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Producing Zones
Three zones in the McLouth field (fig. 3) yield oil or gas: (1) the McLouth sand, (2) the weathered zone at the top of the Mississippian rocks, and (3) a zone of porous dolomite in the undifferentiated Burlington and Keokuk limestones, about 150 feet below the top of the Mississippian beds. Potential producing zones which have yielded oil and gas in other parts of Kansas occur at the top of or in the upper part of the Devonian rocks at the top of the Kimmswick limestone, in the St. Peter sandstone, and at the top of the Arbuckle limestone (fig. 3). These zones have not been tested adequately in the McLouth field.
McLouth Sand
Most of the gas production in the McLouth field comes from a body of basal Cherokee sediments termed the McLouth sand. Several wells yield oil in small amounts from the McLouth sand, but the area of oil production is small compared with that of gas production.
The McLouth sand overlies the eroded .and structurally deformed surface of the Mississippian limestone and consequently has a variable thickness which has a known range of 15 to 95 feet within the area of the McLouth field. The McLouth sand consists of various types of sandstone interstratified with siltstone, clay, and shale. It includes also clay ironstone, coal, and intraformational conglomerate in minor amount. The McLouth sand is frequently referred to as Bartlesville sand with which it has nothing in common except that in some places the Bartlesville also lies near the base of the Cherokee shale. The Bartlesville sand in Oklahoma is a lenticular body of sandstone deposited along the western shore of the Cherokee basin. As the sea advanced northward into the basin, similar shoestring sandstones were deposited along both its eastern and western shores (Bass, 1934; 1936). Sandstones corresponding to the Bartlesville in lithology and stratigraphic position on the eastern side of the basin in Vernon county, Missouri, have been reported by Greene and Pond (1926) and in Crawford and Cherokee counties, Kansas, by Pierce and Courtier (1938). In these places the top of the sand lies 225 to 250 feet below the Ft. Scott limestone. The top of similar shoestring sands in Greenwood county, Kansas, which were studied by Bass, lies about 200 feet below the Fort Scott limestone. The McLouth sand, on the contrary, was deposited in another basin (Forest City), is 450 feet below the Fort Scott, and consists of highly variable sandstones interstratified with various types of shale.
The basal member of the McLouth sand is more nearly equivalent to the Burgess sand which was the earliest deposit of the Cherokee shale in the Cherokee basin. The Burgess sand consists of coarse sand which includes conglomerate in many places. The lowest member of the McLouth sand is similarly composed of coarse angular sand but does not include much conglomerate. It and the Burgess sand are similar in lithology, and both were the earliest deposits of the Pennsylvanian in their respective areas. The McLouth sand, however, includes several productive sand members higher in the section which are separated from each other and from the basal sandstone by beds of shale. The term McLouth sand is, therefore, more inclusive than the term Burgess.
Lithologic zones of two general types are distinguished in the McLouth sand: (1) shale zones consisting mostly of clay shale and micaceous silty shale but also containing beds of clay, siltstone, clay ironstone, and coal, and (2) sandy zones composed of sandstones that show marked lateral variation from well-sorted, porous sandstone to highly argillaceous sandstone. Where the sandy zones consist principally of fine-grained sediments rather than sandstone, they nevertheless contain sandy laminae or thin layers of argillaceous sandstone. These two general types of lithologic zones alternate vertically in the McLouth reservoir (pl. 4) and suggest that cyclic sedimentation occurred. The sandy zones are neither lenticular nor shoestring sands, but are widespread blanket deposits of variable character.
The McLouth sand includes four sandy zones, three of which yield gas or oil from well-sorted porous sandstone facies of the sandy zones where these occur in favorable structural positions. Several wells in favorable structural positions on the crests or high on the flanks of anticlines or domes failed to produce gas or oil from McLouth sands because they penetrated argillaceous facies of the sandy zones. Thus, although structure is the major factor in determining the localization of gas and oil in the McLouth sand, the accumulation and local distribution of gas and oil on the anticlines or domes and the volume of production and open flow of gas are controlled largely by lateral variations in the porosity and permeability of the sandy zones. Each sandy zone tends to act as a unit so far as the distribution of oil and gas is concerned. Thus, a certain well may produce gas from one zone and have a show of oil in a deeper zone in the McLouth, an example being the O. J. Connell No. 1 Edmonds well (SW NE sec. 21, T. 9 S., R. 20 E.). In practically all wells that yield both gas and oil, the oil comes from a deeper sand.
