Applying scanline technique to geological/geomechanical modeling of fracturing systems in carbonate and evaporite deposits from Araripe Basin, NE Brazil

Abstract

This paper presents the development of a new methodology for the geological characterization of naturally fractured reservoirs. Such methodology is based on the following activities: application of scanlines technique, field data surveys (structural measurements, photographic panels, collection of samples), petrophysical analysis, construction of vectorial sections, and construction of computational models based on finite elements meshes. The study for characterization was conducted on two geological formations: Crato (limestone) and Ipubi (evaporites), from the Araripe Basin, NE Brazil. Using the scanline technique, the attributes of the fracturing systems were obtained in mesoscopic (outcrops) and in microscopic (thin sections) scale. The main structures identified in the Crato Formation were extensional fractures (joints and veins) and synsedimentary shear fractures. In the Ipubi Formation we limited our scope to main brittle fractures, classified as vertical to subvertical veins. The construction of the bidimensional geomechanical models was based on vectorial drawings (CAD) on the photographic panels of the outcrops, which were translated to finite element mesh by using routines created in Matlab and LISP languages. This permitted the automatization of the mesh creation process. The computational model then was finished with the incorporation of physical properties – obtained from lab tests –  of hydro-chemical-mechanic constitutive law parameters, and of the initial boundary conditions. In the computational model, the major structures were treated as a discretized continuum medium and the physical properties of their filling materials were assigned to such structures. The final products are files which could be directly processed in the software Code_Bright, to perform numerical simulations.  The proposed methodology allowed the construction of simple, but robust, models for naturally fractured geological formations with low complexity in terms of geometry and faciology. The improvement of the methodology will make it possible to create models which are reliable and can be constructed quickly to perform coupled simulations (hydro-mechanical).