Kansas Geological Survey, Subsurface Geology Series 9, originally published in 1987
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(Cambrian and Precambrian rocks)
Sub-Arbuckle rocks are only locally important host rocks for petroleum reservoirs in Kansas. These rocks include the Reagan Sandstone and locally fractured basement rocks.
The Reagan Sandstone is Late Cambrian in age and averages 40 feet (12 m) in thickness (Goebel, 1968a). It is the basal Paleozoic transgressive sandstone that lies directly on Precambrian basement rocks and as such, its composition and texture can he markedly influenced by the underlying basement. The Reagan can either be quartzose, arkosic, or feldspathic; texturally, it can range from fine to coarse grained.
Oil production from the Reagan is locally important on the Central Kansas uplift where overlying Arbuckle Group rocks are absent due to erosion or nondeposition (figure 13). In such areas, fractured basement rocks underlying the Reagan may also be productive. Both Reagan and basement production occur in close association on buried Precambrian hills formed along structural highs that crop out beneath the sub-Pennsylvanian angular unconformity. Fields producing from Reagan sandstones include the Otis-Albert field in Rush and Barton counties (Miller, 1968) and the Norton field in Norton County (Merriam and Goebel, 1954).
Figure 13--Sub-Arbuckle production.
According to Walters (1946, 1953), fields that produce oil and gas, in part, from fractured Precambrian basement rocks include the Kraft-Prusa, Eveleigh, Trapp, Beaver, and Bloomer fields in Barton County; the Ringwald, Heinz, Orth, and Chase-Silica fields in Rice County; and the Gorham and Hall-Gurney fields in Russell County. These fields align along two north west-southeast-trending uplifts respectively called the Rush rib, which extends from Rush County into Barton County, and the Russell rib, which extends from Russell County into northwest Rice County. The oil from fractured basement rocks in these areas probably migrated into these rocks from overlying Pennsylvanian rocks or nearby Arbuckle dolomites located on the flanks of these structures and paleotopographic highs (Walters, 1953).
The potential for additional sub-Arbuckle production would be localized in areas where uplifts and paleotopographic highs bring these rocks into contact, or near contact, with possible hydrocarbon carrier beds associated with the sub-Pennsylvanian angular unconformity in parts of the Central Kansas and Nemaha uplifts. As it is likely that most major structural anomalies such as these have already been detected in the heavily drilled Central Kansas uplift, the future potential of the sub-Arbuckle rocks in Kansas is probably small. However, the petroleum potential of the 1.1 billion-year-old Central North American rift system (CNARS) is not yet determined (Lee and Kerr, 1983; Dickas, 1984). This geologic province extends from northern Wisconsin southward into Kansas and is located underneath the eastern part of the Salina basin (figure 14; Yarger, 1983). Interlayered arkoses and basalts fill this rift (Scott, 1966), but organic-rich shales may also be present (Lee and Kerr, 1983).
Figure 14--Precambrian basement terranes in Kansas, based on information in Bickford and others (1981) and Yarger (1983).
Thickness of the sedimentary and volcanic sequence in this buried block-faulted geologic province may reach 26,000 ft (8 km; Serpa and others, 1984). The deepest well to date in Kansas, the #1 Noel Poersch, was the first significant test of CNARS rocks (figure 14). This well was drilled to 11,300 ft (3,447 m) in southeastern Washington County in 1984. Although no commercial accumulations of hydrocarbon were found, other wells need to be drilled in the rift to evaluate its hydrocarbon potential.
Arbuckle oil production (figure 15) is mostly concentrated over the Central Kansas uplift and its southward extension, the Pratt anticline. Production is also locally important in southeastern Kansas, such as at the prolific Augusta and El Dorado fields in Butler County. Gas production is locally important in southwestern Barton County and eastern Pawnee and Rush counties.
Figure 15--Arbuckle production.
Rocks of the Arbuckle Group are composed mostly of light gray to white vuggy, cherty dolomite. The unit has been subdivided and correlated with equivalent exposed strata in adjacent states by study of insoluble residues (McCracken, 1955). It is thin to absent in parts of northeastern Kansas, including Marshall, Pottawatomie, Riley, western Nemaha, and eastern Washington counties, due to pre-Simpson uplift and erosion (Lee, 1956). Farther south along the Nemaha uplift, it is locally absent due to pre-Pennsylvanian erosion over several structures in Chase and Butler counties (Jewett 1951, 1954) and on the Cambridge arch in parts of Norton and Decatur counties and locally along basement highs in the Central Kansas uplift (Walters, 1946; Merriam, 1963). In other areas of Kansas, the Arbuckle dolomite can be quite thick. It generally thickens southward and is in excess of 1,000 ft (305 m) thick along the Kansas-Oklahoma state line (Cole, 1975).
The Arbuckle Group is the most significant pay zone on the Central Kansas uplift, having produced approximately 1.4 billion barrels of oil from 1929 to 1968 (Adler, 1971). Several hundred fields are productive from Arbuckle rocks on the Central Kansas uplift. Most of these fields are structural and structural-stratigraphic traps that produce oil or gas from the top of the Arbuckle section, which is in direct contact with unconformably overlying Pennsylvanian beds (Walters, 1958). Porosity is significantly enhanced by solution and weathering at the top of the Arbuckle, where it crops out beneath the sub-Pennsylvanian unconformity (Walters, 1959; Adler, 1971). Dolomitization also enhances its porosity (Walters, 1959).
Off the Central Kansas uplift and parts of the Nemaha uplift, the Arbuckle is generally nonproductive, a major exception being the Voshell field in McPherson County (Hiestand, 1933). Arbuckle rocks constitute a major component of the "Stapleton zone," a porous, weathered zone developed on Cambrian-Ordovician strata that crop out beneath the sub-Pennsylvanian unconformity in the El Dorado field in Butler County (Fath, 1921; Reeves, 1929). The weathered Arbuckle rocks at the El Dorado field were extremely productive with up to 17,000 barrels of oil per day production (Fath, 1921). Nearby at the South Augusta field, daily production of oil per well of up to 7,000 barrels was recorded from weathered Arbuckle rocks (Berry and Harper, 1948). Both the El Dorado and Augusta fields were found by surface geologic mapping.
Scattered Arbuckle production occurs in southeastern Kansas and extends into Oklahoma (Akin, 1964). In this region pre-Chattanooga erosion has stripped off Devonian, Silurian, and Middle and Upper Ordovician strata so the Chatatnooga Shale lies directly on the Arbuckle. The Chattanooga Shale is probably the source rock for the Arbuckle oil fields in southeastern Kansas, such as the Coffeyville field in Montgomery County (Foster, 1929; Jewett, 1954). Like the Central Kansas uplift, the Arbuckle pay zones are almost always close to the top of the unit, but in some fields in Oklahoma, productive zones are reported to be substantially within the Arbuckle (Bloesch, 1954).
In addition to the El Dorado and Augusta fields, major fields that produce oil from the Arbuckle include the Chase-Silica field straddling the Rice-Barton county line, the Bemis-Shutts field in Ellis County, the Hall-Gurney field in Russell County (Riggs and others, 1963), the Trapp field in Barton and Russell counties, the Kraft-Prusa field in Barton County (Walters and Price, 1947), and the Otis-Albert field in Rush and Barton counties (Walters, 1946, 1953, 1958). According to Walters (1958), the distribution of oil and gas in the Arbuckle pay zones over the Central Kansas uplift conforms to the principles of differential entrapment as described by Gussow (1954). Oil-water contacts increase in elevation, and gas content decreases systematically northward in several Arbuckle fields on the Central Kansas uplift, thereby indicating northward migration of Arbuckle oil possibly ultimately derived from Oklahoma. In this model, a given Arbuckle trap on the uplift should have been filled by oil to its spillpoint. Additional oil subsequently channeled into this trap from downdip areas would then migrate through the spillpoint of the trap into other higher traps which would, in time, fill with oil to their spillpoints.
