A GLOBAL DATASET OF ONSHORE GAS AND OIL SEEPS: A NEW TOOL FOR HYDROCARBON EXPLORATION

Abstract

Petroleum seeps have historically been important drivers of global petroleum exploration. Still today they can serve as direct indicators of gas and/or oil subsurface accumulations. In particular the assessment of the origin of seeping gas is a key task for understanding, without drilling, the subsurface hydrocarbon potential, genesis and quality, e.g. the presence of shallow microbial gas, deeper thermogenic accumulations, the presence of oil and non-hydrocarbon undesirable gases (CO2, N2, H2S). Low quality, biodegraded petroleum can also be recognised, before drilling, through specific geochemical features of the seeping gas. Seeps are then indicators of tectonic discontinuities (faults) and fractured rocks; they can also represent geo-hazards and sources of greenhouse gas (methane) and photochemical pollutants (ethane and propane). A new global dataset of onshore gas and oil seeps (GLOGOS) is here presented. GLOGOS includes more than 1150 seeps from 84 countries (version August 2009) and it is continuously updated and expanded. The data-set includes geographical and gas-geochemical data (molecular and isotopic composition of the main gases). Many seeps are recently discovered or never reported in other data-bases. Seeps are catalogued by country and classified in three types: gas seeps, oil seeps and mud volcanoes. All seeps have a bibliographic or www reference. GLOGOS is a unique tool for hydrocarbon exploration, assessment of Total Petroleum Systems and geo-structural studies.