VII Congreso de Exploración y Desarrollo de Hidrocarburos (Simposio de La Geofísica: Integradora del Conocimiento del Subsuelo)

La estimacion del factor Q a partir de Ia sismica de superficie puede tener objetivos varios como mejorar Ia resolucion de las imágenes del subsuelo removiendo el efecto de Ia absorcion de energia en el medio, corregir a distorsion de fase debida a Ia dispersion o analizar las propiedades anelásticas de Ia roca para caracterizacion de reservorios. Los efectos de Ia propagacion de ondas en medios anelásticos afectan Ia respuesta de AVO, por lo que su influencia debe ser considerada en tales estudios. Sin embargo, debido a Ia dificultad en su estimación, son escasos los ejemplos que se encuentran en Ia literatura. En este trabajo se analizan datos terrestres adquiridos con dinamita y se estima el factor Q. El método usado es el de los cocientes espectrales, que estima los valores de Q desde el cociente entre espectros de una ventana somera, tomada como referencia, y una ventana que contiene Ia zona de interés. El valor de Q se computa usando una regresion lineal. Este valor representa un promedio, a partir del que, por medio de simple algebra, se calcula el Q interválico. Finalmente, con los valores estimados, se corrige Ia seccion sismica y se compara con Ia misma sección sobre Ia que se aplica un balance espectral.

In seismic surface, the generated frequencies are much higher than those observed in seismic deep, so the travel time across the weathered layer can cover several cycles of train seismic waves. This layer influences the trajectories of ray in a manner that requires correct in order to obtain the proper location in depth of the reflectors of interest. We propose a method to extrapolate the times obtained from a few Up Holes to a whole section of Resistivities from a Deep Electrical Tomography.

BP and ECOPETROL acquired 450 km2 of 3D seismic information in a complex Piedemonte Llanero zone to the North of Cusiana and Cupiagua fields Colombia. In these projects, the original design geometry was strongly affected by numerous surface obstacles principally due to environmental restrictions. For this reason, it is necessary to use to a regularization technique to guarantee the success of key processes such as velocity analysis and pre-stack migration. In this work, shot points were interpolated between those originally recorded. In this way the distance between sources was reduced from 80 m to 40 m in order to obtain new data equivalent to 184% of the original shooting, increasing coverage by 60%. Original tomography statics and elevations were part of the data interpolated in this case. Coverage maps as well as distance-azimuth attributes of the new geometry were generated and partial stack was examined by offset range. Examining certain offset planes it is possible to observe how missing lines become completed at the same time that large empty spaces are filled. This can be observed in the original seismic time slices.

La Cuenca del Golfo San Jorge tiene un relleno principalmente continental fluvial donde los reservorios son de difIcil correlación y caracterización, por ello es de suma impor tancia contar con un modelo de sedimentaciOn validado para desarroilar el yacimiento.
El yacimiento Canadon Vasco comienza su desarrollo en el año 1990 con información de algunos pozos exploratorios y sIsmica 2D con produccion hasta 1998, luego tiene un impasse hasta el año 2006 que es cuando se decide reactivar el yacimiento; se perforan nuevos pozos y se decide Ia registracion de sismica 3D con un diseno apto para resolucion estructural y estratigrafica que permitio realizar: Interpretación Estructural; permitio ajustar el modelo de inversion tectonica. Análisis de Atributos; principalmente los atributos de amplitudes sismicas identifica ron geoformas en algunos niveles estratigraficos particulares. • De esta manera tue posible identificar el carácter meandriforme, Ia orientaciOn de los reservorios y espesores de los paleo-canales en Ia Secuencia Basal de Ia Fm. Bajo Barreal. Inversion Elástica; permitio identificar en Ia Secuencia Basal de Ia Fm. Castillo las zonas con mayor acumulacion de arenas. • En particular se ha mejorado Ia identificación de zonas con probable mineralizacion
en Castillo inferior. La calibracion realizada en los cubos de Impedancia P y modu lo de Poisson con los pozos EaFu.X-1 y CaVa-25, permite inferir las zonas a desarro lIar con mayor posibilidad de encontrar producciOn de hidrocarburos. • En consecuencia, es posible aplicar un nuevo criterio para decidir en que areas convendria perforar pozos hasta Ia base de Ia Fm. Castillo (aprox. 160Cm.) yen cua es solo hasta Ia Secuencia Basal de Ia Fm. Bajo Barreal (aprox. l000m). De forma tal de hacer mas eficiente el desarrollo del yacimiento y reducir costos. Este trabajo muestra como los datos proporcionados por Ia sIsmica 3D, principalmen te análisis de atributos e inversiOn elástica, permiten realizar un valioso aporte para mejorar el modelo geologico, definir Ia geometria de los reservorios, y proporciona criterios que coadyuvan a definir areas con mejores perspectivas de perforacion.

This case history is an example of how a seismic reservoir characterization project can be successfully executed even in areas of very challenging seismic with a low signal to noise ratio. Additionally the study shows how this is achieved by close cooperation of the Inversion and Data Processing experts involved. Through calibration of the well data with the seismic, the Inversion could quantify the quality of the seismic data and help the data processing geophysicists define parameters and processes that could
be used to further pre-condition the pre-stack data and bring it to the point where it was suitable for the inversion process. This not only made the subsequent Inversion process more successful, by delivering more reliable results, but the calibration process also helped quantify the need, or otherwise, for additional data processing, and to quantify the benefit then obtained. This study thus completed an integrated project that, although stretching from acquisition in 2005, through data processing in 2006, to the Inversion in 2007, did finally constitute an integrated seismic solution from Acquisition to reservoir characterization, completed by cooperation between WesternGeco and Petrotrin of Trinidad and Tobago.

