BazTech - Yadda

1

Second-order approximate refection coefficients of vertical transversely isotropic thin beds

Huang Peidong, Lu Jun, Wang Yun

Acta Geophysica

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2022

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Vol. 70, no 3

1155--1169

EN

Due to the periodicity and rhythmicity of sedimentation, short-term cycles are commonly developed in sedimentary strata. Under the assumption of a long seismic wavelength, such strata can be regarded as a seismic single thin bed with vertical transversely isotropic (VTI) characteristics. A thin interbed can be formed by the stacking of a series of isotropic and VTI single thin beds. In seismic inversion, the interference of multiples and mode-converted waves generated within and between thin beds and transmission losses are ignored. These interferences are hardly addressed in seismic data processing due to being submerged in first arrivals. In this work, to thin interbeds of isotropic and VTI single thin beds, we propose second order approximations of Kennett refection coefficients for PP-, SP-, PS-, and SS-waves, which consider the internal and interlayer wave propagation effects. The numerical analyses show that the proposed approximations are of high accuracy when the P-wave impedance difference in the VTI single thin bed is from−40 to 100% and of strong anisotropy. The proposed approximations can be used for the efficient and accurate simulation of the wavefields of media with thin interbedding, bringing great potential for the studies of the inversion methods for the internal property parameters of thin interbeds.

2

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.

3

Verification of bright spots in the presence of thin beds by AVO and spectral analysis in Miocene sediments of Carpathian Foredeep

Cichostępski K., Kwietniak A., Dec J.

Acta Geophysica

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2019

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Vol. 67, no. 6

1731--1745

EN

Twin structural traps that lie within the Miocene strata of the Carpathian Foredeep that are localized above Cierpisz and Mrowla-Bratkowice highs exhibit identical bright-spot seismic anomalies, but only those associated with the Cierpisz high are profitable gas reservoirs. Bright spots can be a result of weak gas or water saturation, but also seismic interference known as tuning effect. For these reasons, it is crucial to differentiate between seismic anomalies. In this article, we present the possibilities of verification of seismic anomalies that occur within the siliciclastic Miocene sediments of the Carpathian Foredeep with the application of AVO analysis and spectral decomposition. AVO methodology enabled to limit the number of anomalies that are present in the post-stack seismic data. These anomalies, however, may also be a result of tuning which is common for the heterolithic sequences in the Miocene sediments of the Carpathian Foredeep. For classification of anomalies in the view of the above, spectral decomposition based on the Basis Pursuit algorithm was applied. Spectral decomposition enabled to divide AVO anomalies in those that are the result of gas saturation and the tuning effect. Gas-saturated zones are characterized by higher spectral amplitudes of the lower frequency range, whereas tuning effect yields higher spectral amplitudes for the higher frequency content. This relation is visible for the data set and enables qualitative differentiation for the set of seismic anomalies.

4

An iterative inversion of Dual Induction Tool logs from thin-bedded Sandy-shaly formations of the Carpathian Foredeep using a modified simulated annealing method

Wilkosz Michał, Wawrzyniak-Guz Kamila

Acta Geophysica

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2019

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Vol. 67, no. 6

1865--1873

EN

In thin-bedded sandy–shaly Miocene formations of the Carpathian Foredeep, the main source of errors in gas saturation evaluation is the underestimation of resistivity of thin, hydrocarbon-bearing beds, which is the result of the low vertical resolution of induction logging tools. This problem is especially visible in older boreholes drilled in times where the Dual Induction Tool (DIT) was the primary induction tool used for determining the formation resistivity, and in shallowest depth intervals of newer boreholes where the DIT was used instead of newer array tools for cost-saving reasons. In this paper, we show how a global inversion algorithm was used to improve the vertical resolution of DIT logs. Our implementation of an iterative inversion utilizes a one-dimensional formation model, vertical response functions of the DIT, and a modified simulated annealing algorithm to determine the true vertical distribution of the formation resistivity. The algorithm was tested on resistivity logs recorded in a borehole drilled in the Carpathian Foredeep in Poland, where the DIT and the High-Resolution Array Induction (HRAI) tool were run in the same depth interval.

5

Inwersja spektralna oraz dekompozycja spektralna w interpolacji cienkich warstw

Żuławiński K.

Prace Naukowe Instytutu Nafty i Gazu

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2012

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nr 182 wyd. konferencyjne

269--275

PL

Inwersję spektralną i dekompozycję spektralną łączy algorytm oparty na transformacji falkowej o zmiennej długości okna. Interpretacja sejsmiczna, wykorzystująca detekcję i śledzenie cienkich warstw oraz ich wyklinowań, zyskuje narzędzie obiektywnej oceny wyboru możliwych z punktu widzenia interpretatora wersji. Pokazane zostanie zastosowanie obu metod na przykładach modelowych i rzeczywistych.

EN

Both spectral inversion and spectral decomposition are joined by the algorithm of wavelet transform with variable size window. Seismic interpretation with use of detection and tracking of thin-beds and its edges gains universal tool for objective choice among various possible versions. The application of spectral inversion and decomposition for seismic models and real data will be shown.

6

Detekcja i rozdzielczość czasowa, a zdolność rozdzielcza waveletu sejsmicznego w cienkich warstwach

Żuławiński K.

Nafta-Gaz

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2010

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R. 66, nr 11

987-992

PL

W artykule omowiono zdolność rozdzielczą waveletu sejsmicznego w różnych aspektach. Sformułowano kryteria rozdzielczości waveletu sejsmicznego dla zgodnie i przeciwnie spolaryzowanych dubletów. Przedstawiono wpływ wyboru częstotliwości na rozdzielczość dubletów w cienkich warstwach.

EN

In this paper wavelet resolving power is discussed from various aspects. The criteria of wavelet resolution are formulated in regard to equal and opposite polarity doublets. The impact of frequency selection on the wavelet resolving power of the doublets in thin-bed layers is put forward.