ANÁLISIS AVO EN EL YACIMIENTO DE ALTA IMPEDANCIA DEL CAMPO CHUCHUPA
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Universidad Industrial de Santander
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La técnica de puntos brillantes (bright spot) como indicador directo de hidrocarburos ha sido ampliamente usada desde los trabajos de Ostrander (1984) y particularmente en yacimientos de gas. Localizado al Norte de Colombia, el campo de Chuchupa ha producido gas continuamente durante 30 años, pero a pesar del cubrimiento del campo con sísmica 2D no se han observado anomalías de amplitud relacionadas con la acumulación de gas. Para comprender este comportamiento se realizó un análisis de AVO y se caracterizó la respuesta sísmica del yacimiento para encontrar la relación entre el comportamiento de las amplitudes con la acumulación de gas. En esta investigación se utilizaron datos de una línea sísmica Este - Oeste y registros de pozos.
En un primer enfoque se modeló la respuesta sísmica a tope y base del yacimiento generando sismogramas sintéticos usando registros de pozo y se hizo un análisis comparativo con los datos de la línea. Se encontró que el tope del yacimiento está representado por el pico de una ondícula que decrece a medida que aumenta el offset pero que nunca cambia de fase. Cerca de la ubicación del pozo, donde el yacimiento tiene una saturación de gas del 100%, se obtuvo una alta correlación entre los sismogramas sintéticos y los datos reales. En un segundo enfoque, con los datos sísmicos organizados en CDP, se analizaron los gráficos cruzados de intercepto contra gradiente que permitieron discriminar puntos anómalos en el cuadrante IV. Los resultados identificaron una anomalía de Clase-I, la cual no se puede apreciar en secciones sísmicas apiladas por lo que requiere de estudios en datos pre-apilados, como se muestra aquí.
Palabras clave: AVO, Anomalías, Pre-apilado, Yacimiento, Chuchupa, Guajíra.
The technique of bright spot as a direct indicator of hydrocarbons has been widely used since the work of Ostrander (1984), particularly in gas fields. Located at north of Colombia, the Chuchupa field has produced gas continuously during 30 years, but despite the coverage with 2D seismic, amplitude anomalies associated with gas accumulation have not been observed. In order to find the relationships between the amplitude information and the gas accumulation, an AVO analysis was performed to describe the seismic reservoir response. The raw data of a 2D seismic line that crosses the field from East to West and a well log data set were used. In a first approach the seismic response was modeled using well logs, so a comparative analysis between the furnished synthetic seismograms and the real CDP gathers was done. The results indicated that the reservoir´s top is represented by a low amplitude peak which decreases when the offset increases but whose phase remains unchanged. In the well, where the reservoir has 100% gas saturation, a high correlation between the synthetic and real CDP gathers was observed. In a second approach, anomalous clustered points in the IV quadrant were discriminated through intercept versus gradient cross plot analysis. A weak Class-I anomaly was identified, which could not be observed in stacked sections and hence it should be analyzed using pre-stack data. Keywords: AVO, Anomalies, Pre-stack, Reservoir, Chuchupa, Guajira.
The technique of bright spot as a direct indicator of hydrocarbons has been widely used since the work of Ostrander (1984), particularly in gas fields. Located at north of Colombia, the Chuchupa field has produced gas continuously during 30 years, but despite the coverage with 2D seismic, amplitude anomalies associated with gas accumulation have not been observed. In order to find the relationships between the amplitude information and the gas accumulation, an AVO analysis was performed to describe the seismic reservoir response. The raw data of a 2D seismic line that crosses the field from East to West and a well log data set were used. In a first approach the seismic response was modeled using well logs, so a comparative analysis between the furnished synthetic seismograms and the real CDP gathers was done. The results indicated that the reservoir´s top is represented by a low amplitude peak which decreases when the offset increases but whose phase remains unchanged. In the well, where the reservoir has 100% gas saturation, a high correlation between the synthetic and real CDP gathers was observed. In a second approach, anomalous clustered points in the IV quadrant were discriminated through intercept versus gradient cross plot analysis. A weak Class-I anomaly was identified, which could not be observed in stacked sections and hence it should be analyzed using pre-stack data. Keywords: AVO, Anomalies, Pre-stack, Reservoir, Chuchupa, Guajira.