Análise da geometria dos domínios geológicos de sub-superfície a partir de perfis de poços tubulares no município de Fortaleza - Ceará

Abstract

The research seeking the geometric characterization of Fortaleza’s Sedimentary Geologic Domain was based on SIAGAS/CPRM (Mineral Resources Research Company) and GEOHIDRO (Geology Hydrogeology and Services) tubular wells records which combined reach the mark of 1166 tubular wells recorded until December 2012. The wells that had a geologic profile totaling 516 were analyzed according to their lithological characteristics technical-constructive aspects and hydrogeological parameters. After the bibliographic revision and the well’s reports gathering the data contained on that reports were organized in sheets maps tables graphics and figures. So then 274 lithological profiles of the 516 recorded were selected to elaborate the fourteen geologic profiles being seven on N-S direction and seven on W-E direction. These geological profiles allowed a better view of the sedimentary packages as well as the crystalline basement and its contour allowing a much more accurate interpretation about the way the sedimentary domain behaves compared to the top of the basement. From the profiles analysis was conclusive that the sedimentary package tends to increase its thickness when approaches the coast. It was observed that the sedimentary domain contains a Carbonate Formation located on the N/NE part of the area classified at first as a infra-Barreiras formation that becomes more thick when approaches the coast zone. It is worth mentioning that the sedimentary package has a more embracing geometry than that related on previous studies. The analysis of that profiles also revealed elevated parts of the basement (structural highs) and depocenters assimilated to horsts and grabens in N-S direction. Analyzing the top and base data of the 137 wells that contains the mantle of alteration from the basement it was possible to draw its contour and measure the average of its thickness that is something about seventeen meters. Among the structures we can highlight the lineaments located on the east part of NW-SE direction and in the center-south part of NE-SW direction. Secondly the faults of NE direction and the fractures of NE NW and W-E direction are observed in the W SW S center-south and SE parts of the area. Apparently the great drainage segments were affected by the lineaments faults and fractures. On the sedimentary hydrogeological domain the hydrogeological parameters presented the following values: from the data collected on 267 wells that had a profile the average of the Static Level presented was 8.4 meters and from 265 wells with a profile the average output presented was 416 m³/h. Now on the crystalline hydrogeological domain the average values was: from the data collected on 237 wells the average of the Static Level was 8.85 meters and from data collected on 236 wells the average output was 41 m³/h. Now the saturated thickness (here considered the sum of the filter columns) calculated from 378 wells presented an average of 24.4 meters with a standard deviation below 20% which attests a tolerable average dispersion.