A new model of the petroleum system in the Northern Apennines, Italy

A geochemical study on fluids from selected spontaneous seepages and drilled wells was carried out together with geologic investigation and deep cross-sections reconstruction to examine the petroleum system in the western Northern Apennines foothills. The hydrocarbons occurring in the Miocene foredeep units that form the reservoirs are commonly interpreted as generated in a source/reservoir system. However, the low Total Organic Carbon, its elevated dilution in the sediment pile and the limited amount of successions that entered in the oil window indicate a low potential for the hydrocarbons generation. The structures deformation in the Northern Apennines foothills is mainly late Miocene to Pliocene in age and involves successions that are progressively younger towards southeast. The earlier structure forms the Salsomaggiore anticline in the western sector. The comparison of the fluids from the wells and the mud volcanoes shows high geochemical and thermal history similarities. Saline waters originate from the connate pore water entrapped in the Miocene reservoir rocks during their deposition. The gaseous hydrocarbons are a mixture of secondary biogenic methane and primary and secondary thermogenic gases. The associated oils show both early and late maturities. These evidences account for different generation and migration steps, depending on burial conditions and deformation time. The various reservoirs appear confined by the thrust detachment at different depths and by the occurrence of reactivated lateral ramps. These results suggest the occurrence of a common source rock deeper than the Tertiary reservoir units, which progressively entered in the oil window. This source rock could have wide lateral extension, at least comparable with the width of the studied area, and represent a prime exploration target to evaluate the undiscovered oil and gas resources. © 2013 Elsevier Ltd.