Fracture frequency and anisotropy of magnetic susceptibility: A case of study in the Claromecó Basin (PANG 0003 well), southwestern Gondwana boundary

Abstract

The PANG 0003 well records a siliciclastic sedimentary succession corresponding to the Tunas Formation (Permian) in the Claromecó Basin area (Buenos Aires province, Argentina). The aim of this paper is to establish a relationship between fracture frequency in the PANG 0003 exploration well and AMS parameters, as it is a novel research topic that would contribute to the knowledge of the Claromecó basin. Opening-mode I and mode II/III fractures were found in 729 m of unoriented core between 901 m and 170 m recovered. Fracture attributes: inclination, aperture, height, and cement presence are represented by four fracture sets according to the inclination angle; representative kinematic aperture data range from 0 to 5 mm and height constrain by core dimensions. Cement presence is represented by quartz, calcite, and minor pyrite. Fracture description were distributed in lower, middle and upper section of the well according to their fracture frequency (number of fractures per meter). Lower section is represented by a high fracture frequency (13 fractures/meter), which notably diminishes to the middle and upper section of the well (3 fractures/meter). The results indicate that the fracture frequency increases in depth and has a direct relationship with AMS parameters, such as degree of anisotropy (Pj) and magnetic foliation (F). According to previous studies in Sierras Australes outcrops and subsurface for Tunas Formation, tectonic imprint decreases its expression from base to top of the unit and has a positive correlation with fractures studies on cores. This relationship could be used as an alternative methodology to distinguish intervals of high number of fractures in subsurface, in this particular case, for the Claromecó Basin.