Future potential of the Arbuckle rocks include areas where the unit is in contact with possible carrier beds along the sub-Pennsylvanian unconformity. Such areas include structural highs on the Pratt anticline, Central Kansas uplift, and Nemaha uplift. Additional minor production is possible in southeastern Kansas, where nortwest-southeast structural trends paralleling the Chautauqua arch may intersect with north-northeast-south-southwest structural trends paralleling the Nemaha uplift. Stratigraphic traps in the Arbuckle are also a possibility where porous beds within it may truncate along the flanks of an anticline. In cases such as this, the oil in the Arbuckle may not necessarily be found at the culmination, or highest point, of the anticline. Correlation and mapping of porosity zones within the Arbuckle and their subcrop pattern as they are truncated by an overlying unconformity may be useful in finding these types of stratigraphic traps.
Simpson production (figure 16) is primarily limited to south-central Kansas. Production trends are evident along the periphery of the Central Kansas uplift and down the Pratt anticline in localities where the Simpson Group crops out beneath the sub-Pennsylvanian unconformity. Scattered production is also present in Sumner, Butler, and Coffey counties in southeastern Kansas where Simpson sandstones are beveled on the flanks of the Chautauqua arch due to pre-Chattanooga erosion. Production also occurs scattered throughout the Sedgwick basin and isolated localities in the Forest City basin. The Simpson is also a component of the "Stapleton zone," the porous zone that is locally developed beneath the sub-Pennsylvanian unconformity at the El Dorado field in Butler County (Jewett, 1954).
Figure 16--Simpson production.
The Simpson Group is the basal unit of a long-term oceanic inundation on the North American continent called the Tippecanoe transgression (Adler, 1971). Although the Simpson was probably deposited over most of the state, subsequent erosional events have removed it from various parts of the state. Late Mississippian-Early Pennsylvanian tectonic movement accounts for the removal of the Simpson over much of the Central Kansas uplift, the Nemaha uplift, and northwestern Kansas. The Simpson also is absent in southeastern Kansas southeast of a line running from Cowley County to Miami County (Merriam, 1963). The absence of Simpson in this area is due to the broad northwest-southeast-trending Chautauqua arch that developed in pre-Devonian (pre-Chattanooga) time.
The Simpson is thickest off the flanks of the old Chautauqua arch. In northeastern Kansas in the western flank of the Forest City basin and eastern flank of the Salina basin, it reaches a maximum thickness of 150 ft (45 m). In southern Kansas it thickens southward to a maxinium of 250 ft (75 m) in Harper County near the Kansas-Oklahoma state line (Cole, 1975). It continues to thicken southward into Oklahoma where it is divided into several different stratigraphic units (Ireland, 1965). Locally anomalous thicknesses of Simpson rocks in eastern Kansas in which the unit is in excess of 400 ft thick (125 m) are attributed to sinkholes developed in the underlying Arbuckle Group carbonate rocks (Leatherock, 1945).
The Simpson Group in Kansas is dominantly a sand-shale sequence with minor amounts of carbonate rock. The main reservoir rocks within the Simpson Group are light-gray, quartz-rich sheet sandstones sometimes called the St. Peter or Wilcox sandstone (Goebel, 1968b). More than one producing zone can be present. Shales in the Simpson are credited as being source rocks for the oil in the Forest City basin (Newell and others, 1985).
Simpson oil accumulations can be categorized into three geologic settings: 1) structural-stratigraphic and stratigraphic traps in which the Simpson is truncated by the sub-Pennsylvanian unconformity, 2) structural-stratigraphic and stratigraphic traps in which the Simpson is truncated by the pre-Chattanooga unconformity, and 3) structural traps in which the Simpson lies in its normal stratigraphic succession above the Arbuckle Group and below the Viola formation. The first type of trap usually occurs along the periphery of the Central Kansas uplift and along the crest of the Nemaha uplift and Pratt anticline. The second type of trap is characteristic of the Simpson in southeastern Kansas along its subcrop trend on the northern flank of the Chautauqua arch. The third type is found in the Forest City basin, the Sedgwick basin, and southern part of the Salina basin between the subcrop limits of the Simpson.
Fields on the Pratt anticline and the flanks of the Central Kansas uplift where Simpson sandstones truncated by the sub-Pennsylvanian unconformity produce oil or gas include the Coats field in Pratt County (Curtis, 1956; Brewer, 1959), the Brehm field in Pratt County (Willis, 1965) and the Tobias field in Rice County (Waller and Brewer, 1964; Brewer, 1965). Fields producing oil from the Simpson where the Simpson rests directly beneath the sub-Chattanooga unconformity include the O.S.A. and Gillian fields in Sedgwick County (Howell, 1965; Shawver, 1965a, b). Oil fields contained in Simpson rocks in which the Simpson is not beveled by either the sub-Pennsylvanian or sub-Chattanooga unconformities include the McClain field in Nemaha County, the Boggs field in Barber County (Jacques, 1956), the Haven field (Richardson and Matthews, 1956a) and Wisby and Wisby North fields in Reno County (Donnelly, 1965), the Grant field in Harper County (Devlin, 1965), the Greenwich (Cole, 1960) and Wichita fields in Sedgwick County (Scott, 1960), the Wilmington field in Wabaunsee County (Young, 1960), the Fall Creek field in Sumner County (Bass and Lukert, 1959), and the Lindsborg field in McPherson County (Brewer, 1959).
More exploration possibilities exist for finding Simpson oil reservoirs in the three geologic settings mentioned above. Sub-Pennsylvanian structural-stratigraphic traps flanking the Central Kansas uplift and along the Pratt and Nemaha uplift are worthwhile targets. Conspicuous gaps exist in which undiscovered Simpson fields may be present along the Simpson sub-Chattanooga subcrop trend in southeast Kansas. Simpson sandstones may also be long-shot exploration targets in structures in the Sedgwick and deeper parts of the Salina basins inasmuch as shales within the Simpson may be viable oil-source rocks (Newell and others, 1985). Simpson rocks may also be prospective in the Hugoton embayment, but Rascoe (1971) reports this unit is thin in this region and contains poorly developed sandstone beds.
(Middle and Upper Ordovician)
Viola and Maquoketa production (figure 17) is scattered over south-central and northeast Kansas in approximately the same distribution as the underlying Simpson Group (figure 16). Oil production dominates, but both gas and oil are produced on the Pratt anticline. Viola reservoirs and the "Hunton" limestone farther upsection constitute the main producing horizons in the Forest City basin. Both the Viola and Maquoketa produce oil in the southern part of the Salina basin. Elsewhere, Viola production dominates, and the Maquoketa is not a viable reservoir.
Figure 17--Viola and Maquoketa production.
The Viola Limestone occurs throughout the state, except in northwest Kansas, the northern part of the Nemaha uplift, and the Central Kansas uplift due to pre-Pennsylvanian erosion. It is also absent in southeast Kansas due to pre-Chattanooga erosion on the Chautauqua arch (Merriam, 1963). The Viola is thickest in Jewell and Republic counties where it exceeds 300 ft (92 in; Cole, 1975). The Viola is composed of fine- to coarse-grained limestones and dolomites containing variable quantities of chert (Bornemann and others, 1982). Dolomitic limestones characterize the unit in south-central Kansas, but farther north in the Forest City and eastern Salina basin it is almost all dolomite (Goebel, 1969b; Cole, 1975). Types of porosity vary, but intergranular, vuggy, moldic, and fracture porosity all occur (Caldwell and Boeken, 1985; St. Clair, 1985). Informal subdivisions of the Viola in Kansas have been defined by Taylor (1947), Ver Wiebe (1948), and St. Clair (1985).
The Maquoketa formation immediately overlies the Viola but is limited to only the Salina, Forest City, and northern Sedgwick basins. It is dominantly greenish-gray shale (Cole, 1975), but in central Kansas the lower part of this unit is a gray, porous, crystalline dolomite that may be partly equivalent to the upper part of the Viola. This dolomite is well-developed in Saline and northern McPherson counties and constitutes the main reservoir in the Salina-Lindsborg oil-field trend.
