Pitfalls in the seismic interpretation of fault shadow events — Vicksburg formation of south Texas

Bain, Richard C.

doi:10.1190/int-2014-0109.1

Cited by 3 publications

(1 citation statement)

References 4 publications

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“…Por otro lado, se han identificado factores que afectan la imagen de la estructura real como el salto y el ángulo de inclinación de la falla (Martínez y Agudelo, 2009) así como los rápidos cambios de velocidad propias de la zona fallada (Birdus and Artyomov, 2010). En el modelo definitivo se propagan ondas en las estructuras geológicas bajo la falla para conocer donde se reflejan (Alaei, 2012), se actualiza el modelo de velocidad con los registros de pozo y se correlaciona con las estructuras (Bain, 2015). Una tomografía restringida a la zona de falla permitiría construir un modelo de velocidad en profundidad de alta resolución para la PSDM (Birdus, 2007) y la curva de conversión tiempo-profundidad del modelo (Chermak et al, 2009).…”

Section: Introductionunclassified

Metodología De Reducción De Sombra De Falla: Aplicada en Una Zona De La Cuenca Llanos – Departamento De Casanare, Colombia

2017

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RESUMENLa sombra de falla distorsiona la imagen sísmica del bloque yacente de una falla normal o inversa, lo cual se debe a fuertes cambios de velocidad lateral que desvían la trayectoria de los rayos. En la Cuenca Llanos este efecto crea en las imágenes sísmicas falsas estructuras de anticlinales ("pull-up") y sinclinales ("push down o sag"). En este artículo se estudian los factores que generan este efecto y su impacto en las imágenes sísmicas mediante el modelado numérico. Se define una metodología para identificar la sombra y los factores que la causan, y crear el modelo apropiado para la migración PSDM. La metodología se probó en sismogramas sintéticos y se aplicó a una línea sísmica de un sector del Departamento de Casanare-Colombia. Como resultado se obtuvo una imagen en profundidad confiable libre de sombra de falla. Aunque la metodología se usó en un sector con falla normal ésta es aplicable a zonas con fallas inversas.Palabras clave: Sombra de falla, falsa estructura, modelado numérico, cuenca llanos, Casanare. METHODOLOGY TO REDUCE FAULT SHADOW: APPLIED IN A SECTOR OF THE LLANOS BASIN -COLOMBIA ABSTRACTThe shadow fault distorts the image of the hanging block of normal and inverse faults, caused by strong lateral velocity changes that deviates the ray path of waves. In the Llanos basin, this effect creates in the seismic images false structures like anticlines (pull up) and synclines (push down or sag). In this paper, the factors that generate this effect and its impact on the seismic images are studied through numerical modeling. It is defined a methodology to identify the fault shadow and its causing factors, and to create the appropriate model for the pre stack depth migration -PSDM. The methodology was tested with synthetic seismograms and applied to a seismic line recorded in a sector of the Departamento de Casanare-Colombia. As a result, a reliable image in depth free of fault shadow was obtained. Even the methodology was used in a sector with normal fault it is applicable to zones with inverse faults.

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Section: Introductionunclassified

Metodología De Reducción De Sombra De Falla: Aplicada en Una Zona De La Cuenca Llanos – Departamento De Casanare, Colombia

2017

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The evolution of the Dowsing Graben System: implications for petroleum prospectivity in the UK Southern North Sea

Grant

Underhill

Hernández-Casado

et al. 2019

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Upper Permian (Zechstein Supergroup) evaporites have a major control on structural styles and prospectivity in the UK Southern North Sea (SNS). They form the regional super-seal for the main Rotliegend Group (Leman Sandstone Formation) reservoir play fairway immediately beneath. The evaporites have highly variable thicknesses due to the syndepositional basin architecture, differential loading and post-depositional deformation through diapirism and salt withdrawal. The halokinetic activity leads to touchdown (welding) of the supra-salt section onto the sub-salt strata and the development of narrow (up to 15 km-wide) graben systems. The interpretation and depth conversion of well-calibrated, high-quality, 3D post-stack time-migrated (PSTM) seismic data along the southwestern margin of the basin show that a NW–SE-striking elongate extensional Dowsing Graben System transects the area. The graben is defined by a series of large, overlapping, en echelon listric growth faults, with oblique secondary planar faults, which sole-out on two main (deep and shallow) décollement levels in the Zechstein Supergroup and the Middle Triassic Röt Halite Member. Whilst its initial formation was related to Mesozoic extension, the graben system also displays a contractional overprint resulting from regional compression and structural inversion during the Cenozoic. Detailed mapping of the Zechstein Supergroup has revealed that the evolution of the extensional system was influenced by the ESE–WNW-striking anhydrite–carbonate Zechstein shelf-margin. The occurrence of variable-thickness, low-velocity sediments within the graben impacts seismic imaging and depth conversion, leading to prospective structures being overlooked; something that has implications for prospectivity in the SNS and other evaporite basins where similar graben occur.

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Depth migration as a valuable tool for prospect derisking in the Colombian Foothills

Poveda¹,

Patino²,

Mathewson³

2017

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Interpreting land seismic data in the Colombian Foothills poses many challenges. Very often, the data have a low signal-to-noise ratio and the subsurface prospective structures are significantly complex. The level of uncertainty can be so high that even experienced interpreters struggle to reconcile the seismic image with their geologic models. Based on previous knowledge and “fast-track” interpretation of old 2D prestack time migration data (no 3D seismic in the area), we identified two interesting plays for further analysis: a triangular zone (play 1) and subthrust anticlines beneath the frontal fault (play 2). Derisking the different prospects associated with plays 1 and 2 required the application of prestack depth migration (PSDM), which reduce uncertainty regarding the position of the structures, their depth, and even their existence. The seismic image in play 1 structures was improved significantly with better definition of the flanks of the anticlines and the frontal closure of the structures, more coherent events, and sharper definition in fault cut-offs. Some apparent play 2 prospects, that were actually “velocity pull-up” anticlines, were corrected by the depth-migration workflow, whereas other structures experience important modifications in their geometry. In both types of plays, depth migration dramatically changed the initial assessment of prospectivity. Based on the better agreement between seismic and borehole data, significant reduction in residual moveout on final PSDM gathers and more coherent seismic images, we believe that the use of depth migration has allowed us to obtain a more accurate representation of the subsurface, and consequently a more rigorous reserves estimation. The use of PSDM was essential to understand the complexities in the prospects evaluated and the risk associated with their exploration. We consider the lessons learned in this study applicable to similar geologic environments worldwide.

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Pitfalls in the seismic interpretation of fault shadow events — Vicksburg formation of south Texas

Cited by 3 publications

References 4 publications

Metodología De Reducción De Sombra De Falla: Aplicada en Una Zona De La Cuenca Llanos – Departamento De Casanare, Colombia

Metodología De Reducción De Sombra De Falla: Aplicada en Una Zona De La Cuenca Llanos – Departamento De Casanare, Colombia

The evolution of the Dowsing Graben System: implications for petroleum prospectivity in the UK Southern North Sea

Depth migration as a valuable tool for prospect derisking in the Colombian Foothills

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