METHODOLOGY TO REDUCE FAULT SHADOW: APPLIED IN A SECTOR OF THE LLANOS BASIN – COLOMBIA
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Universidad Industrial de Santander
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La 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.
The 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.
The 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.
Keywords
fault shadow, false structure, numeric modeling, llanos basin, Casanare, Sombra de falla, falsa estructura, modelado numérico, cuenca llanos, Casanare