Multi-attribute Analysis and Coloured Inversion of a 3D seismic … · Multi-attribute Analysis and...
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Multi-attribute Analysis and Coloured Inversion of a 3D seismic dataset to increase resolution of structural and stratigraphic features in the subsurface: A case study from Taranaki Basin. Introduction Available Data The aim of this study is to use multiple seismic attributes to delineate subsurface geological features such as faults and channels. More specific objectives are: 1. Use spectral decomposition with Red Green Blue (RGB) colour blending as a tool to visualize subsurface structures and stratigraphy in various time levels and horizons. 2. Coloured inversion to improve the resolution of seismic data. 1. Computation of various structural and stratigraphic attributes. An attribute is a derived quantity from a seismic input set (Figure 2). Semblance:The Semblance attribute can be used to isolate edges from the input data set, i.e. enhancing discontinuities in the horizontal continuity of amplitude. This is a stratigraphic attribute most commonly displayed in grayscale for blending. It is particularly effective for sharpening details. Envelope: The instantaneous envelope represents the reflectivity, i.e. the contrasts of acoustic impedance. In this study, it was mainly used to highlight the boundaries of the channel, but more generally this attribute can be seen as a good starting point to display the main structural trends of the reservoir. Frequency: The instantaneous frequency is the derivative of the phase and is linked with the centered frequency of the signal spectrum. Low frequencies indicate hydrocarbons, fractured zones or sand rich units. High frequencies indicate sharp interfaces or shale rich units. Spectral Decomposition: Spectral Decomposition unravels the seismic signal into its constituent frequencies, allowing the user to see phase and amplitude tuned to specific wavelengths. The amplitude component excels at quantifying thickness variability and detecting lateral discontinuities, while the phase component detects lateral discontinuities. 2. Blending of Attributes: Volume blending combines the information of two or more seismic attributes through opacity control. It aids seismic interpretation by making features of interest more visible and enhancing anomalous features (Figure 3). 4. Coloured Inversion: Coloured Inversion analyses various seismic and well log spectra to define an operator that shapes the average seismic trace spectra to that of a fitted smooth curve which is representative of the average acoustic impedance log spectra(Figure 4). This defines the amplitude spectrum of the required operator. Theory tells us that a 90 degree phase rotation is also required. This is incorporated into the operator. The assumption is that the input seismic data is zero phase. The Coloured Inversion operator is simply applied to the seismic volume using a convolution algorithm. Figure 5 shows the QC of the operator and Figure 6 shows the convolution of the operator with seismic cube. Kora 3D volume in the northern Taranaki Basin (Figure 1) and four drilled wells within the 3D survey have been used in this study. OpendTect and COLOP plugin have been used to perform seismic interpretation and coloured inversion. MONMOYURI SARMA, Elemental Petroleum Consultants Aim Workflow followed: Figure 2: Seismic Attribute Conclusions: • Individual and blended seismic attributes such as semblance and envelope aided strati- structural interpretation by making discontinuities (like faults) and geological features (like channels) stand out. • Very impressive geological features have been observed in the Giant Foresets Formation due to RGB blending. Though it is not a potential reservoir unit in the study area (being too shallow), the sequence stratigraphic concepts from this can be used as an analogue in other basins of interest. Graphical representation of the workflow Key References: Figure 1: Kora 3D seismic volume and the drilled wells Figure 4: Colored Inversion Operator Analysis It is well known that in a composite Red Green Blue (RGB) display, each input attribute volume is mapped individually to the red, green and blue monochromatic components of the RGB space. The intensity of each primary colour represents the intensity of the attribute in that channel. The information within the attributes is “mixed” to produce detailed visualization. Spectral decomposition is carried out at frequency levels 15, 30 and 50 Hz and then blended in RGB space to show interesting geological features. Various channel features are seen flowing radially from the Kora Volcanic vent in the younger succession indicating they were formed during or after the volcanic activities and may be pyroclastic flows. There seems to be a east flowing main channel away from the volcanic centre on the edge of the cube. The drainage pattern seen in the older succession are NE-SW in orientation. 