Kansas Geological Survey, Open-file Report 91-52, p. 57-79
Phillips Petroleum Company
The Texas Panhandle field and adjoining Hugoton field of southwestern Kansas and the Oklahoma and Texas panhandles have produced 60 tcfg since discovery of the Texas Panhandle field in 1918. The two fields are structural-stratigraphic traps producing gas from the Lower Permian, Wolfcampian, Chase Group. The Chase Group in the Oklahoma Panhandle, Guymon-Hugoton area, is approximately 350 ft (107 m) thick and consists of cyclically deposited carbonate and fine-grained, siliciclastic units which can be traced laterally for tens of kilometers using wireline logs. A typical Chase Group depositional cycle in the western part of the Guymon-Hugoton field begins with a thin, light-gray to gray, structureless to burrowed, dolomitic siltstone unit reflecting the initiation of marine transgression and shallow drowning of underlying sediments deposited in supratidal environments. The siltstone is abruptly overlain by light-gray, burrowed, sparsely fossiliferous, very fine grained sandstone reflecting continued transgression and shoreface deposition generally near or below wavebase. The sharp contact of ft siltstone and overlying sandstone may be a marine, transgressive surface of erosion. The sandstone grades upward into a relatively thick, transgressive-regressive limestone and dolomite sequence. Bioclast mudstone, wackestone, and packstone composing the lower part of this sequence record continued transgression and subtidal, open-marine deposition below wavebase in waters perhaps a few meters to a few tens of meters deep. Planar-, low angle-, and cross stratified bioclast and bioclast-intraclast grainstone and washed packstone composing the upper part of the carbonate interval suggest the end of marine transgression and a seaward progradation of carbonate sediments deposited above wavebase in moderate to high-energy, nearshore shoal, upper shoreface, or beach environments. Slightly sandy and argillaceous, dolomite mudstone and wackestone composing the uppermost part of some carbonate intervals may record restricted lagoon to lower tidal flat deposition. The transgressive-regressive carbonate sequence is characterized by primary intergranular and secondary moldic and intercrystalline porosity and is the main Chase Group reservoir facies in the Guymon-Hugoton field. Diagenesis of the carbonate interval included a relatively early dolomitization by downward-migrating, Mg-rich waters from overlying tidal flat environments, meteoric leaching of undolomitized carbonate grains and lime mud, meteoric calcite cementation, and in some cycles, anhydrite cementation of primary and secondary porosity. Chase Group cycles are capped by tan, very fine grained, burrowed, parallel- and ripple-laminated sandstone and reddish brown, dolomitic, siliciclastic mudstone displaying mud cracks, caliche glaebules, and plant root structures. These siliciclastics are a result of continued regression and lower to upper tidal flat deposition and paleosol development.
The Hugoton field of southwestern Kansas and the Oklahoma and Texas panhandles and the adjoining Texas Panhandle field to the south, discovered in 1922 and 1918, respectively, have produced 60 tcfg (Pippin, 1970). The boot-shaped area of the two fields stretches north-south approximately 220 mi (355 km) and varies from about 20 to 55 mi (32-90 km) in width (fig. 1). The Kansas, Oklahoma, and Texas portions of the Hugoton field are referred to as the Kansas Hugoton, Guymon-Hugoton, and Texas Hugoton, respectively. This paper is concerned mainly with the western part of the Guymon-Hugoton field.
Figure 1--Tectonic map of the midcontinent showing location of Hugoton and Texas Panhandle fields (shaded; modified from Campbell et al., 1988).
The Guymon-Hugoton field, Texas County, Oklahoma, is a structural-stratigraphic trap producing gas mainly from the Lower Permian, upper Wolfcampian, Chase Group. The Chase Group in the Guymon-Hugoton field is approximately 350 ft (105 m) thick and consists of areally extensive carbonate, sandstone, and siliciclastic mudstone units which can be traced for tens of miles across the field. These units make up the formations and members of the Chase Group (fig. 2). Structural dip of Chase Group strata in the Guymon-Hugoton field is to the southeast varying from approximately 50 ft/mi (9.5 m/km) along the western edge of the field to 15 ft/mi (2.8 m/km) in the central and eastern parts of the field (fig. 3). Updip facies changes to the west in the Kansas Hugoton and Guymon-Hugoton fields result in decreased porosities and permeabilities in the reservoir intervals of the Chase Group and development of the structural-stratigraphic trap which characterizes the fields. Low-permeability, dolomitic, siliciclastic mudstones, dolomites, and anhydrites of the Sumner Group (Leonardian Series) overlie the gas productive Chase Group in the Guymon-Hugoton field and form an effective seal across the field. The history and regional stratigraphy and structure of the Hugoton and Texas Panhandle fields are reviewed by Rogatz (1961) and Pippin (1970).
