Abstract: 3-D Delineation of the Structural and Stratigraphic Controls on Hydrocarbon Accumulation in the Señal Picada Block, Neuquén Basin, Argentina

Lara, María Ester and Ricardo Veiga - YPF

The Señal Picada block, which is located on the prolific northeastern margin of the Neuquén back-arc basin, produces 1600 m³ oil/day from the Jurassic/Cretaceous Vaca Muerta-Loma Montosa (!) petroleum system. 3-D seismic and well data indicate that hydrocarbon accumulation is controlled by structural, stratigraphic and diagenetic factors.

The structural configuration of the Señal Picada block is defined by two WNW- ESE-trending basement lineaments, that separate a platform area to the north, from the Señal Picada field to the south. These two lineaments are expressed as discontinuous, high-angle normal faults of opposite polarity, that bound a WNW-ESE- trending graben. A central basement high, located at the gap along the facing fault traces, links the oil field with the northern platform, and provides a pathway for the northward migration of hydrocarbons. A series of minor faults, parallel and conjugate to the main structural trend, locally enhance and compartmentalize this basic architecture.

The western facing half-grabens overlap only partially, yielding a slightly asymmetrical cross-section, with the deepest depocenter located along the southern border fault. In contrast, the eastern facing half-grabens overlap almost completely, resulting in a symmetrical cross-section, with a central basement high or "interference accommodation zone." This high relief area, which is productive, developed early, in order to accommodate the space problem created by the simultaneous growth of the facing border faults.

Extensional faulting was more intense and pervasive on the eastern side of the block, where reactivation of the southern border fault during the Valanginian, the Barremian-Aptian and the Cenomanian resulted in an effective trapping mechanism. In contrast, subdued border fault activity to the west, allowed northward migration of Vaca Muerta-sourced hydrocarbons.

The Señal Picada block produces from Valanginian, Upper Loma Montosa subtidal clastic and carbonate reservoirs. Hauterivian/Barremian, marginal marine shales of the Agrio Fm. provide a regional seal. Reservoir quality decreases towards the northeast, as facies vary laterally, from subtidal bars and tidal channels to evaporitic tidal flats. In addition, phreatic and vadose zone diagenetic processes affecting the northern platform area, reduced the primary porosity of the Loma Montosa reservoirs. Thus, in the northern and western parts of the block, hydrocarbon accumulation results from the interplay of structural, stratigraphic and diagenetic factors, whereas, in the eastern part of the block, is structurally controlled.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil