Compressional and shear wave attenuations from walkway VSP and sonic data in an offshore Abu Dhabi oilfield

Seismic attenuation was estimated from compressional (P) and shear (S) waves carefully extracted from three-component vertical seismic profiling (VSP) data. A high sensitivity of attenuation to fluid content was noticed, which shows the advantage of its use as a seismic attribute for reservoir studies. Contrary to most observations in fully saturated sandstones, the magnitude of P to S wave attenuation in the studied carbonate reservoir zones is higher than one. This disagreement is most probably because the fluid flow models developed to describe the attenuation mechanisms in sandstones are not valid for carbonate rocks due their complex texture. Moreover, the magnitude of seismic attenuation in the reservoir zones is controlled by the saturation of pore fluids and clay content. Furthermore, the attenuation magnitudes obtained at sonic and VSP frequencies are of the same order, and compressional and shear attenuations show similar variation at both frequencies. This indicates frequency-independent attenuations in the studied oilfield

Compressional and shear wave attenuations from walkway VSP and sonic data in an offshore Abu Dhabi oilfield

Seismic attenuation was estimated from compressional (P) and shear (S) waves carefully extracted from three-component vertical seismic profiling (VSP) data. A high sensitivity of attenuation to fluid content was noticed, which shows the advantage of its use as a seismic attribute for reservoir studies. Contrary to most observations in fully saturated sandstones, the magnitude of P to S wave attenuation in the studied carbonate reservoir zones is higher than one. This disagreement is most probably because the fluid flow models developed to describe the attenuation mechanisms in sandstones are not valid for carbonate rocks due their complex texture. Moreover, the magnitude of seismic attenuation in the reservoir zones is controlled by the saturation of pore fluids and clay content. Furthermore, the attenuation magnitudes obtained at sonic and VSP frequencies are of the same order, and compressional and shear attenuations show similar variation at both frequencies. This indicates frequency-independent attenuations in the studied oilfield

Investigation of fractured carbonate reservoirs by applying shear-wave splitting concept

In this study, fracture orientations in carbonate reservoirs were determined using a multicomponent velocity analysis based on shear wave splitting. The analysis is based on the estimated velocities of large seismic events with different polarizations. In a fractured zone with a dominant orientation, weak amplitude split shear events, including shear noise, result in shear waves that are polarized toward the symmetry and anisotropy axes and propagate with a common fast and slow velocity, respectively. Thus, a velocity stack should show high coherency anomalies in directions parallel and orthogonal to the fracture strike. Furthermore, because the analysis is applied locally at a specific depth range, it is less susceptible to the effects of overburden anisotropy and noise. The dominant fracture orientations from carbonate reservoirs of four oilfields were compared to those interpreted from fullbore microimager and core data. Fractures in two offshore reservoirs strike NNE-SSW and NW-SE, which are related to Zagros stress. Fractures in two onshore reservoir strikes NE-SW, while in deeper onshore reservoir fractures are aligned with N-S direction. The findings of this study are promising, particularly for the fractured reservoirs especially those located in Abu Dhabi, which are characterized by high heterogeneity and complex fracture network related to complex tectonic history. In order to obtain geometrical parameters of fractures at seismic scale, it is recommended to implement the analysis adapted in this study after acquiring three component zero-offset vertical seismic profiling.Cited as: Diaz-Acosta, A., Bouchaala, F., Kishida, T., Jouini, M. S., Ali, M. Y. Investigation of fractured carbonate reservoirs by applying shear-wave splitting concept. Advances in Geo-Energy Research, 2023, 7(2): 99-110. https://doi.org/10.46690/ager.2023.02.0

Modélisation de la propagation des ondes sismiques dans les milieux viscoélastiques (application à la détermination de l'atténuation des milieux sédimentaires)

