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ABSTRACT: Mechanical Modeling of Tectonic Deformations

Philippe Julien

Finding oil traps is based essentially on interpreting seismic data. The interpretation is often difficult; the geologist generally is faced with several possible solutions because structures are not always clearly defined. Rock mechanics are used to retain only the kinematic solutions that are stable at all times. All the possible evolutions are no longer equally probable. Two different methods were used.

Elasto-plastic behaviors (limestones, sandstones, etc.) are satisfactorily taken into account within a finite element code. It must be able to model the great displacement and large deformations that occur on a geological time scale.

In an experimental approach, conditions of structural deformation are recreated in laboratories using physical models. Results of the numerical modeling have to be calibrated against these experiments. A sedimentary basin has been modeled in this way.

This basin has been numerically modeled. Sedimentation is modeled by a gradual activation of the meshing. The plastic strain is computed at each time step of the deformation. Large values are located along linear zones corresponding to the faults observed on physical models. The creation and propagation of faults are modeled correctly. Moreover, we check that the spacing of the faults depends on the thicknesses of the layers.

Viscous behaviors of salt domes are better taken into account by a finite differences code. Mushroom diapirs and balloon diapirs have been modeled in this way. Other parameters such as the spacing between salt domes may be studied, too.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990