A more complete discussion of the McLouth sand is presented later in this report after the discussion of structure on which some of its characteristics depend.
Top of Mississippian Limestone
The top of the Mississippian is an erosional surface, as has already been pointed out. As a result of structural distortion, peneplanation, and mild dissection, different Mississippian formations were exposed in different areas on this surface when it was submerged and covered by Pennsylvanian deposits. Most of the wells in the McLouth and North McLouth pools find Spergen dolomite on the old surface, but wells in the Ackerland pool and on the east side of the McLouth field find St. Louis limestone on the old surface. A few wells in T. 10 S., R. 19 E. on the west side of the field also revealed St. Louis limestone at the top of the Mississippian. The Warsaw limestone forms the surface of the Mississippian in a few wells on the margins of the field.
Weathering and disintegration of the surface of the Mississippian rocks developed irregular porosity in the exposed rocks. In some localities the openings provided a reservoir for oil and gas. However, neither the dense lithographic St. Louis limestone nor the sucrose silty dolomite of the Spergen which lie at the surface of the Mississippian lend themselves to the development of porosity, and not much gas or oil have come from the weathered zone in the McLouth field. Solution of the dense St. Louis limestone takes place mainly along joints and cracks without developing much porosity. Only one well is known to have found gas in this formation. The Mosbacher No. 1 Dolman well, in the NW SE sec. 27, T. 9 S., R. 20 E., found no oil or gas in the impermeable sand at the base of the McLouth, but a small amount of gas entered the hole from the top of the St. Louis limestone. This zone was acidized and the flow of gas was reported to have increased from 360,000 cubic feet to nearly 3 million cubic feet of gas per day. Traces of oil-stained St. Louis limestone were encountered at the top of the Mississippian in the Miller No. 2 Jim Bell well, in the SW NW sec. 7, T. 10 S., R. 21 E., but no oil was developed.
The Spergen limestone is composed of dense silty dolomite, but weathering of this formation in some places has developed "pin hole" porosity visible under the microscope. Some wells that yielded gas in small amount in the McLouth sand have shown increased gas production when drilled into the underlying Spergen dolomite. This was the case in the McLaughlin and Sons No. 2 Bartlett well, in the SE SW sec. 33, T. 9 S., R. 20 E., which yielded 4,246,000 cubic feet of gas per day in the McLouth sand and increased to 6,100,000 cubic feet per day in the first 10 feet of the Spergen, a gain of 1,754,000 cubic feet. Gas was found in both Spergen dolomite and the McLouth sand in the McLaughlin No. 2 Dark well, in the SE NE sec. 5. The McLaughlin No. 1 Ragan well, in the NW NW sec. 3, also had an increase of gas in the top of the Spergen. Gas gauged at 500,000 cubic feet was reported from the top of the Spergen in the Smythe et at No. 1 Jacobson well, in the SW NW sec. 27, T. 9 S., R. 20 E., and a show of gas was reported in the top of the Spergen in the Smythe et at No. 1 Miller well, in the NE SE sec. 22, T. 10 S., R. 20 E.
Free oil was first noted in Spergen dolomite at the top of the Mississippian in the Young and Longwell No. 1 McLeod well, in the NW SW sec. 4, T. 10 S., R. 20 E., but efforts to increase the production by acidizing the well were unsuccessful. The Gordon and Poole No. 1 Knudson well, in the SE NW sec. 33, T. 9 S., R. 20 E., which is reported to have had only 1 million cubic feet of gas in the McLouth sand, was deepened to the Spergen dolomite where a show of free oil was found. This well was not connected to a pipe line and the well is now reported to have filled with oil which drowned out the gas. Several other wells have encountered shows of free oil in the top of the Mississippian. It is not unusual to find the dolomite and limestone of the Spergen oil stained, particularly in structurally high areas, but no oil has been produced from this zone as yet.
Porous Dolomite Zone of the Burlington and Keokuk
Streaks of oil-stained limestone and dolomite occur in the upper 150 feet of the Mississippian in many wells in areas that are structurally high. The oil stains occur in minutely permeable beds of dolomite and limestone which do not seem to have any regularity of porosity or infiltration. About 150 feet below the top of the Mississippian and 121 to 135 feet below the top of the Warsaw limestone a coarsely crystalline bed of very cherty dolomite which is porous over a large part of northeastern Kansas is encountered. On the structurally high parts of the McLouth anticline this zone yields oil.