The Viola and Maquoketa are not major producers of oil in the Midcontinent, but the most significant production from these units in the Midcontinent occurs in Kansas (Adler, 1971). Major fields in the Forest City basin are almost all structural traps that produce from the Viola. These fields include the McClain, McClain Southwest (McCaslin, 1982; Caldwell and Bocken, 1985), Strahm, Sabetha, and Strahm East fields in Nemaha County (Elster, 1960a, b, c); the Mill Creek (Lewis, 1960a), Newbury (Lewis, 1960b), Ashburn (Brinegar, 1960), Wilmington (Young, 1960), and Davis Ranch fields (Smith and Anders, 1951; Anonymous, 1960a) in Wabaunsee County; and the Comiskey, Comiskey Northeast (Hilpman, 1960), and John Creek fields (Anonymous, 1960b) in Morris County. Structural traps with minor possible stratigraphic components produce from Maquoketa and Viola reservoirs in the Salina-Lindsborg trend in Saline and McPherson counties. These fields, which include the Lindsborg field (Brewer, 1959; Thatcher, 1961), the Smolan field (Talbott, 1954), and the Gillberg, Salina, Swenson, and Olsson fields, are important because they are the major producers in the largely unproductive Salina basin.
The Viola Limestone also produces oil in certain localities where it crops out beneath the sub-Pennsylvanian unconformity such as the "Stapleton zone" of the El Dorado field in Butler County (Biederman, 1966) and in the large Zenith-Peace Creek stratigraphic trap in Stafford County (Imbt, 1941; Paddleford, 1941; Kornfeld, 1943). Other fields include the Deerhead field (Tucker, 1956) and Rhodes field (Clark, 1956; stratigraphic traps in Barber County); the Lerado and Lerado Southwest fields (structural traps in Reno County; McGinness, 1956); the Willowdale (Cruce, 1956) and Alameda fields (King, 1965a, b; structural traps in Kingman County); and the Nescatunga field (Capps, 1965; a structural trap in Comanche County). Gas is structurally trapped in the Viola in the Cunningham field in Kingman and Pratt counties (Rutledge and Bryant, 1937; Page, 1940).
Future potential of the Viola and Maquoketa formations include structural and stratigraphic traps where the units crops out beneath the sub-Pennsylvanian unconformity along the flanks of the Central Kansas uplift and on regional structural highs such as the Nemaha uplift and Pratt anticline. Possibilities also exist for similar traps along the sub-Chattanooga subcrop trend on the northern flank of the Chautauqua arch. The Maquoketa and Viola formations may also be the best potential producing zones in the deeper part of the Salina basin, just as they presently are in the Forest City basin. Although the Viola is present in southwestern Kansas in the deeper part of the Hugoton embayment, it has not yet been productive. Rascoe (1971) attributes this to the absence of adequate seals above the Viola west of Pawnee, Edwards, Kiowa, and Comanche counties. Perhaps future test wells may reveal Ordovician pay zones in this region, if favorable trapping conditions are eventually found.
Silurian and Devonian production trends in Kansas include a broad east-west trend covering six counties in east-central Kansas (Marion, McPherson, Harvey, Reno, Butler, and Sedgwick counties) and a north-northeasterly trend starting in Morris County and extending to the Kansas-Nebraska state line (figure 18). The former trend is in the northern part of the Sedgwick basin; the latter trend is in the axis of the Forest City basin and on the adjacent Nemaha uplift. Silurian and Devonian rocks in Kansas are largely limited to north-central and northeast Kansas, so the small areal distribution of production of this unit is partly a reflection of its limited extent. These rocks are thickest in the northeast part of the state around eastern Nemaha County where they reach a maximum thickness of about 650 ft (200 m; Jewett and Merriam, 1959).
Figure 18--Silurian and Devonian production.
Silurian and Devonian rocks in Kansas are commonly identified by drillers as the "Hunton" formation. This name, which is applied to the package of limestones and dolomites sandwiched between the overlying Chattanooga Shale and underlying Maquoketa Shale, is a misnomer in that the true Hunton Formation in the Midcontinent is a unit of Lower Devonian limestones deposited in the Ardmore and Anadarko basins in southern Oklahoma. Equivalent strata in Kansas are missing due to erosion or nondeposition (Adler, 1971).
The missing Lower Devonian strata in the Kansas "Hunton" rocks represent a significant period of erosion or nondeposition in the rock record that is expressed by only a subtle unconformity. Although the unconformity between the Silurian and Middle Devonian limestones and dolomites can be recognized in a few localities by a zone that carries varying but low percentages of sand grains (Lee, 1943, 1956; Merriam, 1963), the unconformity is difficult to recognize if this sandy zone is absent (Hilpman, 1967). "Hunton" rocks have been zoned, however, on a regional basis by study of insoluble residues and microfossils (Lee, 1956; Ireland, 1967). In cases where these rocks can be differentiated by lithology alone, the Devonian component of the unit is generally composed of gray to brown, fine-grained, crystalline dolomite or limestone with minor chert, whereas the Silurian part is also cherty but generally consists of slightly coarser grained and slightly sandy dolomite with vuggy porosity (Merriam, 1963).
Silurian and Devonian rocks in Kansas are not significant petroleum reservoirs in the Midcontinent (Adler, 1971), but they are locally significant pay zones in the Forest City and northern Sedgwick basins. Fields producing from these rocks in the Forest City basin include the Livengood field in Brown County (Rascoe, 1960); the Sabetha (Elster, 1960a), Strahm (Elster, 1960b), and Strahm East fields (Elster, 1960c) in Nemaha County; and the Davis Ranch field in Wabaunsee County (Smith and Anders, 1951; Anonymous, 1960a). On the Nemaha uplift immediately west of the Forest City basin, Silurian-Devonian rocks that crop out beneath the sub-Pennsylvanian angular unconformity constitute the main pay horizon in the Yaege field in Riley County (Goebel, 1960). Other "Hunton" fields on or flanking the Nemaha uplift include the Fairplay field in Marion County (Stubbs and Wright, 1960) and the Gingrass field in Harvey County (Johnson, 1960).
Some of the fields in Marion and McPherson counties are due to southwestward-dipping "Hunton" rocks being truncated to the north by a broad buried valley filled with the younger Chattanooga Shale. This buried valley, called the McPherson Valley by Lee (1956), is the updip seal for an east-west trend of stratigraphic traps extending across southern Marion and McPherson counties. The fields in this trend include the "Hunton" oil in the multi-pay Hollow-Nikkel field (Bunte and Fortier, 1941), the Graber field in Harvey County, and the Unger field in Marion County (Brown, 1960). Other fields in Kansas producing from Silurian-Devonian rocks include the Goessel field in McPherson and Marion counties, the Burrton field in Reno and Harvey counties, and the Wenger field in Marion County (Jewett, 1954).
Future potential of Silurian-Devonian rocks in Kansas includes additional structural traps that may be found in the Forest City basin. Additional stratigraphic traps may also be found on the south side of the McPherson Valley in the northern Sedgwick basin, but the larger of these traps have probably been found. The continuation of this valley in the Forest City basin in the vicinity of eastern Chase County may be prospective though. Stratigraphic traps on the north side of the valley in northern Marion and McPherson counties are a possibility, but none has been found so far. Perhaps the general west-southwest tilt of the strata north of the valley prohibits formation of such traps. Additional fields on the Nemaha uplift, analogous to the Yaege field in Riley County, are also viable exploration plays.
(Upper Devonian and Lower Mississippian)
Misener sandstone, at the base of the Chattanooga Shale, produces oil from fields scattered throughout central Kansas (figure 19). Major production from the Misener and other sandstones near the base of the Chattanooga Shale is presently concentrated in the Wil field in eastern Edwards County and the Lyons West field in central Rice County.
Figure 19--Chattanooga and Misener production.
