Cypress Sandstone Research Articles

Origin, distribution, and CO2 EOR and CO2 storage resource assessment of selected residual oil zone fairways in the Illinois Basin

Residual Oil Zones (ROZs) are volumes of rock with low, largely immobile, oil saturations that provide opportunities for low carbon intensity oil production via carbon dioxide enhanced oil recovery (CO2-EOR) and associated CO2 storage. Oil shows of varying degree have been observed throughout the Illinois Basin (ILB). This work is the first to assess these shows as ROZs.In the ILB, the distribution of ROZ fairways and prospects is controlled by the geologic setting and oil migration history of the basin. ILB ROZ fairways that are stratigraphically proximal to the source rock are generally widespread whereas fairways developed in formations with a greater thickness of intervening strata are more discrete, an indication of influence from fault systems and fracturing associated with major structures. Within these fairways, 41 ROZ prospects were defined across three formations (Tar Springs Sandstone, Cypress Sandstone, Carper Sandstone) containing a best estimate (P50) of five billion barrels (bbls) of original oil in place (OOIP). For context, this volume is 35% of the estimated 14.1 billion bbls of OOIP in the conventional reservoirs in the ILB. In comparison to the Permian Basin, the ILB ROZ OOIP volume is 20% of the estimated 25 billion bbl of ROZ OOIP within a nine-county area of the San Andres Formation.The CO2-EOR resource of the ILB ROZ prospects exceeds 518 million bbls of oil using CO2 injection via pattern flooding. Associated CO2 storage is estimated to be 411 million tonnes of CO2. This study builds on past efforts to establish the CO2-EOR and associated CO2 storage resource potential of the ILB and presents a methodology that can be used to assess ROZ resources in other parts of the world.

Using clay microporosity to improve formation evaluation in potential residual oil zones: Cypress Sandstone, Illinois Basin

Clay microporosity in sandstones can cause erroneously high water saturation calculations if not properly accounted for and reduces effective pore space when evaluating a formation. We conducted a petrographic study to characterize and quantify the clay mineral microporosity of the fluvial facies of the Mississippian Cypress Sandstone in the Illinois Basin. This data helped achieve more accurate saturation calculations through core and well log analyses in potential Cypress residual oil zones. Petrographic thin sections were analyzed by scanning electron microscopy with backscatter imaging and energy dispersive X-ray spectroscopy. Clay mineral species identified included pore-filling kaolinite books, blocks, and vermicules; chlorite clusters; illite mats; illite-smectite webs; grain-coating inherited chlorite rims; and pore-bridging illite hairs. Volume percentages of microporosity particular to clay mineral species were determined by image analysis. Average microporosity values in kaolinite, chlorite, illite, and illite-smectite were 41%, 57%, 67%, and 65%, respectively. Effective clay mineral volumes, including microporosity, showed a >2-fold increase over estimates determined by X-ray diffraction, constituting an average volume of 4%. Comparing these volumes with gamma-ray log estimates proved Stieber’s work to predict clay volume most accurately. Clay volumes were used as input parameters in the dual-water method for determining water saturation, resulting in greater residual oil saturations than those predicted from Archie’s equation. Accounting for clay microporosity in helium porosimetry measurements of total porosity resulted in an ~11% decrease to effective porosity. Results from this research improve estimates of water saturation and porosity and highlight the importance of studying microscale mineralogical properties during reservoir characterization.

ABSTRACT: Reservoir Characterization for an Alkaline-Surfactant-Polymer Flood of Pennsylvanian and Cypress Sandstone Reservoirs in Lawrence Field Illinois

ABSTRACT: Reservoir Characterization for an Alkaline-Surfactant-Polymer Flood of Pennsylvanian and Cypress Sandstone Reservoirs in Lawrence Field Illinois

Chemical composition and geologic history of saline waters in Aux Vases and Cypress Formations, Illinois Basin

