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Pore-type identifcation of a heterogeneous carbonate reservoir using rock physics principles: a case study from south-west Iran

Emami Niri Mohammad, Mehmandoost Fariba, Nosrati Hossein

Acta Geophysica

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2021

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Vol. 69, no. 4

1241--1256

EN

The characterization of carbonate rocks is a challenging process compared to siliciclastics because of their more intricate pore-space structure. In this study, we applied rock physics methods to a heterogeneous carbonate reservoir located in southwest Iran to identify zones of various pore types, including inter-particle pores, stif (vuggy and moldic) pores, and cracks, from geophysical measurements. We frst constructed two rock physics templates (RPTs) using well logs and used them to quantitatively analyze the efect of various pore types on elastic properties. Using these RPTs, we then implemented an inversion algorithm to estimate the volume fractions of various pores using total porosity and P-wave velocity (Vp) derived from well logs. Next, we have compared the pore-type inversion results and the image log interpretation/core images at the corresponding depth intervals to validate inversion results. This comparison showed that the inversion results are consistent with the measurements. Also, we applied the introduced pore-type inversion algorithm on seismic data to achieve insight into pore-type distribution in the 3D framework of the reservoir under study. The results of these rock physics-based analyses indicate that the inter-particle pores are dominant in the pore-space, while there are stif pores and dispersal cracks in some subzones of the studied depth interval. Additionally, employing the Xu and Payne rock physics modeling procedure, P- and S-wave velocities were estimated using pore-type inversion results at the location of several wells from the studied feld. The calculated mean absolute error and the correlation coefcient indicate a high consistency between the measured and modeled velocities. This research may contribute to permeability prediction and analysis of the diagenetic processes’ impact on reservoir properties.

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Rock physics modelling for determination of effective elastic properties of the lower Paleozoic shale formation, North Poland

Wawrzyniak-Guz Kamila

Acta Geophysica

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2019

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Vol. 67, no. 6

1967--1989

EN

This paper presents an application of rock physics templates constructed with the use of the granular effective medium theory and the shale model to estimate the elastic properties of the Silurian and Ordovician shale formations from the Baltic Basic, Poland. The author uses available logging data from three nearby wells and their petrophysical interpretation to distinguish various lithologies and to determine average matrix mineral composition of each lithology group, essential in further rock physics modelling. Anisotropy estimation and investigation of the relation between various petrophysical parameters precede the rock physics modelling. The logging data cross-plotted in Vp/Vs/ ratio–acoustic impedance domain reveals distinct compaction trend for shales, which is not followed by shales with increased organic matter and calcareous deposits. These two lithology groups present own trends, which are related to increasing kerogen and carbonate minerals contents, respectively. The trends are the subject of rock physics modelling. Granular effective medium rock physics templates are constructed for each lithology group. The rock physics analyses reveal that the elastic properties of strongly compacted shales, including shales with organic matter, might be successfully described by the lower modified Hashin–Shtrikman bound, which is useful in compaction trend modelling. Marly deposits can be modelled in a similar way to shales. The upper modified Hashin– Shtrikman bound provides a better template for carbonates as it models the cementation process. The shale model provides independent rock physics template for shales. Comparison of these two approaches shows that the granular effective medium method better describes the elastic properties of the analysed formations. The paper includes also the proposition of the final rock physics template constructed for the Silurian and the Ordovician formation from the Baltic Basin that can contribute to a better understanding of the elastic properties of the lower Paleozoic shale plays in Poland.

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Well-log based rock physics template of the Vienna Basin and the underlying Calcereous Alps

Tucovic N., Gegenhuber N.

Acta Geophysica

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2017

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Vol. 65, no. 3

441--451

EN

In this study, the ratio of compressional and shear wave velocity versus acoustic impedance as rock physics template for northern part of the Vienna Basin has been derived for siliciclastic rocks based on formation evaluation of well-log data. The results have been verified through wells in different areas drilled in various depths. Additionally, depositional sequences like prograding deltas and braided rivers have been plotted onto the rock physics template to illustrate the effect of changing shale volume. Carbonates below the basin have been included into the study and results from previous projects, based on laboratory data and petrophysical models on certain lithologies in the Vienna Basin, have been used to compare the outcome. The result is a rock physics template which includes important properties such as porosity, true vertical depth and fluid type from log data and which is considered useable throughout different areas and various lithologies of the Vienna Basin.