The Chattanooga Shale is generally identified by drillers in Kansas as the Kinderhook shale. Similarly, sandstones at or near its base can be called Kinderhook sands. The Chattanooga is known as the Woodford Shale in Oklahoma while the basal sandstone is still called the Misener. In Arkansas, the Misener sandstone is identified as Sylamore Sandstone Member (Adler, 1971). The Chattanooga Shale is present over the eastern half of Kansas except for structural highs along the Nemaha uplift where it was eroded in Late Mississippian to Early Pennsylvanian time. In Brown and eastern Nemaha counties, it is greater then 250 ft (75 m) thick, but it generally thins westward to a featheredge in central Kansas (Goebel, 1968c). In northern McPherson and Marion counties, the Chattanooga Shale fills a broad ancient valley eroded into older rocks. This valley, called the McPherson Valley, contains Chattanooga Shale in excess of 250 ft (75 m) in thickness (Lee, 1956). In north-central Kansas, the Chattanooga Shale is a gray, greenish-gray, and red shale with minor limestones (Lee, 1956; Goebel, 1968c), but in southeast Kansas it is a black pyritiferous shale. These latter characteristics suggest it may be capable of generating petroleum.
The Misener sandstone at the base of the Chattanooga Shale is extremely erratic in its development. It can be several meters thick near the Central Kansas uplift but elsewhere, generally away from the uplift, it may only be represented by a slightly sandy zone at the base of the Chattanooga Shale (Goebel, 1968c). Lee (1956) states the Misener sandstone is commonly composed of well-rounded quartz sand grains that probably represent reworked Simpson sandstones. A similar conclusion was made by Amsden and Klapper (1972) for the Misener in Oklahoma. The locus of Misener sand deposition is probably strongly controlled by the northwest-southeast-trending ancestral Central Kansas uplift, the pre-Mississippian predecessor to the Late Mississippian-Early Pennsylvanian Central Kansas uplift.
Sandstones at or near the base of the Chattanooga Shale are not a major source of hydrocarbons in the Midcontinent (Adler, 1971), but they can produce locally significant amounts of hydrocarbons. Two such areas in Kansas, the Wil field in eastern Edwards County (Stevens, 1960; McCaleb and Wheeler, 1965) and the Lyons West field (Ehm, 1965; Wright, 1965), are stratigraphic traps where Misener sandstones are truncated updip by the sub-Pennsylvanian unconformity. Other fields in Kansas which produce petroleum from sandstones at or near the base of the Chattanooga Shale include the Valley Center field in Sedgwick County (Wright, 1960), the Voshell field in McPherson County (Hiestand, 1933), and the Haviland field in Kiowa County (James, 1956).
The presence of the Wil field and Lyons West field is encouraging, because other such stratigraphic traps may be found around the Central Kansas uplift. Elsewhere, predicting the location of Misener reservoirs before drilling is difficult because the unit developed so erratically. Perhaps with cores and other geologic studies, once a Misener pay zone is found, its trend could be predicted and subsequently exploited by follow-up drilling.
Mississippian production extends across all of southern Kansas (figure 20). Oil production dominates on the flanks of the Nemaha uplift and western side of the Cherokee basin, but scattered gas production occurs farther east. Gas and associated oil and gas production occur on the Pratt anticline, Sedgwick basin, and in the Hugoton basin near the Kansas-Oklahoma state line. Oil production without significant gas occurs farther north on the flank of the Hugoton basin southwest of the Central Kansas uplift.
Figure 20--Mississippian production.
Mississippian rocks in Kansas can be divided into two general sequences. The younger group of rocks is Chesteran in age and consists of marine and nonmarine shales and sandstones with minor limestones. Unconformably below the Chester rocks is a group of shallow-marine limestones, cherts, and cherty limestones that are Kinderhookian, Osagian, and Meramecian in age. Although the Chattanooga Shale is in part Mississippian in age, discussion of its production is separate from this section.
Chesteran rocks are quite thick in the Anadarko basin in Oklahoma but are present in Kansas only in the southwestern part of the state underlying parts of Stanton, Grant, Haskell, Morton, Seward, and Meade counties. These rocks are situated in the axis of the Hugoton basin and thicken southward into Oklahoma. The thickness of the Chesteran rocks at the Kansas-Oklahoma state line is approximately 500 ft (150 m) (Goebel, 1968d, e).
The Kinderhookian, Osagian, and Meramecian limestones that underlie the Chesteran rocks in southwestern Kansas are present all over the state except where they have been removed by late Mississippian-early Pennsylvanian erosion over the Central Kansas uplift and parts of the Nemaha uplift. The thickness of the Mississippian rocks is largely dependent on structural movement that occurred during late Mississippian-early Pennsylvanian time. Mississippian rocks are thin to absent by erosion on uplifts and local anticlines but are relatively thick in synclines and basins. The pre-Chesteran-age Mississippian rocks in Kansas are thickest in the Hugoton basin where approximately 1,400 ft (425 m) of these rocks are preserved (Goebel, 1968d, e).
Most of the Mississippian production in the Midcontinent occurs at or near the top of the Mississippian section just below the sub-Pennsylvanian unconformity (Adler, 1971). Solution weathering of the Mississippian limestones commonly produces a residual cherty, porous weathered zone just beneath the unconformity that is called the Mississippian "chat" by drillers. According to Ver Wiebe (1950), "chat" is a modification of the word "chert" and was originally identified as such in wells drilled in the Welch (i.e. Welch-Bornholdt) field in Rice County. The chat is thickest in the vicinity of the Central Kansas uplift and Pratt anticline and can be quite variable in its reservoir characteristics. Porosity and permeability of the chat are difficult to predict, particularly in wildcat locations. In many places it is several meters thick and is difficult to differentiate from overlying Pennsylvanian basal conglomerates that may also serve as reservoir rocks.
Porous oolite zones within pre-Chesteran limestones are also productive in some fields in the Hugoton embayment such as the Pleasant Prairie field in Haskell and Finney counties (Roby, 1959, 1961; Bennett, 1960) and the Nunn (Aukerman, 1959) and Damme (Schmidlapp, 1959) fields in Finney County. Development of the porosity zones within the Mississippian limestones is erratic and therefore hard to predict; nevertheless, they may represent intriguing targets as off-structure stratigraphic traps.
Mississippian rocks produce in several hundred fields in Kansas. Most of the larger fields are combination structural-stratigraphic traps in which porous chat and overlying conglomerates change to nonporous chat or limestone in an updip direction (Adler, 1971). Some traps of this type include the Lost Springs field in Marion County (Shenkel, 1955), the Wherry and Welch-Bornholdt fields in Rice County (McNeil, 1941; Clark and others, 1947), the Spivey-Grabs-Basil field in Kingman and Harper counties (Frensley and Darmstetter, 1965), and the Wil field in Edwards County (Stevens, 1960). Other significant fields in Kansas producing from Mississippian rocks include the Voshell field in McPherson County (Hiestand, 1933), the Winterschied field in Woodson County (Jewett, 1954), the Burrton field in Harvey and Reno counties, and the McClouth field in Jefferson County (Lee and Payne, 1944). Significant Chesteran production occurs in the McKinney field in Meade and Clark counties (Jamieson, 1959) and several other fields in the Hugoton embayment.
The widespread distribution of Mississippian production in both large and small fields indicates this unit will be a potential target horizon in virtually all wildcat wells drilled where Mississippian rocks are present in Kansas. Subtle stratigraphic traps, attributable to varying reservoir quality of the chat and overlying basal Pennsylvanian conglomerates, will probably be exploration targets in densely drilled areas of the state. Although small discoveries may be the norm in the more heavily drilled areas, larger fields may be a possibility in deeper, sparsely drilled areas such as the Hugoton embayment and western Kansas. Mississippian reservoirs are major pay horizons in a recent exploration play in Gove, Ness, and Lane counties southwest of the Central Kansas uplift. This production trend gained significance in the 1970s and continues today as an area of active drilling. Watney and Paul (1983) anticipate many more fields similar to these fields will be found along the subcrop trends of the Mississippian limestones in southwestern Kansas.
(Lower and Middle Pennsylvanian)
Morrow sandstones primarily produce gas from the southern tier of counties in southwestern Kansas (Clark, Meade, Seward, Stevens, and Morton; figure 21). Oil production extends northward from this area to form a triangular producing area with a northern apex in Wallace County. The Atoka interval is not productive in Kansas but is to the south in Oklahoma and Texas.
