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This work addresses the geological and geophysical interpretation of salt structures in selected Brazilian sedimentary basins, from intracratonic Palaeozoic evaporites in the Amazon and Solimões basins to divergent margin evaporite basins formed during the Mesozoic break-up of Gondwana. There is an intriguing correlation between evaporite basins and hydrocarbon accumulations in all the selected basins discussed. The Solimões and Amazonas basins developed evaporite depositing environments as the Middle Carboniferous sea was closing during a plate convergence phase. The salt basin along the eastern Brazilian and western African margins developed along the Mesozoic rifts of the South Atlantic. Regional seismic interpretation and potential field (gravity and magnetic) data over the eastern Brazilian and west African margins suggest a very thick autochthonous salt layer deposited over rifted continental crust and particularly above the thick sag basin sediments over the hyperextended crust that marks the transition from continental to oceanic crust. Most of the hydrocarbon discoveries in the eastern Brazilian and western African margins are in post-salt turbidite and carbonate reservoirs, but recent discoveries in the deepwater salt basins along the southeastern Brazilian margin indicate that pre-salt plays will represent an important contribution to hydrocarbon production in the near future.

The study of microbial carbonates has acquired new significance with the recognition that they retain valuable information related to biomineralization processes associated with microbial activity throughout geological time. Additionally, microbialites have a demonstrated economic potential to serve as excellent hydrocarbon reservoirs. The Lower Cretaceous Cod o Formation, located in the Parnaiba Basin of north-east Brazil, comprises a unique stratigraphic sequence of up to 20 m thick, well-preserved carbonate microbialites. Deposited in a continental basin during the initial break up and separation of South America from Africa in the Early Cretaceous, this lacustrine carbonate sequence provides an excellent example to investigate the palaeoenvironmental conditions controlling microbialite facies development. Based on macroscopic and microscopic observations of outcrop and drill core samples, four microbialite facies (stromatolite, lamina, massive and spherulite) were defined and distinguished by textures and microbial fossil content. Changes in facies type are related to alternating palaeo-water depths, as reflected by 87 Sr/ 86 Sr cycles resulting from fluctuations in the sources of meteoric water. Clumped isotope measurements of stromatolitic fabrics yield precipitation palaeo-temperatures with an average value of 35°C. The d 18 O values of bulk carbonate (À6Á8 to À1Á5& Vienna Pee Dee Belemnite) imply precipitation from water with calculated d 18 O values between À1Á6& and 1Á8& Vienna Standard Mean Ocean Water, reflecting precipitation from variably modified meteoric waters. The d 13 C values of bulk carbonate (À15Á5 to À7Á2& Vienna Pee Dee Belemnite) indicate a significant input of carbon derived from aerobic or anaerobic respiration of organic matter. Combined, the data indicate that the evolution of the Cod o Formation occurred in a closed lacustrine palaeoenvironment with alternating episodes of contracting and expanding lake levels, which led to the development of specific microbialite facies associations. The results provide new insights into palaeoenvironmental settings, biogenicity and early diagenetic processes involved in the formation of ancient carbonate microbialites and, by extension, improve the knowledge of the reservoir geology of correlative units in deep waters offshore Brazil. 155

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We collected socio-environmental data from the inhabitants of a coastal area in the State of Rio de Janeiro, Brazil, in order to investigate the local knowledge about environmental, economic and cultural particularities of the area and the main human activities that impact the environment. Community perceptions from 11 localities in the Região dos Lagos were evaluated. The data analysis can help in the development of specific geoconservation activities for the study area, which is located in the aspirant Geopark 'Costões e Lagunas do Rio de Janeiro'. This initiative of considering community perceptions can help to maintain and protect local geological sites, raise public awareness of environmental matters and help to manage the development of the new Geopark. Furthermore, it can also contribute to the sustainable development of the area and to the planning of effective policies to sustain progress. Taking into consideration the answers and needs of the interviewed communities, the key topics requiring geoconservation activities in the study area are land use planning and biodiversity, urban mobility, continuous monitoring strategy, environmental awareness, wastewater, urbanisation, geotourism, sense of place, waste and economical activities.

The Rb-Sr method has been successfully applied to argillaceous sedimentary rocks in order to supply parameters for the definition of their depositional ages. In many studied cases, despite the geologically significant results, there are doubts concerning the interpretation of the obtained data and their limitations. This happens because sedimentary rocks are considered to be the mixture of detrital fragments of diverse sources, and therefore is the possibility of contain an isotopic record of their source rocks. The Rb-Sr method, when applied to mudrocks, allows constraining absolute depositional ages, owing to the resetting of the isotopic Rb/Sr system during deposition. This process is called isotopic homogenization in the depositional environment. Some special care must be taken with respect to sampling, sample grain size, depositional setting, and mineralogical composition. Nevertheless, questions still remain when concerning this methodology, particularly on the real occurrence and extent of the isotopic homogenization in the sedimentary environments. In the present work, the Rb-Sr method has been applied to samples of sedimentary rocks collected from different units representing several depositional settings from the Paraná Basin. The parameters responsible by the isotopic homogenization of Sr have been evaluated. The obtained results allowed the improvement of the application of the Rb-Sr method to sedimentary rocks, and significant results concerning depositional ages were obtained.

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Cement attack by acid during matrix acidizing operations has created severezonal isolation problems in wells with multiple adjacent permeable zones, operated by PETROBRAS. This effect was observed in several wells treated with conventional HCl-HF acid mixtures, even when cement bond logs prior to the acidjob were excellent. This paper presents a series of lab experiments showing that acetic acid, alone or mixed with HF, dissolves much less cement than HCl and HCl-HF mixtures with the same carbonate dissolving power. The reaction of acetic acid with cement forms a protective skin that inhibits further acid attack. The organic formulations were tested in an acidizing simulator, before being used in the field. The paper also presents field test results which confirmed that the acetic acid mixtures did not break zonal isolation (cement consumption was restrained to the perforated interval) and were able to generate 6- to 40-fold increases in the injectivity and productivity of the wells. Introduction Cement solubility in acids has been shown to be a problem, both in the field and by laboratory testing. Ref. 1 shows that HCl, HCl-HF, and citric acid have a strong detrimental effect on the cement, resulting in weight loss and compressive strength loss. Traditional views held that due to the formation of a protective skin, acid-cement reaction would be limited. However, severe zonal isolation problems have been observed, following HCl-HF treatments. The first approach to solve the problem was the development of acid-resistant cement. These blends use liquid latex that inhibits acid attack by coating cement particles and by reducing the permeability of the cement. Refs. 2 and 3 address the use of acid-resistant cement blends for primary cement and squeeze operations. This solution may be easily applied to new wells, in which the primary cement and squeeze jobs in front of the pay zones are composed of acid-resistant slurries.