Seismic Architecture and Anatomy of a Basin-Scale Lowstand Wedge (Mulichinco Fm, Argentina): Implications for Tight Reservoirs Exploration.

ARISMENDI, S.M.; PASCARIELLO, M.E.; RINCÓN, M.F.; SCHWARZ, E.; OLIVO, M.

Calgary

Congreso; AAPG Annual Convention and Exhibition; 2016

AAPG/SEPM

The Valanginian Mulichinco Formation is a hydrocarbon productive unit of the Neuquén Basin in Argentina, in which potential recoverable resources associated to tight sandstones are estimated in 5 tcf. Although the unit has been extensively studied in outcrops, its extension, internal anatomy, and sand distribution in the adjacent subsurface region is still poorly understood. The aim of this contribution is to present a basinscale characterization of the unit, integrating a vast 3D seismic coverage plus hundreds of wells, together with a refined facies and sequencestratigraphic framework, in order to identify new leads and prospects in underexplored areas. The Mulichinco Formation comprises continental, transitional, and marine deposits accumulated onto a previous marine ramp setting after a major sealevel fall. It therefore represents an exceptional example of a lowstand wedge whose sequence boundary (SB) is named the IntraValanginian unconformity. The basinalscale study encompasses an area of 56000 km2 (about half the extension of the basin), from which 36000 km2 are covered with 3D seismic data of variable quality acquired during the last three decades. Gaps within 3D data are filled with 2D seismic. Moreover, 1600 wells with sonic, density and gammaray logs and 56 wells with core data are available. Standard facies and sequencestratigraphic analysis were carried out in the cores. The results of this study are presented in up to fourteen diporiented regional seismic sections passing through calibration wells from the basin margin to the outcrops in the fold and thrust belt. In all sections the lowstand wedge morphology is clearly identified using consistent markers for its top and base. It thickens gradually from a few meters in the basin borders up to 300 m in the distal portions, having an average length of 150 km. From seismic interpretation, key reflectors are identified. The basal SB and the master transgressive surface at the top are represented by welldefined reflectors. Internally, both reflectors and strata representing different depositional systems show some variability from south to north and, therefore, seismic stratigraphy is the key to understand the lateral and temporal relationships between different stratigraphic intervals. This integrated study allowed to predict and identify new tight sandstone plays within this lowstand wedge and provided a new basinscale exploration model for this prolific hydrocarbon unit.