--> Abstract: Fundamental Relationships Concerning Generation and Migration of Hydrocarbons in a Carbonate/Evaporite Basin, by T. Hillebrand, D. Leythaeuser, and J. Connan; #90987 (1993).

Datapages, Inc.Print this page

HILLEBRAND, THOMAS, Forschungszentrum Julich, Julich, Germany; DETLEV LEYTHAEUSER, University of Cologne, Koln, Germany; and JAQUES CONNAN, Elf Aquitaine (Production), Pau, France

ABSTRACT: Fundamental Relationships Concerning Generation and Migration of Hydrocarbons in a Carbonate/Evaporite Basin

In Guatemala, commercial oil was produced from a Cretaceous-age section of rhythmically bedded carbonate and evaporite rocks deposited in a Sabkha-like environment. A detailed petrographical/sedimentological and organic geochemical study was performed to examine (a) the sedimentary facies (b) the diagenetic overprint of the sediments (c) the organic matter content of each facies and (d) petroleum generation and possible migration pathways. Our overall goal was to develop on the basis of this case study a model for abetter understanding of the generation and migration processes of hydrocarbons in carbonate/evaporite series. From base to top the carbonate/evaporite sequence consists of (1) laminated carbonates (2) a"subtidal facies", (3) algal mats, (4) nodular anhydrites with occasiona ly (5) laminated anhydrites and (6) microdolomites. The commonly observed facies sequence contains the facies types 2, 3, 4 and 6. The organic matter of each of these sedimentologically defined facies has a distinct bulk composition and its characteristic molecular signature. Facies 1, 2, 3 and 5 reveal good to excellent source rock potential, facies 6 shows excellent reservoir characteristics and facies 4 provides the seal. Therefore, this carbonate/evaporite section can be divided into repetitive cm-dm scale units that comprises in close proximity source rock, reservoir rock and seal. Three possible migration pathways allow the vertical and lateral movement ofhydrocarbons: (1) fractures (2) stylolites and pressure solution seams and (3) erosional contacts at the top of each sequence. D e to the individual molecular signature of each facies, recognition of relevant facies-depending compounds allows to determine from which facies hydrocarbons were expelled and along which pathway they migrated. Three possible modes of hydrocarbon expulsion and migration are discussed: (1) Hydrocarbon transport in aqueous solution resulting from the release of water due to the gypsum/anhydrite conversion, (2) "explosive migration" along stylolites due to compaction and overpressuring of pore fluids, and (3) movement of hydrocarbons due to tectonic pressure. The expulsion events can be recognized and integrated into the diagenetic evolution of the section. On the basis of a quantitative treatment of the generation and expulsion in conjunction with modeling of the burial history and the dia enesis of the organic matter for a selected well the overall efficiency of the expulsion and migration processes isestimated. The results of this study may be helpful to understand the petroleum habitat of carbonate/evaporite series worldwide, e.g. the Jurassic of the Aquitaine basin or the Zechstein.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.