3. Synthetic Seismic: Sonic and density log curves are used to compute the acoustic impedance. Well Kora-4 is used for computation of a synthetic seismogram. The resulting acoustic impedance curve is then used by the program to compute reflection coefficients at each interface between contrasting velocities. A wavelet is extracted from the input seismic data. The synthetic wavelet is convolved with the reflection series for the entire well survey to generate a synthetic seismic trace, which is then compared to key seismic events. Acknowledgements: • Coloured Inversion volume improved the resolution of the seismic data. On performing quality checking against Kora-4 and Kora-1A wells, the inverted volume showed improved delineation of the Tangaroa sands, resolved thin part of tuned wedge and improved signal to noise ratio in noise prone zones. This method is fast and can be easily implemented and interpreted. Figure 3: Attribute blending for imaging of geological features Seismic attributes Original Seismic Amplitude Blended attributes Synthetic generation I would like to acknowledge Elemental Group for providing me the opportunity, time and permission to present the work and my colleagues Kate Bromfield, Bill Leask and Brett Rogers for their feedback. I also acknowledge the use of Opendtect opensource seismic interpretation software and COLOP free plugin. Seismic attribute analysis is a method to image and map depositional environments and geomorphology in the subsurface, from seismic reflection character. As different attributes convey different information, interpreting the subsurface structural framework and reservoir distribution requires working with multiple attributes. Multi- attribute analysis and attribute blending have the power to unlock the covariant information embedded in seismic attribute data (Das et al., 2013). Spectral decomposition and coloured inversion are used in this study as tools to improve the seismic resolution. Figure 6: Generating Colored Inversion Attribute Figure 5: QC of the operator Kora-4 Figure 7b: Inverted Seismic Tangaroa sands in the original seismic data has lower resolution and thus difficult to interpret (Figure 7a). Coloured Inversion has sharpened the resolution of the seismic. The signal to noise ratio increased in the noise prone zone near the Kora volcanic vent (Figure 7b). Operator Coloured Inversion Das U.K., Pant D.C., Parida G., Rastogi R., Bhardwaj A., 2013, Application of Multi-Attribute and Spectral Decomposition with RGB blending for understanding the strati-structural features: A case study: 10 th Biennial International Conference and Exposition, Kochi,2013. Lancaster, S. and Whitcombe D., 2000, Fast-track 'colored‘ inversion: 70 th Annual International Meeting, Society of Exploration Geophysicists, Expanded Abstracts, 15721575, 2000. Manral S. S. and Barnes A. E., 2008, Techniques of Volume Blending for Aiding Seismic Data Interpretation:7 th International Conference and Exposition on Petroleum Geophysics, Hyderabad, 2008. Kora Volcanic vent Radial flow Channel Figure 7a: OriginalSeismic Kora-4
Transcript of Multi-attribute Analysis and Coloured Inversion of a 3D seismic … · Multi-attribute Analysis and...
Multi-attribute Analysis and Coloured Inversion of a 3D seismic dataset to increase resolution of structural and stratigraphic features
in the subsurface: A case study from Taranaki Basin.
Introduction Available Data
The aim of this study is to use multiple seismicattributes to delineate subsurface geologicalfeatures such as faults and channels. Morespecific objectives are:
1. Use spectral decomposition with Red GreenBlue (RGB) colour blending as a tool tovisualize subsurface structures andstratigraphy in various time levels andhorizons.
2. Coloured inversion to improve the resolution ofseismic data.
1. Computation of various structuraland stratigraphic attributes. Anattribute is a derived quantity from aseismic input set (Figure 2).
Semblance:The Semblance attribute canbe used to isolate edges from the inputdata set, i.e. enhancing discontinuities inthe horizontal continuity of amplitude. Thisis a stratigraphic attribute most commonlydisplayed in grayscale for blending. It isparticularly effective for sharpening details.
Envelope: The instantaneous enveloperepresents the reflectivity, i.e. the contrastsof acoustic impedance. In this study, it wasmainly used to highlight the boundaries ofthe channel, but more generally thisattribute can be seen as a good startingpoint to display the main structural trendsof the reservoir.
Frequency: The instantaneous frequencyis the derivative of the phase and is linkedwith the centered frequency of the signalspectrum. Low frequencies indicatehydrocarbons, fractured zones or sand richunits. High frequencies indicate sharpinterfaces or shale rich units.
Spectral Decomposition: SpectralDecomposition unravels the seismic signalinto its constituent frequencies, allowingthe user to see phase and amplitude tunedto specific wavelengths. The amplitudecomponent excels at quantifying thicknessvariability and detecting lateraldiscontinuities, while the phase componentdetects lateral discontinuities.
2. Blending of Attributes: Volumeblending combines the information of twoor more seismic attributes through opacitycontrol. It aids seismic interpretation bymaking features of interest more visibleand enhancing anomalous features (Figure3).
4. Coloured Inversion: Coloured Inversion analyses various seismic and well log spectra to define an operator that shapes the average seismic trace spectra to that of a fitted smooth curve which is representative of the average acoustic impedance log spectra(Figure 4). This defines the amplitude spectrum of the required operator. Theory tells us that a 90 degree phase rotation is also required. This is incorporated into the operator. The assumption is that the input seismic data is zero phase. The Coloured Inversion operator is simply applied to the seismic volume using a convolution algorithm. Figure 5 shows the QC of the operator and Figure 6 shows the convolution of the operator with seismic cube.
