Banca de DEFESA: RAFAELA DA SILVA ALVES

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : RAFAELA DA SILVA ALVES
DATE: 23/10/2020
TIME: 08:30
LOCAL: Videoconferencia - https://cutt.ly/6fcqwHK
TITLE:

CONDITIONING OF THE SHALLOW HYDROGEOPHYSICAL AND HYDROGEOCHEMICAL CONTEXT BY FAULTS: THE EXAMPLE OF THE BARREIRAS AQUIFER IN THE AREA OF THE LOW COURSE OF BOA CICA STREAM-RN

KEY WORDS:

Barreiras-RN Aquifer; Neogenous faults; numerical modeling; hydraulic conductivity; geoelectric methods.

PAGES: 131
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUMMARY:

The occurrence of faults in aquifers of a clastic nature conditions, in terms of structural compartmentalization, their geometry and offers an increase in anisotropy which is reflected in variations in hydraulic conductivity, variation in saturated thicknesses, changes in the underground flow pattern and variations in hydraulic gradient. The Barreiras Aquifer, the target of the present study in a sector of the southern coast of the state of Rio Grande do Norte, has a predominantly unconfined hydraulic characteristic and shows itself structurally compartmentalized by Neogenous faults. The area in question involves a battery of 12 producing tubular wells, 39 piezometers, in addition to another 6 for research and monitoring, installed in 2011, which capture about 750 m³/h destined to supply water for inland municipalities with water deficit. The local structure, evidenced by the main faults Boa Cica and Tabatinga, NW and NE respectively, offers complexity to the Barreiras Aquifer, either in quantitative or qualitative terms, the latter case particularly regarding to possible anomalies in the freshwater-saltwater on the coast line. This thesis, through different methodological approaches, presents an analysis of the behavior of the aquifer with emphasis on the role of the Boa Cica and Tabatinga faults in the form of their permeable or semi-impermeable limits, also aiming to simulate the possibility of saline intrusion in the area. In addition, we sought to identify the most promising sectors for the location of new pumping wells, with a view to increasing the water supply and subsidizing sustainable aquifer management. The methodology initially involved the characterization of the structural compartmentalization of the aquifer through correlation in well profiles, 1D inverse geoelectric models and field investigations. The behavior of the aquifer in a structurally controlled environment was simulated using the software Visual MODFLOW. In this context, the numerical models were elaborated considering two different scenarios for the role of failures, such as hydraulic ducts or barriers, respectively, zones of increase and reduction of hydraulic conductivity in relation to the surrounding environment. The results of the simulations were compared with 2D reverse geoelectric sections and aquifer tests carried out in local wells. The 2D geoelectric models, specifically, were used in order to characterize the fault locally near the coastline and whether it would be in the form of a resistive anomaly (compatible with the barrier model) or conductive (compatible with the conduit model). Reinterpretations of aquifer tests were carried out in order to identify possible recoveries of dynamic levels in the vicinity of the faults. The numerical models of density dependent flow, used to simulate saline intrusion in the aquifer, were generated on the SEAWAT platform. Simulations were carried out using as a parameter the current exploitation of 750 m³/h for a period of time equivalent to 20 years. To check the most promising sectors for drilling new wells, in addition to all the methods applied, a saturated thickness map was generated to guide the numerical simulations performed in Visual MODFLOW. The numerical flow model was calibrated with a residual error of 8.9%, considering anisotropies in the aquifer in the form of lateral contacts between different hydraulic conductivities and variations in the saturated thickness resulting from the failures. The simulations carried out showed that the main local faults are compatible with duct models, that is, they correspond to areas of high hydraulic conductivity. Such results were corroborated with the characterization of conductive anomalies in 2D geoelectric imaging, associated with one of the simulated faults, Boa Cica Fault (NW). The aquifer tests, in turn, showed a trend of recovery of dynamic levels as the respective depression cones reach the main fault zones. The calibrated transient model, in accordance with the calibrated flow model, considered the faults as zones of relatively greater hydraulic conductivity and representing preferential paths to the evolution of saline intrusion. This result is also corroborated by the conductive geoelectric anomaly in the Boa Cica Fault (NW), where its kinematic aspect of a transtensional nature favors a greater reach of this saline contamination. Similar results were obtained in simulations involving recharge variations between the dry and rainy periods, with the faults representing preferential conduits to the increase in intrusion. In terms of additional well locations, guided by numerical flow models and a saturated thickness map, they indicate the northeast portion of the study area as the most promising, mainly because it has greater saturated thicknesses (70 to 90 meters). The numerical simulations, in particular, showed that the areas of relative grains are the most propitious for future drilling, in the face of greater available drawdowns and, consequently, greater exploitation flows.

BANKING MEMBERS:
Interno - 1451214 - ADERSON FARIAS DO NASCIMENTO
Externo à Instituição - ANTONIO MAROZZI RIGHETTO - IGARN
Presidente - 1714488 - LEANDSON ROBERTO FERNANDES DE LUCENA
Externa à Instituição - NATALINA MARIA TINOCO CABRAL - FUNASA
Externa ao Programa - 1674419 - VERA LUCIA LOPES DE CASTRO