Seismic Interpretation: Understanding Geological Data

Seismic Interpretation: Understanding Geological Data

The American Association of Petroleum Geology (AAPG) defines seismic interpretation simply as, “the science (and art) of inferring the geology at some depth from the processed seismic record.”

Seismic data is collected from subsurface geology and worked through several models to produce useful information. The goal is a reduction in exploration and development risk of drilling for hydrocarbons.

Gone are the days when wildcatters like the Hamill brothers would pool their last dollars in the hopes of hitting a gusher in an unproven field guided by little more than a hunch and some drill pipe. Today, drilling for oil and gas is more like a business and less like a casino. The successful drilling of a well is the product of data collection, analysis and expert interpretation.

To make sure every dollar invested in a modern oil or gas play is returned with a large enough profit to fuel future operations, oil and gas operators rely on skilled geologists to perform detailed seismic interpretation before they even spud the first well.

What Is Seismic Interpretation?

While the two basic elements of seismic interpretation are reflection/refraction characteristics and the shape of the reflection or refraction, seismic interpretation generally falls into three main categories – structural, stratigraphic and lithologic.

Structural Seismic Interpretation

In structural seismic interpretation, seismic data collected from the field is used to build structural, three-dimensional maps of the subsurface geology. 

These three-dimensional maps of the well-site geology can be used to display a visual representation of the subsurface and distinguish separations between geoclines to help identify the most optimal drilling location.

Stratigraphic Seismic Interpretation

Stratigraphic seismic interpretations help geologists develop chronostratigraphic frameworks based on the patterns of reflections in the seismic data. The boundaries between subsurface regions are identified on the basis of reflection termination patterns and the continuity of the reflections.

Lithologic Seismic Interpretation

Unlike structural and stratigraphic interpretations, lithologic seismic interpretation focuses on changes in porosity, fracture intensity and lithology from the collected seismic data. Lithologic seismic interpretation can provide valuable information in the form of direct hydrocarbon indicators, which could potentially identify the presence of hydrocarbons in the region.

Building an accurate model of subsurface geology and ultimately identifying favorable hydrocarbon reservoir characteristics is the goal of (and the reason for) any seismic interpretation, but an accurate model of the field cannot be built on seismic data alone.

An accurate model that reduces exploration and development risk in an oil or gas field can only be created by analyzing and interpreting all of the useful data available to the geology team.

Petrophysical, historical and drilling data must also be considered when building a reliable model of an intended target.

And while each piece of data can offer valuable insights and help you build a reservoir model, there is a need to limit the amount of data used in your model to avoid cluttering your data-set with excess noise.

Never lose sight of your goal when building and interpreting a geological model of an oil or gas field. Too many dry holes have been drilled with the help of poorly constructed data, and too many productive reservoirs have been off-loaded for a small fraction of what they were worth. 

Ask thoughtful questions and hold your geologist accountable when he or she presents models and recommendations. Geologists must understand the big picture goals for the models they develop.