Figure 21--Morrow and Atoka production.
The Morrow and Atoka sediments were deposited in a large embayment which extends northward from the Anadarko basin situated in the Texas Panhandle and western Oklahoma. The embayment covers much of eastern Colorado and western Kansas where these sediments wedge out eastward and northward along a zone extending from Cheyenne County in northwestern Kansas to Clark and Comanche counties in south-central Kansas. Maximum thickness of the interval in Kansas is in excess of 500 ft (150 m; Rascoe and Adler, 1983). Prior to deposition of the Morrow sediments, the Midcontinent was emergent undergoing erosion during a major fall in worldwide sea level. The Morrow-Atoka interval represents a transgression of the sea, albeit a staggered one, onto a pre-Pennsylvanian erosional surface.
Beach, barrier-island, and offshore-marine sand bars have been described in the lower Morrow (McManus, 1959; Adams, 1964; Khaiwka, 1973a, b; Franz, 1994) and are commonly referred to as the "Keys sandstones" (Rascoe and Adler, 1983). These reservoir rocks are lenticular and range from poor to well-sorted, very fine to coarse-grained, glauconitic, fossiliferous, feldspar-rich to clean quartz sandstones, commonly with pores partly filled by calcite, dolomite, quartz, and kaolinite or chlorite clay minerals (Franz, 1984). The upper Morrow strata was dominated by fluvial-deltaic depositional conditions that reflect a still-stand or minor regression of the sea. Specific depositional environments include stream-mouth bar, distributary-channel, and fluvial point-bar sandstones (Swan.son, 1979; Franz, 1984). These sandstones are commonly coarse-grained, locally conglomeratic, crossbedded, and bear plant fossils. Carbonate cements and clay minerals are again present. The primary source for these sediments appears to have been the Transcontinental arch that crosses northern Colorado and western Nebraska. The Central Kansas uplift and Sierra Grande uplift in southeastern Colorado were locally very important sources of sediment.
The Atoka sediments in southwestern Kansas are a repetitive sequence of thin limestones and shales and reflect a more extensive inundation of the sea onto the continent. Local Atoka-age, lenticular sandstones were probably deposited along the eastern limit as ancient shoreline sediments in western Kansas analogous to the Morrow, although these deposits have yet to be recognized.
Significant oil and gas fields in Kansas produce from primarily lenticular, upper Morrow sandstones ranging in thickness from 2 to 60 ft (0.6-18.2 m). Structural-stratigraphic traps dominate fields producing from Morrow sandstones in western Kansas. Structural objectives have resulted in multi-pay fields with Morrow sandstones, which locally produce across the structures. The Eubank field in Haskell County is a large multi-pay field located on a significant anticline which was revealed by mapping shallower Permian strata. The Morrow is a minor pay here because it contains a lenticular sandstone of limited extent (Fugitt and Wilkinson, 1959). Another Morrow sandstone is an oil reservoir along its pinch out at the north end of the Pleasant Prairie anticline in Finney, Kearney, and Haskell counties (Roby, 1959). Sand accumulated in a structural saddle at the Sequoyah field, a small field in Finney County (Tucker, 1959), and in a lenticular deposit on the crest of another anticline at the Patterson field in Kearney County, a small but highly productive field (Davis, 1959). The Taloga field in Morton County produces oil from several Morrow sandstones on an asymmetric anticline (Anonymous, 1959c).
Significant gas fields producing from the Morrow in southwestern Kansas include the Harper Ranch pool in Clark County, interpreted as an offshore sand accumulation in an embayment along a shoreline (Waite, 1956). The trap in the McKinney field in Meade and Clark counties occurs as an updip pinch out of sandstone discovered using subsurface-geology techniques (Jamieson, 1959); Liberal Southeast field in Seward County, a petroleum accumulation in a lenticular Morrow sandstone reservoir discovered by core drilling of a structural anomaly associated with the Permian Stone Corral marker; Liberal-Light field also in Seward County, a large stratigraphic trap found by random drilling (Strohmeyer, 1959). The Interstate field discovered in Morton County using subsurface and seismic methods produces gas and oil from a lenticular lower Morrow sandstone which crosses an anticline (Anonymous, 1959a). The Sparks field has thick, basal and lower Morrow sandstones on a structural closure discovered by seismic prospecting (Rupp, 1959). The Lexington field in Clark County is a large field associated with a thick, valley-fill Morrow sandstone which rests on an unconformity developed on the Mississippian rocks (Watney and Paul, 1983).
Drilling for Morrow production is concentrated along established production within the southern tier of counties and in Finney and Haskell counties. Recent Morrow discoveries and extensions in extreme western Kansas and eastern Colorado indicate favorable conditions for oil accumulation in these areas (Paul and Beene, 1985).
Morrow sandstone reservoirs are highly lenticular and are the result of a range of depositional conditions. A low drilling density and a lack of cores and detailed knowledge of these rocks have required that exploratory prospects involve, primarily structural trapping. Drilling based on mapping of shallow structural anomalies has been very successful in finding moderate- to large-sized fields such as the Eubank field in Haskell County, Liberal Southeast in Seward County, and Pleasant Prairie field in Finney, Kearney, and Haskell counties. Similarly, the drilling of seismically detected structures has also resulted in significant oil and gas discoveries (such as the McKinney field in Meade and Clark counties, Richfield field in Morton County, and Sparks field in Stanton and Morton counties).
Basal Morrow valley-fill sandstones following a southeast-to-northwest trend analogous to Lexington field in Clark County will offer continued exploration targets. Subsurface methods have been credited with the discovery of some of the Morrow oil and gas fields, including Lexington and Harper Ranch, although reflections of the sandstone reservoir in Lexington field are visible on high resolution, CDP seismic profiles that cross the fieid. What have been found to date are primarily combination structural-stratigraphic traps involving pinch out of sandstones along an unconformity or lensing out of sandstone into shale. As the information base grows, the knowledge of depositional trends should permit improved assessment of characteristics of stratigraphic traps, which should help to lower the risk in their exploration and development.
(Desmoinesian, Middle Pennsylvanian)
A large area of oil and gas production from the Cherokee Group and the Marmaton Group is found in eastern Kansas in the Cherokee basin east of the Nemaha uplift. The map of this production (figure 22) only displays a portion of the producing wells from this interval in eastern Kansas because many of the fields producing from Cherokee and Marmaton reservoirs were discovered and exploited before accurate records were kept on exploratory and production drilling. Another concentration of oil production is on and immediately west of the Central Kansas uplift. Oil and gas production are also scattered across southwest Kansas and the Pratt anticline in south-central Kansas.
Figure 22--Cherokee and Marmaton production.
The Cherokee Group, the lower of the two groups, is a succession of shale with lenticular sandstones, thin coals, and minor limestones (Zeller, 1968). The deposits are predominantly fluvial-deltaic, with minor terrestrial and open-marine rocks. The major producing sandstones in eastern Kansas, such as along the "Golden Lanes," have been described as marine bar deposits and meandering alluvial-stream deposits (Rich, 1923; Rich, 1926; Bass, 1934; Hulse, 1979). Many lesser Cherokee sandstones so abundant in this area of the state have also been described as distributary-channel and crevasse-splay deposits which were part of successive deltaic depositional systems (Harris, 1985). The oil and gas commonly accumulates in updip areas of these sandstone bodies, and consequently they have been classified as combination structural-stratigraphic traps (Busch, 1959).