Plates 5 and 6 are photographs of a rotary core recovered from this zone in the Apperson No. 1 Bower well, in the SE NE sec. 5, T. 10 S., R. 20 E. The core consists of coarsely sucrose dolomite. The cavities are molds of crinoid stems and other broken fossils up to three-eighths of an inch in diameter. The fossil fragments were originally incorporated in the dolomite but because of their solubility they have been leached from the rock, leaving the dolomite pitted and cavernous. Inasmuch as the immediately overlying limestone has not been affected by solution, it is probable that the dolomite was subjected to surface weathering at the time when the calcareous elements were removed and before its burial by the overlying limestone. A disconformity, therefore, seems to be indicated at the surface of the porous zone, but there was so little erosion on its surface that topographic relief has not been recognized. The cavities in the dolomite of the cores are lined with fine bright crystals of dolomite. The darker areas in plate 6 represent cavities that originally contained oil but the intervening light-colored bands, although pitted with similar voids, were not penetrated by the oil.
A thickness of 10 feet of dolomite was cored in the Bower well, of which about 3 feet is unstained or slightly stained with oil and obviously unproductive. It is assumed that the more porous and spongy parts of the cores were broken up in coring and that about 7 feet of dolomite is productive in this well. The thickness of the productive zone in other wells is probably variable but seems to range from 5 to 10 feet.
The dolomite zone was first penetrated in the field in the McLaughlin No. 1 fee well, in the NE NW sec. 4, T. 10 S., R. 20 E., where it was heavily oil stained but probably carried water. The Young and Longwell No. 1 McLeod well, in the NW SW sec. 4, T. 10 S., R. 20 E., the second well in the field, was the first well in which oil was found in this zone. Black oil of 20.7° gravity Bé. filled the well to a height of 1,200 feet. The gravity of this oil was lower than that found in subsequent wells producing oil from the dolomite. This may be due to the fact that this well penetrated a fault through which the lighter constituents of the oil escaped. Its initial production probably was about 25 barrels per day, but the production declined rapidly. The second well in which oil was discovered in the dolomitic zone was the Young and Longwell No. 2 McLeod well, 660 feet to the north, and in which oil of slightly higher gravity was found in April, 1940. The production of oil from this well was irregular because of mechanical difficulties. In February, 1943, the well was acidized and is now reported to be pumping more than 100 barrels of oil per day. The third well, the Young and Longwell No. 3 McLeod well, NE SE sec. 5, T. 10 S., R. 20 E., found oil of 23.5° gravity that flowed by heads for several months. This well yielded approximately 100 barrels of oil per day, and is reported to have yielded over 40,000 barrels of oil in two years. It has not been acidized. In March, 1943, 70 barrels of oil per day were pumped, although 79 feet of cavings are reported in the well.
Other Potential Producing Zones
The Devonian rocks (fig. 3) were deformed and beveled by preMississippian peneplanation and they were covered by the Chattanooga shale in much the same way that the beveled Mississippian rocks later were covered by the Cherokee shale. This beveling left progressively younger Devonian rocks beneath the Chattanooga toward the southeast. In consequence the same rocks occur at the top of the Devonian only in the direction of the pre-Chattanooga strike of the Devonian beds; that is, toward the northeast. A well testing the top of the Devonian at one point will not encounter the same bed as that in another well drilled toward the northwest or southeast, and, except along the pre-Chattanooga strike of the Devonian, wells will penetrate different beds at the top of the Devonian on different anticlines.
During the long period of exposure that preceded Chattanooga deposition, weathering of the Devonian rocks caused solution and development of porosity in the surface beds similar to that at the top of the Mississippian limestones. The Devonian rocks consist of zones of dense and porous dolomite and semi granular fossiliferous limestone and lithographic limestone. Consequently, there is great difference in the character of weathering and the amount of disintegration of the rocks on the ancient surface, so that the permeability and porosity of the eroded surface rocks vary according to the nature of the beds exposed. The lithographic limestone that predominates in the lower part of the Devonian assemblage is similar to the St. Louis limestone and is much less susceptible to the development of porosity under weathering conditions than some of the semigranular limestones and dolomites in the upper part of the Devonian. The failure to encounter porous reservoir rocks in the upper part of the Devonian on one anticline, therefore, does not imply that similar unfavorable conditions occur on others.
