Understanding API Gravity Equations in Excel

API gravity is a measure of how heavy or light a petroleum liquid is compared to water. It is used to compare the densities of different types of oil. For example, if one oil is less dense than another, it has a higher API gravity.

API gravity is calculated by dividing 141.5 by the specific gravity of the oil and subtracting 131.5. Specific gravity is the ratio of the density of the oil to the density of water at a standard temperature of 15°C or 60°F. Density is the mass of a substance per unit volume.

API gravity is expressed in degrees, but it is not an angle. It is a dimensionless quantity, meaning it has no units. API gravity values of most petroleum liquids range from 10 to 70 degrees. The higher the API gravity, the lighter the oil. Lighter oils tend to have more valuable products, such as gasoline and jet fuel, than heavier oils.

API gravity is important for the oil industry because it affects the production, transportation, refining, and pricing of oil. For example, lighter oils are easier to extract from the ground and transport through pipelines than heavier oils. Lighter oils also require less processing to produce high-quality products than heavier oils. Therefore, lighter oils usually have a higher market value than heavier oils.

Basic Theory:

API gravity is calculated using the following formula:

$API = \frac{141.5}{\text{Specific Gravity}} - 131.5$

Where:

$API$ is the American Petroleum Institute gravity.
$\text{Specific Gravity}$ is the ratio of the density of a substance to the density of a reference substance (usually water).

Procedures in Microsoft Excel:

Gather Data: Collect the necessary data, including the specific gravity of the liquid.
Set Up Excel Table: Create a table in Excel with columns for specific gravity and API gravity.
Apply Formula: In the API gravity column, apply the formula:
$API = \frac{141.5}{\text{Specific Gravity}} - 131.5$
Scenario: Consider a scenario where the specific gravity of a crude oil sample is 0.85.

Excel Implementation:

Specific Gravity	API Gravity Formula Result
0.85	=141.5/A2-131.5

Result in Excel:

$API = \frac{141.5}{0.85} - 131.5 \approx 34.47$

MATLAB Comparison:

% MATLAB code to calculate API gravity
specific_gravity = 0.85;
API = 141.5 / specific_gravity - 131.5;
disp(['API Gravity (MATLAB): ', num2str(API)]);

MATLAB Result:

$API \approx 34.47$

Conclusion:

Both Excel and MATLAB produce the same API gravity result, emphasizing the accuracy and reliability of the API gravity equation. This tool is vital in the petroleum industry, aiding engineers in characterizing and analyzing crude oil properties.