Estratigrafía de alta resolución y su implicancia para el modelado 3D de reservorios en la Formación Lajas (Grupo Cuyo) - Anticlinal de Picún Leufú - Cuenca Neuquina

Abstract

In the South part of the Neuquén basin (Picún Leufú anticline), the Jurassic deposits of the Lajas Formation have outcropping sections with very good state of preservation and high lateral continuities. These characteristics favor the use of these rocks as analogues for hydrocarbon reservoirs. Several previous researchers have studied this geological Formation. The section, constituted by fluvio-deltaic deposits, presents, according to others researchers, three sedimentary sequences of low frequency (3rd order). They also recognize a major regional unconformity (Intrabajocian) that is recognize over all the extensión of the Huincul’s Dorsal, between the first and second sequences, which divides the analyzed unit into two sections. The present work was carried out in the lower portion of the Lajas Formation below the mentioned regional unconformity. Two (predominantly progradational) sequences of low (>8 km extension) and ten of medium (3-8 km) frequencies - corresponding to the previous 3rd and 4th orders - were described. The definition and mapping of high frequency sequences (<300 m) is one of the contributions of this article. From the data collected in the 19 outcrop sections, the sedimentological and paleogeographic characterizations of the analyzed section were established. The stratigraphic framework defined and applicable to the study area is based on the individualization of medium frequency sequences and was very important for the preparation of 3D geological models. The stratigraphic analysis of the medium frequency sequences allowed identifying that the progradation of the deltaic system varied from 250˚ to 350˚. The observation of the high frequency sequences enhance the understanding of vertical distribution and lateral extension of permeability barriers (fade out?) and sandy bodies (potential reservoirs). The results obtained from the simulations of facies, with different provided data (bibliographic vs. field-collected), showed qualitatively and quantitatively the degree of success that high-resolution stratigraphy can bring to 3D reservoir modeling and to its application in the optimization of hydrocarbon exploitation.