Seventy-six samples of formation waters were collected from oil wells producing from the Aux Vases or Cypress Formations in the Illinois Basin. Forty core samples of the reservoir rocks were also collected from the two formations. Analyses of the samples indicated that the total dissolved solids content (TDS) of the waters ranged from 43,300 to 151,400 mg/L, far exceeding the 35,400 mg/L of TDS found in typical seawater. Cl-Br relations suggested that high salinities in the Aux Vases and Cypress formation waters resulted from the evaporation of original seawater and subsequent mixing of the evaporated seawater with concentrated halite solutions. Mixing with the halite solutions increased Na and Cl concentrations and diluted the concentration of other ions in the formation waters. The elemental concentrations were influenced further by diagenetic reactions with silicate and carbonate minerals. Diagenetic signatures revealed by fluid chemistry and rock mineralogy delineated the water-rock interactions that took place in the Aux Vases and Cypress sandstones. Dissolution of K-feldspar released K into the solution, leading to the formation of authigenic illite and mixed-layered illite/smectite. Some Mg was removed from the solution by the formation of authigenic chlorite and dolomite. Dolomitization, calcite recrystallization, and contribution from clay minerals raised Sr levels significantly in the formation waters. The trend of increasing TDS of the saline formation waters with depth can be explained with density stratification. But, it is difficult to explain the combination of the increasing TDS and increasing Ca/Na ratio with depth without invoking the controversial ''ion filtration'' mechanism.

Laboratory Experiments and Reservoir Simulation Studies in Support of CO2 Injection Project in Mattoon Field, Illinois, USA

Abstract This paper describes the results of rock and fluid property measurements and of the reservoir simulations associated with the demonstration of CO2-assisted oil recovery in the Cypress Sandstone reservoirs at Mattoon Field, Illinois. This work provided technical support for the field project. Results from core flood tests indicate that oil recovery from immiscible displacement of reservoir crude oil with carbon dioxide will increase with displacement pressure. Miscible displacement of oil with CO2 from the Cypress Sandstone reservoirs at Mattoon field is not possible. As shown by the slim-tube experiments, the minimum miscibility pressure (MMP) of Mattoon oil is close to the formation parting pressure of the Cypress Sandstone at Mattoon field. Nevertheless, phase behaviour experiments show that dissolved CO2 significantly enhanced oil recovery through oil swelling and viscosity reduction at pressures below miscibility conditions. Numerical simulations of CO2 injection into various reservoirs within the Sandstone were performed. A straight CO2injection program and a water alternating gas (WAG) injection program were simulated and compared in both the A-sandstone of the Pinnell Unit and E-sandstone interval of the Sawyer Unit. In the Pinnell Unit, the simulated results show an inefficient displacement of reservoir oil by CO2 and that neither of the two methods will be economically feasible because of the poor interwell communication and limited areal extent of the producing interval. This result is supported by the low oil recovery from the field CO2 injectivity tests in the Pinnell Unit. On the contrary, simulated results show that a significant amount of additional oil can be produced from the Sawyer Unit. The wateralternating- gas (WAG) injection program yielded more oil than water injection alone. The simulated results also indicate strategically- placed new wells will enhance the recovery of additional oil. Introduction This work provided technical support for a CO2-assisted oil recovery demonstration project funded by a cost-shared agreement (Cooperative Agreement number DE-FC22-93BCI4955) between the United States Department of Energy and American Oil Recovery, Inc. (AOR). The Mattoon Field, which is the site of the project (Figure 1), was discovered in June 1940. Development included approximately 420 producers and 90 dry holes drilled on a 4.05 ha (10 acre) well spacing. The principal reservoirs are found in the Cypress, Rosiclare and Aux Vases Sandstones of the Mississippian System (Figure 2). Secondary recovery was initiated in 1952 utilizing Pennsylvanian brine as well as treated municipal sewage water(1). The target intervals for additional oil recovery with CO2 are the Chesterian Cypress Sandstone reservoirs in the Mattoon field. In general, Cypress Sandstone reservoirs are the most prolific in Illinois(2). Recent studies(3,4,5) show that Cypress reservoir sandstones consist of four to five stacked layers having varying reservoir quality and often separated by thin shaly sandstone or calcareous beds. Because of the variations in reservoir quality, some layers are not as efficiently swept as others during water flooding. Such layers will contain more bypassed mobile oil than others. Furthermore, Cypress Sandstone reservoirs typically have high immobile oil saturation.