Figure 2--Chase Group stratigraphy in Guymon-Hugoton field, Texas County, Oklahoma (after Zeller, 1968; Campbell et al., 1988; and Chaplin, 1988).
Figure 3--(A) Regional structure map of the Hugoton and Texas Panhandle fields (from Pippin, 1970) and (B) structure map of Guymon-Hugoton field including location of Stonebraker A-112 (from Siemers and Ahr, 1990).
Prior to the 1986 decision by the Kansas Corporation Commission which allowed infill drilling in the Kansas Hugoton, one well was drilled per section in the Hugoton field. Production from the Guymon-Hugoton field is mainly from the upper and middle puts of the Chase Group, primarily the Herington and Krider Members and the Winfield Formation. Guymon-Hugoton wells typically have produced for 2-6 bcfg. Portions of the upper, middle, and lower parts of the Chase Group including the Herington and Krider Members, Winfield Formation, and Towanda and Fort Riley Members are productive in the Kansas Hugoton. As a result, Kansas Hugoton wells typically have cumulative productions significantly greater than those of Guymon-Hugoton wells. Drilling depth to the top of the Chase Group in the Guymon-Hugoton field vanes from approximately 2,150 ft (655 m) in the northwestern part of the field to 3,150 ft (960 m) in the eastern part of the field. Productive intervals stratigraphically below the Chase Group in the Kansas Hugoton and Guymon-Hugoton fields include the Lansing, Kansas City, Marmaton, and Cherokee Groups and the Morrow Formation, all of which are Pennsylvanian in age, and the Mississippian St. Louis Limestone and Chesteran Series.
Numerous companies, in particular Santa Fe, Anadarko, Conoco, Mobil, Phillips, and OXY USA, Inc., have cored the Guymon-Hugoton Chase Group in recent years to acquire reservoir data. Cores from the OXY USA, Inc. Stonebraker A-112, sec. 13, T. 3 N., R. 12 E. CM, Texas County, Oklahoma, recovered all but the lowermost 5 ft (1.5 m) of the Chase Group and include 12.5 ft (3.8 m) of the overlying Wellington Formation of the Sumner Group. The lithologies, pore systems, depositional environments, diagenesis, and cyclic sedimentation of the Chase Group as observed in the Stonebraker A-112 cores are the focus of this study.
The Hugoton field in the Oklahoma and Texas panhandles lies in the western part of the Anadarko basin (fig. 1). The northern part of the field in southwestern Kansas occurs in the Hugoton embayment, a northern extension of the northwestern part of the Anadarko basin. During upper Wolfcampian Chase Group deposition, the Hugoton embayment and western part of the Anadarko basin formed a shallow-marine ramp which dipped gently eastward. Coarse arkosic sediments were shed off the emergent Front Range and Sierra Grande uplifts to the west and the Amarillo and Wichita uplifts to the south Rascoe, 1988) (fig. 4). The Amarillo and Wichita uplifts were buried partially by Wolfcampian, arkosic sediments and further covered by carbonates of the Brown Dolomite which is stratigraphically equivalent, at least in part, to the Chase Group (Rascoe, 1988). Rascoe stated that upper Wolfcampian sediments were deposited on the Apishapa uplift in eastern Colorado and subsequently removed during Leonardian time. Chase Group deposition in Kansas extended eastward across the Central Kansas uplift and in Oklahoma into the deeper portions of the Anadarko basin.
Figure 4--"Upper" Wolfcampian lithofacies of the western Midcontinent, outline of Hugoton and Texas Panhandle fields shown (from Rascoe, 1988).
Siemers and Ahr (1990) stated that the Chase Group in the Guymon-Hugoton field is composed of cyclical, shoaling-upward, peritidal sequences deposited on a low-relief ramp. This cyclical deposition is well displayed in Chase Group cores from the OXY Stonebraker A-112. A "typical" Chase Group depositional cycle as defined from the Stonebraker A-112 is composed of a relatively thin, transgressive siltstone and very fine grained sandstone unit gradationally overlain by a thick, transgressive-regressive, carbonate interval and capping the sequence a regressive, fine-grained sandstone and reddish-brown, siliciclastic mudstone (fig. 5).
Figure 5--Typical Guymon-Hugoton Chase Group depositional cycle as interpreted from the Oxy USA, Stonebraker A-112 core (sec. 13, T. 3 N., R. 12, E. CM), Texas County, Oklahoma.
