Edward Jenner

Azimuthal AVO Methodology and data examples

Azimuthal AVO (AVOA) has become a popular method of fracture detection in both carbonate and sandstone reservoirs. Previous methods often relied on stacking the multiazimuth data into offset and azimuth bins, often using only two azimuth sectors perpendicular to each other. This can mix the data over a significant azimuth range and does not allow for meaningful error estimates. Once the data have been stacked into azimuth bins, information on azimuthal distribution is lost. Each azimuth sector is treated as if it has equal weight, even though one sector may have significantly lower fold and thus a lower signal-to-noise ratio. It has also been suggested that the results of azimuth sectoring analyses are often influenced by acquisition geometry.

Interpreting seismic data in the presence of azimuthal anisotropy; or azimuthal anisotropy in the presence of the seismic interpretation

Measuring P-wave azimuthal anisotropy has been in the recent past an elusive task; therefore, the interpreter ignored this attribute of the seismic data and left the subject to the research and technology group geophysicists. Conversely, the interpreting geophysicist knew that, when measured, the anisotropy could yield important reservoir properties related to fractures and stress fields. However, little did we suspect that P-wave azimuthal anisotropy both in velocity and AVO would change our perception of data interpretation as is happening now.

Combining VTI and HTI anisotropy in prestack time migration: Workflow and data examples

Accounting for anisotropy in P-wave data processing is now recognized as an important step in improving the quality of seismic data. The quality of final migrated images, prestack gathers, and any attributes derived from the seismic data can all be improved. Commonly, two forms of anisotropy are considered. The first and most common is vertical transverse isotropy (VTI), or the closely associated tilted transverse isotropy (TTI). This anisotropy is often caused by fine layering of sediments, with the layering smaller in scale than the seismic wavelength. In the case of VTI the bedding planes are horizontal, while in TTI they are dipping.

Estimation of Azimuthally Varying Attenuation From Wide-azimuth P-wave Data

By assuming that Q is frequency independent, and the medium at each particular azimuth the medium is laterally homogeneous, we use the spectral ratio method and a regularized linear inversion scheme to estimate the quality factor in azimuth-sectored data. The regularization parameters are chosen by a χ criterion that is based on estimates of the variance in the data. Tests on synthetic data show that this regularized inversion provides robust estimates of Q for signal-to-noise ratios lower than those observed in the data.

Preserving azimuthal velocity information: experiences with Cross-spread noise attenuation and Offset Vector Tile PreSTM

Summary We review our experiences with a number of surveys where azimuth al velocity information is successfully preserved through signal processing and PreSTM imaging. The application of 3D noise attenuation using cross-spread sorted data significantly improves the S/N of azimuthal information. Offset vector tile (OVT) binning is shown to be an efficient method for preserving azimuthal information through prestack imaging allowing post migration analysis using surface-fitting methods. The benefits of using these velocity analysis results for a further migration with an azimuthally varying velocity model are also demonstrated.

Fracture Network Characterization From P- And S-wave Data At Weyburn Field, Canada

Combining post-stack S-wave polarization analysis and Pwave azimuthal normal moveout (ANMO) velocity analysis, we obtain anisotropic parameters to characterize the fracture network of the reservoir interval at Weyburn field, Saskatchewan, Canada. The results indicate that the survey area can be divided into two main sections with different fracture properties. The seismic signatures in the northern zone are consistent with an orthorhombic symmetry medium, while the southern section is consistent with a symmetry lower than orthorhombic. The southern zone coincides with areas where salt has been dissolved from the Prairie Evaporite below the reservoir. This correlation suggests that the salt withdrawal modified the stress state in the reservoir, resulting in different fracturing regimes south and north of the salt dissolution edge.

Pre‐stack time migration using VTI + HTI velocity models; workflow and data examples

P n i y p o r t o s i n a r o f g n i t n u o c c A s i g n i s s e c o r p a t a d e v a w e h t g n i v o r p m i n i p e t s t n a t r o p m i n a s a d e z i n g o c e r w o n q e h T . a t a d c i m s i e s f o y t i l a u q d e t a r g i m l a n i f f o y t i l a u m o r f d e v i r e d s e t u b i r t t a y n a d n a s r e h t a g k c a t s e r p , s e g a m i d e v o r p m i e b l l a n a c a t a d c i m s i e s e h t . y l n o m m o C , o w t o r t o s i n a f o s m r o f d e r e d i s n o c e r a y p g n i s s e c o r p e m i t n i ; I T V . I T H d n a I T V , s e m i t l e v a r t n o s t c e f f e e h t f o s m r e t n I o r t o s i n a y p n o n s a f l e s t i s t s e f i n a m t a s e m i t l e v a r t c i l o b r e p y h s t e s f f o g n o l y p o r t o s i n a I T H e l i h w r o f e l b i s n o p s e r s i s n o i t a i r a v e m i t l e v a r t e c r u o s h t i w h t u m i z a r e v i e c e r .

Semblance‐based interval VTI parameter estimation: a comparison of methods

We compare three different methods for semblance-based interval VTI parameter estimation from non-hyperbolic moveout. Using both synthetic and field data, we show that both the rational interpolation and the generalized moveout equation provide substantial improvement in accuracy over the standard Grechka-Tsvankin method. Our semblance analysis differs from standard semblance analysis in that it is directly done as a function of the interval parameters in a layer-stripping fashion. We show that for models up to extreme levels of anellipticity and offset-to-depth ratios up to at least 4, both methods can be considered nearly exact. Therefore, either the RI or the GME method allow accurate initial model building from nonhyperbolic moveout analysis, which can be further improved in depth-domain imaging and velocity-analysis, or can be used to improve the S/N ratio in time-domain imaging in layered VTI media. A field data example shows that both the RI and GME produce virtually the same results. The implementation of the generalized moveout equation is in practice, however, slightly faster than the rational interpolation method.