Gas geochemistry of the Macuspana Basin (Mexico): thermogenic accumulations in sediments impregnated by bacterial gas

A gas survey was performed in the Macuspana basin (South of Mexico). Two di stinct gas families were identified: Family 1 is represented by homogeneous and purely thermogenic gas, associated with condensates expelled at the en d of the oil window, and Family 2 is composed of a mixture of bacterial dry gas and thermogenic gas derived from source rocks at high maturity. Chemic al and isotopic parameters as well as noble gas data provided information a bout the sources, the proportions of mixing, and directions of hydrocarbon migration of these two families. Considering the risk associated with furth er oil and gas exploration in the basin, deeper zones present higher explor atory interest for Family 1 gas fields and associated oil accumulations. In contrast, the bacterial gas fields should be considered a less promising t arget for future oil and gas exploration. (C) 2000 Published by Elsevier Sc ience Ltd.