Potential for Basin-Centered Gas Systems in the Neuquén Basin, Early-Middle Jurassic Tight-gas Reservoirs (Cuyo Group)

Raggio, Fernanda¹; Luna, E.; Lopez Peze, G.; Jorgensen, L.; Coppo, R.; Spath, F.; Atencio, M.; and Di Benedetto, M.
¹[email protected]

The Neuquén basin in west central Argentina contains the major gas resources of the region. During the last years, significant gas accumulations derived from low-permeability Middle-Jurassic reservoirs of the Lajas Formation has been analyzed as potential unconventional tight gas targets. The Cuyo Group represents part of the initial Mesozoic rifting episodes of the basin. It is mainly composed of two main Units: Los Molles Formation and Lajas Formation, with an aerial distribution and thickness that imitates the geometry of the previous Upper Triassic rift depocenters. From base to top, these sequences represent a coarsening-upward succession of marine deposits, where the argillaceous Los Molles Formation, consisting of basinal shales, turbidites and sandstones, represents one of the main gas-prone source rocks of the basin. These Units are in close proximity to the Lajas Formation, characterized by a thick succession of very low permeability sandstones sequences, describing a shallowing upward depositional environment.

Regarding the complexity in reservoir properties observed in wells results, the Cuyo Group system enclosed much of the characteristics for being classified as a Basin-Centered Gas accumulation, like very low permeability sandstones, proximity to mature source rock, gas saturated reservoirs with little or no free water, the lack of water-gas contact downdip, and a heterogeneous geopressure distribution. The original main productions were associated to the structural traps on the shoulders of the depocenters; so a more evolved phase of exploration planning is required to focus on the deeper parts of the basin where these unconventional systems are more common to occur.

Geophysical techniques were used to highlight the main potential areas to explore these tight-gas systems. Considering that one of the main parameters to identify sweet spots includes higher pressure zones, offset wells sonic velocity logs and seismic interval velocities were used to indicate gas-charged regions with an abnormally pressured profile. The integration and 3D visualization between seismic inversion, velocities, pore pressure and volume attributes show that these zones were mainly related to anomalously low seismic velocities and show a lateral and vertical discontinuous distribution.

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013