At least five depositional cycles are recognized in the Chase Group in the Stonebraker A-112. These cycles are areally extensive and can be traced across the Guymon-Hugoton field using wireline logs and cores. The five Chase Group cycles discussed in this study are, in ascending order, the Wreford-Matfield, Barneston-Holmesville, Towanda-Gage, Winfield-Odell, and Krider-Paddock. The Wreford, Ft. Riley member of the Barneston, Towanda, Winfield, and Krider are mainly transgressive-regressive carbonate units, and the Matfield, Holmesville, Gage, Odell, and Paddock are predominantly regressive mudstones (fig. 6). Sandstones and dolomites of the Herington Member, upper Chase Group, and the overlying, reddish-brown, siliciclastic mudstones may represent an additional Chase Group depositional cycle. This sequence is markedly different, however, from the underlying cycles and is not included in the following discussion.
Figure 6--Coregraph and wireline logs, Oxy USA, Inc. Stonebraker A-112, Texas County, Oklahoma. [A larger Acrobat PDF version of this figure is available.]
The lowermost beds of a typical Chase Group depositional cycle are light-gray to gray, dolomitic siltstone (plate I-A and I-B). This structureless, mottled, or faintly pamllel-stratified, siltstone interval is generally 1-2.7 ft (0.3-0.8 m) thick and gradationally or abruptly overlies finer grained, reddish-brown, siliciclastic mudstone of the underlying depositional cycle. Mudstone and siltstone clasts are rare in the siltstone.
Light-gray, dolomitic and calcareous, very fine grained sandstone sits abruptly on the gray siltstone (plate I-B). This sandstone is absent to 6.5 ft (2 m) thick in Chase Group cycles cored in the Stonebraker A-112. Gray to dark-gray, argillaceous laminations and layers in the sandstone are typically irregular and discontinuous due to burrows. Horizontal, tube-shaped burrows 0.1-0.3 inch (0.25-0.75 cm) in diameter are common (plate I-C), and bioclasts, generally scarce echinoderms (crinoids) and bryozoans, are present in some beds. Ripple and planar stratification are rare.
The gray siltstone records drowning or flooding of supratidal/paleosol sediments and deposition in quiet, shallow, marine waters. Marine waters may have passed downward into immediately underlying, reddish-brown, supratidal/paleosol sediments altering their color to brownish gray. Overlying, light-gray sandstone records continued marine transgression and subtidal deposition in a relatively shallow, low- to moderate-energy, shoreface setting. Waves and currents depositing these sands scoured into the underlying transgressive mud and silt resulting in a marine, transgressive surface of erosion.
Transgressive sandstones of the Chase Group depositional cycles thin eastward from the Stonebraker A-112. These sandstones are absent in cored Chase Group cycles in the OXY Stonebraker A-113 (sec. 7, T. 3 N., R. 14 E. CM) 7 mi (11.3 km) to the east. Similarly, there is no mention by Siemers and Ahr (1990) of stratigraphically equivalent, transgressive sandstones in the Phillips Petroleum Sheil 2R (sec. 34, T. 2 N., R. 15 E. CM) nor the Buf 3 (sec, 27, T. 2 N., R. 15 E. CM) approximately 13 mi (21 km) to the southeast of the A-112. Ahr and Siemers suggested that dolomudstones containing lithoclasts of the immediately underlying regressive units characterize the Chase Group transgressive intervals. Siltstone clasts generally are rare or absent in the transgressive siltstones and fine-grained sandstones in the Stonebraker A-112 cores.
A relatively thick carbonate interval gradationally overlies the transgressive siliciclastic unit in a typical Chase Group depositional cycle. Chase Group carbonates vary from 30 to 57 ft (9.1-17.4 m) thick in the Stonebraker A-112 cores and thin westward as the Chase Group becomes progressively more siliciclastic. The carbonate intervals in the Stonebraker A-112 are divided into an upper and a lower part mainly on the basis of micritic and siliciclastic content, carbonate grain types, and sedimentary structures.
Light- to dark-gray, in some cycles sandy and argillaceous, limestone and dolomite compose the lower 1.5-25 ft (0.46-7.6 m) of the Chase Group carbonate intervals in the Stonebraker A-112. Void-filling anhydrite cement and replacement anhydrite nodules are rare to scarce in these rocks. Limestones and dolomites are burrowed, bioclast mudstones, wackestones, and packstones, the most common fossil debris being echinoderms (crinoids), bryozoans, and less numerous brachiopods (plates I-E and I-VB). Osagid-coated grains are common to abundant in the lowermost beds of most carbonate intervals (plates I-D and IV-E).
Rocks composing the lower part of a typical Chase Group carbonate in the Stonebraker A-112 reflect deposition below or near wavebase in open-marine waters perhaps a few meters to a few tens of meters deep. Osagid-coated grains record moderate wave or current energy sufficient to intermittently move these grains about on the seafloor. Overlying bioclast mudstones, wackestones, and packstones reflect deeper, quiet-water, offshore or shelf deposition below normal wavebase. These carbonates are less fossiliferous, more micritic, and slightly darker in color than those composing the upper part of the carbonate interval and probably record the maximum transgressive phase of a typical Chase Group depositional cycle (fig. 5). This maximum transgressive phase is best developed in the Barneston-Holmesville cycle where it is represented by dark-gray, sandy and argillaceous, fossiliferous, dolomitic limestone of the Florence Limestone (plate I-F).
