ALBERDI, MARGARITA, OSWALDO GALLANGO, ARMANDO RUGGIERO, and NIDYA JORDAN, Intevep, S.A., Caracas, Venezuela, and ERIC LAFARGUE, I.F.P., Rueil Malmaison Cedex, France

ABSTRACT: Heterogeneity of the Organic Matter in the Guayuta Group, Eastern Venezuelan Basin

The purpose of this study is to evaluate the organic matter heterogeneities in the Guayuta Group as a principal hydrocarbon source rock in the Eastern Venezuelan Basin. In order to do this, thirteen wells and five work stations on outcrops of the Interior Mountain Belt were analyzed to study the regional and vertical variations in the geochemical characteristics of the organic matter.

It is possible to detect significant differences in quality and quantity of the organic matter, which could be corroborate the regional development of two organic facies from North to South in the Maturin Subbasin. The septentrional organic facies show excellent characteristics as source rock.

The study of vertical distribution of organic matter was carried out in a well of northern part of the Monagas state, which represents the meridional organic facies. It shows an irregular input of continental organic matter, thermally immature. Besides, the organic matter content was low (around 1.5%) without depth tendencies. These sediments are clastic and bioclastic in contrast with carbonates and pelagic shales of the Guayuta Group in the Interior Mountain Belt.

The outcrop samples studied show a high total organic content (2-6%) despite the high maturity determined on kerogen. The systematic study of this geochemical parameter show pseudocicly relationships with a general tendency to increase toward the bottom of the section. V, Ni, and S determinations could indicate that anoxic conditions were developing toward the North where the marine organic matter was sedimenting.

The results of this study are in agreement with paleogeographic model of sedimentation during middle and late Cretaceous, with sources of sediments from South and a progressive depth of the basin toward the North.

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.