Structural Sweet Spots Prediction for Vaca Muerta Formation Base on Differential Subsidence Process

Ernesto Cristallini
Laboratorio de Modelado Geológico (LaMoGe), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires

The sweet spots investigated in unconventional reservoirs are in some cases associated with areas in which the layers are subjected to tension and are more easily fractured. The Laboratorio de Modelado Geológico (UBA-CONICET) is working on techniques to predict these areas within the Vaca Muerta Formation of the Neuquén Basin. The idea is based on a common scenario in the rift basins and in particular in the Neuquén Basin, in which the compaction of the filling of half-grabens is different and greater than that those of the surrounding basement rocks. This fact makes that the sag units (e.g.. Vaca Muerta) subside more above the ancient half-grabens than outside them and that sag beds stretch above the limits of the half-grabens. Sag units including Vaca Muerta Formation have greater potential to be naturally and artificially fractured inside these stretching positions than in other areas. However, in general the seismic surveys are not targeted to display the deep structures and it is not easy to visualize the limits of the half-grabens that gave rise to the basin. Because of this, we are testing a technique where residual thickness maps of sag units are used to locate this stretching regions. This technique consists in using the interpretation of several sag units in 3D seismic, calculating thickness maps between them and removing the regional component to isolate only the local signature of the differential subsidence process. These maps illuminate residual thickness and thickness differences related to the effect of differential subsidence. We are working on an algorithms similar to curvature calculations (Gaussian and maximum) for isolating the tension and stretching areas within the residual thickness maps and therefore, to predict structural sweet spots for the selected region. As the process of differential subsidence occurs until today, local stretching areas calculated are currently in force.

AAPG Search and Discovery Article #90165©AAPG 2012 GEOSCIENCE TECHNOLOGY WORKSHOP, 2-4 December 2012, Buenos Aires, Argentina