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1

Multiscale evaluation of a thin-bed reservoir

Lis-Śledziona Anita

Geology, Geophysics and Environment

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2021

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Vol. 47, no. 1

5--20

EN

A thin-bed laminated shaly-sand reservoir of the Miocene formation was evaluated using two methods: high resolution microresistivity data from the XRMI tool and conventional well logs. Based on high resolution data, the Earth model of the reservoir was defined in a way that allowed the analyzed interval to be subdivided into thin layers of sandstones, mudstones, and claystones. Theoretical logs of gamma ray, bulk density, horizontal and vertical resistivity were calculated based on the forward modeling method to describe the petrophysical properties of individual beds and calculate the clay volume, porosity, and water saturation. The relationships amongst the contents of minerals were established based on the XRD data from the neighboring wells; hence, the high-resolution lithological model was evaluated. Predicted curves and estimated volumes of minerals were used as an input in multimineral solver and based on the assumed petrophysical model the input data were recalculated, reconstructed and compared with the predicted curves. The volumes of minerals and input curves were adjusted during several runs to minimalize the error between predicted and recalculated variables. Another approach was based on electrofacies modeling using unsupervised self-organizing maps. As an input, conventional well logs were used. Then, the evaluated facies model was used during forward modeling of the effective porosity, horizontal resistivity and water saturation. The obtained results were compared and, finally, the effective thickness of the reservoir was established based on the results from the two methods.

2

Evaluating Electrical Anisotropy Parameters in Miocene Formations in the Cierpisz Deposit

Bała M., Cichy A.

Acta Geophysica

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2015

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Vol. 63, no. 5

1296--1315

EN

The electrical anisotropy of rocks is generally an effect of alternating layers of thin-bedded sandstones and shales with clear lamination. Thin-bedded rock sequences can be treated as an anisotropic medium described by two resistivities: horizontally to the bedding RH and vertically to the bedding RV. Such sequences have fairly low resistivity and, as a result of poor vertical resolution of conventional electric tools, one can sometimes fail to distinguish them from the adjoining shales. This paper presents the possibility of calculating the anisotropy parameters based on resistivity logs recorded with a laterolog tool (DLL) and an induction tool HRAI. We have also performed an analysis of the ambiguity of the results and attempts to assess the water saturation (SW) generating cross-plots based on calculated resistivities, RH and RV. It is very important to correctly evaluate the resistivity of sandstone interbeds when calculating water saturation (SW) and hydrocarbon saturation (SG), in formulating an integrated quantitative interpretation of anisotropic formations.

3

Czy anizotropia elektryczna może być wywołana zmianami nasycenia wodą i gazem w mikro- i makroporach skał miocenu?

Bała M.

Przegląd Geologiczny

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2013

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Vol. 61, nr 9

523--531

EN

The paper presents the problem of evaluation of variation in the electrical anisotropy coefficient for sandstone-shaly Miocene deposits depending on water and gas saturation of the pore space. A rock model built of alternating layers with varying micro- and macroporosity is discussed. This may correspond to a rock formation composed ofparallel thin layers of sandstones or mudstones and claystones, which are dominated by macro- and micropores, and are characterized by different grain size or grain sorting. The anisotropy coefficient is then affected by changes in electrical resistivity in individual layers that are a result of changes in saturation.

4

Evaluation of electric parameters of anisotropic sandy-shaly Miocene formations on the basis of resistivity logs

Bała M.

Acta Geophysica

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2011

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Vol. 59, no. 5

954-966

EN

In this paper, electrical properties of an anisotropic rock formation are discussed. Electrical anisotropy parameters, i.e., horizontal resistivity, R H , and vertical resistivity, R V , and anisotropy coefficient in the sandyshaly Miocene formation, are determined on the basis of induction logs and laterologs. Graphs of R V = f(R H) calculated for different resistivities of sandstones and shales and variable volumes of those two components allow us to conclude about the correctness of the applied method for determining the resistivity parameters of autochthonous Miocene formations.