The Upper Jurassic Smackover formation in northern Louisiana and surrounding states has been explored and drilled for decades, yielding considerable volumes of hydrocarbons.
Early on, the action entailed the penetration of large structures. This was done by mapping shallower horizons or with 2-D seismic data.
As drilling progressed, it became apparent that the Smackover depositional system was far more complex than initially thought.
A more sophisticated approach was needed to decipher the challenging geology.
“As the geologists’ understanding of system variability improved with well density, the same improvement was not readily apparent in the seismic imaging of these complex architectures until fairly recently,” said AAPG member Jeffrey Ross, senior geophysicist at Whiting Petroleum Corp.
Whiting is studying a part of the Smackover area looking for unconventional opportunities in the Lower Brown Dense zone in the Lower Smackover and some shallower secondary conventional targets.
To that end, a serendipitous event occurred up front.
“Geokinetics called and said they were going to shoot 3-D in the area,” Ross said, “and the map they drew covered a lot of our acreage, so we said we’re in.”
He noted that the ensuing non-exclusive Millerton survey shot in 2013-14 covered approximately 205 square miles in North Louisiana between the towns of Haynesville, Springhill and Homer.
“Robust field acquisition procedures yielded superior quality field data, and modern PSTM processing resulted in excellent structural delineation of complex fault-block geometries associated with underlying Louann salt movement,” Ross noted.
A processing stream was initiated parallel to that of Geokinetics, and the final unfiltered product of this stream was handed off to Geotrace to apply their proprietary BE bandwidth extension processing.
“It was our opinion that (their) utilization of the continuous wavelet transform, or CWT, to increase bandwidth would be superior to using typical industry techniques,” Ross said, “in that the CWT should theoretically improve signal-to-noise in the extended
frequencies.”
The final bandwidth extended data set was “tested” by applying the relative colored acoustic impedance inversion technique, which can be used for high-resolution qualitative analysis.
He offered a brief overview of some of the considerable information derived from the Smackover seismic effort overall.
“Results of this test revealed an excellent correlation of the band-limited acoustic impedance with the known Smackover carbonate intervals penetrated by well control,” Ross said. “It was extremely useful in aiding the interpretation of the higher order
sequences.
“The high frequency imaging afforded by the bandwidth-enhanced 3-D seismic volume reveals a complicated interplay between accommodation, or volume, driven by relative sea level and syndepositional salt movement,” he added.
“Loading of the Louann salt during progradation of Upper Smackover clinoforms resulted in areas of increased accommodation where salt was being evacuated,” he noted, “and, conversely, areas of decreased accommodation in areas on salt ridges.
“As the Upper Smackover prograded across these salt ridges, a departure from ramp geometry is observed, and clinoforms become steeper and develop a pronounced break in slope,” Ross continued.
Following the Upper Smackover deposition, faults cut through the entire sequence immediately downdip of salt ridges, according to Ross. This activity resulted in large displacement synthetic listric normal faults that sole out in the Louann salt.
The Millerton 3-D seismic acquisition survey – along with the subsequent application of special bandwidth extension processing and inversion to these data – has proven to be an invaluable assist to the geoscientists interested in the area.
Ross itemized a number of conclusions reached for the project:
- Good 3-D seismic is never a bad idea in areas with complex geology.
- Bandwidth extension isn’t voodoo.
- Relative colored inversion is cheap, quick and supplies a strong uplift in interpretability of areas of rapid facies change.
- Global eustasy is not the only significant driver of Smackover deposition; local tectonics and halokinesis have a role as well.
- Classic Smackover A, B and C nomenclature obfuscates a much more complex depositional architecture.
“This has conclusively demonstrated,” he added, “that seismic acquisition and processing in the Smackover of northern Louisiana has finally caught up to the level of detail available to geologists in this complicated and intriguing area.”