Britannica Sources used in this answer

How can hydrocarbon traces in water samples help locate a subsurface petroleum trap?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Multiple large offshore petroleum oil rigs with cranes and equipment stand in the ocean, connected by walkways above the water. — petroleum Liquid petroleum (crude oil)—which is refined into gasoline, diesel, heating fuels, asphalt, plastics, and other useful chemical compounds—is often extracted from the ground using a series of drills and pumps.

Hydrocarbon traces in water samples serve as a form of geochemical prospecting, where researchers analyze samples to identify anomalies—concentrations that deviate from expected background levels.1

In the context of petroleum exploration, instruments can detect minute traces of natural gas in seawater or other water sources. Because petroleum and natural gas migrate through subsurface rock formations, these traces can indicate that hydrocarbons have leaked from a deeper reservoir toward the surface. By systematically measuring these trace elements or chemically influenced properties, geoscientists can identify the specific types of hydrocarbons present in an area and potentially narrow the search radius for a subsurface trap.3214

However, it is important to note that these geochemical surface methods are not applicable to the vast majority of petroleum reservoirs, as most do not exhibit leakage to the surface. Consequently, they are typically used in conjunction with other investigative techniques, such as seismic surveys and geologic mapping, to reduce exploration risk.35