4D地震SEG杰出讲师课程Lecture 5 - Repeatability and 4D Acquisition

Kragh and Christie (2002)
2013 SEG Distinguished Instructor Short Course - Acquisition Slide 8
Practical Issues with Repeatability Measures
• • • • Calculate over multiple time windows Remove time shifts before calculating NRMS Display in map view and using histograms Use multiple measures to characterize repeatability
2013 SEG Distinguished Instructor Short Course - Acquisition
Slide 6
Normalized RMS Difference (NRMS)
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2013 SEG Distinguished Instructor Short Course - Acquisition
Control in the field
Handle in processing
Slide 5
4D Image Repeatability Measures
• Repeatability measures typically determined – In time window(s) – Away from production changes • How is repeatability measured? – Bandwidth and amplitude consistency – Correlation coefficient and time alignment errors – Match filter consistency – Signal distortion ratio – Normalized RMS difference and predictability
2013 SEG Distinguished Instructor Short Course - Acquisition
Geometry
Everything else
Slide 11
Some Factors That Affect Repeatability
• Acquisition differences – Sail line orientation and heading – Source-receiver spacing – Streamer feather – Source and receiver depths – Coverage due to obstructions – Receiver coupling • Near surface variations • Sea level, sea state and swell noise, water temperature, salinity • Residual multiple energy • Ambient and shot-generated noise • Geological factors – Shallow gas – Geological dip
Kragh and Christie (2002)
2013 SEG Distinguished Instructor Short Course - Acquisition Slide 7
Predictability (PRED)
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= 0 if traces uncorrelated = 1.00 if traces correlated, even if amplitude scales are different = 1.00 if traces anti-correlate
Sum over time lag
• Sensitive to noise • Less sensitive than NRMS to static, phase, and amplitude differences
2013 SEG Distinguished Instructor Short Course - Acquisition
Slide 2
What Is Repeatability?
• A measure of seismic image similarity for multiple vintages of seismic data • Image repeatability = distortion +noise • It is a function of – Acquisition geometry High COS – Ambient conditions – Overburden complexity Medium – Processing similarity COS Low • Impacts 4D success and COS interpretation uncertainty
= 0 if perfect repeatability = 1.41 if difference of random noise = 2.00 if traces anti-correlate
• Sensitive to static, phase, and amplitude differences • Typical “good” values range from 0.1 to 0.3 • Geologic overprint on NRMS – Biased to low values in high reflectivity areas – Biased to high values in low reflectivity areas • Sensitive to trace misalignment
• Acquisition differences – Sail line orientation and heading – Source-receiver spacing – Streamer feather – Source and receiver depths – Coverage due to obstructions – Receiver coupling • Near surface variations • Sea level, sea state and swell noise, water temperature, salinity • Residual multiple energy • Ambient and shot-generated noise • Geological factors – Shallow gas – Geological dip
Detectability Repeatability
2013 SEG Distinguished Instructor Short Course - Acquisition
Slide 3
Some Factors That Affect Repeatability
• Acquisition differences – Sail line orientation and heading – Source-receiver spacing – Streamer feather – Source and receiver depths – Coverage due to obstructions – Receiver coupling • Near surface variations • Sea level, sea state and swell noise, water temperature, salinity • Residual multiple energy • Ambient and shot-generated noise • Geological factors – Shallow gas – Geological dip
NRMS 0.9 0.7 0.5 0.3 0.1
2013 SEG Distinguished Instructor Short Course - Acquisition ide 9
0.1
0.3
0.5 NRMS
0.7
0.9
Frequency and Dip Dependence
Model Data
Contours: NRMS Difference Eiken et al. (2003)
2013 SEG Distinguished Instructor Short Course - Acquisition Slide 10
Some Factors That Affect Repeatability
Outline
• Seismic repeatability – Quantitative metrics – Causes of nonrepeatability – Required acquisition effort • Strategies for marine 4D seismic acquisition – Towed steamer – Ocean bottom cable – Permanent seismic systems • Strategies for land 4D seismic acquisition • Summary
2013 SEG Distinguished Instructor Short Course - Acquisition
Geometry
Everything else
Slide 4
Some Factors That Affect Repeatability
• Acquisition differences – Sail line orientation and heading – Source-receiver spacing – Streamer feather – Source and receiver depths – Coverage due to obstructions – Receiver coupling • Near surface variations • Sea level, sea state and swell noise, water temperature, salinity • Residual multiple energy • Ambient and shot-generated noise • Geological factors – Shallow gas – Geological dip
Repeatability and 4D Acquisition
“If I had thought about it, I wouldn’t have done the experiment. The literature was full of examples that said you can’t do this.” — Spencer Silver (inventor of Post-it adhesive)