Sidnei Pires Rostirolla

A fast MATLAB program to estimate the multifractal spectrum of multidimensional data: Application to fractures

A MATLAB^(R) program based on the Hou algorithm for estimation of fractal dimension and multifractal spectrum of fractures is presented. The program performance was tested with many synthetical fractals and field data. Interpolation and sampling effects on the fractal dimension and multifractal spectrum estimation were also studied. Some common problems related to the fractal dimension and multifractal spectrum are also discussed.

Bayesian assessment of favorability for oil and gas prospects over the Recôncavo basin, Brazil

This paper presents a Bayesian approach to evaluate remaining potential of oil and gas in the Reconcavo basin, Brazil. The purpose is to test a new Bayesian weighting methodology and quantify the favorability for the existence of new fields in the basin. The methodology implies organization of petroleum system data in descriptive models with which results from drilling are manipulated statistically, including analysis of geologic factors that are spatially correlated with both producing and dry areas. In the first stage of modeling, the essential elements (reservoir, seal, and overburden rocks) that control the fundamental processes of generation, expulsion, migration, and entrapment of petroleum accumulation are defined throughout integration of previously published data. The petroleum accumulation models of Reconcavo basin comprise generation from Neocomian shale rocks of the Gomo Member (Candeias Formation), vertical migration along extensional and transfer faults, and accumulation in tilted horsts with Upper Jurassic prerift reservoirs (Sergi Formation) or in Neocomian turbidite reservoirs in stratigraphic/combined traps (Candeias and Marfim formations). Probability distributions and weights are then calculated through Boolean operations among producing and dry areas and each diagnostic criterion evaluated through descriptive models such as source bed thickness, onset of organic maturation, presence or absence of faults and structural blocks, reservoir thickness, and seal distribution. The final stage of evaluation consists of spatial integration of raster maps that are weighted according to their necessity and sufficiency conditions, the results being presented as favorability maps. The characterization of favorable areas and their comparison with known fields suggest that such a Bayesian approach can contribute to the understanding of petroleum systems as a practical approach that considers the spatial nature of exploration variables.

Structural styles of the intracratonic reactivation of the Perimbó fault zone, Paraná basin, Brazil

Abstract The style and origin of intracratonic deformation along the Perimbo fault zone (PFZ) in the Parana basin, Santa Catarina State, southern Brazil, is defined by the integration of outcrop, borehole, aerial photography, and digital terrain modeling data. Typical structures are high-angle strike-slip and oblique-slip normal faults in the Permian sedimentary cover that propagate upward from medium-angle reverse faults in the underlying Precambrian basement. Regional and minor structures suggest blind transtensional faulting and tilting of the overlying strata controlled by the basement heritage. A hypothesis linking deformation between the cover and the basement is proposed on the basis of a structural analysis of a branched fault pattern striking N40–50E and N70–80E. Semi-detailed scale mapping shows that the PFZ has a complex history of polyphase reactivation and is characterized as a plate margin fault in the Proterozoic, evolving to an intracratonic fault in the Phanerozoic, with a main period of reactivation in Permian or Permian–Triassic transition times. The reported data imply that fault reactivation is characterized by normal to left-lateral strike-slip faulting produced by strain propagation from the La Ventana orogenic belt toward the continental interior.

Late Paleozoic glacially related sandstone reservoirs in the Paraná Basin, Brazil

Upper Paleozoic glacially related sandstones of the Itarar Group constitute thick and complex hydrocarbon reservoirs in the intracratonic Paran Basin of southern Brazil. Because these sandstones were deposited in both glacial and nonglacial environments, they show a high degree of variability in facies. In this article, we analyze outcrop and shallow well data to describe facies heterogeneities and their reservoir-quality implications. A regional subsurface sequence-stratigraphic framework was built, based on both strike- and dip-oriented well-to-well correlations. A well-exposed sandstone succession correlative with the main reservoir interval in the subsurface was selected in the eastern part of the basin. The Vila Velha sandstone comprises an up to 100-m (328-ft)-thick, unconformity-bounded, sand-rich succession composed of four stacked facies assemblages. Vertical facies succession shows a transition from glacial and glaciomarine to periglacial shallow-marine and nearshore settings, which define a retrogradational-progradational succession. Channel-mouth bars and wave-modified shoreline sandstones in the progradational section contain stratigraphically predictable reservoir-quality lithofacies. In subsurface, gas-bearing sandstone intervals with the same well-log response occur below unconformities, which control the overall reservoir geometry.

Bayesian and multivariate methods applied to favorability quantification in recôncavo Basin and Ribeira Belt, Brazil

A methology to define favorable areas in petroleum and mineral exploration is applied, which consists in weighting the exploratory variables, in order to characterize their importance as exploration guides. The exploration data are spatially integrated in the selected area to establish the association between variables and deposits, and the relationships among distribution, topology, and indicator pattern of all variables. Two methods of statistical analysis were compared. The first one is the Weights of Evidence Modeling, a conditional probability approach (Agterberg, 1989a), and the second one is the Principal Components Analysis (Pan, 1993). In the conditional method, the favorability estimation is based on the probability of deposit and variable joint occurrence, with the weights being defined as natural logarithms of likelihood ratios. In the multivariate analysis, the cells which contain deposits are selected as control cells and the weights are determined by eigendecomposition, being represented by the coefficients of the eigenvector related to the system’s largest eigenvalue. The two techniques of weighting and complementary procedures were tested on two case studies: 1. Recôncavo Basin, Northeast Brazil (for Petroleum) and 2. Itaiacoca Formation of Ribeira Belt, Southeast Brazil (for Pb-Zn Mississippi Valley Type deposits). The applied methdology proved to be easy to use and of great assistance to predict the favorability in large areas, particularly in the initial phase of exploration programs.

