--> 3-D Palinspastic Reconstruction of Prograding Units Oblique to the Tectonic Transport: An Analysis of the Early-Middle Jurassic Cuyo Gr. in the Aguada Toledo Anticline, Neuquén Basin (Argentina)

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3-D Palinspastic Reconstruction of Prograding Units Oblique to the Tectonic Transport: An Analysis of the Early-Middle Jurassic Cuyo Gr. in the Aguada Toledo Anticline, Neuquén Basin (Argentina)

Abstract

Prograding units have been proved to be an effective configuration for unconventional plays in many basins in the world. The Cuyo Gr. consists of 1000 m thick deposits composed mainly by siliciclastics, representing the first sedimentary record in Neuquén Basin, southwest Argentina. The lowest 500 m are progradational, so that the distal portions of this sigmoids correspond to deep water TOC rich shales. Time equivalent shallow water sandstones located at breaks represent the main unconventional tight gas target at this position in the basin. In proximal positions, this system consists of a fluvial environment composed of sand-shale alternation. The deposition of the Cuyo Gr. evolved from east to west during the Early to Middle Jurassic interval. The Aguada Toledo anticline is a smooth and asymmetric W-E striking structure, approximately 22 km long and 6 km wide. This anticline is related to a fault that dips steeply to the N, so that the anticline resulted from inversion of two Triassic half grabens during Jurassic and Cretaceous times. The analysis of the Cuyo Gr. in the Aguada Toledo structure involved geological interpretation of 3D seismic volumes over 200 Km2. This structure has been drilled by more than 10 wells located in the hanging wall that go across the entire sedimentary column, allowing an accurate and stable time to depth conversion. Historically, the kinematic evolution of this structure has been unravelled through restoration of 2D cross sections. However, the high angle between the NW-SE tectonic transport vector during Jurassic times and the E-W progradation direction led to unsatisfactory results. The 3D sequential restoration of the oldest prograding units presented here allowed us to place the wells in their exact location at the time of deposition of each interpreted seismic event, and therefore, acquire an accurate picture of the prograding system. The results of this analysis enabled: 1) a better understanding of the correlation between the shelf break sandstones and 2) an improvement in the paleodepositional interpretation and facies distribution. This methodology could be a first step in order to improve the reconstruction of scenarios with highly oblique tectonic transport and prograding directions, allowing a better exploration as well as field development plans in both, conventional and unconventional plays.