Avaliação da variação sedimentológica em uma área da plataforma continental sob a atuação da indústria petrolífera
Petroleum exploration activity occurs on the offshore Potiguar Basin, from very shallow (2-3 m) until about 50 m water depth, extending from Alto de Touros (RN) to Alto de Fortaleza (CE). Take in account the biological importance and the heterogeneity of sediments on this area, it is necessary th...
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| Format: | Dissertação |
| Langue: | por |
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Universidade Federal do Rio Grande do Norte
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| Accès en ligne: | https://repositorio.ufrn.br/jspui/handle/123456789/19840 |
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| Résumé: | Petroleum exploration activity occurs on the offshore Potiguar Basin, from very
shallow (2-3 m) until about 50 m water depth, extending from Alto de Touros (RN) to Alto de
Fortaleza (CE). Take in account the biological importance and the heterogeneity of sediments
on this area, it is necessary the understanding of the sedimentological dynamics, and mainly
the changes generated by petroleum exploration to prevent possible damages to environment.
Despite the intense activity of oil exploration in this area, research projects like these are still
rare. In view to minimize this gap, this study was developed to evaluate sedimentological,
mineralogical and geochemical changes in the vicinity of a exploration well, here designated
as well A, located on the Middle continental shelf, near the transition to Outer shelf. The well
selected for this study was the first one drilled with Riserless Mud Recovery technology
(RMR) in Brazil. The main difference from this to the conventional method is the possibility
of drilling phase I of the well with return of drilling material to the rig tank, minimizing fluid
and gravel discharging around the vicinity, during this phase. Monitoring consisted of three
surveys, first of them done before start drilling, the second one done 19 days after the end of
drilling and the third one done one year after then. Comparison of the studied variables
(calcium carbonate and organic matter content, sediment size, mineralogy and geochemistry)
was done with their average, median and coefficient of variation values to understand the
changes after drilling activity. Because operating company technical reasons, the well location
was changed after the first survey (C1), resulting in a shift of the sampled area on the two last
surveys (C2 e C3). Nevertheless, the acquired data presented a good correlation, with no loss
to the mean goal of the study. The sedimentological, mineralogical and geochemical analyzes
were done at Federal University of Rio Grande do Norte (UFRN). The results indicated a
predominantly sandy environment along the three surveys. It was noticed that the first survey
(C1), presented different values for all the studied variables than to the second (C2) and third
(C3) surveys, which had similar values. Siliciclastic sediments are prevalent at all surveys,
and quartz is the main component (more than 80%). Heavy minerals (garnet, turmaline, zircon
and lmenite), rock fragments and mud aggregates also was described. Bioclastic sediments are
dominated by coralline algae (more than 45%) and mollusks (more than 30%), followed by
benthic foraminifera, bryozoans and worm tubes. More rarely was observed ostracoda and
spike of calcareous sponge. Because the low changes of the sediments at the studied area and
by the using of RMR method in the drilling, it was possible to conclude that drilling activity
did not promote significant alteration on the local sediment cover. Changes in the studied
variables before and after drilling activity could be influenced by the changing in the
sampling area after survey 1 (C1). |
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