Quantitative evaluation of the geotechnical risk associated with a stratigraphic trap in the Neuquén Basin of Argentina

Abstract

Judicious integration of interpretation methods can help determine the geotechnical risk when evaluating hydrocarbon traps. However, few quantitative evaluations of stratigraphic traps have been documented; those require quantitative integration of seismic and well data, which is performed digitally on a workstation, and require that seismic time, as well as amplitude and phase attributes, tie at existing wells. The process requires rigorous data preparation, based on seismic petrophysics, that in-cludes integration of techniques (seismic, sonic, ultrasonic), integration of scales, and integration of disciplines. In the following case study, I analyze all aspects of the hydrocarbon system associated with a stratigraphic trap of Avile sands in the Neuquen Basin, by using a combination of regional facies analysis, seismic petrophysics, seismic impedance inversion, and AVO analysis. What makes this study unique are the purely stratigraphic nature of the trap, the interpretation of unconventional land AVO applied to Creta-ceous sands, the use of seismic petrophysics to calibrate seismic signatures, and the presence of an adverse factor due to surface volcanics. Neuquen is a back-arc basin of Mesozoic age in the western portion of central Argentina (Figure 1) that developed over a Permo-Triassic volcanic arc which constitutes “economic” basement. Thick marine sediments were deposited during Jurassic and Cretaceous times. The basin evolved into a foreland during the Tertiary, when the region underwent compression from the west (Andean deformation). Many modern stratigraphic and paleontologic interpretations of the basin exist. Legarreta and Ulian (1991) discussed the importance of eustatic sea level changes in controlling regional stratigraphic patterns during the Jurassic to Early Cretaceous period, when the basin underwent tensional stress and experienced relatively low subsidence rates. I will focus on the Andico cycle, which forms a first-order sequence bounded by unconformities of regional tectonic significance (Figure 1). Figure 1. Stratigraphic chart of Neuquen Basin. Stratigraphic potential exists in the …