A Thermal Model for Sedimentary Basins: the case of Lusitanian Basin, Portugal

Abstract

The thermal history of a sedimentary basin represents an important control on generation of gas and oil in source rocks, being heat flow one of the major input parameters in basin modeling. This work presents an approach to estimate the present heat flow through the design of a thermal model applied to a small sector of the Lusitanian Basin and supported in data obtained in two deep boreholes drilled onshore and designated by – Montalegre #1 and Sobral #1. From these wells a lithostratigraphic column was established. The well Sobral #1 have a total depth of about 3000 m, showing a generic lithology of siltstones, claystones, limestones, marls and dolomites, cutting formations from Upper Jurassic to Triassic. In the bottom this well intersected also Paleozoic schists from the hercynian basement. The Montalegre #1 well have a total depth of about 2000 m and shows a litostratigraphic column similar to Sobral #1 cutting also formations from Upper Jurassic to Palaeozoic. From the knowledge of the input parameters of the several identified lithologies, namely thermal conductivity and radiogenic heat production, obtained from local measurements or from reference databases, a bi-dimensional thermal model was developed for heat flow and geothermal gradient estimations. The contribution of the basement and the heat flow from the mantle was also taken in account in the calculations.

The calculated data was then compared with experimental data acquired in other deep borehole drilled in the Lusitanian sedimentary basin in order to evaluate the present thermal setting in the studied sector of the same basin.

AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015