Geology 56606660 Applied Geophysics 16 Feb 2018 Last
Geology 5660/6660 Applied Geophysics 16 Feb 2018 Last Time: Reflection Data Processing • Step IV: Migration returns reflection energy to its “true” location on the two-way travel-time image… Depth migration uses velocity structure from NMO correction to convert travel time to depth (improving image resolution; removing e. g. velocity pull-ups/pull-downs) Seismic Reflection Interpretation • Data collection: Huge quantities of data! Redundancy is key! • 2 D profiling still used for initial reconnaissance, but 3 D is industry standard for prospects • 3 D gives higher resolution, better positioning (enables migration of “out-of-plane” seismic reflection energy) For Tue 20 Feb: Burger 200 -253 (§ 4. 4 -4. 7) © A. R. Lowry 2018
Haakon Fossen 2010 Seismic Interpretation
Haakon Fossen 2010 3 -D seismic cubes • Better resolution • Better positioning • 3 D view options
3 D Data: 3 D Seismic Haakon Fossen 2010 • Collected by shooting many parallel lines ~25 m apart • Migrated together to increase accuracy and to create a coherent data volume (cube) • Collected over all offshore oil and gas fields • Underpins the geometric understanding of an oil field
Haakon Fossen 2010
Haakon Fossen 2010 Data acquisition
Haakon Fossen 2010 Resolution • Vertical • Lateral
Haakon Fossen 2010 Vertical resolution Relationship between bed thickness and acoustic impedance contrast for Vertical seismic resolution in terms of seismic resolution of a tuning thickness: When top to base layer. of a layer is less than 1/4 wavelength, constructive/destructive interference results in apparent single wavelet.
Color convention: Blue for positive amplitude, red for negative… Haakon Fossen 2010 Note how weaker amplitude synclinal layers fade out!
Haakon Fossen 2010 Lateral resolution: Faults are sharp, imaged offsets less so…
Haakon Fossen 2010
Haakon Fossen 2010
Haakon Fossen 2010 Lateral positioning • Choice of migration velocities affects horizontal positioning of signals • Horizontal resolution typically 50 -100 m • Serious concern when drilling high-precision wells, e. g. close to faults. • Resolution may depend heavily on pilot wells
Haakon Fossen 2010 Directional drilling/steering technology is another reason for accurate depth migration!
Haakon Fossen 2010 Seismic quality Depends on: • Acoustic impedance contrast • Depth ( frequency) • Layer thickness ( interference) • Properties of overlying layers • Source energy • Processing parameters • Acquisition direction • Instrumentation
Haakon Fossen 2010 Seismic inversion In industry, the process of determining what physical characteristics of rocks and pore fluid could have produced a given seismic image/data set
Haakon Fossen 2010 Correlation
Haakon Fossen 2010
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