AVAZ Inversion Research Articles

Geofluid discrimination in stress-induced anisotropic porous reservoirs using seismic AVAZ inversion

Geofluid discrimination in stress-induced anisotropic porous reservoirs using seismic AVAZ inversion

Azimuthal analysis of pp-wave attenuation in a fractured medium covering a target layer using wide-azimuth seismic survey data

The paper considers PP-wave attenuation in an anisotropic fractured medium covering the target layer. Azimuthal and offset variations of inverse quality factor (QVOA) were estimated from 3D seismic data by a software module developed in IPGG SB RAS. Spectral ratio method was used to estimate attenuation. We used developed QVOA inversion module on 3D CDP data from one of the fields in the Republic of Serbia. The distributions of fracturing orientation and attenuation anisotropy degree in the layer of Neogene rock are presented as results. This layer covers Paleozoic basement, which is the main target layer for oil exploration in this area. The obtained distributions should be considered during AVAZ inversion interpretation of reflections from Paleozoic basement due to possible footprints.

Azimuthal amplitude difference inversion constrained by azimuth velocity anisotropy

SUMMARYAmplitude variation with incident angle and azimuth (AVAZ) inversion is usually used for estimating subsurface medium properties from azimuthal stacked seismic data for fracture prediction. And weak anisotropy parameters play an important role in the fracture prediction of shale reservoirs. However, the low contribution of the anisotropic parameters to the reflection coefficient and too many condition numbers of forward solver lead to insufficient inversion stability of the anisotropic parameters. Therefore, a new azimuthal-amplitude-difference inversion method with the azimuth-velocity-anisotropic constraints is proposed to improve the stability of inversion and obtain a reasonable estimation of anisotropic parameters. The azimuthal amplitude difference AVAZ forward solver in the anisotropic medium is initially established from a rewritten approximate reflectivity equation and variable substitution. Sensitivity analysis of estimated parameters of the rewritten approximate reflectivity indicates that our approach is sufficiently suitable for seismic inversion of anisotropic parameters. Furthermore, an azimuthal amplitude difference Bayesian AVAZ inversion approach with azimuth-velocity-anisotropic constraint is developed to improve the stability of the inversion. We add Gaussian noise to the synthetic seismic records and assume the Cauchy distributions as a prior constraint on the model parameters. The anisotropic information obtained from the azimuth-velocity-anisotropic inversion is utilized as a constraint for improving the stability of inversion. Synthetic data tests reveal that the anisotropic parameters can be estimated stably even with moderate noise. Field data tests illustrate the feasibility and reliability of the presented inversion method for estimating anisotropic parameters in a shale reservoir with vertical or near-vertical fractures.

AVAZ-инверсия как перспективный инструмент динамической интерпретации сейсмических данных

AVAZ-инверсия как перспективный инструмент динамической интерпретации сейсмических данных

Application of AVAZ inversion algorithm based on exact formulas to a wide-azimuth seismic survey data

Results of applying of nonlinear AVAZ inversion optimization algorithm to data from 3D wide-azimuth seismic survey in the Republic of Serbia are presented. The algorithm is based on exact reflection coefficients formulas for PP reflection from anisotropic medium. We compare it with a conventional algorithm based on Ruger linear approximation of P-wave reflection from a boundary between isotropic and anisotropic (HTI) media. Maps of fracture orientation and anisotropy degree are more detailed in the case of using AVAZ inversion based on exact formulas. The results are in general accordance with the FMI well data, which indicates reliable performance of the algorithm.

TESTING OF AN OPTIMIZATION ALGORITHM FOR AVAZ INVERSION ON SYNTHETIC DATASET

In the paper, we study an optimization algorithm for a nonlinear AVAZ inversion of PP reflections from an anisotropic media. The algorithm is based on the exact formulas for PP wave reflection coefficient for an anisotropic HTI medium and could be applied in the case of strong-contrast boundary and various anisotropy degree. Algorithm testing on synthetic dataset for radial survey system shows that estimation of anisotropy parameters γ , δ and HTI medium symmetry axis is robust in the case of signal to noise ratio ≥ 5. For estimation of parameter ε far offset data is needed.

Study of the influence of anisotropy parameters on reflection coefficients from a boundary between two azimuthally anisotropic media

The paper considers an algorithm for calculating reflection coefficients from boundary between two HTI media. Analysis of the presence of anisotropy above and below the target boundary, as well as variations in the parameters of HTI media, was done. Interpretation of reflection data from the boundary between two HTI media with neglect of anisotropy above or below potentially leads to significant errors in estimation of symmetry axes directions, and hence fracturing orientation. Overestimation/underestimation of an elastic parameter in the overlying HTI medium could lead to a corresponding overestimation/underestimation of similar parameter in the underlying target layer in the result of AVAZ inversion. Furthermore, among the anisotropy parameters Thomsen parameterγhas most significant influence on the reflection coefficients dependences. Thus, the parameterγcould be used foremost as a result of the AVAZ inversion.

