Mississippi Lime: Good Things On The Horizon

At first glance it seems there’s not much overtly new about drilling in the Mississippi Lime – or overtly new about the Mississippi Lime play, either, for that matter – a play that oozes from northern Oklahoma through southern Kansas (and some say, perhaps, to Nebraska).

After all, the industry has been vertically drilling the play for over 50 years, as evidence of the area’s more than 15,000 vertical wells.

But here’s the key word in that last paragraph: Vertically.

And that’s why we’re talking about it now. In the Mississippi Lime, there are good things – wait for it – on the horizon.

“Mississippian carbonate and chert reservoirs in northern Oklahoma and southern Kansas have been productive for decades,” said AAPG member Matthew Pranter, professor and Lew and Myra Ward Endowed Chair in Reservoir Characterization at the University of Oklahoma.

Pranter and others from the university’s ConocoPhillips School of Geology and Geophysics are part of the Mississippi Lime Consortium, which is focusing, specifically, on the thick Mississippian-age carbonate sequence in northern Oklahoma and southern Kansas that includes heterogeneous reservoirs of fractured limestone, porous sucrosic dolomites, tripolite and spiculities (fine sedimentary rocks).

Image Caption

Result of multi-attribute unsupervised seismic-facies classification within the Mississippian limestone using texture-attribute volumes. Courtesy of ConocoPhillips School of Geology and Geophysics. For a closer look use the image gallery (right).

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At first glance it seems there’s not much overtly new about drilling in the Mississippi Lime – or overtly new about the Mississippi Lime play, either, for that matter – a play that oozes from northern Oklahoma through southern Kansas (and some say, perhaps, to Nebraska).

After all, the industry has been vertically drilling the play for over 50 years, as evidence of the area’s more than 15,000 vertical wells.

But here’s the key word in that last paragraph: Vertically.

And that’s why we’re talking about it now. In the Mississippi Lime, there are good things – wait for it – on the horizon.

“Mississippian carbonate and chert reservoirs in northern Oklahoma and southern Kansas have been productive for decades,” said AAPG member Matthew Pranter, professor and Lew and Myra Ward Endowed Chair in Reservoir Characterization at the University of Oklahoma.

Pranter and others from the university’s ConocoPhillips School of Geology and Geophysics are part of the Mississippi Lime Consortium, which is focusing, specifically, on the thick Mississippian-age carbonate sequence in northern Oklahoma and southern Kansas that includes heterogeneous reservoirs of fractured limestone, porous sucrosic dolomites, tripolite and spiculities (fine sedimentary rocks).

And what’s coming, he adds, is what’s exciting.

“While the Mississippian interval was initially produced by vertical wells, it has become a significant unconventional play for horizontal development,” Pranter said.

And that’s because wells, with advance in horizontal drilling and completion techniques, can connect the compartmentalized nature of the Mississippian interval, thus increasing the production originally observed in vertical wells.

As with all innovative ideas, however, there are challenges.

“The geological controls on reservoir-quality distribution and production,” he said, “are still elusive.”

The Team Approach

The multidisciplinary OU team, which includes 15 graduate students and is funded through a collection of grants from government and industry sponsors, also includes:

  • Seismic interpretation and processing: AAPG member Kurt Marfurt (principal investigator, AASPI).
  • Engineering, characterization and fluid-flow simulation: Deepak Devegowda, assistant professor, Mewbourne School of Petroleum and Geologic Engineering.
  • Sedimentologist and Diagenesis, AAPG member R. Doug Elmore.
  • Geophysics of unconventional reservoirs and micro-seismic analysis: Jamie Rich, co-principal investigator and assistant professor.

“To better constrain 3-D reservoir models,” Pranter said, “the team also is using engineering-petrophysical methods (such as machine learning and pattern-recognition algorithms; see related story on page 10) to estimate lithologies in non-cored wells and 3-D seismic attributes to predict ‘sweet spots’ in the Mississippian that are commonly associated with various silica-rich carbonates and fractures.”

This team approach, all involved agree, means research can be explored from many different angles, including the relationships between data acquired at different scales, such as core, log and seismic data, for example, and those that come from different sources, such as well completions and drilling data.

Pranter said most of the fields originally were produced on closed structural highs and porosity pinch-outs associated with diagenesis and erosion.

“Given the advances in horizontal drilling and completion techniques, wells can connect the compartmentalized nature of the Mississippian interval,” he said, “thus increasing the production originally observed in vertical wells.”

An Opportunity Awaits

The Mississippi Lime (70-80 wells) is a significant reason for the turnaround in the area’s crude oil supply, counting for approximately 22 percent of Oklahoma’s production, which is up 100,000 barrels since 2005, or 37 percent.

Along with North Dakota’s Bakken (180-190 wells), Texas’ Eagle Ford (220-230 wells) and the Permian Basin in Texas and New Mexico (500 wells), the Mississippi Lime is a vital player now in the national conversation.

On this point, there is an interesting dynamic to the Mississippi Lime: It is relatively shallow, with sections between 300 and 500 feet, and found at depth between 3,000 and 6,000 feet, contrasting with the Bakken’s 9,000-10,000-foot depth and the 4,000-15,000-foot depth for both the Eagle Ford and Permian/Delaware Basin.

Additionally, its geology is interbedded, with areas of thin porosity alternating with tight limestones and topped by Mississippi chat – a varied combination of chert, limestone and dolomite.

This is the challenge – but this also is the opportunity.

“Building upon their geophysical expertise at OU in the Mississippian,” Pranter said, “the group continues to explore the correlation of seismic attributes (such as volumetric curvature, P-impedance, S-impedance and azimuthal anisotropy) to fractures (measured by image and production logs) and lithology/lithofacies.”

This includes conducting integrated and multidisciplinary studies of the Mississippian reservoirs from several angles – geological, geophysical and petroleum engineering.

“The data and methods,” he said, “are key to defining the seismic pattern (texture) associated with tripolite “sweet spots.”

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