The top of the Devonian rocks has been penetrated in only six wells in the McLouth field. The well that penetrated the oldest rocks at the surface of the Devonian is the McLaughlin and Sons No. 1 Thorpe well, in the NE NE sec. 27, T. 10 S., R. 20 E., which encountered dense lithographic limestone lacking in porosity and unstained by oil. Three wells which penetrated slightly younger Devonian rocks have been drilled in the McLouth field. The Apperson No. 1 Bower well, in the SE SE NE sec. 5, T. 10 S., R. 20 E., a rotary well, is structurally the highest in the field and the one most favorably situated to test the Devonian. Twenty feet of dolomite at the top of the Devonian was cored. The core consists of sucrose dolomite, in part heavily stained with oil. The porosity, however, was microscopic and the dolomite failed to yield oil. This zone, however, was not acidized. Gas was reported from Devonian rocks in the discovery well, the McLaughlin and Sons No. 1 fee well. The hole, which was drilled on the flank of the Mississippian dome, was full of water when drilled into the Devonian and some observers have expressed doubt as to the source of the gas. The cuttings consist of slightly porous dolomite like that in the Bower well but there were no indications of oil. The third well drilled to the Devonian in the McLouth pool, also below the crest of the dome, is the Young and Longwell No. 1 McLeod well, in the NW SW sec. 4, T. 10 S., R. 20 E. The Devonian rocks, in a zone 12 to 25 feet below the top, consist of microscopically pitted lithographic oil-stained limestone. The overlying Devonian beds are dense impervious unstained dolomite.
The Smythe et at No. 1 Miller well, in the NE SE sec. 22, T. 10 S., R. 20 E., penetrated unstained dense lithographic Devonian limestone. The Jackson No. 1 Shughart well, in the SW SW sec. 6, T. 9 S., R. 20 E., 6 miles north of the McLouth pool, penetrated coarsely crystalline porous dolomite stained with oil at at the top of the Devonian. The oil stains were lighter in color than those noted elsewhere in the McLouth field. This well was definitely not on anticlinal structure, but the dolomite of the cuttings seemed to be sufficiently porous to provide a reservoir under favorable structural conditions.
In addition to these wells, the following wells in northeastern Kansas are known to have found oil stains and shows of oil in the upper rocks of the Devonian: McCain No. 1 Doane, sec. 34, T.12 S., R. 22 K; Kerlyn No. 1 Wise, sec. 28, T. 12 S., R. 20 E.; Forrester No. 1 Altenbernd, sec. 35, T. 12 S., R. 20 E.; Schiltz No. 3 Davis, sec. 33, T. 18 S., R. 18 E.; and Roxane No. 1 Fisher, sec. 19, T. 11 S., R. 22 E. These occurrences are significant because they imply that oil once circulated in the weathered zone at the top of the Devonian. Structural or lithologic conditions favorable to the accumulation of oil evidently were absent at the places drilled. Other oil pools similar to those in the Falls City field of Nebraska probably will be found in the Devonian in northeastern Kansas on anticlines where the top of the Devonian is porous. Structural conditions were favorable in the Bower well but the dolomite lacked porosity. Porosity seemed adequate in the Shughart well but there was no anticlinal structure. In the other wells mentioned, porosity was inadequate to form a reservoir and so far as known anticlinal structure was also lacking.
The basal part of the Devonian in most areas adjoining the McLouth field consists of very sandy limestone. The basal beds consist of slightly dolomitic sandstone in the two wells which have been drilled through this zone in the McLouth field, the Apperson No. 1 Bower well and the McLaughlin No. 1 Thorpe well. In the Bower well, traces of tar were noted in the coarse sandstone cuttings. It is possible that somewhere this sandstone may be found sufficiently free from calcareous or dolomitic cement to provide a suitable reservoir.
The Kimmswick limestone (the Viola limestone of Oklahoma) is productive of oil in central Kansas and in the Dawson pool of the Falls City field on the northwest side of the Forest City basin. The Bower well penetrated coarsely crystalline dolomite with medium-sized voids at the top of the Kimmswick. The Thorpe well penetrated dense sucrose dolomite. Neither well showed oil traces.
The St. Peter sandstone, which is similar to the Wilcox sand of Oklahoma but probably of slightly different age, contained water in the Bower and Thorpe wells. Sand from the top of the St. Peter formation in the Thorpe well showed faint indications of oil when tested with chloroform, and a show of oil was reported by the operator. A trace of tar was observed in St. Peter cuttings and in cuttings of sandy dolomite 40 feet below the top of the Arbuckle limestone from the Apperson well. These shows of tar were so small, however, that they may be the result of contamination.
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