Sedimentología y estratigrafía secuencial de alta resolución de reservorios no convencionales de origen deltaico del Miembro Pilmatué (Formación Agrio, Cuenca Neuquina)

Abstract

This contribution presents a facies, depositional and sequence-stratigraphic analysis of the upper half of the Pilmatué Member (Agrio Fm., Valanginian-Hauterivian) in the Mangrullo Field, located in central Neuquén Province, Argentina, in order to characterize siliciclastic unconventional (tight) reservoirs. For this study, 300 m of cores from four wells were described, subsequently integrated with their petrographic and petrophysic data, as well as with well-log suites from 17 wells. Twelve facies associations (FAs) were identified and interpreted in the unit that represents mainly delta plain, proximal delta-front and distal delta-front-prodelta settings of fluvio-dominated deltas, but also wave-influenced deposits of proximal delta-front to distal delta front-offshore were recognized. Vertical and lateral transitions of facies associations allowed for the identification of five depositional sequences (S-08, S-09, S-10, S-11, S-12) representing progradation of the entire deltaic system, which are bounded by regionally extensive transgressive surfaces. Internally, these sequences are composed of high-frequency sequences in which progradation distance and orientation, as well as facies belts can be quantitatively defined. Transgressive surfaces bounding both type of sequences are most commonly associated with thin, carbonate-rich intervals that are good correlation markers. Since 2015 the gas-bearing tight reservoirs of the Pilmatué Member are on production. The results of this study allowed for a detailed characterization of different sandstone-type reservoirs within a refined depositional and sequence-stratigraphic framework that helps defining better development strategies for the field.