-The main objective of this study is to find a relationship between permeability and porosity, in the range 0 up to 50%, so that the permeability could be estimated only through geophysical parameters. This relationship should be consistent with the statistically expected values in sedimentary basins, and it should include the positive correlation between permeability and porosity in consolidated media and the negative correlation in unconsolidated ones. We have also developed another relationship between formation factor and permeability, considering that the values of porosity and pore fluid resistivity are known from other sources different from resistivity logs. -The method for determining these relationships has been to generate functions with the expected geometry and to fit them to empirical data drawn from published papers. As a result we obtained a new relationship between porosity and permeability, with cementation exponent as added variable, and a new relationship for indirect estimation of permeability from the formation factor. Given the formation factor dependence with clay content, we have also developed a theoretical relationship to calculate the formation factor in a clayey media, assuming that clay content is known from other logs. In this relationship, we have not taken into account the presence of non-conductive liquid phases, such as oil.Comparison of the results obtained from these expressions with data collected in the literature leads to conclude that it is possible to determine the permeability of each layer in any zone from resistivity logs, if both the clay content and the resistivity of the interstitial fluid are known.Résumé -Estimation géophysique de la perméabilité dans les milieux sédimentaires avec des porosités comprises entre 0 et 50 % -L'objectif principal de cette étude est de trouver une relation entre la perméabilité et la porosité dans la gamme de 0 à 50 %, de sorte que la perméabilité puisse être estimée seulement par des paramètres géophysiques. Cette relation doit être statistiquement compatible avec les valeurs attendues dans les bassins sédimentaires, et inclure la corrélation positive entre la perméabilité et la porosité dans les milieux consolidés et la corrélation négative dans ceux non consolidés. Nous avons également développé une autre relation entre le facteur de formation et la perméabilité, étant donné que les valeurs de la porosité et de la résistivité du fluide des pores sont connues de diverses sources autres que les diagraphies de résistivité. La méthode de détermination de ces relations a été générée en fonction de la géométrie attendue, et ajustée aux données empiriques des documents publiés. En conséquence, nous avons obtenu une nouvelle relation entre la porosité et la perméabilité, en utilisant l'exposant de cimentation comme une variable supplémentaire, et un nouveau rapport à l'estimation indirecte de la perméabilité à partir du facteur de formation. Compte tenu de la dépendance du facteur de formation avec la teneur en argile, nous avons ...
A procedure to automatically correlate well logs measured in boreholes that are located in continental siliciclastic basins by using two different methods is shown. The first method is applied to the parametric layers that were determined in each borehole starting from the values of their geophysical parameters and consists of correlating, by cross-association, the columns formed by these layers. The second method consists of cross-correlating the geophysical stretches or units, which are established as sets of layers with similar characteristics that are sufficiently different from the average values in the adjacent stretches. The evaluation of the correlation results requires showing the criteria that are used for determining the parametric layers that are obtained from the well logs, the result of which is called segmentation in this study. This evaluation also requires to show the techniques that are used to determine the geophysical stretches by a process that is called stretching in this study. The reason for using different correlation methods is that cross-association of layers provides high resolution but relatively smaller spatial extent, whereas cross-correlations of geophysical stretches provide higher spatial extent but lower resolution. Thus, the cross-association results have been used both to assess the correlations in boreholes that are relatively close (distances<10 km) and to support the establishment of the stretch correlation criteria. The developed methodology is applied to a set of boreholes located in the Duero Basin (Spain). From the results obtained, an evaluation of the correlations with respect to the distances between boreholes was carried out. Furthermore, it is shown that the correlations between geophysical stretches enable identifying the correspondences between these and the tectono-sedimentary sequences (activation-relaxation of a tectonic phase) that are established in the literature.
Abstract. This paper reports on the methodology developed for a new hydraulic interpretation of flowmeter logs, allowing a better characterization of continental hydrological basins. In the course of a flowmeter log, different flow stretches are established, mostly corresponding to permeable layers (aquifers), among which there are other stretches mainly corresponding to less permeable layers (aquitards). In such hydrological basins of sufficient thickness, these flow stretches may not have the same hydraulic head. This fact brings about the need for a new hydraulic interpretation that provides the actual distribution of horizontal permeability throughout the aquifer at depth. The modified hydraulic interpretation developed in this study focuses on the differences of the effective pressure gradient (considered the difference between the hydraulic head in the well and the hydraulic head of each stretch) experienced by the different flow stretches along the well, due to the existence of different hydraulic heads. The methodology has been developed starting from a water well located in a multilayered aquifer within the so-called Madrid basin (the north-western part of the continental basin of the Tagus River), located in the centre of the Iberian Peninsula. In this well, a step-drawdown pumping test was conducted, in which the pumping rate versus drawdown and the specific capacity versus drawdown showed discrepancies with Darcian behaviour and an exponent of the Jacob equation of less than 1. Flowmeter logs were then recorded for different discharge rates and pump depths; the resulting water input from deeper permeable layers did not appear to show the expected relation with respect to drawdown. With the proposed methodology the results comply with the expected linearity and the cited discrepancies are solved.
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