Seismic inversion, also known as seismic interpretation, is an indispensable geophysical technique used to reveal the internal structure of the Earth and its potential oil, gas and mineral deposits. How does it work? Let’s find out!
Seismic Inversion Explained
Seismic inversion is a technique used to generate images of the Earth’s subsurface from measuring acoustic waves that are transmitted into the ground. When seismic waves are transmitted into the ground, they spread out to form a wavefront at the surface with one wave going deeper than another. As these wavefronts hit different layers of rock, some will be refracted (bent) by the rock layer or scattered (detected) as energy deposits. This energy is then detected by receivers which send information back to computers where it can be processed and inverted to produce an image of what is under ground. The data acquired from this process allows for better understanding of geological structures such as salt domes, faults, and oil reservoirs.
The process is most commonly done using an array of up to 60 seismometers on a half-mile grid pattern buried about 1 foot below the surface. Data from these sensors are combined together to create one signal called a common-shot gather. The common-shot gather records all the incoming sound waves simultaneously and produces many more traces in both time and space than just recording individual seismic events. From this data, we can create two dimensional images that depict the relative reflectivity of various zones in the earth’s crust which provides information about subterranean features like salt domes or oil reservoirs
What Is Its Purpose
Seismic inversion is a technique used to process and analyse seismic data, also known as seismic surveys. This technique is used to determine the physical properties of the subsurface in an area of interest. To use this technique, it can be helpful to have a surface survey or borehole data to confirm that there are some geologic boundaries at depth. Using the boundary information, you will be able to tell what kind of layers are beneath the surface such as whether there are faults or volcanic zones within a layer. You can then infer how these properties may change with depth based on your initial survey data.
Frequently Asked Questions
Q. What is seismic inversion?
- Seismic inversions are used to estimate subsurface information, such as rock types or fluid content, by comparing recorded data with the geologic models. They are often used for enhanced oil recovery by estimating shale properties (inclusion of non-shale rocks) to find the best places to drill.
Q. How is it different from a standard reflection survey?
- The most obvious difference between a seismic reflection survey and an inversion is that there are no reflections with seismic inversions, they use first-arrivals instead of last-arrivals which can provide estimates at different depths than a standard reflection survey using well logs.
Use Case Examples
In its simplest definition, seismic inversion is the process of analysing a data set collected from the earth’s surface to reconstruct what would have been picked up on a seismic profile. This is accomplished by extrapolating certain properties from the volume of data that can be retrieved. The most common use for seismic inversion is determining geological depth profiles; these depth profiles can give information on potential oil deposits, earthquakes zones, petroleum leaks or pollution spills. Seismic inversions also make it possible to see fault lines in underground mines or tunnels to ensure safety of miners and personnel who work there.
