Seismic_Interpretation slides, presentation
- 1. SUBSURFACE MAPPING TECHNIQUES Topik Kedua : DR.rer.nat Awali Priyono Program Studi Geofisika INSTITUT TEKNOLOGI BANDUNG 2006
- 2. Seismic Interpretation Step • Seismic picking • Fault interpretation • Contouring • Time structure map • Velocity modeling • Depth conversion • ---------------------------------------------- • Hydrocarbon indicator • Stratigraphic modeling • Pitfalls in interpretation • The search for sandstone reservoir • The search for carbonate reservoir
- 3. Basic Seismic Mapping • This is no longer done by hand, but via the use high-powered interpretative or graphic workstations that rapidly access huge volumes of 2D & 3D seismic data
- 4. Synthetic seismogram, with geologic marker, sonic log, wavelet, and surface seismic
- 5. Seismic Well Tie and Tracing
- 7. 3D Visualization • ‘Slice & Dice’ the 3D seismic volume in a variety of different orientations –in-line, cross-line and time slices –horizon and fault slices • Co-visualization of multiple seismic attributes –multi-volume rendering and analysis • Increasing use of auto- tracking technologies and smart ‘applets’ the recognize geological features
- 8. Subsurface Structure Mapping Real Normal Fault Network Resulting 3D Structural Model Structure Contour Map Derived from 3D Model
- 9. Coherency • Quantitative measure of the lateral continuity of seismic events • Actively enhances the imaging of small discontinuities such as faults, fractures, or channel margins at or close to the limit of seismic resolution –such features would be more or less impossible to map using traditional manual picking techniques • Excellent for defining lateral extent of and linkage within fault networks
- 10. Fault Recognition • Detection limit ability to resolve difference between adjacent seismic traces function of TWT sample size, signal:noise ratio of data. interpretation can be assisted by seismic coherence or other edge detection enhancement attributes. • Thin bed Resolution limit ultimate control on contrasts in seismic character in stratigraphy on either side of fault (1/4 dominant wavelength)
- 12. Depth Structure Map • Well reservoir picking • Seismic to well tie • Seismic horizon picking • Time structure map • Depth structure map Depth Structure + Hc Contact Bulk Volume Crucial step Velocity model
- 14. Time and Depth Migration Zero offset section Time migration Depth migration
- 15. Seismic Pull-Up • Horizon effects adjacent to fault surface footwall drag folding or fault “shadow” ray path are artifacts from seismic time migration normal fault, low velocity layer normal fault, high velocity layer fault propagation fold ( after Trinchero, 2000 )
- 16. Seismic Sequence Analysis The procedure of picking unconformities and correlative conformities on seismic sections so as to separate out the packages involved with different time depositional units
- 18. Unconformities Sequences are terminated by unconformities or a concordant
- 19. Onlap
- 20. Seismic Facies-Analysis Aim: Analysis of the character of the eflections amplitude, continuity, continuity and configuration) inside a seismic sequence to predict the depositional environment
- 21. Reflection patterns on seismic sections Internal Structures
- 24. Seismic Patern that Indicate Sealevel Changes
- 25. Three-Dimensional Shapes of Seismic Facies Units
- 26. Depth Slice
- 30. Hydrocarbon Indicator Reflection coefficients depend on Velocity and density of sedimentary rocks depend on Porosity and pore-filling fluids
- 31. Anomalies that could be associated with hydrocarbon accumulations under some conditions • Bright spot: Overlying rock has higher velocity than brine filled reservoir rock, lowering the reservoir rock velocity by filling it with hydrocarbon increases the contrast and increases the amplitude • Dim spot: Overlying rock has lower velocity than brine filled reservoir rock, filling it with hydrocarbon decreases the contrast and decreases the amplitude • Flat spot: Where a well-defined fluid contact is present (gas-oil or gas-water) the contrast may be great enough to give a fairly strong reflection that may stand out because of its flat attitute • Polarity reversal Where the overlying rock has a velocity slightly smaller than that for the reservoir rock, lowering the reservoir rock velocity by hydrocarbons may invert the sign of the reflection, producing a polarity reversal
- 33. Dim Spot Dim spot associated with gas accumulation in porous carbonates overlain by shales.
- 34. Stacked Hydrocarbon Accumulation High amplitudes (bright spots) & Flat spots & Polarity reversals
- 35. Resolution Resolution refers to the minimum separation between two features such that we can tell that there are two features rather than only one. Comparison between the wavelength of a 30-Hz Signal, Big Ben and a Log of a drilling.
- 36. Vertical Resolution Vertical resolution means: How thick must a layer be, to discern the top and bottom of the specific layer. Theoretically, a layer can be distinguished when it has a thickness of ¼ wavelength (Rayleigh-Criterium).
- 37. Resolution of Two Boundaries Depends on Wavelength Decreasing image separation