Tidal Flats and Tempestites: An Integrated Approach to an Atypical Facies of the Cypress Sandstone: ABSTRACT

The Cypress Sandstone (Mississippian Chesterian series) is a major hydrocarbon-producing formation in the Illinois basin. Depositional settings consisting of fluvial and deltaic environments are recognized throughout the basin. Upon the southern flank of the Moorman syncline in the Stringtown field, a distal facies of the Cypress depositional system is recognized as a stormswept tidal flat. Developed above marine shales, a lower shoreface/platform facies is interbedded with carbonate-rich tempesite storm deposits. High clay concentrations within the sands create non-reservoir conditions, characterized by low permeabilities and high irreducible water content. As proximal tidal environments build seaward, a scour channel downcut into the lower shoreface/platform facies. Continuing tidal flat progradation deposited lower and middle tidal-flat pay sands on the scour surface. Overlying upper tidal-flat strata provide the seal for this reservoir. Regional transgression destroyed the balance of the prograded tidal flat, preserving the sequence only within the deep scour features. Lithologically, the pay sands are classified as quartzarenites and sublitharenites, the latter containing appreciable concentrations of shale rock fragments and feldspars. The development of secondary moldic porosity is the primary determinant of reservoir quality, derived from the dissolution of rock fragment fabrics. Geophysical well logs and Formation MicroScanner data analysis were correlated tomore » core lithogies, and were successfully used to identify various facies within the Cypress Sandstone section. Early development wells flowed oil, due to overpressured reservoir conditions.« less

Varieties of Chlorites and Illites and Porosity in Mississippian Sandstone Reservoirs in the Illinois Basin

Shallow marine, Mississippian, siliclastics in the Illinois basin, although predominantly quartz, contain other minerals that directly influence the porosity and permeability of these reservoir rocks. These sandstones contain more chlorite and kaolinite, relative to illite, than the authors have observed for shales from other Chesterian and Valmeyeran strata. Clay mineral suites in reservoirs appear to be diagenetic. The Aux Vases Sandstone contains illite, illite/smectite, and chlorite; kaolinite is absent. The Cypress Sandstone contains illite, illite/smectite, chlorite, and kaolinite. Chlorite in the Aux Vases Sandstone varies from moderately Fe-rich to Mg-rich, whereas the chlorite in the Cypress Sandstone is uniformly Fe-rich. As the percentage of clay minerals in these rocks decreases, the proportion of chlorite to other clay minerals increases. In some chlorites, the width of the 003 and 005 peaks at half-height is greater than that of the 002 and 004 peaks. This suggests an interlayering of a 7{angstrom} mineral, probably berthierine- or serpentine-like. SEM photos show chlorite coating quartz grains. In some samples there are quartz overgrowths in spite of the presence of a coating of chlorite; in others, chlorite interlayered with the 7{angstrom} phase seems to have interfered with or suppressed overgrowths. Correspondingly, there is a correlation betweenmore » the 7{angstrom} phase/chlorite and porosity. Therefore, identification of the type of chlorite in a potential reservoir may be an indicator of porosity, as well as a guide for selecting completion and stimulation treatments.« less

Effects of Diagenesis on Reservoir Quality Within Two Cypress Reservoirs in the Illinois Basin

One billion bbl of oil have been produced from the Chesterian Cypress Formation in the Illinois basin. These heterogeneous reservoirs may consist of deltaic, marine-reworked deltaic, and/or reworked marine sandstone within mixed siliciclastic-carbonate environments. Thin section, x-ray diffraction, and scanning electron microscopy coupled with energy dispersive x-ray analysis indicate that the effects of diagenesis play a significant role in reservoir quality of Mattoon and Parkersburg fields in Illinois. Five separate Cypress sandstones may be present at Mattoon field (Coles County), a predominantly stratigraphic trap, produces from three distinct Cypress strata. In these fields, reservoir quality is reduced when quartz overgrowths and later stage, blocky mosaic ferroan-calcite cement occlude pore throats. Authigenic clay minerals occur as pore-lining particles that inhibit fluid-flow. Clay minerals preset are illite, mixed-layered illite/smectite, chlorite, and kaolinite. Reservoir quality is enhanced through dissolution of early ferroan-calcite cement, dissolution of detrital feldspar, and microfracturing. Completion, stimulation, and production programs within the heterogeneous Cypress sandstone reservoirs would be improved by recognition of mineral relationships and diagenetic overprints. Developments programs may need to include the use of clay stabilizers in mud clean-out acid treatments.

