Dissertações em Geofísica (Mestrado) - CPGF/IG
URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/4993
O Mestrado Acadêmico pertente a o Programa de Pós-Graduação em Geofísica (CPGF) do Instituto de Geociências (IG) da Universidade Federal do Pará (UFPA).
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Navegando Dissertações em Geofísica (Mestrado) - CPGF/IG por Orientadores "HOWARD JUNIOR, Allen Quentin"
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Item Acesso aberto (Open Access) Detecção do contato entre camadas através do perfil de indução(Universidade Federal do Pará, 1996-08-21) MARQUES JÚNIOR, José; HOWARD JUNIOR, Allen Quentin; http://lattes.cnpq.br/6447166738854045Two of the main objectives in petrophysical log interpretation are to determine geologic bed boundaries and fluid contacts. For these, the induction log has several important properties: it is sensitive to fluid type and distribution in the pore space, the induction measurement is accurately modeled as a convolution of formation conductivity and the tool response function. The first property assures good discrimination of the reserves and at the same time delineates oil-water contacts. This information permits a fundamental zoning of the well log. The second property follows from the quasi-linear relationship between the induction log and formation conductivity. Thus it is possible to use linear system theory, and in particular digital filter design to adaptively deconvolve the original signal. The idea in this work is to produce an algorithm capable of identifying contacts between beds traversed by a borehole, given the apparent conductivity read by an induction tool. To simplify the problem, the formation model is assumed to be a distribution of plane-parallel homogeneous beds. This model corresponds to a rectangular formation conductivity profile. Using the digitized input log, inflexion points are obtained numerically as extrema of first derivatives. This generates a first approximation of the real formation profile. This estimated profile is then convolved with the tool response function giving an estimated apparent conductivity log. A conditioned least-mean-square cost function is defined in terms of the difference between measured and estimated apparent conductivity. Minimizing the cost function yields the bed conductivities. The optimization problem of finding the best rectangular profile for induction data is linear for amplitudes (bed conductivities), but non-linear estimation for bed boundaries. In this case amplitudes are estimated by linear least-squares maintaining fixed contacts. A second pass maintains fixed amplitudes and computes small changes in bed boundaries using a linearized approximation. This processes is iterated to obtain successive refinement until a convergence criteria is satisfied. The algorithm is applied on synthetic and real data showing the robustness of the method.Item Acesso aberto (Open Access) Estimativas da condutividade térmica dos minerais e rochas e influência de parâmetros térmicos e petrofísicos na resistividade aparente da formação(Universidade Federal do Pará, 1995-08-09) COZZOLINO, Klaus; HOWARD JUNIOR, Allen Quentin; http://lattes.cnpq.br/6447166738854045The present study carries out estimates of thermal conductivity in the principal rock-forming minerals, as well as estimates of the average conductivity of the solid phase of five common lithologies (sandstones, dolomites, limestones, anhydrites, clay lithologies). Several thermal models were compared, permitting the verification of one as the most appropriate to represent the aggregate of minerals and fluids of which rocks are composed. The results of this study can be applied to a wide variety of thermal models. The chosen methodology is based on a non-linear regression algorithm denominated Random Search. The algorithm's behaviour is evaluated with sinthetic data before being applied to real data. The geometric mean model is used in the regression to obtain the values of thermal conductivity in these rock-forming minerals. The regression method used in each lithological sub-group gave the following values for average thermal conductivity in the solid phase: sandstones 5.9 ± 1.33 W/mK, limestones 3.1 ± 0.12 W/mK, dolomites 4.7 ± 0.56 W/mK anhydrites 6.3 ± 0.27 W/mK and for argillceous lithologies 3.4 ± 0.48 W/mK. In the sequence the fundaments for the study of heat diffusion are presented in cylindrical coordinates. The effects of invasion of mud filtrate into the formation are considered using an adaption of simulation of well injection techniques originating in theories developed in reservoir engineering. Assuming the original temperature of the formation as a reference, the relative errors in apparent resistivity can be estimated. In this phase of the work the finite differences method is used to measure distribution of the well-formation temperature. Simulation of the invasion is carried out in cylindrical coordenates via an adaptation of the Buckley-Leverett equation into carthesian coordenates. Effects such as the appearance of mudcakes in the borehole, gravity and capilliary pressure are not taken into consideration. The radial distribution of resistivity is obtained via the distribution of saturation and temperature, and is convolved with the radial geometrical factor of the induction tool (transmissor-receiver), resulting in the apparent resistivity of the formation. Admitting as reference the original temperature of the formation, the relative errors in apparent resistivity are obtained at each time. Through variation of certain parameters, it becomes clear that the porosity and original saturation of the formation can be responsible for serious errors in the measurement of resistivity, especially if such readings are taken immediately after drilling (MWD). The difference in temperature between well and formation is the principal cause of such errors. In situations where this difference is large, therefore, profiles with- induction tools should only be carried out between 24 and 48 hours after the well has been drilled.