Determination of the principal directions of azimuthal anisotropy from P-wave seismic data

Mallick, Subhashis; Craft, Kenneth L.; Meister, Laurent; Chambers, Ron

doi:10.3997/2214-4609.201408643

Cited by 34 publications

(41 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Such measurements are referred to as amplitude variations with offset and azimuth (AVOA). This is a well-developed method of fracture analysis from seismic data (e.g., Lynn et al, 1996;Mallick et al, 1998;Ruger, 1998).…”

Section: Fracture Systems -Numerical Models and Analysis Methodsmentioning

confidence: 99%

Fracture properties from seismic scattering

Burns¹,

Willis²,

Toksöz³

et al. 2007

The Leading Edge

View full text Add to dashboard Cite

Fractures scatter seismic energy and this energy can be analyzed to provide information about fracture direction and density. Laboratory and numerical (finite difference) models of fractures show that scattered energy varies with the seismic acquisition direction relative to the orientation of parallel fracture sets. Data acquired normal to fracture strike displays forward and backscattered energy that is canceled in the stacking process, while data acquired parallel to the fracture strike contains forward scattered and guided waves that are enhanced by stacking. The Scattering Index method estimates the fracture orientation by comparing wavelet changes in the data from azimuthal stacks. Fracture density or spacing can be estimated by spectral methods that include f-k analysis of backscattered energy or analysis of spectral notches as functions of azimuth. Application of these methods to data from a fractured carbonate field results in fracture orientation and density estimates that are consistent with borehole measurements. II. IntroductionThe seismic trace is a complex aggregate of reflected and scattered signals from subsurface formation interfaces and heterogeneities. Although many varieties of random noise may also be present in the trace, we know from reacquiring the same seismic survey that seismic data are highly repeatable, indicating that significant information about the subsurface is contained in the trace yet not used by our standard analysis methods. Seismic scattering is a type of signal contained in the data that is generally not utilized. Most of our processing methods are focused on optimizing the specular reflections from subsurface lithology or fluid boundaries for structural and stratigraphic interpretation. The presence of small-scale heterogeneities, creating variability in seismic properties that are on the order of a wavelength or less, will also generate seismic signatures. However, the scattered signals will appear to be less coherent and not be correlated over long distances. Such signals are generally treated as 'random noise' in the sense that stacking and deconvolutional processes may effectively remove them in many situations. Because these signals contain information about the subsurface at smaller scales it would be beneficial to find ways to extract and utilize them. One particular application where this is true is in the area of fracture characterization. Fractures can cause significant scattering since they generally have large contrasts in elastic properties compared to the surrounding rock. In addition this contrast will be greatest for those fractures that 'open', and therefore have the largest impact on reservoir productivity. Although fractures may exist with a variety of orientations in the subsurface due to changing stress regimes over time, those fractures that are oriented 2 parallel to the present day maximum horizontal stress direction will be open and generate the most scattering. Over the past several years we have developed several methods for using scat...

show abstract

Section: Fracture Systems -Numerical Models and Analysis Methodsmentioning

confidence: 99%

Fracture properties from seismic scattering

Burns¹,

Willis²,

Toksöz³

et al. 2007

The Leading Edge

View full text Add to dashboard Cite

show abstract

“…Furthermore, the greater development of the fracture, the stronger the anisotropy and the greater the oblateness of the ellipse is (Mallick et al 1998;Sun et al 2013aSun et al , b, 2014a. So, both strength and direction of fractures can be predicted.…”

Section: Technical Principlementioning

confidence: 99%

“…In the case where more than three acquisition azimuths have been acquired, with three unknowns, the equation can be solved as an overdetermined problem (Mallick et al 1998). …”

Section: Technical Principlementioning

confidence: 99%

Study of the relationship between fractures and highly productive shale gas zones, Longmaxi Formation, Jiaoshiba area in eastern Sichuan

Sun

Liu

et al. 2018

Pet. Sci.

