Velocity model influence in the position and geometry of a prospect area located in VSM Basin, by image ray tracing

Abstract

Complex structures like subthrust show high risk during the definition of structural traps in time (PSTM) and depth (PSDM) low quality seismic images, so we can use the structural interpretation in time or depth domain to evaluate the velocity model influence in the position and geometry of a prospect area. Ecopetrol acquired a 3D PSTM seismic program in 2011, which has been reprocessed twice in order to improve PSTM image in fault shadow zones and clarify the structural setting to define the closure in a possible trap in the study area to reduce the exploratory risk.In addition, we did an exercise of 2D geophysical modeling using time-depth and depth-time conversion in one inline from the 3D survey. We use time to depth conversion based in image ray tracing, and a structural model interpreted in time (PSTM) and where we test three different velocity field scenarios to do a sensitivity analysis in the velocity model. Then, for depth to time conversion by image ray, we used two different structural models and with velocities derived from RTM seismic processing. Image ray establish a link between time and depth and allows a quick evaluation of structural geometry and pull-up effect presence simultaneously in both domains.

Aplicación del método de iluminación por campo de onda en un modelo subthrust en la Cuenca del Valle Superior del Magdalena (Colombia)

“…The velocities for each geologic unit were defined using wells and seismic information (Figure 3) from a close area with similar subthrust structures in Neiva Sub-Basin (Macellari et al, 2003;Duarte et al, 2019). Then, a geophysical model was generated with the velocity scenario.…”

“…The velocity model needs to be consistent with the structural geology and stratigraphy following the sequence in age and using details about velocity information (Etris et al, 2001). For this reason; our velocity model was compound using the velocities described in Figure 3, estimated for this study area in Neiva Sub-Basin using the reported velocities in Macellari et al (2003), where used basement velocities from a stratigraphic well and we also took the velocities reported in Duarte et al (2019), where used velocity information from wells and seismic velocities. According to Yan and Xie (2016), illumination analysis by wavefield provides vital information regarding the response of an imaging system to subsurface structures.…”

“…Also, the most recent (2015 -2017) 2D and 3D seismic information (which possibly has better image quality) is confidential in this area of Colombia. The main target of this work is to try a 2D geophysical modelling applying wavefield illumination method, from two different seismic interpretations associated to one velocity scenario built from wells and seismic velocities (Macellari et al, 2003;Duarte et al, 2019) in a two stages methodology; in order to evaluate if the illumination could be improved for this section even in the zones under Chusma and Upar faults.…”

“…There is a structural configuration that exhibits possible structural traps located below the Chusma and Upar faults which present high dips that produce fault shadow zones. Therefore, the proposed structural styles and geological models were first studied (Blanco and De Freitas, 2003;Jiménez-Díaz, 2008;Macellari et al, 2003) and two different geological models were interpreted for the same seismic image (PSDM), taking into account that the stratigraphy in this part of the basin shows strong velocity contrasts (rocks of the Saldaña Formation overlying the sedimentary sequence) (Macellari et al, 2003;Duarte et al, 2019).…”