Testing the Linear Scanline Method for Fracture Distribution Assessment in Multi-Deformed Evaporite Beds of Northeast Brazil, to Improve Geomechanical Models

Miranda, Tiago; Barbosa, Jose A.; Neumann, Virginio H.; Gomes, Igor; Matos, Gabriel; Santos, Rafael

The deformation in evaporite deposits involves the creation of many features including folding, fracturing and faulting. This study evaluates the classical scanline method to access aspects like fracture density and frequency in gypsum and anhydrite deposits from the Ipubi Formation (Araripe Basin, Northeast Brazil). We study fractures that are filled by secondary minerals such as fibrous or satin-spar gypsum, as well as shale.

The main objective was to obtain information regarding the relation between the groups of structures, their origin and relationship with formation timing. Results will be used to build computational models that consider fracturing importance in the geomechanical modeling of evaporitic deposits.

Measurements obtained from the zones of intense fracturing were taken via vertical and horizontal scanlines. Fracture orientation, morphology, crosscutting relationships, composition and texture of fracture fill were recorded for each fractures set. As the discretization of the large number of small fractures is impossible, the research will address this difficulty using the scanline information through homogenization techniques (numerical modeling). The results showed that there were two main sets of filled fractures. First, the vertical veins trending ENE and second, the horizontal veins trending NNW. The opening-mode fractures range from 0.5 mm to 80 mm among veins and shear fractures.

Applying these techniques in evaporite deposits represents a pioneer effort to address this type of investigation. The scanline method was useful in describing fracturing networks in evaporitic deposits. The transfering of this information into homogeinized models appears to be useful tool in helping to create computational geomechanical models.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013