Seismic AVAZ inversion for orthorhombic shale reservoirs in the Longmaxi area, Sichuan

Seismic AVAZ inversion method based on an orthorhombic model can be used to invert anisotropy parameters of the Longmaxi shale gas reservoir in the Sichuan Basin.. As traditional seismic inversion workflow does not sufficiently consider the influence of fracture orientation, we predict fracture orientation using the method based on the Fourier series to correct pre-stacked azimuth gathers to guarantee the accuracy of input data, and then conduct seismic AVAZ inversion based on the VTI constraints and Bayesian framework to predict anisotropy parameters of the shale gas reservoir in the study area.We further analyze the rock physical relation between anisotropy parameters and fracture compliance and mineral content for quantitative interpretation of seismic inversion results. Research results reveal that the inverted anisotropy parameters are related to P- and S-wave respectively, and thus can be used to distinguish the effect of fracture and fluids by the joint interpretation. Meanwhile high values of anisotropy parameters correspond to high values of fracture compliance, so the anisotropy parameters can reflect the development of fractures in reservoir. There is two sets of data from different sources, including the content of brittle mineral quartz obtained from well data and the anisotropy parameters inverted from seismic data, also show the positive correlation. This further indicates high content of brittle mineral makes fractures developing in shale reservoir and enhances seismic anisotropy of the shale reservoir. The inversion results demonstrate the characterization of fractures and brittleness for the Longmaxi shale gas reservoir in the Sichuan Basin.

AVAZ inversion for fracture weakness based on three-term Rüger equation

Fracture is one of the most important migration channels and accumulation spaces in hydrocarbon reservoirs. For unconventional hydrocarbon reservoirs, especially for shale reservoirs, the accurate prediction of fracture distribution can help improve the hydrocarbon production. With the development of seismic monitoring techniques, wide-azimuth acquisition and processing techniques are being increasingly used to describe the distribution of subsurface factures. The P-wave AVAZ inversion based on seismic anisotropy is one of the most important and commonly used methods for fracture prediction. In this paper, we develop an inversion algorithm to acquire the normal and tangential fracture weakness based on P-wave reflection anisotropy and wide-azimuth seismic data. The newly developed algorithm can effectively utilize the amplitude information of large offset data to retrieve the fracture weakness which is related to the fracture density and fluid fillings. Two synthetic data examples show that the fracture weakness can be accurately estimated by using the newly proposed AVAZ inversion method. Our inversion method can obtain reliable fracture identification results even when seismic data are contaminated by random noise, which demonstrates the reliability and noise resistance of the inversion method. Finally, the method is successfully applied to a 3-D physical model data with an equivalent area of 100 km2. The predicted fracture distribution result is consistent with the designed physical model and is highly related to the locally geological structures of the target reservoir. Through synthetic and physical model data studies, we demonstrate that the proposed inversion method is an effective approach to directly evaluate the fracture distribution in the reservoir.

