Crude Calculation

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Crude Calculations

1.Definitions. 1.1 Free water. The measured volume of water in a tank not in suspension with the liquid in the tank at observed temperature. Expressed in cubic meter or/and barrels. 1.2 Total Observed Volume (TOV). The t9tal measured volume of all petroleum Iiquids,BS&W,and free water at observed temperature. . Expressed in cubic meter orland barrels.

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1.3 Gross Observed Volume (GOV). The total volume of all petroleum liquids and BS&W,but excluding free water,at observed temperature. Expressed in cubic meter or/and barrels. GOV = TOV - Free Water 1.4 Net Observed Volume (NOV). The total volume of all petroleum products but excluding free water and BS&W at observed temperature. Expressed in cubic meter and/or barrels. NOV = TOV - Free Water - BS&W NOV = GOV - BS&W

1.5 Gross Standard Volume (GSV).

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The total volume of all petroleum products and BS&W,but excluding free water corrected by the appropriate volumecorrectionfactor (VCF) for observed temperature and density to a standard temperature. Expressed in cubic meter or barrels. GSV = GOV x VCF GSV = GOV at 15°C/60°F 1.6 Net Standard Volume (NSV). The total volume of all petroleum products excluding BS&W and free water corrected by the appropriate volumecorrectionfactor (VCF) for observed temperature and density to a standard temperature. Expressed in cubic meter and/or barrels. NSV = NOV x VCF NSV = NOV at 15°C/60°F

1.7 Total Calculated Volume (TCV1 The total volume of all petroleum products and BS& W corrected by the

appropriate volumecorrectionfactor for observed temperature and density to a standard temperature and all free water at observed temperature. Expressed in cubic meter and/or barrels. . TeV = GSV + Free Water 1.8 Bottom S~diments and Water (BS&W). Quantity of sediments and water into the total amount of petroleum products. Expressed as a percentage as determined by tests. 1.9 Observed TemQerature. Temperature of cargo measured at various places in the tank. Mean temperature is determined. 1.10 Standard Temperature. Tem'perature of 15°e in the metric system,or 60°F in the American system. All volumes must be converted to this temperature before comparing. .

2. Relationship: density, specific density , API Gravitv. Gravity is a mass-per-unit-volume relationship. With petroleum products the relationship is expressed as specific gravity. The following definition applies: mass of given volume oil at to

kg

mass of equal volume water at to

kg

Specific gravity =

Temperature normally equal to 60°F or 15°e. Specific gravity is sometimes called relative density oil density at GO°F

kg/l

water density at GO°F

kg/l

Relative density GO/GO°F=

Specific gravity is being replaced by density expressed in kg per m3. ~

The following definition applies: mass of given volume of oil

kg

volume of oil at ee

m3

Density of oil at tOe =

In the USA the API gravity is being used. API gravity is an arbitrary scale, calibrated in degrees and related to the specific gravity by the following relation':

API gravity

=

141,5

- 131,5 Specific gravity GO/GO°F

1:

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3. Mass and weiqht relationship. 3.1 Mass.r The mass of a substance is the quantity it contains. It is independant of external conditions.ln oil measurement, it is often referred to as weight-in-vacuo. The metric unit is the kg where 1000kg equals 1 metric tonne. Following relationship applies:

mass of oil =volume of oil at tOCx oil densi~y attOC 3.2 Weight.

The weight of a substance (calledweight-in-air)is the mass which a substance appears to have when weighted in air. The we.ightis calculated using the followingequation: weight of oil =volume of oil x weight correction factor

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3.3 Weiqht Correction Factor (WCF). The weight correction factor must be obtained from the appropriate table in the Petroleum Measurement Tables. In the American system the WCF can be obtained from table II "Long tons per barrel at 60°F against API gravity at 60°F". In the metric system the WCF can be obtained from table 56 "Kilograms per liter at 15°C and liters at 15°C per metric ton against density at 15°C". The WCF can be easily obtained by subtracting 0.0011 kg!1from the density at 15°C. Unfortunately it is much easier to subtract than to consult Table 56.This has led to the problem that it is no longer obvious which density is used:

the density

WCF.

or the

4.Unit Conversion. Units can be easily interchanged by using the approprtate table from petroleum measurements Table Vol XI "Entry with API" or Vol XII "Entry with Relative Density". It is extremely important however to be aware of the following fact: "Like can only be compared with like".