The upper part of a typical Chase Group carbonate in the Stonebraker A-112 is yellowish-tan, light-gray to gray limestone and dolomite with locally common anhydrite cement and nodular, replacement anhydrite. Limestones and dolomites are bioclast and bioclast-intraclast packstones, washed packstones, and grainstones (plate III). Ooid-bioclast grainstone and ooid grainstone compose much of the middle and upper parts of the carbonate interval in the Krider-Paddock cycle (plate III-E and F). The most common carbonate grains in the middle and upper parts of the Chase Group carbonates are echinoderms (crinoids), bryozoans, and intraclasts. Brachiopods, green algae, pelecypods, small mobile forams, ostracodes, peloids, algal-coated grains, and ooids vary from rare to common. Fusulinids and gastropods are rare. Sedimentary structures are planar and low-angle stratification, small- to medium-scale cross -stratification, and burrow mottling. Oolitic grainstone of the Krider-Paddock cycle displays medium-scale, bidirectional, cross stratification (plate II-B). The uppermost part of the carbonate interval in the Towanda-Gage and Krider-Paddock cycles is gray to light-gray, slightly sandy and argillaceous dolomite characterized by a sparse biota (bioclast wackestone), scarce to common, horizontal, tube-shaped burrows, and in places irregular, discontinuous laminations.
The middle and upper parts of a typical Chase Group carbonate record basinward progradation of carbonate sediments and marine regression. Washed packstones and grainstones reflect deposition in moderate- to high-energy, shallow, marine waters a few meters or less in depth. The depositional setting was most likely shallow, nearshore bar or upper shoreface to beach. Abundant and diverse biota of packstone beds suggests deposition in well-circulated, open-marine waters just seaward of or along deposition strike with high-energy, shoreface sediments. Sparsely fossiliferous dolomites composing the uppermost few meters of the Towanda and Krider carbonates record shallow, restricted, marginal marine deposition landward of high-energy, carbonate-sand shoals. This depositional setting was most likely restricted lagoon or lower tidal flat. The upper part of the carbonate interval in the Barneston-Holmesville and Winfield-Odell cycles displays rare desiccation cracks filled by reddish-brown, silty clay or dolomite cement. These structures suggest periodic subaerial exposure.
The Barneston-Holmesville cycle differs from other Chase Group depositional cycles in that the transgressive and regressive carbonates, Florence and Ft. Riley Limestones, respectively, are separated by a gray to light-gray, bioturbated, argillaceous and dolomitic siltstone/very fine grained sandstone (plate II-A). This siliciclastic interval, termed the Oketo Shale, is 32 ft (9.7 m) thick. Clay-size material in this interval decreases upward, and the Oketo grades into burrow-mottled, fossiliferous, dolomitic, very fine grained sandstone and sandy dolomite of the lower Ft. Riley Limestone. Lamination in the Oketo Shale has been destroyed by burrows, most commonly Teichichnus and less numerous, small, horizontal, tube-shaped burrows resembling Planolites. The Oketo Shale is a shoaling-upward, siliciclastic interval reflecting deposition below wavebase in a lower shoreface setting.
Chase Group carbonates are gradationally overlain by tan to light-olive-gray, dolomitic, very fine grained sandstones and reddish-brown, dolomitic, siliciclastic mudstones. The sandstones commonly have reddish-brown, mudstone laminae and layers up to a few centimeters thick. Horizontal, and less numerous vertical, tube-shaped burrows are common in the sandstones (plate II-C). Ripple stratification is common in some cycles. Anhydrite occurs as replacement nodules and intergranular cement in very fine grained sandstone of the Krider-Paddock cycle.
Reddish-brown, dolomitic, siliciclastic mudstones and siltstones of this unit display faint, mud-filled, desiccation cracks and light-colored, dolomite, caliche glaebules. Glaebules are subspherical to irregularly shaped and occur as isolated individuals or coalesce to form irregularly shaped masses (plate II-E). Glaebules are rarely calcite. Some glaebules have calcite- or dolomite-cemented cracks and tubular shaped features. The latter may be plant-root structures. Plant-root action is suggested also by hig-hangle, greenish-gray, variably calichified, mottled mudstone areas with sparse carbonaceous material (plate II-D). Erosional surfaces overlain by reddish-brown, mudstone clasts are rare, and stratification is typically not apparent in rocks of this unit. Replacement anhydrite although generally rare is common in reddish-brown mudstones and siltstones of the Paddock Member, Krider-Paddock cycle. Detrital clays are predominantly illite. Kaolinite, chlorite, and smectite occur in small amounts.
