Conventional tools, unconventional application

Combo Seismic Approach Defines Fractures

Formation fractures, whether natural or hydraulically induced, are a must-have for the most economic production from unconventional resource plays, with their characteristically tight reservoir rocks where excessively low indigenous permeability and porosity impede hydrocarbon flow.

Unfortunately, there’s seldom anything simple about these fractures, with their highly variable features.

Making sense of them is the challenge confronting the geoscientists in their quest to identify the superior drill spots for optimal production.

To understand and delineate fracture trends, the industry regularly employs varying seismic techniques, including the processing of seismic attributes, i.e. geometric attributes, definition of azimuthal variation of amplitude and microseismic surveys, among others.

The approach frequently used, in an effort to conserve time and capital, entails reliance on a singular seismic technology.

Yet a combination of certain seismic techniques ordinarily can deliver the most bang for the buck.

The combo approach and its advantages were presented in the Ziad Beydoun Memorial Award for best poster at the AAPG 2011 International Conference and Exhibition in Milan.

Dubbed “Fracture Detection Interpretation Beyond Conventional Seismic Approaches,” the presentation focused on a study done by AAPG members Stan Abele, vice president of geoscience technology at IHS-owned Seismic Micro-Technology at the time and currently employed at LMKR, and geophysicist Rocky Roden, who consults for IHS.

“Spectral decomposition analysis can be used to determine the optimal frequency bands that define fracture lineations,” Abele said. “These optimally defined frequency volumes can then be processed for geometric seismic attributes to significantly improve the interpretation of fracture trends and increase understanding of the reservoir.

“Interpreting the optimal frequency band for seismic attribute processing requires a systematic methodology of frequency analysis and amplitude normalization,” he noted.

“Combining spectral decomposition and geometric seismic attributes has shown to not only improve fracture identification,” he said, “but also more clearly define stratigraphic variations in most geologic settings.”

Abele elaborated on the terminology:

Spectral decomposition is an imaging tool that breaks down the seismic signal into its component frequencies.

Several frequency windows may highlight different aspects of the geology when used as input into the calculation of geometric attributes for fracture analysis.

Geometric attributes respond to changes in reservoir structure and stratigraphy.

The Dip of Maximum Similarity and the Instantaneous Dip are two of the most popular attributes used for discontinuity mapping, especially mapping faults in 3-D. They may be the most valuable attributes for structural mapping for many interpreters, according to Abele and Roden.

Maximizing Data’s Value

The presentation at the Milan meeting was based on a study utilizing five square miles of recently acquired pre-stack time-migrated 3-D seismic data provided by Global Geophysical Services from the south Texas Eagle Ford shale resource play, where the production is enhanced through the drilling and fracture treatment of horizontal wells.

Well and microseismic data were provided by Tulsa-based Petrohawk Energy Corp.

“When we got these data, it seemed like a natural place to apply this ‘unconventional’ seismic technique,” Abele said. “The Eagle Ford has enough complexity in the fracturing to where it’s the natural area to apply this kind of project.

“Understanding the existing fault and fracture patterns in the Eagle Ford is critical to optimizing well locations, well plans and fracture treatment design,” he continued.

“Detailed analysis of seismic data is essential in deriving maximum structural information to assist in economic development of the hydrocarbons in place.

“Microseismic data acquired during fracture treatments support the predicted orientation of faulting and variations in fracture patterns,” he noted.

Roden emphasized that even though their effort entailed an unconventional seismic approach, it is not new or groundbreaking. The tools are available, and the technique is not overly time consuming or expensive.

The kicker is that it can maximize the value you derive from your data.

And it doesn’t require the expertise of a geophysicist dedicated solely to this type seismic application. In fact, Abele noted that it can be a part of the ordinary geoscience work environment and likely be informative to less experienced interpreters, while reminding others that it may be worth taking that extra step to produce more analysis.

He summarized conclusions from the study:

  • Geometric seismic attributes can provide enhanced detail that is useful for structural interpretation and fault/fracture detection.
  • Spectral decomposition is used to determine which frequency band provides the highest resolution results for the target zone.
  • Calculating geometric attributes on the frequency band volume which provides the highest resolution enhances results and understanding of fine-detail geological properties.
  • Viewing results from multiple frequency bands may contribute additional insight into the overall structural nature of the reservoir.

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Awarding

Stan Abele
Stan Abele

Stan Abele and Rocky Roden will receive the Ziad Beydoun Memorial Award on April 22, during the opening ceremony of the AAPG Annual Convention and Exhibition in Long Beach, Calif. They are being honored for presenting the best poster at the AAPG 2011 International Conference and Exhibition in Milan.

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