Navegando por Orientadores "EVANS, Hilton Bernard"

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Acesso aberto (Open Access)
Aplicação de tratamento estatístico multivariante em dados de perfis de poços da Bacia de Sergipe-Alagoas
(Universidade Federal do Pará, 1991-09-27) BUCHEB, José Alberto; EVANS, Hilton Bernard
A series of multivariate statistical techniques (cluster, principal component and discriminant analysis) was tested and applied to well log data from the Camorim field (offshore Sergipe State, Brazil) in order to identify facies previously defined through core description. The second step in the process of facies determination was supported by auxiliary methods (compositional and sequence facies analysis), which produced better results in the calibration of rock-log data, when combined with the multivariate techniques. The facies determination, once established, permits the refinement of the process of formation evaluation, enabling the examination of each facies separately. This procedure made it possible to choose, for each lithology, the parameters used in log interpretation. In parallel, this process allowed the summation of thickness, porosity, fluid saturation and the adoption of different cut-offs for each group, separately. Other applications included: enhancement in the estimation of porosity and permeability, the adaptation of algorithms designed for fast porosity estimation, the mapping of variables useful in the characterization of the vertical variability of the reservoir rocks and the automatic generation of stratigraphic sections. Finally, the possibility of integration of the work from this study with statistical systems of reservoir description, other facies determination techniques currently being developed and the utilization of multivariate statistical methods in well log data, as an auxiliary exploratory tool, were illustrated.
Acesso aberto (Open Access)
Aplicação do gravímetro de poço em problemas de avaliação de formação no Brasil
(Universidade Federal do Pará, 1992-02-27) GONÇALVES, Carlos Augusto; EVANS, Hilton Bernard
The first borehole gravity survey in Brazil was carried out during October and November of 1990 in Sergipe-Alagoas basin through a joint program between the Federal University of Pará, PETROBRAS and United States Geological Survey. The principal purpose of the survey was to test the applicability of this tool in Brazilian sedimentary basins. Another purpose was to compare the borehole gravimeter (BHGM) data with existing open-hole density log (CDL). The survey was conducted in three wells in Carmópolis field and the data were transformed to miligals, corrected for tide, drift and terrain effects and preliminary density values calculated. The region in which the surveys were carried out consists of an evaporite sequence overlying basement rock ocurring relatively near the surface. The large contrast between these units and the rest of sedimentary section results in vertical gravity anomalies. It is necessary to correct the BHGM density data for these anomalies. The resulting BHGM density data were then compared to that obtained from the CDL. Furthermore, lithology parameters defined from well log data were used to calculate porosities from both the BHGM and CDL density data, showing possible new oil intervals that can be tested.
Acesso aberto (Open Access)
Avaliação dos reservatórios do Campo de Ubarana-RN, com baixas resistividades
(Universidade Federal do Pará, 1990-10-12) RAMOS, Eduardo Moreira; EVANS, Hilton Bernard
A new model for quantitative evaluation of shaly sand is proposed based on bibliography and clay mineral distribution in the pores of reservoir rocks. This model takes in account for two extra conductivity types besides the normal electrolytic conductivity one present in porous rocks. One conductivity type is due to surface conductance of clay minerals, which increases or decreases as result of their capability of cationic exchange. The second conductivity type behaves independently as a parallel system due to the microporous network formed by the clay minerals lining or bridging the grains of a shaly rock. The new equation was tested against several other equations and showed the best correlation with the Waxman & Smits equation. Both equations, the proposed one and the Waxman & Smits, have a similar approach to the clay conduction system. The new model was used in three different zones of the Ubarana oilfield (Potiguar basin, Brazil) It was verified that: (1) in two low resistivity zones (there was the possibility of) oil production was possible because the resistivities were supposedly affected by highly conductive minerals; and (2) one effective oil tested and producing tone of highly resistivity. The water saturations calculated with the new equation for the two low resistivity zones were above 50%, suggesting subsaturation and a continous resistivity phase through the salt water (about 85,000 ppm of NaCl) present in the pores. The practical results shown herein suggest that the proposed equation is theoretically consistent and must be exhaustively used in future evaluation projects of the Ubarana and similar oilfields in Brazilian sedimentary basins.
Acesso aberto (Open Access)
Interpretação de perfis dos carbonatos fraturados da Bacia do Pará-Maranhão
(Universidade Federal do Pará, 1991-09-27) LARANJEIRA, Alberto Antônio dos Santos; EVANS, Hilton Bernard
The purpose of this study is to present an evaluation of the Tertiary carbonate sequence in the Pará-Maranhão basin, based on the interpretation of well logs. Two wells, X and Y, were selected to be studied. The data processing was carried out using the LOGCALC software facilities installed on the Petrobrás IBM-3090 computer, and also the DLPS routines of the VAX-8600 at the Universidade Federal do Pará. Three distinct carbonate rock types were identified. The discrimination of these lithotypes allows a close control of the matrix parameters, and better volumetric estimates (porosities and saturations). The evaluation of porosities and saturations is difficult in this area because of the characteristics of the carbonate rocks: the lithology is complex, the water salinity is low, about 10,000 ppm equivalent NaCl, the matrix density is high, and the carbonates are fractured. The fractures strongly influence the logging tool responses, including the fracture identification log, the porosity logs, the resistivity logs, and the spectral gamma logs of 1-PAS-11 well. These fractures also cause the porosity exponent, m, to be low, less than 1.5, a value generally related to fractured rocks. Models developed by Rasmus (1983) and by Porter et al.(1969) were tested for the saturation estimates. The Archie relationship, with characteristic values for a and m, was also applied in this study. In the fractured zones, the variable porosity exponent gives better results than other models, for calculating water saturations. Thus, we can locate and evaluate the fracture zones by using the Archie relationship with the variable porosity exponent, mR, from the Rasmus model, referred to in this study as Rasmus saturation.