Deposition Analysis Based on Electric-Log Character of Cypress Sandstone (Chesterian) in Illinois: ABSTRACT

Four major deposystems were mapped in the Cypress Sandstone using SP (spontaneous potential) and resistivity log character in a statewide cross-section grid. Illinois was a shallow, gently sloping embayment subject to periodic influx of sediment and changes in sea level during Late Mississippian (Chesterian) time. Cypress log character varies predictably from the eastern margin of Illinois to the western erosional limit. Deposystem interpretations based on log character have identified (1) a deltaic zone characterized by thin sandstones interbedded with shale and siltstone in easternmost central Illinois, (2) an offshore marine zone characterized by sand bodies 50-150 ft thick, displaying blocky SP in a 20-mi wide band in east-central Illinois, (3) an offshore marine zone characterized by sandstone bodies 15-40 ft thick in central Illinois, and (4) an offshore marine zone characterized by predominantly shale log character in west-central Illinois. Presence of the shale coincident with the DuQuoin monocline suggests that Cypress deposition was influenced by structural expression of the monocline.

Petrology and Depositional Environments of Sample Member (Mississippian): Redevelopment Target in Lawrence Field, Illinois: ABSTRACT

Although the giant Lawrence field (400 million bbl oil recovered since the early 1900s) has been extensively waterflooded since the 1950s, opportunities for continued development are still being found. One ongoing redevelopment is in the Sample member of the Mississippian Ridenhower Formation in Sec. 17-20, T4N, R12W. During the 1950s waterflooding was initiated in the area with wells dually completed in the Sample and overlying Cypress Sandstone. Cypress average permeability is 10 times greater than the Sample's, so most of the injection went into the Cypress. Many wells were eventually plugged back to that zone. A well was recompleted in the Sample in 1987 with an initial production of 56 BOPD. Since then, 18 additional producers have been drilled. Two cores and 40 modern well logs were used to develop a facies model of the Sample member. Cored lithologies include very fine-grained flaser-bedded shaly sandstone, fine-grained ripple-bedded sandstone, and fine to medium-grained cross-bedded sandstone. Small slump features and shale rip-up clasts occur at the base of the sandstone. Small slump features and shale rip-up clasts occur at the base of the sandstone. Minor occurrences of bidirectional cross-bedding and reactivation surfaces were observed. No burrows were identified. The Sample Member ismore » interpreted as a tidal-flat shoreline environment, with tidal channel, ebb tidal delta, and muddy tidal-flat facies present in core or inferred from well-log response. Correlation of SP logs with facies type permitted extrapolation of facies throughout the redevelopment area. A series of time-sequence facies distribution maps identifies a tidal-flat shoreline environment prograding across a shallow carbonate shelf.« less

Preliminary Reservoir Characterization of a Chesterian Cypress Sandstone in Illinois Basin: ABSTRACT

Reservoir characterization was undertaken, based on detailed analyses of a core in the middle Mississippian (Chesterian) Cypress Sandstone from an overlooked pay zone in the Parkersburg field, Edwards County, Illinois. The purpose of the study was to evaluate the producing interval in order to prescribe specific completion and recovery techniques for optimization of oil production. The Cypress pay at Parkersburg is variable, with both economic and marginal wells. Evaluation techniques included log analyses, thin-section petrography, porosity and permeability analysis, x-ray diffraction, and Scanning Electron Microscopy (SEM) with Energy Dispersive System (EDS) analyses.

Tidal Deposition of Cypress, Ridenhower, and Bethel Sandstones (Chesterian, Late Mississippian), La Salle Anticlinal Belt, Lawrence and Crawford Counties, Illinois: ABSTRACT

Sandstones in the Chesterian (Late Mississippian), including those in the Cypress, Ridenhower, and Bethel, are major oil producers in the Illinois basin. Significant oil reservoirs occur as structurally influenced stratigraphic traps along the northwest-trending La Salle anticlinal belt of Lawrence and Crawford Counties, Illinois. Analyses of electric logs, sand thickness maps, and sedimentary structures show that these sandstones were deposited in tide-dominated deltaic, tidal-flat, and subtidal environments. Coarsening upward, tide-dominated deltaic sequences inferred from spontaneous potential (SP) log signatures are composed of prodelta shales, delta-front shales and silts, and distributary-mouth bar sands. Tidal-flat sand bodies are indicated by SP log signatures with blunt bases and tops. Cores from these 20 to 70-ft (6 to 21 m) thick, laterally discontinuous units contain: (1) fine to medium-grained, rippled sandstone with infrequent rippled shale laminations, (2) lenticular bedding with little bioturbation, (3) flaser bedding, (4) bioturbated sandstone and shale that were apparently horizontally bedded, (5) plant fragments in shale, and (6) channel lag consisting of deformed shale clasts and rounded carbonate mud pebbles. Off the flanks of the anticlinal belt, the Cypress, Ridenhower, and Bethel coalesce into single massive sand units up to 200 ft (61 m) thick, distinguished by blocky SP log signatures with abrupt bases and tops. Sand thickness maps showing these units as long linear bodies aligned parallel with major anticlinal axes suggest that they are subtidal sand ridges. End_of_Article - Last_Page 628------------

