Mapping distribution of fractures in a reservoir with<i>P-S</i>converted waves

Ata, Elias; Michelena, Reinaldo J.

doi:10.1190/1.1437141

Cited by 42 publications

(24 citation statements)

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“…A receiver gather in Figure 20 indicates the amount and direction of the anisotropy. P impedance S impedance Ata and Michelena (1995) show an example of three 3-C seismic lines arranged in a star pattern in Venezuela. After processing and analysing the data, they find indications of fracture direction from their calculated anisotropy.…”

Section: Anisotropy and Fracture Analysismentioning

confidence: 99%

Converted‐wave seismic exploration: Applications

Gaiser²,

et al. 2003

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Converted seismic waves (P-to-S on reflection) are being increasingly used to explore for subsurface targets. Rapid advancements in multicomponent acquisition methods and processing techniques have led to numerous applications for P-S images. Uses that have arisen include sand/shale differentiation, carbonate identification, definition of interfaces with low P-wave contrast, anisotropy analysis, imaging through gas zones, shallow high-resolution imaging, and reservoir monitoring. Marine converted-wave analysis using 4-C recordings (a three-component geophone plus a hydrophone) has generated some remarkable images. BACKGROUND

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Section: Anisotropy and Fracture Analysismentioning

confidence: 99%

Converted‐wave seismic exploration: Applications

Gaiser²,

et al. 2003

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“…We also consider the VpjVs estimation from the processing of P-S converted wave data. Ata and Michelena (1995) find that an average VpjVs ratio of 2.5 yields well focused P-S sections above and below the target zone. Saturated fluid contents are expected to be water and oil in the reservoir.…”

Section: Azimuthal Avo and Fvo Analysesmentioning

confidence: 95%

“…The P-S converted wave data collected in this area exhibit significant azimuthal anisotropy in the form of travel time a nd amplitude differences on the SI and S2 shear components which are interpreted to be fracture effects (Ata and Michelena, 1995). If the azimuthal variations in AVO and FVO gradients can be attributed to the effects of fractures, the three lines have different orientations relative to the principal orientation of fractures.…”

Section: Azimuthal Avo and Fvo Analysesmentioning

confidence: 99%

Azimuthal offset‐dependent attributes (AVO and FVO) applied to fracture detection

Shen¹,

Sierra²,

Burns³

et al. 1999

SEG Technical Program Expanded Abstracts 1999

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Using the amplitude versus offset (AVO) and the frequency versus offset (FVO) information, the diagnostic ability of P-wave seismic data in fracture detection is investigated. The offset-dependent attributes (AVO and FVO) are estimated by using an eigenvector based estimation technique, the multiple signal classification frequency estimator. These attributes are applied to the determination of principal orientation of fractures in carbonate fractured reservoirs located in the Maporal field in the Barinas basin of southwestern Venezuela. Our studies show that, in the crack normal direction, P-wave reflectivity is characterized by a large increase of amplitude with offset (large positive AVO gradient) and a large frequency decay with offset (large negative FVO gradient). In the crack strike direction, P-wave reflectivity is characterized by a wide range of AVO gradients but a small variation of FVO gradients. The analyses of inverted offsetdependent velocities and theoretical calculations show that the lateral heterogeneity in the reservoir zone can lead to large variations of AVO signatures. The offset-dependent frequency attribute can help lessen the ambiguity in fracture detection.. The combination of the offset-dependent frequency attribute is more beneficial than using the offset-dependent amplitude attribute alone.

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“…Work by several authors (e.g. Ata and Michelena, 1995;Schultz and Toksöz ,1996;Daley et al, 2002;Nakagawa et al, 2002;Wu et al, 2002;Nakagawa et al, 2003;Willis et al, 2004a) using ultrasonic scale modeling and numeric simulation have demonstrated complicated, azimuthally varying scattering patterns by simulating systems of subsurface, aligned fractures. The scattered seismic energy not only provides information about the fracture orientation, but can also be analyzed to provide information about the fracture spacing (Willis et al, 2004a) and fracture density (Pearce, 2003).…”

Section: Introductionmentioning

confidence: 99%

Characterization of in-Situ Stress and Permeability in Fractured Reservoirs

Burns¹,

Toksoz²

2005

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During the past six months we have adapted our 3-D elastic, anisotropic finite difference code by implementing the rotated staggered grid (RSG) method to more accurately represent large contrasts of elastic moduli between the fractures and surrounding formation, and applying the perfectly matched layer (PML) absorbing boundary condition to minimize boundary reflections. Two approaches for estimating fracture spacing from scattered seismic energy were developed. The first relates notches in the amplitude spectra of the scattered wavefield to the dominant fracture spacing that caused the scattering. The second uses conventional FK filtering to isolate the backscattered signals and then recovers an estimate of the fracture spacing from the dominant wavelength of those signals. Both methods were tested on synthetic data and then applied to the Emilio field data. The spectral notch method estimated the Emilio fracture spacing to be about 30 to 40 m, while the FK method found fracture spacing of about 48 to 53 m. We continue to work on two field data sets from fractured carbonate reservoirs provided by our industry sponsors-the offshore Emilio Field data (provided by ENI-AGIP), and an onshore reservoir from the Middle East (provided by Shell). Calibration data in the form of well logs and previous fracture studies are available for both data sets. In previous reports we showed the spatial distribution fractures in the Emilio Field based on our calculated scattering index values. To improve these results we performed a map migration of all the scattering indices. The results of this migration process show a very strong correlation between the spatial distribution and orientation of our estimated fracture distribution and the fault system in the field. We observe that the scattering index clusters tend to congregate around the fault zones, particularly near multiple faults and at fault tips. We have also processed a swath of data from the second data set (the onshore carbonate field). FMI data are available from a number of wells for comparison to our seismic scattering analysis results. The agreement is very good, providing confidence that these methods can be applied to land seismic data that do not have the ideal azimuthal coverage. I. Executive SummaryThe purpose of this project is to develop and implement large-scale numerical models to quantify the effects of fracture parameter variations on seismic reflection signals and in-situ stress variations on flexural modes in boreholes. These models will be used as the basis of data analysis and inversion routines for estimating the heterogeneous fracture distribution in fractured reservoirs from seismic and borehole field data.Fracture property distributions estimated from seismic data will be used to estimate the permeability tensor in the reservoir for input to reservoir simulators.During the past six months we have adapted our 3-D elastic, anisotropic finite difference code in two ways. First, we implemented the rotated staggered grid (RSG) method to more ac...

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Mapping distribution of fractures in a reservoir withP-Sconverted waves

Cited by 42 publications

References 0 publications

Converted‐wave seismic exploration: Applications

Converted‐wave seismic exploration: Applications

Azimuthal offset‐dependent attributes (AVO and FVO) applied to fracture detection

Characterization of in-Situ Stress and Permeability in Fractured Reservoirs

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