The U.S. geological survey´s project BIRDDOG (basic investigation of remotely detectable deposits of oil and gas)

An experimental program to develop an integrated remote sensing-geochemical petroleum exploration technique has been established by the U.S. Geological Survey. Briefly, the concept is based on previous and ongoing research within the U.S. Geological Survey which demonstrates that imperfect rock seals capping petroleum and natural gas deposits may permit large volumes of low-molecular-weight hydrocarbons to escape to the surface, with one or more of the following results: (1) the slowly seeping hydrocarbons chemically and biochemically oxidize; (2) liberated CO2 is incorporated into carbonates, forming pore-filling cements invested with unique isotopic signatures; (3) gas, expansive under depressurization, evaporates near-surface pore water, likewise precipitating isotopically distinctive pore cements; (4) the highly reducing hydrocarbons and associated compounds cause discoloration of surface strata by reduction and dissolution of iron. All these late diagenetic alteration phenomena reflect the subsurface distribution of petroleum. The BIRDDOG program in part attempts to explore for these kinds of surface anomalies using the following integrated approach.