In petroleum production, “wet natural gas” refers to gas recovered along with crude oil at the wellhead. Compared to dry pipeline-grade methane, identify the key property that is typically higher in wet natural gas due to the presence of heavier hydrocarbons (ethane, propane, butanes).

Introduction / Context:
Natural gas encountered at the wellhead often contains a spectrum of hydrocarbons. When produced together with crude oil, the gas is called wet natural gas because it includes significant amounts of heavier components beyond methane. This composition difference drives important property changes, especially energy content.

Given Data / Assumptions:

• Wet gas contains methane plus heavier hydrocarbons (C2–C4+).
• Dry gas is largely methane after processing.
• Comparison is on typical custody-transfer or volumetric basis.

Concept / Approach:
On a per unit volume basis, heavier hydrocarbons (ethane, propane, butanes) have higher heating values than methane. Therefore, a mixture that contains these “NGL” components will usually exhibit a higher gross calorific value than a lean, methane-dominant gas stream. The presence of C3/C4 also raises the dew point and requires appropriate handling.

Step-by-Step Solution:

Verification / Alternative check:
Gas quality calculations (e.g., Wobbe Index and HHV per standard cubic meter) increase with richer heavy-end content, confirming the trend for wet gas versus dry gas.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing mass-basis versus volume-basis comparisons; custody transfer and utility billing typically use volumetric energy content.

Final Answer:
Calorific value