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

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

Calgary

Congreso; AAPG/SEPM Annual Convention and Exhibition.; 2016

AAPG/SEPM

The Valanginian Mulichinco Formation is a hydrocarbon productive unit of the Neuquén Basin in Argentina, in which potentialrecoverable resources associated with tight sandstones are estimated as 5 tcf. Although the unit has been extensively studied inoutcrops, its extension, internal anatomy, and sand distribution in the adjacent subsurface region is still poorly understood. Theaim of this contribution is to present a basin-scale characterization of the unit, integrating a vast 3D seismic coverage plushundreds of wells, together with a refined facies and sequence-stratigraphic framework, in order to identify new leads andprospects in underexplored areas. The Mulichinco Formation comprises continental, transitional, and marine deposits thataccumulated on a previous marine ramp setting after a major sea-level fall. It, therefore, represents an exceptional example of alowstand wedge whose sequence boundary (SB) is named the Intra-Valanginian unconformity. The basinal-scale studyencompasses an area of 56,000 km2 (about half the extent of the basin), from which 36,000 km2 are covered with 3D seismicdata of variable quality acquired during the last three decades. Gaps within 3D data are filled with 2D seismic. Moreover, 1600wells with sonic, density and gamma-ray logs and 56 wells with core data are available. Standard facies and sequencestratigraphicanalysis were carried out of the cores. The results of this study are presented in up to fourteen dip-oriented regionalseismic sections passing through calibration wells from the basin margin to the outcrops in the fold and thrust belt. In allsections the lowstand wedge morphology is clearly identified, using consistent markers for its top and base. It thickens graduallyfrom a few meters in the basin borders up to 300 m in the distal portions, having an average length of 150 km. From seismicinterpretation, 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 fromsouth to north, and, therefore, seismic stratigraphy is the key to understand the lateral and temporal relationships betweendifferent stratigraphic intervals. This integrated study allowed prediction and identification of new tight sandstone plays withinthis lowstand wedge and provided a new basin-scale exploration model for this prolific hydrocarbon unit.