Fault finding

Tool Aids Interpretation

American Association of Petroleum Geologists (AAPG)
Geological expression technology adds another optional tool – and a lot more dramatic color and images – for the fault finding process. Graphics courtesy of ffA
Geological expression technology adds another optional tool – and a lot more dramatic color and images – for the fault finding process. Graphics courtesy of ffA

The oil and gas industry is heavily populated with creative, forward thinking individuals working earnestly to find solutions to the varied challenges indigenous to this highly complex business.

This ensures a steady, seemingly unending flow of both brand new and improved technologies coming into the marketplace in response to demands posed by such diverse, challenging entities as the Arctic, the deep water, the always-complex shale plays – and a multitude more.

The ubiquitous use of seismic technology, for instance, keeps the industry players on their collective toes looking for new, more efficient approaches to data use and interpretation. After all, the value of seismic data lies within the information the data contain.

A recent study focused on interpreting complex structural information from 3-D seismic by using novel “Geological Expression” techniques instead of conventional manual picking methods offers a unique example of industry ingenuity.

A post-stack 3-D seismic dataset acquired from the Exmouth sub-basin of the Northern Carnarvon basin offshore the northwest shelf of Australia was used to test the techniques. The study was conducted by geoscientists at ffA-GeoSciences, which is headquartered in Aberdeen, Scotland.

According to ffA: “The idea behind Geological Expression is to strike a balance between enabling the interpreter(s) to bring all of their experience to help guide the process of extracting useful information from seismic data, while simultaneously harnessing the processing power of fast GPU processors to provide objective data analysis.

“This dramatically speeds up the interpretation process,” the company claims, “as the data can be manipulated quickly to extract real geological features.”

Australian Case Study

AAPG member Tom Wooltorton, sales support geoscientist in the ffA Houston office, presented a paper on the Geological Expression technique at the recent annual meeting of the Gulf Coast Association of Geological Societies (GCAGS), and afterward provided a succinct look at drawbacks of the commonly used manual interpretation approach.

“Structural interpretation of 3-D seismic is achieved principally through manual picking of faults on inlines and crosslines and then defining the geological context of the results,” Wooltorton said.

He noted that this can be inefficient for several reasons:

  • Manual interpretation is highly time consuming, and it’s difficult to process more than a portion of the data by the eye.
  • There is a high risk of subjectivity, especially with poor quality or ambiguous data.
  • Commercial pressures may mean the work may be rushed.

These limitations are in stark contrast to the advantages afforded via the data-driven, interpreter-guided Geological Expression workflow approach to understanding and defining the 3-D morphology of the geological elements within the seismic data, according to Wooltorton:

  • Significant reduction in time required to generate geologically meaningful results.
  • Transforming the data into a form relative to structural interpretation enables rapid access to the information.
  • Enhance the value of the original seismic data by ensuring full information content is utilized.

“The particular advantage of the data-driven method in the instance of the (Australia) study is the richness of information present in the seismic data,” Wooltorton emphasized.

The Geological Expression workflows applied to the Australian shelf seismic cube adequately demonstrated the wealth of knowledge of the structural geology that can be obtained without resorting to manual interpretation.

“Using volumetric interpreter guided data analysis and extraction methods, based on 3-D seismic attribute analysis, a structural history was interpreted and supported by statistical information,” Wooltorton said.

“To determine the broad structural trends of the seismic reflections, volumetric dip and azimuth cubes were computed from the conditioned data,” he noted. “The dip and azimuth cubes also were combined in one volume that displayed the results in a two-dimensional color map.”

Wooltorton commented that upon visual interpretation, the DipAzi-combined volume immediately provided contextual information.

For example, a clear change in structural trend is shown across an angular conformity.

Hope for the Future

When all was said and done, the study analysis revealed “fault system activity and movement that occurred over several tectonic phases, including evidence suggesting a loss of integrity in a known sealing lithology.”

The effort required only a few days, including processing of the post-stack seismic data.

“One of the most striking things about this study is the amount of interpretive information that can be obtained in such a short amount of time,” Wooltorton exclaimed.

He noted also that the geological setting of the particular part of the area studied is well known and explored. This enabled the end results of the study to be validated via known data.

The study overall was designed to reach beyond the technology itself.

“Over and above the technical objectives, the aim of this study was to evaluate how the potential of 3-D seismic can be exploited in a way that goes beyond the 2-D mindset that still dominates most facets of seismic interpretation,” Wooltorton said.

“Considerable effort has been expended in recent years on improving technology and hardware for interpretation tools,” he noted. “But relatively little effort has gone into innovating new techniques that aren’t subject to historical limitations.”

If more studies similar to the test case can be implemented and translated to real world commercial value, then the next generation of seismic interpretation techniques may be innovated in a variety of other capacities, according to Wooltorton.

“Often,” he said, “the impression is that while there are plenty of creative minds in seismic interpretation looking at new techniques, the constraints of time and commercial pressure prevent these from being explored.”

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