Tan, very fine grained sandstone and reddish-brown, dolomitic, siliciclastic mudstone and siltstone make up the uppermost unit of a typical Chase Group depositional cycle. Sandstones displaying common, tube-shaped, horizontal and vertical burrows, reddish-brown mudstone laminae and layers, and ripple cross stratification record intertidal deposition. Caliche glaebules, root structures, clay-filled desiccation features, and the reddish-brown color which characterize dolomitic mudstones and siltstones capping the Chase Group depositional cycles reflect maximum regression, and supratidal deposition, and paleosol development. Silt and very fine grained sands in these mudstones/siltstones may be in part eolian. Prezbindowski et al. (1988) and Siemers and Ahr (1990) suggested that reddish-brown, dolomitic mudstones of the Gage and Odell are paleosol deposits. Regressive, siliciclastic units of the Chase Group depositional cycles thicken westward toward Wolfcampian continental terranes.
Transgressive-regressive carbonate units in the upper Chase Group are the major Permian gas reservoirs in the Guymon-Hugoton field. These intervals are the Krider Member of the Krider-Paddock cycle and Winfield Formation of the Winfield-Odell cycle. The Herington Member overlying the Krider-Paddock cycle is also gas productive in the Guymon-Hugoton field. These units as well as transgressive-regressive carbonates of the Towanda Member (Towanda-Gage cycle) and Ft. Riley Member (Barneston-Holmesville cycle) are gas productive in the Kansas Hugoton field to the north.
Primary intergranular and less common, secondary biomoldic and intercrystalline porosity characterize grainstones and washed packstones of the middle and upper parts of the transgressive-regressive carbonates (plates III and IV-A). Oomoldic porosity is present in dolomite grainstones of the Krider Member. Bioclast packstones and wackestones which make up the lower beds of the carbonate intervals display mainly biomoldic and secondary intercrystalline porosity (plate IV-C and D). Biomolds are most likely leached green algae and mollusks. Intragranular porosity is volumetrically minor, and open fractures are generally rare in Chase Group carbonates cored in the Stonebraker A-112. Core porosities are typically 7-14% with slightly lower porosities, as low as 4%, in some wackestones and packstones. Maximum permeabilities are generally 0.1-4.0 md. Permeabilities are significantly higher in the Krider transgressive-regressive carbonate unit ranging commonly from 0.1 to 12 md and up to 155 md.
Primary intergranular porosity in grainstones and washed packstones of the Wreford, Ft. Riley, Towanda, and Winfield carbonates has been partially occluded by calcite cement. Carbonate grains in these rocks typically have isopachous rims of very finely to finely crystalline, equant to bladed calcite. Pore centers are cemented or partially cemented by medium to coarsely crystalline, equant calcite readily distinguishable from the earlier, equant to bladed, calcite cement (plate III-D). Echinoderm fragments display medium- to coarsely crystalline, calcite overgrowths. Replacement anhydrite occurring as nodules and small, blade-shaped crystals, 0.5-1.25 cm in length, is scarce in the Ft. Riley and Towanda carbonates and locally common in carbonates of the Winfield and Krider. Coarsely crystalline, in places poikilitic, anhydrite cement fills or partially fills biomolds and intergranular pores in carbonates of the Krider Member and Winfield Formation significantly reducing porosity in some beds. Siemers and Ahr (1990) stated that anhydrite cementation is the chief cause of porosity and permeability reduction in the Winfield Formation and Krider Member in the Phillips Petroleum Buf 3 and Sheil 2R cores from the south-central part of the Guymon-Hugoton field.
Dolomite in the transgressive-regressive carbonates of the Barneston-Holmesville, Towanda-Gage, and Winfield--Well cycles is typically finely to medium crystalline and selectively replaces micrite matrix, micritic intraclasts, and micrite filling intragranular pores within skeletal fragments. Bioclasts generally are not dolomitized (plate IV-C and D). Wackestones and packstones vary from 10% to 60% dolomite in most Chase Group carbonates in the Stonebraker A-112. Washed packstones and grainstones are typically 1-30% dolomite. Void-filling dolomite cement is atypical, the exception being the Krider Member which is entirely dolomite and anhydrite. Dolomite replaces lime mud matrix and carbonate grains and occurs as void-filling cement in the Krider.