La modélisation de la propagation des ondes dans les milieux complexes 3d, inhomogènes, isotropes et viscoélastiques (milieux I.I.V.), est un sujet intéressant et largement d actualité. cette modélisation aide pour la connaître la géométrie et les propriétés physiques des milieux géologiques. La viscosité du milieu de propagation est modélisée par la prise en compte de vitesses de propagation complexes. Le phénomène de propagation est modélisé par la théorie des rais avec la prise en compte de l hypothe se de faible viscosité (hypothèse non restrictive dans le domaine de la géophysique). Lles expressions analytiques des coefficients de réflexion transmission entre deux milieux viscoélastiques ont été établies avec une étude numérique de l effet de la faible viscosité sur ces coefficients a été menée. Le code anray est, a l origine, un code de simulation de la propagation des ondes dans les milieux inhomogènes 3d purement élastiques. son développement repose sur la théorie des rais. Le code anray a ensuite été modifie (anrayq), afin de l adapter a la simulation de la propagation des ondes dans les milieux I.I.V. les résultats numériques du code anrayq, ont été confrontés aux résultats numériques issus du code 5kb, code de simulation base sur la méthode de réflectivité. Enfin, des données sismiques 3d, acquises lors de la campagne hydratech (Ifremer 2002), dans une région caractérisée par la présence des hydrates de gaz et du gaz libre, ont été simulées a l aide du code anrayq. le profil de l atténuation viscoélastique a été aussi déterminé a partir de ces données sismiques, afin de localiser les hydrates de gaz et le gaz libre dans les couches sédimentaires.Seismic wave propagation modeling in 3d complex media, inhomogeneous, isotropic and viscous-elastic (I.I.V. media) is an interesting and wide topical subject. this modeling helps to know the geometry and physical proprieties of geological media. The viscosity of the propagation medium is modelled by taking complex propagation velocities into account. The propagation phenomenon is modeled by ray tracing theory with considering weakly viscosity hypothesis (is not restrictive hypothesis in the geophysical field). Analytical expression of reflection/transmission coefficients between two viscous-elastic media are done, with a numerical study of viscosity effect in these coefficients. The originally anray software, based on ray theory, is used for a wave propagation simulation in the inhomogeneous 3d and purely elastic media. The anray software is modified (anrayq), in order to use t in simulation of wave propagation in I.I.V. media. The numerical results of anrayq software are compared with those of skb software, based on reflectivity method. Finally, a 3d viscous-elastic data, acquired during hydratech cruise (Ifremer 2002), are simulated by using the anrayq software. Finally, 3d seismic data, acquired during hydratech cruise (ifremer 2002), from a region characterized by the presence of gas hydrates and free gas, are simulated by using anrayq software. A viscous-elastic profile is also determined from the seismic data, in the order to locate the presence of gas hydrates and free gas in the sedimentary layers.BREST-BU Droit-Sciences-Sports (290192103) / SudocPLOUZANE-Bibl.La Pérouse (290195209) / SudocSudocFranceF

Experimental and digital investigations of heterogeneity in lower cretaceous carbonate reservoir using fractal and multifractal concepts

Abstract Characterization and prediction of reservoir heterogeneity are crucial for hydrocarbon production. This study applies the multifractal theory using both numerical and experimental data to characterize quantitatively the heterogeneity of pore structures in Lower Cretaceous limestone reservoir from the United Arab Emirates. Fractal dimensions calculated from three dimensional digital images showed good correlation (R2 =  + 0.69) with experimental high-pressure mercury injection (HPMI) measurements. Moreover, both experimental and numerical fractal dimensions correlate well with experimental HPMI porosity measurements. Multifractal parameters such as the non-uniformity degree of the pore structures Δα, the asymmetry degree in the vertical axis Δf(α), the concentration of pore size distribution α 0 and the asymmetry degree in the horizontal axis R d estimated from digital and experimental data correlated well and revealed ability to quantitatively describe samples heterogeneity. The ranges of digital and experimental multifractal parameters provided the means to differentiate between homogeneous and heterogeneous samples

Strategic Placement of Accelerometers for Structural Health Monitoring of a Complex Unreinforced Stone Masonry Hindu Mandir

The BAPS Hindu Mandir, recently constructed in Abu Dhabi, UAE, is a complex unreinforced stone masonry structure built from thousands of sculpted sandstone and marble pieces employing ancient Indian techniques called Shilp Shastra. The entire structure is substantially large with a footprint size of 5,100 m2 and unique so that it is not covered by modern seismic design standards. Its performance was verified by conducting dynamic field tests presented herein. The most vulnerable substructure was identified based on both engineering judgement and modal analysis of the entire structure employing a detailed 3D finite element model, which was validated via the field experiments. A “local” model was developed for the identified vulnerable substructure which significantly reduced model complexity and allowed to overcome computational limitations. Based on the response of the local model, the relative importance of the sensor locations was determined via a Displacement Index method in addition to a reduction of the total variance of spectral accelerations using conditional probability theory. Through this approach, a methodology for selecting the optimal sensor placement with application on the complex unreinforced stone masonry Hindu Mandir is proposed

Estimation of Seismic Wave Attenuation from 3D Seismic Data: A Case Study of OBC Data Acquired in an Offshore Oilfield

Previous studies performed in Abu Dhabi oilfields, United Arab Emirates, revealed the direct link of seismic wave attenuation to petrophysical properties of rocks. However, all those studies were based on zero offset VSP data, which limits the attenuation estimation at one location only. This is due to the difficulty of estimating attenuation from 3D seismic data, especially in carbonate rocks. To overcome this difficulty, we developed a workflow based on the centroid frequency shift method and Gabor transform which is optimized by using VSP data. The workflow was applied on 3D Ocean Bottom Cable seismic data. Distinct attenuation anomalies were observed in highly heterogeneous and saturated zones, such as the reservoirs and aquifers. Scattering shows significant contribution in attenuation anomalies, which is unusual in sandstones. This is due to the complex texture and heterogeneous nature of carbonate rocks. Furthermore, attenuation mechanisms such as frictional relative movement between fluids and solid grains, are most likely other important causes of attenuation anomalies. The slight lateral variation of attenuation reflects the lateral homogeneous stratigraphy of the oilfield. The results demonstrate the potential of seismic wave attenuation for delineating heterogeneous zones with high fluid content, which can substantially help for enhancing oil recovery