Acesso aberto (Open Access)
Melhoramento da resolução para camadas delgadas de perfilagens existentes em áreas específicas de produção-exploração
(Universidade Federal do Pará, 1990-11-28) AIZMAN, Luiz; EVANS, Hilton Bernard
In well Iogging, there is a great interest in techniques that enhance the vertical resolution of the tool responses. In this work we develop a technique that enhances the vertical resolution of the logs obtained with the induction logging tool named in the bibliography 6FF40, by means of an algorithm that makes use of estimative methods through the least square technique. This method makes possible the processing of a set of recorded data in a computationaly efficient way. This algorithm requires only the values assumed as tool coeficients and an estimative for the noise present in the recorded data. As an ilustration we used intervals of a log run in an area where the 6FF40 tool is known to have poor vertical resolution. In order to verify the efficiency of the used algorithm, the processed logs were correlated with the gamma-ray and with the spherically focused log of the well 7-LOR-18-RN, which have a better vertical resolution, confirming the enhanced resolution in thin layers that could not be easily recognized on the previously log. The algorithm was also tested with synthetic data demonstrating its efficiency in calculating more representative values for Rt.
Acesso aberto (Open Access)
Simulação de perfis nucleares de poço em formações complexas
(Universidade Federal do Pará, 1993-04-26) SILVA, Jadir da Conceição da; EVANS, Hilton Bernard
The identification and description of lithological parameters of a formation are essential in the evaluation of complex formations. Based on this, the combination of the nuclear tool response in uncased wells has been used systematically. The resultant logs can be considered as the interaction between two distinct phases: • The radiation transport phase from a source to one or more detectors through the formation. • The detection phase that consists of the collection of radiation, its transformation into current pulses, and the spectral distribuition of these pulses. As the presence of the detector does not strongly affect the radiation transport result, each phase can be simulated independent of the other, which allows us to introduce a new type of model in which the transport phase and the detection phase are uncoupled. In this work, the final response is simulated combining transport numerical solutions with a library of the detector responses to different incident energies and for each specific source - detector array. The radiation is calculated by the Finite Elements Method (FEM), as a 2½-D scalar flux derived from the numerical solution of the multigroup diffusion approximation of the Boltzmann transport equation in phase space. This is known as P1 approximation, where the variable direction is expanded in terms of the Legendre orthogonal polymonials, leading to the dimensionality reduction of the problem in such a way as to let it be more consistent with the FEM, where the flux depends only on the spatial variable and the physical properties of the formation. The NaI(Tl) response function is obtained separately by the Monte Carlo method (MC) where the life of a particle within the scintillator crystal is reconstructed simulating interaction by interaction the position, direction and energy of the different particles using a random number technique with associated appropriate probabilities laws. Each type of interaction (e.g., Rayleigh, Photo-electric, Compton and Pair production) is determined similarly and the simulation is concluded when the detector response functions are convolved with the scalar flux. The final response is the pulse-height spectrum of the simulated system. From this spectrum, a set of channels called detection windows are then selected. The count rates in each window show different dependencies on density and lithology. This fact allows one to use a combination of these windows in determining the density and photoelectric absorption factor of the formation. According to the method developed in this work, the logs in both thin and thick layers can be simulated. The performance of the method has been tested in complex formations, mainly where the presence of clay minerals, feldspars and micas have produced considerable effects sufficient to perturb the final response of the sonde. The results show that it is possible to identify physical and lithological parameters in formations having densities between 1.8 and 4.0 g/cm3 and photoelectric absorption factors in the interval of 1.5 to 5.0 barns/e-. The concentrations of Potassium, Uranium and Thorium can be obtained through the introduction of a new system of calibration which corrects the effects due to high variances and negative correlations observed on the mass concentration of Uranium and Potassium. In the simulation of the CNL response using the Tittle polynomial regression algorithm, it is verified that due to the limited vertical resolution of this sonde, the porosity value is poorly measured for most layers of thickness less than the source - far detector spacing, thus it has application only in thick layers. A new method was developed to solve this problem; the contribution of the relative area of each layer within the maximum information zone is determined. Thus, this neutron porosity makes possible an in-depth evaluation of expected CNL porosity-lithology response, convolving that area factor with the local formation porosity index, considering only thick layers. The presence of perturbating minerals is solved by considering the formation as formed by a predominant base matrix mineral, totally saturated by fresh water; the rest of the components are then considered as a perturbation of this base case. These results enable the calculation of synthetic well logs that can be used in inversion schemes in order to get a more detailed quantitative evaluation of complex formations.