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Comparasion between volumes and capacities must be done at the same temperature.

.

5.Cargo Calculations. 5.1 Metric system. Schematic layout of calculations. I

Observed density

Density @ 15°C in vacuo

\fI(CF in

air

II

I' i

Ullage

t

Temperatures

Waterdip

UllaQe Tables

Tt+T~~Tb'Tm

I

TOV-H20

GOV

(Gross

m3 observed volume)

GOV * VCF

.1

GSV

(Gross

Oil mass

m3 standardvolume)

in vacuo

GSV*density @ 15°C

G

I GSV

r--

Weight in MT

Notes:

. Given:

TOV

.

GSV MT

Free Water. "

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r

H2O MT -ROB/OBO MT TCV MT

GSV

m3

+H20 -ROB/OBO TCV m3

:1

Temperature and Observed Density I ;~ "' " ..! A ~T ..! " aiIr I nI IV, I (anU In I '- T II " e'" de U ) 2) weight in vacuo ( = oil mass) Tabies used: 53A - 56 54A - The relationship between barreis and cubic meters is very precise if same temperatures are used" 1 Bbl = 0.158987 m3 1 m3 = 6.28981 Bbls - Temperatures: see "Calculating Representative Cargotemperatures". - Free water: m3 x 1.025 = MT (if seawater)

oI + \ "' h+ - Can'LJh e "v a l", 'vU'. a ed " 1J YVelg II.

-

Examole :

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-

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- TOV: 100000m3 at 30°C Density: 0.8520 at 15°C VCF from Tab!e 54A: 0.9873 t

WCF from Table 56 : 0.8509 100000 x 0.9873:;; 98730 m3

- GSV:;;

- Weight in vacuo = 98730 x 0.8520"= 84117.96 MT (= oil mass) - Weight in air = 98730 x 0.8509 = 84009.36 MT General remark concefT\jng metric calculations: In the metric system both weight in air and weight in vacuo can be easily calculated. But this can lead to confusion if calculation form is not clearly labelled. Table 53A: Table 54A: Table 56:

Generalized crude oils.Correction of observed density to density 15°C, Generalized crude oil.Correctionof volume to 15°C(againstdensity at 15°C). Kilogram per liter at 15°C and liters at 15°C per MT against density at 15°C,

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5.2 American system. Schematic layout of calculations:

API

WCFin

air

UlJage

Temperatures

Waterdip

Ullaqe Tables Tt + Tm + Tb= Tm 3 TOV *6.28981 m3

Free H2O m3 MT LT *6.28981 Bbls

Bbls

6A

TOV-H20

GOV Bbls

GOV*VCF GSV Bbls @ 60°F

GSV*WCF (LT/Bbl

GSV Weight in LT

in air

= T.11 MT/Bbl = T.13)

GSV LT H2O LT -ROB/OBQ LT TCV LT

GSV Bbl +H20 Bbl -ROB/OBO Bbl TCV Bbl

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, Notes:

- Temperature: see" Calculating Representative Cargotemperatures". - Oil weight is calculated ( weight in air) : oil mass can only be calculated by converting API to density and to preform the metric system calculation. - For calculations in LT table II must be consulted for calculations in metric ton table 13. - If in LT the free water must also be converted to L1. ( LT = MT x 1.016047) - The calculations for LT are the most accurate.

Exam~ - TOV = 100000 m3 . - TOV = 628981 Bbls at 86°F

API 34,49

- VCF from Table 6A : 0.9877 - WCF from Table 11 : 0.13309 - WCF from Table 13: 0.13520

- GSV = 628981 x 0..9877 = 621244.54 Bbls - Weight in air= 621244.54 x 0.13309 = 82681.4 LT = 621244.54 x 0.13520 = 83992.3 MT

-

(If formula for LT / MT conversion is being used, a tonnage of 84008.2 MT is found a difference of about 16 MT) Used . as auide: .

- Essomarine

conversion tables and charts.

- BP publicationof Lionel Downer. - Shell publication Januari 1980 Cargo Calculations.