Banca de DEFESA: JULIANA GOMES RABELO

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STUDENT : JULIANA GOMES RABELO
DATE: 27/11/2019
TIME: 09:00
LOCAL: Auditório do Departamento De Geofísica
TITLE:

Study of high permeability fracture zones through structural mapping and numerical modeling in Jandaíra Formation, Potiguar Basin

KEY WORDS:

Fractures; Karst; Numerical Model; Jandaíra.Formation

PAGES: 100
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUMMARY:

This research investigates how fractures associated with the stress field (SH_max) influence the increase of porosity and secondary permeability, as well as the development of karst features of the carbonate rocks of Rosário Outcrop (Jandaíra Formation - Potiguar Basin). The study presents the interpretation of Unmanned Aerial Vehicle (UAV) images, numerical modeling data and field research. Through the UAV image was performed the structural interpretation and preparation of lineament maps, surface and topographic dissolution, and topographic profiles. The structural analysis performed in the field had the characterization of centimeter structures, such as veins, tectonic stylolites and distensional structures, as well as metric structures as normal faults. Numerical modeling investigates how fractures subjected to a maximum compression stress NW (current stress field in the Potiguar Basin) influences the dilatancy process and plastic flow and, consequently, the karstic development. Field results indicate that the main structures, generated by a transcurrent stress field with maximum horizontal compression NS and maximum horizontal distension ES, are compatible with NS veins, distensional fractures (I-mode) and E-W to ENE-WSW tectonic stylolites, perpendicular to stratification, compatible with the same stress field. The linkage of these structures forms continuous fractures up to 100 m in length and 15 m deep, which allows the fluid to flow vertically along the fracture planes, which can reach the depositional planes, also favoring horizontal dissolution. These plane intersection zones generate zones of high connectivity that leads to increased porosity and permeability, generating structurally controlled conduits, being responsible for the development of caves, collapse structures and large fractures. The results of the numerical models indicate that the accumulated stress along the pre-existing fractures generates zones that favor the increase of porosity and permeability, favoring the karstic development. NW fractures, orthogonal to the stress field (SH_max), and fractures at the intersection of NE-SW and NS fractures were the sites with the largest increase in dilatancy and the presence of plasticization, that is, the preferred sites for karstic development. The results of numerical modeling when compared to dissolution maps show realistic results for the development of karst features. The behavior of pre-existing fractures can greatly contribute to the understanding of the development of secondary porosity and permeability in carbonate rocks, as well as in the development of karst features.

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