Seismic Imaging and Reflection Surveys

The seismic reflection method sends controlled acoustic energy into the ground and records the echoes from buried interfaces, then processes them into detailed images of subsurface geology.

Definition

Seismic imaging and reflection surveys comprise the method of generating subsurface images from seismic waves reflected off geological interfaces, through controlled-source acquisition and a processing sequence that culminates in migration to place reflectors in their correct positions.

Scope

This topic covers the acquisition, processing, and interpretation of seismic reflection data: source and receiver geometry, the common-midpoint method and normal-moveout correction, stacking, deconvolution, velocity analysis, and migration. It treats the construction of images from raw shot records, the distinction between time and depth sections, and the principles of seismic interpretation for structure and stratigraphy. The emphasis is on how reflected seismic energy is turned into images of the subsurface for exploration and characterization.

Core questions

• How are seismic reflection surveys acquired in the field?
• What processing steps turn raw records into an interpretable image?
• What does seismic migration do, and why is it needed?
• How are seismic images interpreted for structure and stratigraphy?

Key concepts

• Common-midpoint method and stacking
• Normal-moveout correction and velocity analysis
• Deconvolution and noise suppression
• Seismic migration and imaging
• Time versus depth sections and interpretation

Key theories

Common-midpoint stacking

By recording each subsurface point with many source-receiver pairs and summing the traces after moveout correction, the common-midpoint method enhances reflections against noise and yields the velocity information needed for imaging.

Seismic migration

Migration repositions reflected energy from its recorded location to the true subsurface position of the reflector, collapsing diffractions and correcting for dip, and is the key step that converts a seismic record into a structurally accurate image.

Mechanisms

A controlled source such as an air gun or vibrator radiates energy that reflects from interfaces where acoustic impedance changes; arrays of receivers record the returning wavefield, and processing corrects for the geometry and velocity of the overburden, suppresses noise and multiples, and migrates the energy so that each reflection is placed at the depth and position of the boundary that produced it, yielding an image of subsurface structure.

Clinical relevance

Reflection seismology is the principal tool of petroleum exploration and reservoir characterization, is used in coal and mineral exploration, crustal studies, and increasingly for monitoring subsurface carbon dioxide storage and geothermal reservoirs.

History

Reflection seismology emerged commercially in the 1920s and 1930s for oil exploration; the introduction of the common-midpoint method, digital recording and processing in the 1960s, wave-equation migration pioneered by Claerbout, and three-dimensional surveys progressively turned it into a high-resolution imaging method.

Key figures

• Jon Claerbout
• Öz Yilmaz
• Robert Sheriff

Seminal works

• sheriff1995
• yilmaz2001
• claerbout1985

Frequently asked questions

What is seismic migration?

Migration is a processing step that moves recorded reflections to the true positions of the rock boundaries that caused them and focuses energy spread out by diffractions; without it, dipping layers and complex structures would appear mislocated and blurred in the seismic image.

Why is the same midpoint recorded many times?

Recording each subsurface point with many source-receiver combinations and summing the results, after correcting for travel-time differences, strengthens genuine reflections relative to random noise and provides the velocity information needed to image the subsurface accurately.