Paleochannel Across Louden Anticline, Fayette County, Illinois: Its Relation to Cypress (Chesterian) Stratigraphic Entrapment of Petroleum: ABSTRACT

Structural mapping of the base of the Beech Creek (Barlow) Limestone across Louden oil field, Fayette County, Illinois, reveals a northwest-southeast trending saddle that is more than 1.5 km wide and 6 km long, and is perpendicular to the major axis of the Louden anticline. This depression coincides with the abrupt appearance of a thick, fine-grained, argillaceous limestone (so-called Barlow) subjacent to a regionally normal thickness of coarse-grained, bioclastic Beech Creek Limestone. Sandstone beds in the Cypress Sandstone, which generally underlie the Beech Creek, are thin or absent beneath this area of false Barlow. This feature is believed to be a major tidal channel that breached deposits of shallow marine or eolian sands that had accumulated along the crest of the anticline. The trend of the channel, perpendicular to the anticlinal axis, and the restriction of the channel to the crestal area only, with no apparent extension off-structure, strongly suggest that the Louden anticline was topographically high during Cypress deposition. The channel was filled during latest Cypress deposition by marine shales and fine-grained limestone (false Barlow). During the main phase of sand deposition, the channel profoundly influenced local sandstone depositional patterns; two thick, offshore sand bars or barrier islands accumulated near its southeastern terminus along the flank of the anticline. These flank ng sand bodies pinch out updip against lagoonal shales and are true stratigraphic traps that have since produced several million barrels of petroleum. The recognition of large marine bar sand bodies in the Cypress Sandstone opens new prospects for oil exploration in the Illinois basin. Henceforth, Cypress sandstones should not be viewed as massive blanket sands or overlapping fluvial channel sands, but rather as complex sequences of shallow marine sandstone. Favorable areas to explore for stratigraphic traps in the Cypress include the flanks of major anticlines, areas of thick false Barlow, and near linear gaps in the areal distribution of Cypress production. End_of_Article - Last_Page 1282------------