Kora 3D volume in the northern Taranaki Basin (Figure 1) and four drilled wells within the 3D survey have been used in this study. OpendTect and COLOP plugin have been used to perform seismic interpretation and coloured inversion.
MONMOYURI SARMA, Elemental Petroleum Consultants
Aim
Workflow followed:
Figure 2: Seismic Attribute
Conclusions:• Individual and blended seismic attributes
such as semblance and envelope aided strati-structural interpretation by makingdiscontinuities (like faults) and geologicalfeatures (like channels) stand out.
• Very impressive geological features havebeen observed in the Giant ForesetsFormation due to RGB blending. Though it isnot a potential reservoir unit in the studyarea (being too shallow), the sequencestratigraphic concepts from this can be usedas an analogue in other basins of interest.
Graphical representation of the workflow
Key References:
Figure 1: Kora 3D seismic volume and the drilled wells
Figure 4: Colored Inversion Operator Analysis
It is well known that in a composite Red Green Blue (RGB) display, each input attribute volume ismapped individually to the red, green and blue monochromatic components of the RGB space.The intensity of each primary colour represents the intensity of the attribute in that channel. Theinformation within the attributes is “mixed” to produce detailed visualization. Spectraldecomposition is carried out at frequency levels 15, 30 and 50 Hz and then blended in RGB spaceto show interesting geological features. Various channel features are seen flowing radially fromthe Kora Volcanic vent in the younger succession indicating they were formed during or after thevolcanic activities and may be pyroclastic flows. There seems to be a east flowing main channelaway from the volcanic centre on the edge of the cube. The drainage pattern seen in the oldersuccession are NE-SW in orientation.
3. Synthetic Seismic: Sonic and density log curves are used to compute the acousticimpedance. Well Kora-4 is used for computation of a synthetic seismogram. The resultingacoustic impedance curve is then used by the program to compute reflection coefficients at eachinterface between contrasting velocities.A wavelet is extracted from the input seismic data. The synthetic wavelet is convolved with thereflection series for the entire well survey to generate a synthetic seismic trace, which is thencompared to key seismic events.
Acknowledgements:
• Coloured Inversion volume improved the resolution ofthe seismic data. On performing quality checkingagainst Kora-4 and Kora-1A wells, the inverted volumeshowed improved delineation of the Tangaroa sands,resolved thin part of tuned wedge and improved signalto noise ratio in noise prone zones. This method is fastand can be easily implemented and interpreted.
Figure 3: Attribute blending for imaging of geological features
Seismic attributesOriginal Seismic Amplitude
Blended attributes
Synthetic generation
I would like to acknowledge Elemental Group for providing me the opportunity, time and permission to present the work and my colleagues Kate Bromfield, Bill Leask and Brett Rogers for their feedback. I also acknowledge the use of Opendtect opensource seismic interpretation software and COLOP free plugin.
Seismic attribute analysis is a method to imageand map depositional environments andgeomorphology in the subsurface, from seismicreflection character. As different attributes conveydifferent information, interpreting the subsurfacestructural framework and reservoir distributionrequires working with multiple attributes. Multi-attribute analysis and attribute blending have thepower to unlock the covariant informationembedded in seismic attribute data (Das et al.,2013). Spectral decomposition and colouredinversion are used in this study as tools toimprove the seismic resolution.
Figure 6: Generating Colored Inversion AttributeFigure 5: QC of the operator
Kora-4
Figure 7b: Inverted Seismic
Tangaroa sands in the original seismic data has lower resolution and thus difficult to interpret (Figure 7a).
Coloured Inversion has sharpened the resolution of the seismic. The signal to noise ratio increased in the noise prone zone near the Kora volcanic vent (Figure 7b).
Operator
Coloured Inversion
Das U.K., Pant D.C., Parida G., Rastogi R., Bhardwaj A., 2013, Application of Multi-Attribute and Spectral Decomposition with RGB blending for understanding the strati-structural features: A case study: 10th Biennial International Conference and Exposition, Kochi,2013.
Lancaster, S. and Whitcombe D., 2000, Fast-track 'colored‘ inversion: 70th Annual International Meeting, Society of Exploration Geophysicists, Expanded Abstracts, 15721575, 2000.
Manral S. S. and Barnes A. E., 2008, Techniques of Volume Blending for Aiding Seismic Data Interpretation:7th International Conference and Exposition on Petroleum Geophysics, Hyderabad, 2008.
Kora Volcanic ventRadial flow
Channel
Figure 7a: Original Seismic
Kora-4
