Basin Scale Study of a Tight Gas Reservoir: Paleoenviromental Evolution of a Shallow Marine System in the Early-Middle Jurassic, Neuquén Basin, Argentina

Abstract

The early-middle Jurassic Cuyo Group of the Neuquén Basin has great potential as tight sand reservoir. The sedimentary succession of up to 2500 m thick shows significant variations from deep-marine, shelf-margin to inner-shelf deltaic and fluvial systems. An integrated understanding of the sedimentary system/facies distribution in a regional framework is essential to identify potential gas targets. This study discusses the impact of a regional conceptual model on the potential development of this tight gas unit at exploration and development scales.

A basin scale interpretation was performed on the integration of an extensive subsurface database including 15000 km² of 3D seismic surveys and available well data such as cores, logs, thin sections, biostratigraphy, zircon dating and production data. Ten depositional prograding seismic sequences were identified. Each cycle exhibits a different shelf-to-slope arrangement as the basin progressively got filled in a northwest/west direction. Paleogeography and facies distribution evolved through time from a shallow, low- gradient ramp setting during early basin configuration, to a well-defined shelf-to-slope profile that persisted until the basin shrinkage.

Four regional schematic cross-sections show the main stratigraphic discontinuities, variations of internal geometries within each cycle, and changes in the supply-accommodation space relationships. These sections together with the isochronous maps of each cycle were used as inputs to build regional facies maps that document the evolution of the sedimentary infill. Outcrops located in the western margin of the Neuquén Basin show a complete source-to-sink profile, providing a unique analog to validate the interpretation of the subsurface conceptual model. Biostratigraphy and zircon dating linked outcrop and subsurface time intervals. Dating of the main stratigraphic surfaces allowed us to extrapolate our interpretation of the architectural elements and their geometrical relationships to areas with limited well data.

The proposed conceptual model shows for the first time the chronostratigraphic relationships between deep-marine, shelf-margin and continental facies of the Cuyo Group at the basin scale. Paleogeographic reconstructions of the main facies belts in time and space will open new exploration and development opportunities for this tight gas system.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018