Abstract: The Thermal Maturation Degree of Organic Matter from Source Rocks Revealed by Well Log Including Examples from Murzuk Basin, Libya

V. Negoita, A. Gheorghe

The customary technique used to know the organic matter quantity per rock volume as well as the organic matter maturation stage is based on geochemical analyses accomplished on a preselected number of samples and cuttings drawn from boreholes during the drilling period.

But the same objectives can be approached without any extracost using the continuous measurements of well logs recorded in each well from the ground surface to the total depth.

During the diagenetic stage, the identification of potential source rocks out of which no hydrocarbon have been generated may be carried out using a well logging suite including Gamma Ray Spectrometry, the Compensated Neutron/Litho Density combination and a Dual Induction/Sonic Log.

During the catagenetic stage the onset of oil generation brings some important change in the organic matter structure as well as in the fluid distribution throughout the pore space of source rocks. The replacement of electric conductive water by electric non-conductive hydrocarbons, together with water and oil being expelled from source rocks represents process of different intensities dependent of time/temperature geohistory and kerogen type.

The different generation and expulsion scenarios of hydrocarbons taking place during the catagenetic and metagenetic stages of source rocks are very well revealed by Induction and Laterolog investigations.

Several crossplots relating vitrinite reflectance, total organic carbon and log-derived physical parameters are illustrated and discussed.

The field applications are coming from Murzuk basin, where Rompetrol of Libya is operating.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France