AplicaciOn de una nueva herramienta dieléctrica para Ia caracterizacion de yacimientos de crudo pesado de Ia Faja PetrolIfera del Orinoco. Una nueva herramienta dieléctrica ha sido introducida en los reservorios de crudo pesado en a Faja del Orinoco, dándonos una forma alternativa para evaluar Ia saturacion de agua, particularmente en el caso de agua de formacion relativamente fresca y aguas de formacion variables, que es el caso en Ia Faja del Orinoco. Las condiciones particulares encontradas en a cuenca del Orinoco también se prestan a Ia implementación de un esquema de inversion que permite extraer una medicion a 4 pulgadas en Ia pared de pozo, suficientemente profunda como para leer en Ia zona virgen. Esta medicion ha resultado ser muy robusta aün en condiciones de pozo muy rugoso. En consecuencia, ahora se reconoce que zonas de arenas de baja resistividad anteriormente descuidadas contienen cantidades significativas de petroleo, una conclusion que no podia ser alcanzada basada solamente en el análisis de resistividad.

In order to analyze the basal sequence of the Carboniferous System and the development of its lower deposits (Fm. Tupambi), a reference horizon time slice (the top of the Devonian Iquiri Fm.) was used. The analysis was performed over an 80 ms window
centered on the reference horizon, and it was sampled every 4 ms. This gave us the opportunity to define the existence of eight channel sequences, five with dominant SE - NW direction and three with about E-W directions. The NW - SE channels are characterized by superimposed fluvial systems deposits, and the E - W ones by fluvio glacial systems deposits. The difference between these kinds of deposits is seismically manifested by their geometry and the degree of reflector continuity that define their internal structure. The use of 3D visualization software was very useful in order to identify the relation between the seismic and geologic features.

In this work we introduce a new method to fully determine the elastic parameters of a thin-bed using prestack seismic data. These parameters include thickness, P- and S-wave velocities, and density. We obtain the exact solution for the AVA response of a thin-bed considering converted P-waves, S-waves and all the associated multiples. We carry out the estimation of the thin-bed parameters in the amplitude spectrum domain using simulated annealing. Contrarily to using zero-offset data, we show that the use of AVA data (PP data only) contributes to increase the robustness of this inverse problem under noisy conditions as well as to significantly reduce its inherent non-uniqueness. To further reduce the nonuniqueness, simulated annealing allows us to easily impose appropriate bounding constraints to the parameters of the upper and lower media, which need not to be known accurately. We illustrate the method by inverting noisy synthetical gathers corresponding to simple wedge models. In addition, we stochastically estimate the uncertainty of the solutions by running simulated annealing several times. The results show that a thin-bed can be fully determined with a high degree of confidence far below the tuning thickness.

Structural interpretation in Subandean fold-and-thrust belts has many uncertainties, especially when the seismic image is not adequate. In order to improve the geologic interpretation of the Ingre Structure in Bolivia the magnetotelluric (MT) method was applied.
The method determines the resistivity distribution of the subsurface from measurements of naturally occuring electric and magnetic fields. The studied subandean structure is formed by a surface anticline, with a Carboniferous nucleus, and a deep Silurian-Devonian anticline, detached from the former by Upper Devonian rocks tectonically piled-up. The objective of this study was to obtain the structural image of Paleozoic formations at 3500-5000 mbgl. The information available in the area consisted of surface data and a strike seismic line of poor quality. MT data was acquired over five lines perpendicular to the structure, forming a non uniform grid. The first processes were ‘blind’ 2D and 3D inversions, without any geologic control. In these, conductive zones could be separated from a resistive core that corresponds to the deep anticline. 2D inversions controlled by geological models were also performed. These allowed the feasibility of different models and the method’s sensibility to be tested.

Spectral analysis of magnetic anomalies to calculate Curie-temperature isotherm: A methodology to estimate crustal heat-flow for San Juan and La Rioja provinces, Argentina. A method to estimate the depth extent of magnetic sources was applied to the
magnetic anomalies from our terrestrial magnetic data base. The analysed region involving the Precordillera Cuyana and the Sierras Pampeanas of San Juan and La Rioja, including the Famatina System. The top (Z~) and bottom (Zb) boundaries of the magnetized crust were calculated from power-density spectra of the total-field anomalies on 2-D ninety windows with 1 .5°xl .5° size. The depths obtained for the bottom of magnetized crust are assumed to correspond to Curie point depths. The values thus obtained for the Precordillera range between 29 and 40 km, whereas for the Sierras Pampeanas, in the Sierra de Pie de Palo, and other mountain chains along the Bermejo-Desaguadero lineament, such depth ranges between 20 and 35 km. From Curie point depths we have proposed a map of heat flow in the studied region. The patterns of heat flow are distinct on the Precordillera and on the Pampean region. The Precordillera geologic province is characterized by low heat flow and deep Curie depths, whereas the Sierras Pampeanas geologic province is characterized by high heat flow and shallow Curie depths. A significant heat flow extending in Northeast-Southwest direction seems to be directly related to Juan Fernández Ridge trace.