ИЗУЧЕНИЕ ТРЕЩИНОВАТОСТИ В КАРБОНАТНЫХ КОЛЛЕКТОРАХ ПРИПЯТСКОГО ПРОГИБА (РЕСПУБЛИКА БЕЛАРУСЬ) ПО СЕЙСМИЧЕСКИМ ДАННЫМ 3D

In the summary are presented the results of technology of deep full-azimuthal angular migration and AVAZ-inversions in difficult seismogeological conditions of salt-dome tectonics in the study of carbonate reservoirs at great depths. In comparison with migration of Kirhgof are received deep images of objects of higher permission and detail. For the first time in the territory of the Republic of Belarus is made the estimation of fracturing of reservoirs based on seismic data. According to the results of the analysis, the distribution of the crack density and their orientation are directly related to the productivity and the results of the wells hydrodynamic studies. Key words: seismic exploration, processing of seismic data, deep-full azimuth migration, reflection seismogram, directional seismogram, collector, fracturing References Aleksandrov A.A. et al. 2012. The project for 3D / 3C field seismic surveys at Yuzhno-Ostashkovichi field - Field Seismic Exploration Management, «Belorusneft Production Association». Rechitsa. 50 p. (In Russian) Hartsov Y.A. et al. 2006. Report on the topic: «Analysis and generalization of the results of geological prospecting works on the premises of RUE» Belorusneft Production Association for 2005» - Uprgeologii RUE» Production Association «Belorusneft». Gomel. 165 p. (In Russian) Hartsov Y.A. et al. 2009. Report on the topic: «Analysis and generalization of the results of exploration work on the premises of RUE» Production Association «Belorusneft» for 2008». Uprgeologii RUE «Production Association» Belorusneft». Gomel. 399 p. (In Russian) Gromyko V.M. et al. 2014. Report on the topic: «Processing and interpretation of seismic data in order to identify, prepare for drilling of structures and detailing the construction of deposits in the territory of the RUE Production Association» Belorusneft» in 2013. BelNIPIneft RUE «Production Association» Belorusneft», Gomel. 247 p. (In Russian) Dubinin B.A. et al. 2017. Report on the theme: «Conducting exploration works on the premises of RUE Production Association» Belorusneft» for 2016». BelNIPIneft. RUE Production Association Belorusneft Gomel. 475 р. (In Russian) Konyushenko A.S., Solgan V.D., Shumilyak V.M. 2014. The experience of the application of ES360 and AVAZ inversion technology under the conditions of the salt dipole tectonics at Yuzhno-Ostashkovichskoye field for the study of fracturing in intersoil and salt-bed carbonate collectors of the Upper Devonian of the Pripyat deflection. Minsk, Lithosphere. #2 (41). Р. 146-156 (In Russian) Canning A. and Malkin A. 2008. Removing NMO/migration stretch effects for improved AVO analysis, Hyderabad: 7th Conference and Exposition on Petroleum Geophysics. Р. 341-366. Koren Z., Ravve. I., Ragoza E., Bartana A. 2008. Full-azimuth Subsurface Angle Domain Wavefield Decomposition and Imaging: Geophysics, 76 no. 1. S1-S13. 19 FIGS.10.1190/1.3511352https://doi.org/10.1190/1.3511352

Application of prestack orthotropic AVAz inversion for fracture characterization of a deep carbonate reservoir in northern Kuwait

Prestack anisotropic (orthotropic symmetry) AVAz inversion of full-azimuth 3D seismic data for fracture characterization of the upper Najmah Formation in northern Kuwait was conducted. This formation comprises a thin, tight, naturally fractured carbonate overlying a kerogen-rich shale source rock. The inversion methodology uses an orthotropic system of symmetry that is appropriate for analysis of vertical transverse isotropic (VTI) anisotropic rock layers containing swarms of aligned vertical fractures. Measured seismic amplitudes show good agreement with synthetic models created at different well locations, indicating reliable representation of fractures in amplitude data. Inversion results show good agreement with well and drilling data. Rock-physics modeling shows a relationship between elastic properties and seismic anisotropy and between elastic properties and reservoir properties, such as porosity and fracture density.

AVAZ inversion for fracture weakness parameters based on the rock physics model

Subsurface fractures within many carbonates and unconventional resources play an important role in the storage and movement of fluid. The more reliably the detection of fractures could be performed, the more finely the reservoir description could be made. In this paper, we aim to propose a method which uses two important tools, a fractured anisotropic rock physics effective model and AVAZ (amplitude versus incident and azimuthal angle) inversion, to predict fractures from azimuthal seismic data. We assume that the rock, which contains one or more sets of vertical or sub-vertical fractures, shows transverse isotropy with a horizontal axis of symmetry (HTI). Firstly, we develop one improved fractured anisotropic rock physics effective model. Using this model, we estimate P-wave velocity, S-wave velocity and fracture weaknesses from well-logging data. Then the method is proposed to predict fractures from azimuthal seismic data based on AVAZ inversion, and well A is used to verify the reliability of the improved rock physics effective model. Results show that the estimated results are consistent with the real log value, and the variation of fracture weaknesses may detect the locations of fractures. The damped least squares method, which uses the estimated results as initial constraints during the inversion, is more stable. Tests on synthetic data show that fracture weaknesses parameters are still estimated reasonably with moderate noise. A test on real data shows that the estimated results are in good agreement with the drilling.

Applying full–azimuth angle domain pre-stack migration and AVAZ inversion to study fractures in carbonate reservoirs in the Russian Middle Volga region

Inovemstev Alexander Nicolaevich, Stepanov Igor Viktorovich, Galkin Alexander Vasilyevich and Zvi Koren introduce full-azimuth angle domain imaging which in an onshore seismic exploration application resulted in a higher resolution and more informative depth image than conventional migration technology.