Diagenesis of the Chase Group carbonates was strongly influenced by waters migrating downward from overlying tidal flat and paleosol environments which prograded over the transgressive-regressive carbonates. Progressive evaporation in and to semiarid tidal flat and paleosol environments led to the formation of caliche glaebules and drove pore fluids to hypersalinity, resulting in the precipitation of calcium sulfate minerals (gypsum or anhydrite). Precipitation of calcium sulfate minerals produced relatively dense brines with elevated Mg/Ca ratios. These brines passed downward dolomitizing underlying carbonate sediments of the transgressive-regressive carbonates. Carbonate mud or micrite was selectively dolomitized, while bioclasts typically remained aragonite and calcite (plate 4C and D). Selective dolomitization of lime mud or micrite was related to the high surface area to volume ratio of the mud and may be indicative of relatively rapid dolomitization. Complete dolomitization of the Krider carbonate is most likely related to the unusually thick, overlying tidal flat and paleosol sequence of the Paddock, Herington, and Wellington Formation (Sumner Group). This interval contains scattered anhydrite layers 1-3 inches (2.6-7.7 cm) thick in the Stonebraker A-112 cores. Dolomitization related to the precipitation of evaporite minerals in and to semiarid tidal flat settings was reviewed by Moore (1989) and by numerous authors in Concepts and models of dolomitization (Zenger et al., 1980).
Following dolomitization, meteoric waters migrated through the transgressive-regressive carbonates leaching aragonite and high-magnesium calcite bioclasts (mainly mollusks and green algae) and undolomitized carbonate mud and micrite. Meteoric waters may have been charged with C02 and organic acids produced in overlying soil horizons, enhancing their ability to leach carbonate grains and lime mud. Leaching by relatively fresh, meteoric waters created moldic (leached bioclasts and ooids) and intercrystalline (leached carbonate mud and/or micrite) porosity. Moore (1989) stated that selective dolomitization of carbonate mud followed by the introduction of freshwaters and preferential dissolution of carbonate grains and undolomitized lime mud and micrite is a common process in sabkha-subtidal sequences.
As carbonate dissolution continued, meteoric waters became progressively enriched in calcium carbonate. Upon saturation calcite was precipitated as very finely to coarsely crystalline cement. Calcite cement includes echinoderm overgrowths, very finely to finely crystalline, isopachous, equant to prismatic, rim cement, and finely to coarsely crystalline, blocky calcite filling the interior portions of intergranular and moldic pores (plate III-A-D). Some very finely to finely crystalline, rim cement has a bladed morphology and may reflect early, marine cementation (plate III-D).
Anhydrite cement occluding or partially occluding intergranular and moldic porosity appears to have postdated the major phase of dolomitization and meteoric dissolution of carbonate grains and lime mud. Anhydrite and/or gypsum probably precipitated from sulfate-rich brines originating in overlying supratidal environments. Siemers and Ahr (1990) stated that anhydrite cementation of Chase Group carbonates was nearly contemporaneous with a second generation of dolomite cementation characterized by relatively clear, euhedral rhombs and clear overgrowths on earlier, more turbid, brownish dolomite. This relationship is suggested in the Krider Member in the Stonebraker A-112 where a late-stage dedolomitization has leached early, more soluble, dolomite crystals, leaving clear rims of less soluble, second generation dolomite.
Transgressive and regressive sandstones of the Chase Group depositional cycles typically are not perforated in the Guymon-Hugoton field. Perforated Chase Group sandstones are restricted to the Winfield--Odell and Krider-Paddock cycles and the overlying Herington Member. Transgressive and regressive sandstones thin eastward (basinward); consequently, perforated sandstone intervals generally occur in the western part of the field.
Core porosities of the transgressive and regressive sandstones in the Stonebraker A-112 are generally 8-16%, and maximum permeabilities are 0.1-6.5 md. Pore types are intergranular, less common intercrystalline, and rarely leached feldspar (plate IV-F). The sandstones are cemented or partially cemented by calcite, dolomite, and quartz overgrowths. Anhydrite cement is common in regressive sandstone of the Krider-Paddock cycle.
Reddish-brown, dolomitic, siliciclastic mudstones and siltstones capping the Chase Group depositional cycles generally have core porosities of 7-12%. Porosity is intercrystalline and micron-size pores associated with clay minerals. Core permeabilities are typically less than 1 md. permeabilities of a few tens up to 200 md are related to fractures, most of which are thought to be coring induced. Low-permeability, reddish-brown mudstones of the Chase Group depositional cycles may form partial barriers to the vertical migration of fluids in the Guymon-Hugoton field.
ft (107 m) of cyclically deposited carbonates and fine-grained siliciclastics reflecting open-marine shelf to supratidal deposition. A typical Chase Group depositional cycle as defined from the Stonebraker A-112 core consists of a thin, transgressive, fine-grained siliciclastic unit overlain by a porous, transgressive-regressive carbonate interval and capping the cycle a regressive, fine-grained sandstone and dolomitic, siliciclastic mudstone unit. Five depositional cycles are recognized in the Chase Group in the Guymon-Hugoton field. These cycles are, in ascending order, the Wreford-Matfield, Barneston-Holmesville, Towanda-Gage, Winfield-Odell, and Krider-Paddock. Sandstones and dolomites of the Herington Member, upper Chase Group, and overlying reddish-brown mudstones may represent an additional but markedly different depositional cycle. The Chase Group depositional cycles typically vary from 50 to 95 ft (15-29 m) thick over much of the field and can be traced laterally for several tens of kilometers using wireline logs. The cyclic character of Chase Group carbonates and fine-grained siliciclastics reflects the interaction of carbonate sedimentation, eustatic changes in sea level, shelf subsidence, and perhaps regional tectonism.
