Natural Fracture Characterization in Aptian Carbonates, Araripe Basin, NE Brazil

Abstract

This paper addresses fracture characterization in an Aptian laminated limestone, the Crato Formation, cropping out in the Araripe Basin (NE, Brazil) using a scanline technique. This unit has been used as a geological analogue of buried naturally fractured carbonate reservoirs. In recent years, studies of fractured reservoirs have drawn considerable attention due to their significance for oil production and enhanced recovery. The study was based on the use of traditional scanline surveys, and the recording of fracture orientation, morphology, crosscutting relationships, composition, texture of fracture fill, fracture aperture-size distribution (frequency), spatial distribution (coefficient of variation), and strain for each fracture set. The main fractures identified in the Crato Formation were shear- and opening-mode fractures (veins) and with stylolites also present. In this study we focus on opening-mode fractures, which strike in two main directions, NNW-SSW (set 1) and NE-SW (set 2), and are filled by recrystallized calcite. Fractures of set 2 have a wider kinematic aperture and spacing range and are more likely to be clustered than are fractures of set 1 (NE). These results have been used to populate computational models that consider the widespread fracture system in the geomechanical modeling of carbonate reservoirs.