Artificial maturation of a high volatile bituminous coal from Asturias (NW Spain) in a confined pyrolysis system: Part I. Petrographic, geochemical and molecular studies

Abstract

The objective of this work is to estimate the hydrocarbon production in the Central Asturian Coal Basin (NW Spain) by using: • the maturation simulation of the coal in laboratory by confined pyrolysis, and • the study of the petrographic (% R r ), geochemical ( T max) and molecular changes during the artificial maturation process. Confined pyrolysis was carried out inside gold cells under a pressure of 700 bar at several temperatures (330, 360 and 400 °C) and durations (24, 120 and 720 h). Artificial maturation from lower to higher temperature showed an evolution of macerals by comparing the raw coal and the solid residues after the pyrolysis. The vitrinite content increases and the inertinite and liptinite contents decrease. The porosity also increases with an increase of the pore size and eventually, coalesces. The vitrinite reflectance (% R r ) increases from 0.78 for the raw sample to 2.98 for the solid residues at 400 °C. Organic geochemical parameters exhibit a similar trend with an evolution from oil window to the gas window. HI and T max of original coals of this basin indicate a predominant gas- to oil-proneness. A decrease of total extract yields and changes in aliphatics, aromatics and polars contents is also showed by increasing maturation. Aromatization reactions transform aliphatic and polar molecules at high temperature.