View full text Add to dashboard Cite

Shale fractures are an important factor controlling shale gas enrichment and high-productivity zones in the Longmaxi Formation, Jiaoshiba area in eastern Sichuan. Drilling results have, however, shown that the shale fracture density does not have a straightforward correlation with shale gas productivity. Based on logging data, drilling and seismic data, the relationship between shale fracture and shale gas accumulation is investigated by integrating the results of experiments and geophysical methods. The following conclusions have been drawn: (1) Tracer diffusion tests indicate that zones of fracture act as favorable channels for shale gas migration and high-angle fractures promote gas accumulation. (2) Based on the result of azimuthal anisotropy prediction, a fracture system with anisotropy strength values between 1 and 1.15 represents a moderate development of high-angle fractures, which is considered to be favorable for shale gas accumulation and high productivity, while fracture systems with anisotropy strength values larger than 1.15 indicate over-development of shale fracture, which may result in the destruction of the shale reservoir preservation conditions. Keywords Azimuthal anisotropy Á Fracture prediction Á Shale Á Shale gas Á Shale reservoir preservation conditions IntroductionAccording to the 2013 statistics from the United States Energy Information Administration, the global technically available resource of shale gas is up to 2.07 9 10 14 m 3 (EIA 2013). China is rich in shale gas too. The shale resources in China are mainly located in the Sichuan, Ordos, Bohai Bay, Songliao, Tarim and Junggar Basins, with an estimated volume in place between 1.5 9 10 13 and 3.0 9 10 13 m 3 (Zhang et al. 2008;Jia 2017;Jiang et al. 2015;Wang et al. 2016). Shale gas fields of the Sichuan Basin are mostly located in the Fuling area in eastern Sichuan; and the Weiyuan, Changning, Zhaotong and Fushun-Yongchuan areas in southern Sichuan. Among these, the shale gas fields of the Jiaoshiba area in Fuling contribute an annual production of 5.0 9 10 9 m 3 (Guo 2016a, b; Wang 2017). Both the reservoir space and accumulation mechanisms of shale gas are complex (Liang et al. 2012; Gale et al. 2014;Deng et al. 2015;Tenger et al. 2017), and it is difficult to ascertain the key factor controlling shale gas accumulation (Guo and Zhang 2014;Jin et al. 2016;Guo et al. 2017). This comprehensive study considers that shale fractures are a key factor controlling shale gas accumulation and productivity. For conventional oil and gas, shale fractures serve as both oil and gas accumulation space and migration channels for hydrocarbons. However, drilling results have shown that natural shale fractures are not always positively correlated with high productivity. Particularly in fracture over-developed reservoirs, the shale gas production rates seem to be inadequate. Therefore, it is imperative to determine how to establish the relationship between fracture development and the production by available geological and geophysical methods...

show abstract

“…For aligned, vertical fractures the P-wave AVO response is azimuthally dependent. The azimuthal variations in the P-wave reflections have been observed in field data by different authors, such as Lynn, (1996), Mallick et al (1998), Teng (1998), Perez et al (1999), Shen et al (2002). One important advantage of this method is that it can provide localized information at the interface of interest, unlike the travel time methods, which describe the cumulative effect over larger scales.…”

Section: Introductionmentioning

confidence: 99%

Multi-Attribute Seismic/Rock Physics Approach to Characterizing Fractured Reservoirs

Mavko¹

2004

View full text Add to dashboard Cite

Most current seismic methods to seismically characterize fractures in tight reservoirs depend on a few anisotropic wave propagation signatures that can arise from aligned fractures. While seismic anisotropy can be a powerful fracture diagnostic, a number of situations can lessen its usefulness or introduce interpretation ambiguities. Fortunately, laboratory and theoretical work in rock physics indicates that a much broader spectrum of fracture seismic signatures can occur, including a decrease in P-and S-wave velocities, a change in Poisson's ratio, an increase in velocity dispersion and wave attenuation, as well as well as indirect images of structural features that can control fracture occurrence.The goal of this project was to demonstrate a practical interpretation and integration strategy for detecting and characterizing natural fractures in rocks. The approach was to exploit as many sources of information as possible, and to use the principles of rock physics as the link among seismic, geologic, and log data. Since no single seismic attribute is a reliable fracture indicator in all situations, the focus was to develop a quantitative scheme for integrating the diverse sources of information. The integrated study incorporated three key elements:The first element was establishing prior constraints on fracture occurrence, based on laboratory data, previous field observations, and geologic patterns of fracturing. The geologic aspects include analysis of the stratigraphic, structural, and tectonic environments of the field sites. Field observations and geomechanical analysis indicates that fractures tend to occur in the more brittle facies, for example, in tight sands and carbonates. In contrast, strain in shale is more likely to be accommodated by ductile flow. Hence, prior knowledge of bed thickness and facies architecture, calibrated to outcrops, are powerful constraints on the interpreted fracture distribution. Another important constraint is that fracturing is likely to be more intense near faults -sometimes referred to as the damaged zone. Yet another constraint, based on world-wide observations, is that the maximum likely fracture density increases with depth in a welldefined way. Defining these prior constrains has several benefits: they lead to a priori probability distributions of fractures, that are important for objective statistical integration; they limit the number of geologic hypotheses that need to be theoretically modeled; they provide plausible models for fracture distributions below the seismic resolution.The second element was theoretical rock physics modeling of optimal seismic attributes, including offset and azimuth dependence of traveltime, amplitude, and impedance signatures of anisotropic fractured rocks. The suggested workflow is to begin with an elastic earth model, based on well logs, theoretically add fractures to the likely facies as defined by the geologic prior information, and then compute synthetic seismic traces and attributes, including variations in P and S-wave velo...

show abstract

Determination of the principal directions of azimuthal anisotropy from P-wave seismic data

Cited by 34 publications

References 0 publications

Fracture properties from seismic scattering

Fracture properties from seismic scattering

Study of the relationship between fractures and highly productive shale gas zones, Longmaxi Formation, Jiaoshiba area in eastern Sichuan

Multi-Attribute Seismic/Rock Physics Approach to Characterizing Fractured Reservoirs

Contact Info

Product

Resources

About