Controls on composition and diagenesis of the Upper Cretaceous wave- and riverdominated deltaic deposits of the Austral-Magallanes Basin: impacts on reservoir properties

MOYANO PAZ, DAMIÁN.; COMERIO, MARCOS; RICHIANO, SEBASTIÁN; GÓMEZ DACAL, ALEJANDRO R.; MUÑOZ OLIVERO, TOBIAS; POIRE, DANIEL G.; VARELA, AUGUSTO N.; BUCHER, JOAQUIN

MARINE AND PETROLEUM GEOLOGY

ELSEVIER SCI LTD

Año: 2022 vol. 138

0264-8172

The composition of sedimentary successions is controlled by tectonic, climate, depositional conditions and diagenesis. The present study evaluates the influence of these controlling forces on the resultant composition of sandstone-dominated deposits and the possible impact in potential hydrocarbon reservoirs.The La Anita Formation is a deltaic-coastal siliciclastic succession which accumulated during the Lare Cretaceouos foreland phase of the Austral-Magallanes Basin. Samples from this unit were analyzed by conventional petrography, X-ray diffraction and scanning electron microscopy in order to obtain a full spectrum of its detrital, authigenic and diagenetic composition. The analyzed sandstones were classified as litharenites which come from the fold-thrust belt region and from the magmatic arc located toward the westward basin boundary and show no vertical variations. The clay mineral composition based on X-ray diffraction is characterized by variable proportions of illite, smectite, kaolinite and mixed-layer illite-smectite with the sporadic presence of chlorite. The origin of clayminerals and cross-cutting relations of diagenetic products were determined by SEM observations. Stratigraphic variations associated with differences in the clay mineralogy indicate a change of the climatic conditions during the depositions of the unit. Diagenetic processes affecting the porosity are considered as controlled mainly by the lithologicalnature of the deposits and depositional facies. Sandstone porosity values range from moderate to good (~8-13%). Some of the analyzed samples in fluvial-dominated deltaic deposit (upper unit) show significant hematite and calcite cement mainly as pore filling, which commonly acts by reducing pore spaces. Contrary, the wave-dominated deltaic deposits (lower unit), has a lower potential to develop hematite and calcite cementation and maintain relatively high intergranular porosity and good potential reservoir properties.