LOCACE / BALISS : un test de la cohérence géologique d'une interprétation sismique Locace / Baliss: Test of the Geologic Coherence of Seismic Interpretation

• Main Author: Moretti I.
• Format: Article
• Language: English
• Published: EDP Sciences 2006-11-01
• Series: Oil & Gas Science and Technology
• Online Access: http://dx.doi.org/10.2516/ogst:1991028
• ISSN: 1294-4475; 1953-8189

Durant quatre années l'Azienda Generale Italiana Petroli (AGIP), la Société Nationale Elf Aquitaine, l'Institut Français du Pétrole (IFP) et Total Compagnie Française des Pétroles ont joint leurs efforts pour développer un outil de géologie structurale et un programme de rétro-déformation. Le but était d'améliorer le pointé des sections sismiques en validant l'interprétation faite par des tests de cohérence géométrique. Une section qui peut être rétro-déformée en suivant le principe de conservation de la matière est dite équilibrée. Ce projet de recherche a abouti à la réalisation de deux logiciels LOCACE et BALISS. LOCACE (LOgiciel de Construction Assistée de Coupes Equilibrées) travaille à partir d'une section géologique. BALISS (BALanced Interpretation of Seismic Sections) permet d'appliquer à l'image sismique profondeur les principes de l'équilibrage. Cet article rappelle les fondements de cette méthode, les différents types de déformation - rigide, couche à couche, cisaillement simple - leur mise en oeuvre dans LOCACE/BALISS et la philosophie de l'utilisation de ces logiciels. <br> The need to use concepts of structural geology for seismic interpretation is something that is often difficult to apply because of the complexity of the zones investigated and especially because of the lack of interaction among specialists in the different areas of exploration. Likewise, quantitative geology is fairly recent, and computerized tools for structural geology are still rare although there is a multitude of them in geophysics. The existence of graphic workstations and computerized tools favoring the effective interactivity of software packages now makes it possible to integrate this implementation. The two French oil companies, Total Compagnie Française des Pétroles and Elf Aquitaine, together with Institut Français du Pétrole (IFP) have joined their efforts since 1987 to develop a tool for testing the geologic and geometrical coherence of sections. Azienda Generale Petroli (AGIP) joined this research group in 1988. Two software packages have been created. The first one, LOCACE (LOgiciel de Construction Assistée de Coupes Equilibrées), is a tool for geologists wanting to balance a section, i. e. to check to see whether the present geometry is compatible with a probable prior state and that a deformation path exists without any loss of material between the two states. The cross-section can then be restored to build its geometry before its deformation and thus to quantify the history of the burial and/or emersion of series. The second software, BALISS (BALanced Interpretation of Seismic Sections), has to do with the depth seismic image and serves to improve picking by using the results of a retrodeformation performed with LOCACE. In particular, it horizontalizes reflectors, not solely by an offsetting of traces along the vertical, but according to geologic deformation criteria that combine the conservation of areas and lengths. Four deformation modes are used to describe large-scale upper-crustal deformations. First, the flexural-slip method in which the slip occurs parallel to the beds (Fig. 1). Flexural slip is a line-balancing technique based on the deformation of a dip-domain grid and preserving both bed lengths and area. LOCACE is use to apply this method even for layers with thickness variations (Fig. 2). Then the simple shear method, in which shear is imposed in a given direction), might be the right method for synsedimentary faulting in an extensional area but might lead to wrong results in a compressional area (Fig. 4). Rigid deformation, i. e. rotation and translation, can be added to any of these methods together with decompaction, which is computed by standard backstripping method that takes various lithologies into account. For incompetent layers, such as a salt sheet for instance, overall area conservation may be applied. After describing the basic principles of the balancing of geologic sections and the different deformation modes formulated as equations by LOCACE, we show how these principles can be used for restoring a seismic image as can be done with BALISS.