The lowermost lithologic unit of a typical Chase Group depositional cycle is a thin, light-gray to gray, structureless, mottled, or faintly parallel-stratified, dolomitic siltstone. These rocks overlie reddish-brown, dolomitic, siliciclastic mudstones which cap the underlying cycle. They are differentiated from the underlying rocks by their color, decrease in clay-size matrix, and the presence of burrows or burrow mottling. The light-gray siltstone suggests a marine transgression and shallow drowning or flooding of supratidal and soil-forming environments. The siltstone is abruptly overlain by light-gray, burrowed, sparsely fossiliferous, very fine grained sandstone reflecting continued marine transgression and slightly higher energy, shoreface deposition. The sharp contact of the siltstone and overlying sandstone may be a marine, transgressive surface of erosion. Transgressive sandstones are absent in the eastern, more basinward portions of the Guymon-Hugoton field, reflecting increased distance from Wolfcampian siliciclastic source areas to the west.
A relatively thick limestone and dolomite sequence gradationally overlies the fine-grained, transgressive sandstone in a typical Chase Group depositional cycle. The lower part of this sequence is bioclast mudstone, wackestone, and packstone, and in some cycles, osagid-coated-grain packstone. These rocks suggest continued marine transgression and sedimentation in subtidal, open-marine waters perhaps a few meters to a few tens of meters deep. Bioclast grainstone and washed packstone of the middle and upper puts of the carbonate interval record the seaward progradation of carbonate sedimentation and a marine regression. The paucity of carbonate mud and presence of intraclasts, ooids, and planar, low-angle, and cross stratification reflects deposition above wavebase in moderate- to high-energy, nearshore bar, upper shoreface, or foreshore (beach) environments. Gray to light-gray, slightly sandy and argillaceous, dolomite mudstone and wackestone composing the uppermost part of the carbonate interval in some cycles may record restricted lagoon to lower tidal flat deposition landward of high-energy carbonate shoals. Transgressive-regressive carbonate units are characterized by primary intergranular and secondary moldic and intercrystalline porosity and are the main Chase Group reservoirs of the Guymon-Hugoton field. Porosity is occluded by calcite, dolomite, and anhydrite cement. The diagenetic sequence characterizing Chase Group carbonates in the Stonebraker A-112 includes minor marine cementation; dolomitization by downward migrating, Mg-rich, tidal flat/paleosol waters; leaching of undolomitized carbonate grains and lime mud by meteoric waters; meteoric calcite cementation of primary and secondary porosity; anhydrite cementation and a second generation of dolomite precipitation; and a rare, late-stage leaching of first-generation dolomite.
Chase Group depositional cycles are capped by tan, very fine grained, burrowed, parallel- and ripple-laminated sandstone and reddish-brown, dolomitic, siliciclastic mudstone. Mudstones are unstratified or rarely burrowed and display caliche glaebules, mud-filled desiccation cracks, and plant-root structures. The sandstone records lower to middle, tidal flat deposition and the mudstone supratidal deposition and paleosol development. This siliciclastic unit represents the maximum regressive phase of a typical Chase Group depositional cycle. Regressive siliciclastic sandstones thin eastward away from siliciclastic source areas to the west.
This study was conducted while the author was employed by Oxy USA, Inc., a division of Occidental Petroleum. The author would like to dunk Occidental Petroleum for releasing the study and in particular Dick Scott, Bill Bryan, and Jerry Easter for their earnest cooperation in this matter. Phillips Petroleum, the author's current employer, provided assistance in preparing the text and poster. Special thanks to Phillips employees Lea Ann Fronkier who graciously typed the text, Kelly Curtis who skillfully prepared the text figures and poster, and W. W. Souder and W. D. Byrd who granted me time to get my Guymon-Hugoton thoughts in place. Lynn Watney willingly lent his insights into late Paleozoic cyclic sedimentation, a worthy contribution. Special thanks also to Cristen J. Smith, whom I unwillingly disregarded during the preparation of this text.
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[Note: An Acrobat PDF file containing all of the plates is available.]
