partial pressure, sour-rated materials are mandatory.	locked — published standard
H2S personal alarm set point H2S_ALARM_PPM	10	ppm	5.000 – 20.000	1	HSE	OSHA / client HSE case	locked — published standard
H2S immediately dangerous to life or health H2S_IDLH_PPM	100	ppm	100.000 – 100.000	1	HSE	NIOSH	locked — published standard

Assumption

Value

Unit

Allowed range

Rev

Owner

Basis

H2S partial pressure threshold for sour service

H2S_PARTIAL_LIMIT

0.05

psia

0.050 – 0.050

Materials

NACE MR0175 / ISO 15156-1

rationale

At or above this partial pressure, sour-rated materials are mandatory.

locked — published standard

H2S personal alarm set point

H2S_ALARM_PPM

ppm

5.000 – 20.000

HSE

OSHA / client HSE case

locked — published standard

H2S immediately dangerous to life or health

H2S_IDLH_PPM

100

ppm

100.000 – 100.000

HSE

NIOSH

locked — published standard

Recent changesaudit trail

When	Who	Change
No changes recorded yet.

When

Who

Change

No changes recorded yet.