Correlação gamaespectrométrica de afloramentos e poços: estudo de caso na Formação Ponta Grossa (Bacia do Paraná, Brasil)

In analogue modeling, ground gamma-ray spectrometric data of the Devonian Jaguariaiva, Tibagi, and Sao Domingos members of the Ponta Grossa Formation (Parana Basin) allowed for a better understanding of the spatial distribution of lithotypes. Correlations based on gamma-ray values obtained from deep well logging could be improved. Ground values, spaced 50 cm in sandstones and 100 cm in shales, were taken along four sections: Arapoti, Tibagi, Jaguariaiva, and Ponta Grossa. The sections were 30, 250, 12, and 16 meters thickness, respectively. The results show that both ground and deep values reflect the gradual clay enrichment trend noticed along the Arapoti section (transition beds between Furnas and Ponta Grossa formations). Along the Tibagi section (Jaguariaiva Member), total organic carbon values are in direct relation to ground and deep gamma-ray values, and good gamma-ray spectrometric and granulometric correspondence is observed between both deep and ground data along 250 meters of Ponta Grossa Formation outcrops. Along the Jaguariaiva section, clear decrease of intensity is observed in sandy layers, with abruptly lower values at the contacts with basal sandstones of the Itarare Group. Along the Ponta Grossa section, the Tibagi Member, with its notably higher sand-fraction content, shows a gamma-ray signature compatible with the coarsening upward observed in well data. The Sao Domingos Member, a massive clayey interval of the Ponta Grossa Formation, is characterized by high gamma-ray values in both investigation levels. Ground gamma-ray spectrometry combined with detailed outcropdescriptions and deep source data proved to be useful in the establishment of analogue models for the Ponta Grossa Formation in the Parana Basin.

GeoGrid3D: a program to insert faults in 3D geological model for fluid simulation

This Paper show an application of geological and geophysical data integration into a flow simulation 3D model. A free program was used to do this flow simulation (Boast from United State Department of Energy). But to use this free simulator, a new program was build (GeoGrid3D). This program came with a special feature that can insert faults into the 3D model and also have other functions to get specific data codifications for Boast recognition. Outcrops from Permian sedimentary rocks and shallow seismic are used as data for this reservoir framework 3D model. Petrophysical properties were distributed using rules from interpretation of correlation done with facies and stratigraphic analysis of the outcrops. The main petrophysical model was built, and to test GeoGrid3D functions, other tree tectonic situations of faults comportament are also generated. The gas saturation, after flow simulation, confirms that changing faults permeabilities inside the reservoir will change gas production in rocks like this model.

Propriedades fractais de arenitos fraturados do Canyon Guartelá

The statistical and geometrical properties of fracture systems were obtained by analyzing remote sense images and outcrop data, in the Region of Guartela Canyon, in the central-eastern of Parana State. The probability distributions of fractures, with their parameters and attributes, were obtained through extensive statistical exploration of data. These parameters were used as input data for generating 3-D stochastic fractures models through the “discrete fracture network - DFN” method. The modeling is performed by using the code FRED®. To study the persistence of statistical parameters in multiple scales were used remote sensing images (SRTM, Landsat TM7 and aerial photos), covering a scale range from outcrops (few meters) to basin scales (hundreds of kilometers). The results indicated the presence of power-law (fractal) statistics for the spatial and size distributions. Fractals distributions were found for all sets studied, in some cases with different fractal exponents. The implications of fractal behavior for the generation of discrete fracture network, and consequently for the hydraulic properties, are briefly discussed.

ESTUDO DA RELAÇÃO ENTRE LINEAMENTOS ESTRUTURAIS E A EXPLORAÇÃO DE ÁGUA SUBTERRÂNEA POR MEIO DA ANÁLISE DE FAVORABILIDADE

Favorability analysis has been applied as a method to evaluate the correlation between the structural lineament and flow behavior in aquifers. The analysis was carried out in the outcropping areas of Tubarao Group, between the cities of Campinas and Sorocaba (Sao Paulo State, Brazil). The study area was chosen because of its geological complexity and the consequent lower predictability of well performance before drilling. To apply this method, we considered as “mineralized” areas those regions with highest specific capacity values, taking also into account six types of variables interpreted from radar images Landsat 7-ETM, Shuttle Radar Topography Mission (SRTM) and structural geological maps. The results reveal that the region encompassing between the cities of Elias Fausto and Monte Mor presents the best correlation with structural lineation which can be a factor in the high potential for groundwater exploration in this area.