Organic matter maturity in Northern Italy: Some determining agents

Abstract

In previous AGIP studies concerning the origin of oil in Northern Italy thematurity evolution of the source rocks beneath a thrust plate and the anomalous depth-trends of maturity parameters were exained. This paper focuses on the possible effects of different thermal histories and of high pressure on the catagenesis of kerogen. The effects of overthrusting on the degree of maturity of source rocks is investigating in two areas of the Northern Apennines: near the Cortemaggiore oil and gas field and Ponte del'Olio No. 1 well respectively. The model by Angevine and Turcotte is used for reconstructionof the temperature evolution, and that by Tissot and Espitalié to model the hydrocarbon generation. In addition it was examined how different thermal histories affect the oil to gas ratio computed according to Tissot/Espitalié. The results for sediments beneath thrust plates which are subjected to rapid increases in temperature, are compared to those typical of regularly subsiding basin. In the Po basin intervals of abnormally pressured sediments were drilled. In the Lombardy area the organic matter appears immature in Early Jurassic and Late Triassic sediments at depth even down to 6000 m as recognized by different maturity parameters. Possible causes for the low maturity levels of the organic matter are examined, with particular emphasis on the effects of high pressures.