In western Kansas the Cherokee Group becomes much more marine, with limestones eventually replacing the sandstones of the east, particularly in the upper Cherokee. The Cherokee Group was deposited on an extensive pre-Pennsylvanian erosion surface on the flanks and over the crests of the Central Kansas uplift where it locally pinches out. Lenticular sandstones occupy the lower Cherokee including those that fill valleys incised into the underlying strata, apparently cut by rivers directed off the Central Kansas uplift (Walters and others, 1979). The basal Pennsylvanian sandstones and conglomerates locally deposited during the Cherokee and Marmaton intervals are best developed in the vicinity of uplifts, which were a major source area for these deposits. The basal Pennsylvanian conglomerate can range in age up to Missourian in local areas on the crest of the Central Kansas and Nemaha uplifts, where the Kansas City Group rests directly on the Precambrian and Arbuckle (Merriam, 1963). In general, the age of the basal Pennsylvanian deposit would be oldest on the lower flanks of these uplifts and become progressively younger up into their crests. Lower Pennsylvanian strata are limited to the lower reaches of the basins as previously described. The basal Pennsylvanian sandstones are classified here as Middle Pennsylvanian and are included in the Cherokee and Marmaton map (figure 22).
Marmaton and Cherokee limestones are productive across western Kansas. The strata are components of cyclothems and the main producing units are regressive (upward-shallowing) limestones. High-energy deposits such as oolitic limestones or mud-dominated carbonate buildups are altered and leached by exposure of these carbonates to weathering late during the development of each cycle (Caldwell, 1985). Daniels (1985) describes a later period of dissolution after burial of carbonate and a resultant porosity formation which may have a significant impact on local reservoir development.
The Cherokee sandstones of southeastern Kansas constitute some of the oldest exploration plays in the Midcontinent including the initial oil discovery for the state in Miami County in 1860. Rapid development did not occur until the early 1900s. By 1904, principally from Cherokee reservoirs in eastern Kansas, annual oil production was over four million barrels. Extensive development of Cherokee oil and gas fields took place from Miami to Montgomery counties from 1900 to 1910. The large oil pools in "Bartlesville" shoestring sandstones, which are part of the "Golden Lanes," such as the Smock-Sluss, Weaver, and Fox-Bush fields in Butler County and the Sallyards pool in Greenwood County were found and developed in the 1920s (Jewett, 1954). The Busch City oil field in Anderson County is an example of a shoestring-sandstone stratigraphic trap having dimensions of up to 55 ft (17 m) in thickness, 1,000 to 2,000 ft (300-600 m) in width, and 14 mi (23 km) in length (Charles, 1941; Reinholtz, 1982). The Coffeyville field, one of the first to be developed in Kansas, is a large structural strafigraphic trap located on a dome along the Chautauqua arch and includes gas production from the lenticular Cherokee sandstones (Jewett, 1954).
Seismic, core drilling, and subsurface methods have been employed to find anticlinal closures with Marmaton and Cherokee pay zones in western Kansas. Some reservoirs are commonly lenticular sandstones, others are limestones with local porosity development. Recognition and prediction of rock properties is therefore important in order to understand the extent of these reservoirs. An example of a significant field in western Kansas includes Damme field in Finney County, a structural trap with multiple pays including an oolitic Marmaton limestone (Schmidlapp, 1959). The Nunn field in Finney County and the Llanos field in Sherman County are multi-pay pools discovered using seismic. Both have pay zones in both the Cherokee and Marmaton groups (Aukerman, 1959; Byers, 1959). Subsurface and core drilling were also used to substantiate the Llanos prospect before it was drilled.
The Eubank field in Haskell County is a large multi-pay field on an anticlinal closure discovered using subsurface geology. It produces from oolitic Cherokee limestone and dolomitic and oolitic Marmaton limestones (Fugitt and Wilkinson, 1959). The Pleasant Prairie field in Finney, Kearney, and Haskell counties is analogous to the Eubank field (Roby, 1959).
Examples of basal Pennsylvanian sandstone and conglomerate pay zones include structural-stratigraphic traps in multi-pay fields including the Wil field in Edwards and Stafford counties, an updip pinch out of conglomerate (McCaleb and Wheeler, 1965); and the Sunny Slope and Groff fields in Trego County and the Southeast Oro pool in Pawnee County where the Cherokee is almost entirely composed of sandstone or conglomerate that pinches out northeastward onto the Central Kansas uplift (Ash, 1965; Costa, 1965). Stratigraphic traps have been few, but one in particular, the small Sun City pool in Barber County tested an amazing 3,000 barrels of oil per day in the discovery well from a locally thick, very vuggy, coarsely crystalline Marmaton limestone, locally referred to as the Massey zone (Spaulding, 1959). Similar opportunities for stratigraphic traps include sand-filled paleochannels described by Walters and others (1979).
Several small fields produce from a lower Cherokee sandstone called the Burgess in the Salina basin in central Kansas including Ash Grove, Bonaccord, and Bonaccord Northeast in Dickinson County (Steder, 1960). The Yaege field in Riley County includes oil production from the basal Pennsylvanian conglomerate (Goebel, 1960).
Desmoinesian sandstones of southeast Kansas and northeast Oklahoma have been the most productive Pennsylvanian reservoirs of the Midcontinent. Substantial carbonate buildups equivalent to the Marmaton of Kansas are major producers along the rim of the Anadarko basin in central Oklahoma (Rascoe and Adler, 1983; Michlick, 1984).
Development of reservoirs in the Desmoinesian stage in southeastern Kansas is mature with thinner once-uneconomic zones now being sought in northeast Kansas in the Forest City basin, drilling density is still relatively low. Recent discoveries of oil and gas in the southeastern part of the Forest City basin are an optimistic sign that additional reserves will be found (Paul and Beene, 1985). Surface and subsurface mapping used to search for structural traps will continue to be the mainstay of exploration in this area as dictated by the economics of the anticipated small reservoirs. Seismic surveys may provide more opportunities, but will be done in a restricted way. Enhanced oil recovery will provide many opportunities in the future for eastern Kansas because of low drilling costs and certain favorable characteristics of the reservoirs that make them suited for existing enhanced oil-recovery processes (Ebanks, 1975).
Recent successes in the Marmaton and Cherokee limestones and sandstones in western Kansas are occurring as companies explore low-relief structures in less heavily drilled areas west of the Central Kansas uplift (Paul and Beene, 1985). Integrated studies of stratigraphic and sedimentologic information from wireline logs, cuttings, and cores should help to optimize the selection of structures that provide better opportunities for favorable reservoir development.
(Missourian, Upper Pennsylvanian)
Oil production from Missourian-stage strata is widespread over western and central Kansas (figure 23). It is concentrated over the Central Kansas uplift but is more widely scattered in adjacent basins. Gas production is limited in these same areas and, in addition, includes extreme eastern Kansas and southwestern Kansas on the flanks of the Cimarron arch.
Figure 23--Lansing, Kansas City, and Pleasanton production.
Missourian strata in Kansas are divided from bottom to top into the Pleasanton, Kansas City, and Lansing groups. The Pleasanton Group is primarily composed of shale and lenticular sandstones. These sandstones, locally referred to as the Hepler and Knobtown, serve as gas and oil reservoirs in eastern Kansas where the Pleasanton Group is thicker and the sandstones best developed. The Kansas City and the Lansing groups are a sequence of alternating limestones and shales, commonly combined in the subsurface and referred to as the Lansing-Kansas City. These later two groups are by far the dominant Missourian-producing intervals in Kansas. Seven or more major limestones comprise the Lansing-Kansas City throughout the subsurface. One or more can serve as a reservoir unit which varies according to local attributes of the limestone. The reservoir limestone is commonly the regressive limestone of a cyclothem, analogous in kind to those in the overlying Virgilian Pennsylvanian strata. The Hushpuckney and Stark shale members of the Swope and Dennis formations locally serve as gas reservoirs in southeastern Kansas where they are black and fractured. These strata are part of a considerable succession of cyclic sediments called cyclothems. The four-component cycle in the Lansing and Kansas City groups commonly has a thin, lower transgressive limestone overlain by a marine shale which is commonly black and high in natural gamma radiation. The marine shale commonly serves as a subsurface marker for correlation. The main reservoir rock is the succeeding member of the cyclothem, the regressive limestone which by definition represents a shallowing-upward unit. The regressive limestone commonly has a porous, commonly grain-rich reservoir interval near its top. The grain-supported fabric is the result of high-energy marine depositional conditions. The shallow-water and exposed conditions occurring shortly after deposition of the rock have commonly significantly enhanced the original porosity and permeability of the regressive limestone. Furthermore, local, low-relief structural anomalies appear to be favored sites for reservoir development (Watney, 1980, 1984, 1985).
