3D multicomponent seismic characterization of a clastic reservoir in the Middle Magdalena Valley Basin, Colombia

Abstract

The main goal of this research is to characterize the combined structural-stratigraphic trap of the Tenerife Field in the Middle Magdalena Valley Basin (MMVB), Colombia. For the rst time in Colombia the structural and quantitative interpretation of modern three-dimensional multicomponent (3D-3C) seismic imaging enables a geometric description, a kinematic interpretation of the structural styles, and the facies distribution of the reservoir. A seismic petrophysics work- ow to better achieve the seismic well-tie. Edited and check-shot calibrated P-wave sonic logs were obtained and coecients of the Gardner and Castagna equations were calibrated to match the density and shear-wave velocity depth trends for the basin. Seismic modeling was performed to evaluate the PP and PS seismic response of the reservoir interval (Mugrosa Formation). The structural interpretation methodology involves a 3D fault-correlation and horizon picking for both PP- and PS-PSTM data volumes. Geometric attributes such as coherence and curvature were used to enhance the structural discontinuities. The main unconformity of the Middle Eocene (MEU) was interpreted, and an attributeassisted interpretation of the reservoir was conducted in detail. While P-wave data provided most of the structural interpretation, converted-wave data provide a better understanding of the faults. Traditionally, compressive thrust-propagation folds and tectonic inversion have been considered as the main mechanisms controlling the deformation in the MMVB. However, the new interpretation shown in this work provides a dierent structural concept that involves two major structural styles: 1. Under the MEU the Late Cretaceous and Early Paleocene deformation, dominated by east-verging thrust and partially inverted Mesozoic normal faults, is preserved. Associated folds exhibit a iii north-south strike, and their structural development is controlled by a long-lived structural element that dominates the area (the Infantas Paleo-high). 2. Northeast striking younger normal faults indicate younger local extension, that aects the entire Cenozoic sequence. Normal faults are, in fact, the structural heterogeneities that most aect the geometry of the reservoir compartments in Tenerife Field. This normal faulting oriented oblique to the maximum horizontal stress, together with the associated folding, can arise from a left-lateral shear deformation that creates a local trans-tensional regime. Hence, the structure of Tenerife Field at the top of the Oligocene sandstones, can be described as a two-way closure anticline within a negative ower structure. In addition, Upper Eocene - Early Oligocene syn-tectonic deposits are also documented in this work, dating the last episode of deformation associated with the Infantas Paleohigh uplift. The value of multicomponent data goes beyond the structural interpretation since it provides an independent seismic measure of shear-wave velocities for obtaining VP/VS ratios from interpretation and for performing elastic inversion. From the interpretation of both PP and PS data, the interval VP/VS ratio was computed for the entire Mugrosa Formation. Forward modeling of PS wave response showed that computing VP/VS ratio from picking thin intervals may lead to erroneous values since it is not possible to interpret the same seismic events in both PP and PS data. Nonetheless, analysis of the full-waveform (dipole) sonic log together with Gamma Ray measured in the reservoir interval, showed that there is a close correlation between lithology and VP/VS ratio. VP/VS 1:85 is an eective upper bound to characterize sandstones from ne grained rocks. Further, a model-based elastic inversion of acoustic impedance and VP/VS ratio performed using the PP volume and the sonic logs available, allowed to nd stratigraphic features in the Mugrosa and Esmeraldas formations. The attribute extraction from the inverted P-wave amplitude for both acoustic impedance and VP/VS ratio allowed the characterization of stratigraphic features, in particular some channel geometries that are interpreted as part of a meandering uvial system (point bars and crevasse splays). The lithological and petrophysical correlation of additional attributes from the elastic inversion and AVO is not reliable since there is no independent density, porosity, resistivity, permeability, etc., measurements to guarantee accurate and stable results; nonetheless VP/VS analysis using multicomponent seismic in the MMVB shows signicant promise. Therefore, the acquisition of critical log data with new well drilling as well as an additional multi-attribute analysis based on AVO and a joint PP-PS inversion are strongly recommended.