The density of a sample of crude oil is 700 kg/m3. Calculate the API gravity. Determine the classification of the crude oil
The Correct Answer and Explanation is:
To calculate the API gravity of a crude oil sample, we use the following formula: API gravity=141.5SG at 60°F−131.5\text{API gravity} = \frac{141.5}{\text{SG at 60°F}} – 131.5API gravity=SG at 60°F141.5−131.5
Where:
- SG (specific gravity) is the ratio of the density of the crude oil to the density of water at 60°F (which is approximately 1000 kg/m³).
Step 1: Calculate Specific Gravity
Given:
- Density of crude oil = 700 kg/m³
- Density of water = 1000 kg/m³
SG=7001000=0.7\text{SG} = \frac{700}{1000} = 0.7SG=1000700=0.7
Step 2: Calculate API Gravity
API gravity=141.50.7−131.5=202.14−131.5=70.64\text{API gravity} = \frac{141.5}{0.7} – 131.5 = 202.14 – 131.5 = 70.64API gravity=0.7141.5−131.5=202.14−131.5=70.64
API gravity ≈ 70.64°
Step 3: Classify the Crude Oil
Crude oil is classified based on its API gravity as follows:
- Light crude oil: API gravity > 31.1°
- Medium crude oil: API gravity between 22.3° and 31.1°
- Heavy crude oil: API gravity < 22.3°
- Extra heavy crude: API gravity < 10°
Since the calculated API gravity is approximately 70.64°, this sample is classified as light crude oil.
Explanation
API gravity is a standard measure used by the petroleum industry to describe how heavy or light a petroleum liquid is compared to water. The scale is set so that most petroleum liquids have values between 10 and 70. If a crude oil has an API gravity greater than 10, it is lighter than water and will float on it. If the API is less than 10, it is heavier and will sink.
In this case, the oil has a density of 700 kg/m³, which is much less than that of water. This leads to a high API gravity value, indicating the crude oil is very light. Light crude oils are typically more valuable because they yield a higher percentage of gasoline and diesel during refining.