The largest Missourian fields in the state are structural traps on the Central Kansas uplift, including the only giant field (116 million barrels ultimate recovery) in the Lansing-Kansas City--the Hall-Gurney field in Barton and Russell counties (Rascoe and Adler, 1983). Other large fields on the Central Kansas uplift include the Bemis-Shutts field in Ellis County, and the Trapp field in Russell and Barton counties. The majority of other fields in Kansas are combination structural-stratigraphic traps. Examples include the Alameda field in Kingman County, which produces from multiple zones including two limestones in the lower Kansas City Group. This field is located along the crest of one of a series of northeast-southwest-trending faulted anticlines located in the northeastern portion of the Sedgwick basin (King, 1965a, b). The Rosedale field, also in Kingman County, is another field with multiple pays, including a limestone reservoir in the Kansas City Group with local vuggy porosity development (Richardson and Matthews, 1956b). This field was found using seismic profiling as an exploration tool.
The Valley Center and Goodrich fields in Sedgwick County are multi-pay fields with up to four producing limestone intervals in the Lansing-Kansas City characterized by erratic porosity development These fields were discovered through core drilling and also are located on one of the prevailing northeast-southwest-trending anticlines in the Sedgwick basin (Wright, 1960; Kirk, 1960). The Fitzsimmons field in Pratt County is analogous to the above fields but produces from only one limestone in the Kansas City, where it is thick with moldic and vuggy porosity development (Brown, 1956). The Tobias field in Reno County is another multi-pay field on an anticline on the southeast edge of the Central Kansas uplift. A single limestone in the Lansing Group is producing in association with the local thickening of the unit (Brewer, 1965).
The Cambridge arch in northwest Kansas is another locus of Missourian petroleum reservoirs. The Adell anticline in Sheridan County is the site of a number of Lansing-Kansas City oil fields (Merriam, 1963). The Adell field is a large multi-zone Lansing-Kansas City pool discovered by core drilling and seismic confirmation (Lane, 1959a). Other fields such as the Hardesty and Jennings fields (Lane, 1959b, c) and the Pollnow field (Anonymous, 1959b) and Warner field (Curtis, 1959), all in Decatur County, are seismic or core-drilled discoveries found on anticlinal closures which produce from up to three limestones in the Lansing-Kansas City. Porosity is localized or discontinuous in these fields (Curtis, 1959).
The area west of the Central Kansas uplift has been the focus of recent activity of wildcat exploration and development (Paul and Beene, 1985). The Pendennis South field in Lane County is an example of an established field discovered using seismic interpretation. A northeast-trending anticline produces from five zones in the Lansing-Kansas City in which the porosity is variable, primarily associated with oolitic limestones (McCoy, 1965). The large Wil field in Edwards County contains a Missourian pay zone in the Kansas City Group, a porous, fossiliferous, oolitic limestone situated on a local structural closure (McCaleb and Wheeler, 1965). The Pleasant Prairie field is a large anticlinal trap covering parts of Finney, Kearney, and Haskell counties. Oolitic limestone lenses associated with carbonate buildups which cross these and other structures in the area are locally productive (Roby, 1959; Brown, 1984). Eubank field in Haskell County (Fugitt and Wilkinson, 1959) has multiple pays of this type located on a strong north-south anticlinal trend. A half-dozen Lansing-Kansas City oolitic and grainstone reservoirs produce from intervals that locally thicken over the structure. The general patterns in thickness do not correlate with structure (Brown, 1963).
Cahoj field in Rawlins County in northwestern Kansas produces from all carbonate zones in the Lansing and Kansas City groups at varied locations in the field. Cahoj is situated on a well-defined structure with an excess of 25 ft of closure on the top of the Lansing Group. Oil production is not confined to structural closure but follows divergent porosity development in carbonate rock in flank positions. Early structural deformation apparently produced topographic relief which substantially influenced both depositional environments and early diagenesis (Watney, 1990).
The Wilsey-Wilde gas area in Morris County in eastern Kansas produces from multiple zones including an oolitic limestone in the Lansing-Kansas City on a structural closure over the Nemaha uplift (Smith, 1960). The Davis Ranch pool in Wabaunsee County is an anticlinal closure in the Forest City basin discovered by surface mapping. It is a multi-pay field including one limestone zone from within the Lansing-Kansas City Group (Smith and Anders, 1951).
Missourian oil and gas fields are distributed widely across southwest Nebraska (DuBois, 1985; Prather, 1985), Kansas, Oklahoma, and Texas. These accumulations are in structural, stratigraphic, and combination structural-stratigraphic traps developed in a variety of rocks, including sandstone, carbonate, and granite wash (Rascoe and Adler, 1983).
Pure stratigraphic traps have been found in the Missourian section, but these are small and thus far insignificant to overall production. Abbyville field in Reno County is a one-well field with a single pay zone in oolitic limestone in the lower Kansas City that is neither structurally high or low. It was discovered by random drilling (Anonymous, 1956). A concerted effort to understand the regional deposition and diagenesis of the carbonate-reservoir rocks may reduce the risk in the search for stratigraphic plays in this region.
(Virgilian, Upper Pennsylvanian)
The distribution of oil and gas fields in the Virgilian-stage strata is similar to Missourian strata below and is associated with major structural features such as the Central Kansas uplift, the Pratt anticline, and restricted portions of the Nemaha uplift (figure 24). Scattered fields are present in the Sedgwick basin and western Kansas, and a large gas area occurs in Morton County. Oil production is concentrated over the northern Central Kansas uplift.
Figure 24--Douglas, Shawnee, and Wabaunsee production.
The Virgilian Stage, comprising the Douglas, Shawnee, and Wabaunsee groups, is composed of cyclic limestones, shales, and minor sandstones and coal. The carbonate reservoirs of the Shawnee and Wabaunsee groups are predominately shallowing-upward, regressive limestones producing primarily from the Toronto, Topeka, and Howard limestones. The sandstones are generally lenticular and are thickest in southern and southeastern Kansas. The Douglas Group is primarily shale with intervals of sandstones and thin limestones, thickening from less than 50 ft (15 m) in northwest Kansas to greater than 400 ft (120 m) in southeast Kansas (Jewett and others, 1968). The depositional environments change from predominately marine in western and central Kansas to marginal marine in southern and southeastern Kansas and eventually to fluvial in central Oklahoma (Ball, 1964). Thick sandstones in central Kansas pinch out northward onto a marine shelf in the western Sedgwick basin and provide for notable stratigraphic traps.
The Greenwood gas area in Morton County is a structural-stratigraphic trap that produces on the northeast flank of the Cimarron arch where porous carbonate grainstones and oolites pinch out into nonporous carbonate and clastic rock (Wingerter, 1959, 1968). Seventeen different limestones in the Wabaunsee and Shawnee groups produce in over 250 wells from this third-largest gas field in the state. Several other notable stratigraphic traps involve the updip pinch out of sandstones in the Douglas Group, including the Rhodes field in Barber County discovered by core drilling (Clark, 1956) and the Whelan pool, also in Barber County, which produces from the Elgin Sandstone Member of the Shawnee Group. Unlike the Rhodes field, the Whelan pool was discovered by random drilling (Brewer, 1956). The Nurse field in Barber County and the Lerado pool in Reno County are combination structural-stratigraphic traps caused by a pinch out of Douglas sandstone over the crest of an anticlinal closure (Douglass, 1956; Steincamp, 1965). An extensive "Stalnaker" sandstone which grades northward into shale along a zone from Harper, Kiowa, Sedgwick, Cowley, and Chautauqua counties has provided many opportunities for gas accumulation such as that described for Sullivan field in Harper County (Walton and Griffith, 1985).
