Wichita, Kansas, September 22, 1991
[Originally published in 1991 as Kansas Geological Survey Open-file Rept. 91-52. This is, in general, the original text as published. The information has not been updated.]
Cores presented in this workshop are key elements of integrated geologic studies and have enhanced resultant interpretations of subsurface geology. The cores have been specifically used to interpret genetic units of strata that have posed particular correlation problems, to evaluate petroleum reservoirs in mature oil and gas fields to maximize their development, to establish a rock framework for near-surface reservoir analogs, to evaluate horizontal-drilling potential, and to estimate methane reserves in coal beds.
Cores have long provided fundamental data for interpreting subsurface geology. The envelope of available information in the subsurface is continually expanding through introduction of new tools to image and sample the subsurface, including new wireline logs, seismic devices and engineering-testing tools, formation samplers and bottomhole quartz-pressure sensors. At the same time, geologists are seeking knowledge about increasingly more subtle characteristics of the strata from cores. These studies are vital in order to calibrate new tools and to substantiate refined stratigraphic, sedimentologic, and diagenetic interpretations.
Regardless of the approach or type of subsurface analysis, cores continue to be necessary to verify what is indirectly observed or measured through these other methods and devices. Accordingly, the role of core has not diminished, but rather increased. For example, sequence stratigraphy and genetic stratigraphy, its predecessor, have vastly improved accuracy and precision of geologic interpretations. Cores are central to establishing the genetic stratigraphic framework. Cores are also the basis for improving depositional models used to describe known reservoirs and to predict other occurrences in the basin. Two of the contributions describe the genetic stratigraphy of the Permian Chase Group--Page Twiss's study of a long near-outcrop core in northeastern Kansas and Craig Caldwell's investigation of a core from the Chase Group of the Hugoton field in the Oklahoma Panhandle.
Exploration targets in the midcontinent, while they have been generally decreasing in size and are becoming less numerous, still are viable targets for independents and a few major oil companies. However, significant reserves of new oil continue to be found in subtle stratigraphic and combination traps which require new perspectives in their search. Several presentations in this workshop address stratigraphic intervals that have associated prolific reservoirs sought in recent exploration and development efforts in western Kansas--the St. Louis oolitic grainstone (Abegg) and upper Morrow sandstones (Blakeney-DeJarnett and Krystinik). In addition, two displays describe potentially significant, but relatively undeveloped intervals in western Kansas-Atokan and lowermost Cherokee strata in southwest Kansas (Youle) and Desmoinesian-Missourian? sandstones in extreme southeastern Colorado (Caldwell). While CDP seismic profiling is an important tool for locating many of the new fields, cores and well logs provide the basis for calibrating these seismic data and for characterizing the reservoir and developing optimum strategies for oil extraction.
Near-surface analogs to petroleum reservoirs can be cored and logged less expensively than deeply buried reservoirs. In addition, nearby outcrops and boreholes provide additional means to acquire rock data at various levels of detail and scale. Together these data provide the opportunity to construct detailed three-dimensional models of reservoir analogs and aid in improving the understanding of the makeup of petroleum reservoirs.
Shallow, high-resolution seismic surveys can also accompany these data, helping to further constrain the limits of surfaces and define the geometries of the stratal units. Accordingly, geological models can be made more precise. The midcontinent area has accessible, shallow equivalents to many of the Paleozoic reservoirs. Progress reports on two Upper Pennsylvanian near-surface analog studies are presented in this core workshop (Feldman and Franseen, written as a field-trip guidebook for this midcontinent meeting and the other in the display by French).
Cores are a primary source of data to carry out specialized geologic-engineering studies such as the analysis necessary to define horizontal-drilling targets (Fritz et al., this volume). A firm understanding of the geology of the reservoir is essential for proper design and implementation of the horizontal hole. The interpretation of fractures, stratification, permeability, anisotropy, and general definition of hydraulic flow units has relied on the results of core analysis.
Efforts to revive older, developed oil and gas fields through concurrent, integrated geological-engineering analysis is being undertaken throughout the U.S. This program is an underpinning of the U.S. Department of Energy's National Energy Strategy to sustain domestic oil production. Bypassed mobile oil may be significant in fields because of compartments that isolate oil and prevent it from being produced in existing boreholes. Strategic infill drilling, including horizontal boreholes may find these remaining pockets of oil. Furthermore, previous waterflooding may have only effectively flushed oil from the more permeable sites in the reservoir. New designs in waterflooding, including permeability modification via polymers, may be a solution. Cores again are critical to evaluation of the reservoir. Cunningham and Newell display cores used in such an integrated study of the large Zenith field from Stafford County, Kansas.
The development of coal-bed methane derived from shallow Desmoinesian Cherokee Group strata in southeastern Kansas has been stimulated with present tax incentives. It was an overlooked resource of gas until methane was demonstrated to be extractable from subsurface coal beds. Although cuttings of coal are adequate for gas extraction, the chemistry of the coals is best analyzed from cores. Stoeckinger describes how to assess coal-bed methane potential using examples of cores of coal beds that have served as sources of methane in southeastern Kansas.
We extend our sincere thanks to all the participants for the considerable effort that they have put into the displays and the papers. Thanks is given to the companies who permitted employees to take the time to participate, handling their expenses and providing assistance in getting the displays to this meeting. Appreciation is extended to Phillips Petroleum for providing color plates in Caldwell's papers and for donating some of the materials used during the session.
Appreciation is extended to Marla Adkins-Heljeson for editing and desktop-publishing and to Jennifer Sims for assisting in preparation of artwork and layout of book.
The core displays are located in the combined Crystal I and II rooms at the Ramada Inn in downtown Wichita. The layout of these displays is shown on the attached floor plan (fig. 1). Last minute changes may affect this plan slightly, but will be noted in handouts available at the time of the session. The displays are listed in the notes alphabetically by author. The locations of the core displays roughly follow an order from stratigraphically highest to lowest. Fig. 2 shows the stratigraphic distribution of the cores and fig. 3 is a map of Kansas, Oklahoma, and the eastern portion of Colorado, annotated with locations of the cores used in the workshop.
Magnifying lenses are available to borrow for those that need them.
Refreshments are provided.
W. Lynn Watney, Anthony W. Walton, Craig D. Caldwell, and Martin K. Dubois, Workshop Organizers, September 4, 1991
Figure 1--Location of displays and sessions.
Figure 2--Stratigraphic distribution of the cores presented in the workshop.
Figure 3--Map of Kansas, Oklahoma, and eastern Colorado, annotated with the locations of cores presented in the workshop.
Kansas Geological Survey
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Web version created June 29, 2012. Original publication date 1991.