Plate I--Transgressive siltstone and sandstone unit and transgressive-regressive carbonate unit.
A--Towanda-Gage cycle, and overlying, transgressive, gray siltstone of the Winfield-Odell cycle.
B--Gray, transgressive siltstone abruptly overlain by transgressive, very fine grained, burrowed sandstone, Barneston-Holmesville depositional cycle. Contact may represent a marine, transgressive surface of erosion.
C--Transgressive, light-gray, burrowed, very fine grained sandstone of the Barneston-Holmesville depositional cycle.
D--Transgressive, osagid-coated-grain packstone of the Florence Limestone, Barneston-Holmesville cycle.
E--Transgressive, argillaceous and sandy, dolomitic, bioclast wackestone and packstone of the Towanda Member, Towanda-Gage cycle. Dolomitic limestone gradationally overlies transgressive, very fine grained sandstone composing the lower 3 cm of the slabbed core. Large bioclasts in the wackestone are bryozoans.
F--Transgressive, argillaceous and sandy, dolomitic, crinoid wackestone/packstone of the Florence Limestone, Barneston-Holmesville cycle. Small white nodules are anhydrite.
Plate II--Regressive sandstone and dolomitic mudstone unit and transgressive-regressive carbonate unit.
A--Burrowed, argillaceous and dolomitic, very fine grained sandstone of the Oketo Shale, Barneston-Holmesville cycle. Burrows are predominantly Teichichnus.
B--Regressive, medium-scale cross stratified, ooid-bioclast grainstone (dolomite) of the Krider Member, Krider-Paddock cycle.
C--Burrowed, very fine-grained sandstone and reddish-brown, silty to sandy mudstone of the regressive siliciclastic phase, Odell Formation, Winfield-Odell cycle.
D and E--Regressive, reddish-brown, silty to sandy mudstones of the Odell Formation, Winfield-Odell cycle (photo D) and Gage Member, Towanda-Gage cycle (photo E). Light-colored areas are dolomite caliche. Calichification of the sample shown in photo D may have been related to plant-root action.
F--Regressive, sandy dolomite with gray anhydrite nodules, Paddock Member, Krider-Paddock cycle. Dolomite displays mud-filled desiccation cracks.
Plate III--Transgressive-regressive carbonate unit.
A-D--Regressive, bioclast and bioclast-intraclast grainstones of the Winfield Formation. Carbonate grains are green algae (A), crinoids (C), bryozoans (B), and intraclasts (I). Intergranular and secondary moldic porosity are occluded by calcite cement. Grains typically display equant to bladed, very finely to finely crystalline, isopachous, rim cement (RC). A later, medium- to coarsely crystalline, equant calcite cement (CC) fills or partially fills the remaining porosity. Intergranular porosity (IP) and secondary biomoldic porosity (MP) are minor (photos A and B: 30x, photos C and D: 125x).
E--Regressive, ooid grainstone of the Krider Member displaying intergranular porosity filled by blue epoxy. Intergranular porosity is occluded in places by coarsely crystalline, poikilitic, anhydrite cement (AN). Ooids are finely to medium-crystalline dolomite (30x).
F--Anhydrite-cemented (AN), regressive, bioclast-ooid grainstone of the Krider Member. Moldic porosity (NV) is filled by blue epoxy. Carbonate grains are finely crystalline dolomite (30x).
Plate IV--Transgressive-regressive carbonate and regressive sandstone units.
A--Regressive, sandy, dolomite wackestone of the upper part of the Krider Member. The sample displays fine-grained, detrital quartz (Q), moldic porosity filled by blue epoxy, and in the center of the photo a large grain replaced and/or cemented by anhydrite (AN) and dolomite (30x).
B--Transgressive, sandy, bioclast wackestone of the lower part of the Towanda Member. Bioclasts are mainly crinoids (C). Siliciclastic sand is fine- to very fine grained (30x).
C and D--Limy dolomite, bioclast wackestone of the lower part of the Winfield Formation. The matrix is dolomite. Bioclasts, stained red by alizarin red S, are calcite. Bioclasts are bryozoans (B) and brachiopods (BR). Porosity filled by blue epoxy appears to be largely intercrystalline (IP) and lesser biomoldic (photo C: 30x, photo D: 80x).
E--Sandy, osagid-coated-grain packstone of the transgressive Florence Limestone, Barneston-Holmesville cycle. Bioclasts are concentrically coated by encrusting forms (EF) and blue-green algae (30x).
F--Fine-grained, regressive sandstone of the uppermost Winfield Formation, Winfield-Odell cycle, displaying intergranular porosity (filled by blue epoxy) and minor amounts of finely crystalline, dolomite cement (arrows) (80x).
Kansas Geological Survey
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Web version created June 29, 2012. Original publication date 1991.