The Lerado pool in Reno County produces from Langdon and Indian Cave sandstones of the Wabaunsee Group in addition to Douglas sandstone. The Howard and Topeka limestones locally produce oil from structures on the Cambridge arch in northwest Kansas such as at the Jennings field in Decatur County. The Toronto Limestone Member has continued to be an important oil-producing interval on anticlinal closures in southwestern Kansas, such as the Holt field in Seward County (Jacques, 1959).
Eighteen percent of the ultimate gas production from all Pennsylvanian fields in the Midcontinent will likely come from just two large Virgilian stratigraphic traps: the Greenwood and the Mocane-Laverne gas areas in the Oklahoma Panhandle (Rascoe and Adler, 1983). Stratigraphic traps will also be important finds in the future for the carbonate reservoirs of the Shawnee and Wabaunsee groups, but will likely remain secondary in importance to the more oil-prone, older Pennsylvanian targets. Sandstones in the Douglas Group will continue to be important producing intervals in south-central Kansas. Regional studies using core and log interpretation will help to identify favorable trends for exploration not apparent today.
Permian strata serve as reservoirs for one of the largest gas accumulations in the western hemisphere, in the Panoma and Hugoton gas areas in southwestern Kansas (figure 25). These fields produce from the Council Grove or Chase groups, respectively. Small shallow Permian gas fields are also scattered across the southern Central Kansas uplift, Pratt anticline, over limited portions of the Nemaha uplift, and on local anticlines in the Sedgwick and southern Salina basins from the Chase, Council Grove, and Admire groups. Isolated occurrences of oil production are found on the Nemaha and Central Kansas uplifts, and in west-central Kansas from reservoirs in the Admire Group.
Figure 25--Undifferentiated Permian production.
The Permian System of Kansas is a thick stratigraphic interval. It crops out at the surface along nearly a north-south line in eastern Kansas and reaches a thickness in excess of 3,500 ft (5,600 m) in southwestern Kansas (McKee and others, 1967). The Permian is divided from bottom to top into the Admire, Council Grove, Chase, Sumner, and Nippewalla groups (O'Connor and others, 1968). The Lower Permian Gearyan Stage, consisting of the lower three groups, accounts for essentially all of the reported Permian gas and oil production (figures 26, 27, and 28). A small amount of Sumner gas has been produced from Russell County on the Central Kansas uplift and scattered wells in southwestern Kansas (figure 29). The Hollenberg limestone of the lowermost portion of the Sumner Group has reported gas shows and may be locally producing in the Hugoton gas area (Paul, personal communication, 1986). The strata from the lower, most productive three groups are cyclic deposits of marine limestones, dolomites, and shales and nonmarine red silty shales and mudstones deposited during the waning stages of repetitive marine inundation of the Midcontinent during the late Paleozoic Era.
Figure 26--Admire production.
Figure 27--Council Grove production.
Figure 28--Chase production.
Figure 29--Sumner production.
Reservoir-quality rocks in the Permian strata are commonly the uppermost, dolomitized regressive carbonates of each repetitive sequence. Secondary porosity such as skeletal and anhydrite molds, vugs, and intercrystal line porosity between dolomite crystals is most common and results in low, irregular permeability. These carbonate-dominated marine deposits are overlain and grade westward into continental red-bed clastics. This transition causes a porosity pinch out in western Kansas resulting in large stratigraphic traps in the giant Hugoton (Chase) and Panoina (Council Grove) gas areas. The Hugoton field is the largest gas accumulation in the western hemisphere (Hemsell, 1939; Page, 1940; Hinton, 1952; Kleen, 1956; White, 1981; Abdullah, 1983; Rascoe and Adler, 1983). The Hugoton stratigraphic trap may also be assisted by an east-directed hydrodynamic flow (Mason, 1968; Pippin, 1970). The Hugoton-Panhandle gas area of Kansas, Oklahoma, and Texas covers some 5 million productive acres from which an estimated 76.5 trillion cubic ft of gas will be ultimately produced. The combined thickness of the pay zones within the Chase Group averages 50-60 ft (15-18 m) in the Hugoton gas area of Kansas (Furbush, 1959). Gas accumulations in the Council Grove Group are scattered across western Kansas but are concentrated in the Panoma field which underlies Hugoton, but extends farther to the west (figure 27).
Shallow buried dolomite reservoirs of the Chase Group in central Kansas, such as in Rice County, result from secondary porosity in dolomitized limestone. Best porosity occurs in local accumulations of grain-supported carbonates where skeletal grains are dissolved (Glossa, 1982). The occurrence of this improved porosity appears to be closely related to structural highs (figure 28). Shallow Permian gas production also occurs in central Kansas in the Indian Cave sandstone of the Admire Group in similar positions on the crests of structures (figure 26). The Wilde, Wilsey, and Alta Vista fields in Morris and Chase counties produce from the Indian Cave sandstone in the Admire Group in structural-strafigraphic traps along the crest of the Nemaha uplift (Merriam, 1960; figure 26).
Outside of the giant-sized oil accumulation in the Panhandle field in the Texas panhandle, the Permian strata should continue to provide small, shallow gas reservoirs including bypassed and overlooked zones on structures with established deeper pay zones. Gas detection, readily available today but not originally used in early drilling, should provide many opportunities for additional gas reserves in central and western Kansas. The price and market for natural gas will determine the feasibility of this development.
The Upper Cretaceous chalks of the Niobrara Formation account for virtually all the Mesozoic gas production (figure 30); a single exception being an abandoned well that produced gas in western Sheridan County from the Codell sandstone member of the Carlile Shale which immediately underlies the Niobrara. Niobrara production in Kansas is presently limited to a small area in northwestern Kansas, including Cheyenne, Rawlins, Sherman, Thomas, Sheridan, Wallace, and Logan counties. The porous chalk that constitutes the reservoir rock was deposited during a major transgression of the sea. The Niobrara Chalk is divided into two members--the Fort Hays Member and the overlying Smoky Hill Member (O'Connor, 1968). The Fort Hays Member, named after an area of outcrop in central Kansas, is a clean chalk averaging 40-85 ft (12-25 m) thick. The most productive gas zones are in the Smoky Hill Member, which is also referred to as the Beecher Island Zone. The Smoky Hill Member averages some 600 ft (180 m) in thickness (Hattin, 1981).
Figure 30--Niobrara production.
The gas in the Niobrara is biogenic, having formed at temperatures less than 75° C by anaerobic-bacterial decay of organic matter apparently indigenous to the Niobrara itself (Rice and Claypool, 1981). Active exploration for these gas deposits has included eastern flanks of the Denver basin, immediately east of the Rocky Mountains and the Los Animas arch in eastern Colorado, and along the Chadron-Cambridge arch in northwest Kansas, northeast Colorado, and western Nebraska.
Late Cretaceous and Early Tertiary deformation associated with the uplift of the Rocky Mountains produced many small faults and low-relief anticlines and domes which led to gas entrapment (Brown and others, 1982). Although the chalk is highly porous, it has very low permeability. However, the chalk is brittle and it fractures during folding and faulting, thereby enhancing its reservoir characteristics. The gas accumulations are therefore primarily in structural traps with rates of production strongly controlled by local fracturing. Matrix porosity in chalks varies directly with depth. Porosities over 40% are present at the shallow depths in Kansas and contribute favorably to reservoir development (900-1,200 ft [275-375 m]; Lockridge and Scholle, 1978). Hydraulic fracturing with foam during well completion has significandy improved the recovery and economics of the Niobrara reservoirs (Hanley and Van Horn, 1982).
Natural gas was discovered in the Niobrara near Goodland, Kansas, in 1912, which led to the development of the Goodland gas area. With rising gas prices and the new foam-fracture stimulation in the mid-1970s, a flourish of discoveries occurred as small fields throughout northwest Kansas and adjacent areas in Colorado and Nebraska were developed (Brown and others, 1982). Exploration has been limited to areas of shallow burial where matrix porosity is high. Additional exploration and development of these shallow gas deposits will be encouraged with a favorable price and market for the gas.
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Kansas Geological Survey, Energy Research
Placed on web June 2008; originally published 1987.
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