How to read Seismic Survey?

Introduction to Seismic Surveys

Seismic surveys are an essential tool in the geosciences, providing valuable insights into the structure and composition of the Earth’s subsurface. These surveys are widely used in a variety of industries, including oil and gas exploration, geothermal energy exploration, and geological mapping. Understanding how to read seismic surveys is critical to accurately interpreting the data and extracting meaningful information. In this article, we provide a comprehensive guide to reading seismic surveys effectively.

The basics of seismic surveys

Seismic surveys involve the generation and detection of seismic waves, which are waves of energy that propagate through the Earth’s subsurface. These waves are generated by seismic sources, such as explosives or vibrating devices, and their reflections and refractions are recorded by seismometers or geophones. The recorded data is then processed and analyzed to create a detailed image of the subsurface.
When reading a seismic survey, it is important to understand the key components of the data. The most basic element is the seismic trace, which represents the amplitude of the recorded seismic waves over time. Seismic traces are typically represented as a vertical line on a seismic slice, with each trace corresponding to a specific location on the Earth’s surface.

Another important aspect of seismic surveys is the concept of seismic horizons. Seismic horizons are interpreted boundaries between different geological strata or formations. They are identified by distinct changes in seismic wave patterns, such as amplitude variations or abrupt velocity changes. These horizons provide valuable information about subsurface structure and help identify potential hydrocarbon reservoirs or other geological features.

Interpreting Seismic Attributes

Effective interpretation of seismic data requires a good understanding of seismic attributes. Seismic attributes are quantitative measurements derived from the seismic data that provide additional information about the subsurface. Some common seismic attributes are amplitude, frequency, phase, and coherence.
Amplitude is one of the most widely used seismic attributes. It represents the strength of the reflected or refracted seismic waves and can be indicative of lithology or fluid content. High amplitudes can indicate the presence of hydrocarbons, while low amplitudes can indicate non-productive zones.

Frequency is another important attribute that describes the number of oscillations or cycles of a seismic wave per unit of time. Higher frequencies are associated with shorter wavelengths and are sensitive to small-scale geological features such as fractures or thin beds. Lower frequencies penetrate deeper into the subsurface and provide information about larger scale structures.

Phase is a seismic attribute that describes the relative timing of the arrival of seismic waves. It can be used to identify faults or other discontinuities in the subsurface by observing changes in the phase relationships across these features.

Coherence is a measure of the similarity or consistency between seismic traces. It is used to identify continuous reflectors or stratigraphic layers and is particularly useful for mapping geological features that extend laterally.

Constructing a Seismic Section

A seismic section is a two-dimensional representation of the subsurface created by arranging multiple seismic traces on a horizontal line. It provides a visual representation of geologic structures and can help identify potential exploration targets.

When constructing a seismic section, it is important to consider the spatial relationships between seismic traces. The vertical spacing between the traces, known as the sampling interval, affects the resolution of the seismic section. Smaller sampling intervals result in higher resolution, but also increase data volume and processing requirements. The horizontal spacing between traces, known as the line spacing, determines the lateral coverage of the seismic section.

Several techniques can be used to improve the interpretation of a seismic section, including filtering, migration and amplitude scaling. Filtering involves modifying the seismic data to emphasize certain frequencies or remove unwanted noise. Migration is a process that corrects for the curved paths of seismic waves in the subsurface, allowing for a more accurate representation of geologic structures. Amplitude scaling adjusts the amplitudes of seismic traces to enhance the visibility of subtle features.
In summary, reading seismic requires a combination of geological knowledge, understanding of seismic attributes, and interpretation skills. By analyzing seismic traces, identifying seismic horizons, interpreting seismic attributes, and constructing seismic sections, one can gain valuable insight into subsurface structure and improve geological understanding. Seismic surveys continue to be a vital tool in various scientific and industrial applications, contributing to our understanding of the Earth’s subsurface and facilitating resource exploration and development.

FAQs

How to read Seismic Survey?

Reading a seismic survey involves analyzing the data obtained from conducting seismic exploration to understand the subsurface geology. Here are the key aspects to consider:

What is a seismic survey?

A seismic survey is a method used to gather information about the Earth’s subsurface by generating and recording seismic waves. These waves are generated by controlled explosions or by using specialized equipment to vibrate the ground.

What are seismic survey data?

Seismic survey data are the recorded measurements of the seismic waves that have traveled through the Earth and have been detected by geophones or other sensitive instruments. These measurements are collected at various locations and can provide insights into the subsurface structures.

How are seismic survey data presented?

Seismic survey data are typically presented as seismic profiles or sections. A seismic profile is a graphical representation of the subsurface, showing how the seismic waves have reflected or refracted at different geological layers. These profiles are usually displayed as a series of wiggly lines known as seismic traces.

What are seismic traces?

Seismic traces are the wiggly lines displayed on a seismic profile. Each trace represents the recorded energy from a specific location or receiver. By analyzing the patterns and characteristics of these traces, geoscientists can interpret the subsurface structures and identify features such as faults, stratigraphic layers, and hydrocarbon reservoirs.

What are seismic horizons?

Seismic horizons are distinct boundaries or layers within the subsurface that can be identified on a seismic profile. These horizons represent changes in rock properties, such as lithology or seismic wave velocity. Geoscientists interpret seismic horizons to map the spatial distribution of geological features and to identify potential drilling targets.