Lithologic Character of Chester Rocks in Illinois-Kentucky Fluorspar District

This paper describes the lithologic character of the formations of the Chester series in the Illinois-Kentucky Fluorspar district from a study of cores obtained by diamond drilling. This study has extended over a period of more than 9 years and during the course of the work nearly 350,000 feet of core have been examined from an area about 20 by 30 miles in extent. Lithologic details not discernible in ordinary exposures are detectable in the cores. The Chester rocks vary notably in lithologic character and thickness. In parts of the district the lithologic variations are nearly uniform in a given direction but in general there is no apparent uniformity of change for any appreciable distance. The variations in thickness are not uniform either parallel with, or at right angles to, the strike and are the result of non-uniform deposition and differential erosion during the Chester epoch. The Renault formation consists of four well defined and persistent zones, a basal limestone and overlying shale, the Shetlerville member, and an upper limestone and overlying shale, the Downeys Bluff member. The Renault ranges from about 40 to 137 feet thick, the thickest sections occupying a triangular area with its apices at the Beard, Skelton, and Royal properties (Fig. 1). The thicker Renault sections are generally characterized by a prominent upper shale. The Shetlerville member in the western part of the Fluorspar district exhibits a rather uniform increase in limestone and a decrease in shale toward the south. Elsewhere there is no uniform directional variation. The Bethel sandstone contains less shale than other Chester sandstones. Its thickness is between 55 and 105 feet, the thickest sections occupying a belt from northwest to southeast across the center of the district. The Paint Creek is one of the most variable Chester formations both in lithologic character and thickness. The thickness ranges from 0 to 63 feet; the thickest sections are in the northwest and southeast parts of the district. It is almost entirely interbedded thin shale and sandstone layers in the northern and western areas. The most conspicuous lithologic change is the increase in calcareous sediments, especially limestone, toward the southeast. The Cypress sandstone, 70-125 feet thick, is similar to the Bethel except for a greater amount of shale especially in the southern and southeastern parts of the district. The shale beds do not occupy a consistent position in the section. The Cypress-Golconda contact is transitional, with a shale zone between the top sandstone of the Cypress and the lowest limestone of the Golconda in many localities. This zone is in most places non-calcareous and even sandy and might well be called Cypress rather than Golconda as has been done in this paper. The Golconda, 100-200 feet thick, consists of interbedded limestones and shales without lithologic zones which are persistent throughout the district. The Barlow sand which occurs in places in the northern and eastern parts of the district is cons stently near the middle of the formation. The Hardinsburg is a quartz sandstone with variable amounts of shale and ranges in thickness from 68 to about 140 feet. The shales occur in different parts of the sections in different localities but in general are in the middle and upper parts. It is thickest in the southeastern part of the district. The Glen Dean consists of interbedded shales and limestones much like the Golconda but generally with purer limestones than other Chester formations. It is 45-75 feet thick; the greatest thickness is in the south-central part of the district. Considerably less information about the upper Chester has been obtained by drilling. The Tar Springs consists of interbedded sandstone and shale 65-145 feet thick. The Vienna limestone and shale vary from 30 to 106 feet in thickness. The Waltersburg, 40-87 feet, consists of sandstone and shale; the shale is most conspicuous in the middle part of the formation. The Menard, 75-120 feet thick where drilled, consists of interbedded limestones and shales, which do not occur as persistent zones. Complete sections of the higher Chester formations have not been drilled. It is concluded that many of the clastic Chester sediments are of continental origin and that the marine parts of the section were deposited in relatively shallow water. End_Page 1777------------------------------

Geology of Mattoon Field, Illinois: ABSTRACT

The interesting features of the Mattoon field are: (1) the history of its discovery; (2) the dual-completion methods used; and (3) the very lenticular condition of its sands. 1. The Mattoon anticline in Coles County--180 miles south of Chicago--was generally known in 1937. The first well, drilled in 1939, made a total of 132 barrels. In 1940, four more wells, with only one producer (the discovery well), had practically condemned exploitation in spite of the verification of the structure. Three years later a small well extended the potential field and was followed by a series of mediocre wells. In 1945, or five years after the discovery well was completed, an independent operator completed a 100-barrel well, 3/4 mile from the discovery, renewing the general interest. A boom soon developed when a well was completed, producing 1,200 barrels. Rapid extensions defined a potential area of 7,000 acres, a major field. 2. Wells in the two main shallow producing sands, less than 2,000 feet deep, soon were dually completed with successful results. The Cypress sandstone, with as much as 40 feet of saturation, produced with the more commonly developed Rosiclare sand and sandy limestone. A 7-inch oil string was set on the top of the lower sand with aluminum pipe opposite the Cypress sand. Both sands were shot with nitroglycerine, tested individually by setting a temporary, drillable plug, and produced together. Wells are drilled to 2,000 feet in 7 days, with two rock bits and four retips. However, the dual completion takes 20 days of spudder time. Average total cost of single completion is $15,000. The dual method increases the cost to $18,000. Electric logs were made on all wells and gave good quantitative results. One problem could not be solved by electric logs: differentiation between gas and oil in the Cypress. However, a gas-oil level was determined by drill-stem tests on the crest of the structure. Within 14 months 114 wells had been drilled, of which 22 were dry holes and 92 were producers, with an average initial production of 148 barrels. Peak production was reached in June, 1946, with 15,500 barrels daily. Steady decline was experienced during the next 12 months, and in June, 1947, the daily production was down to 5,500 barrels daily. Total recovery from 5,500 producing acres is estimated at 17 million barrels. 3. Detailed electrical-log cross sections are presented to show the extremely lenticular condition of the sands. A considerable area on the top of the structure remains undrilled. A gas cap in the upper Cypress sand has not been exploited. The west part of the City of Mattoon also remains undrilled due to communitization problems, in spite of its potential productivity. The Aux Vases sand was found extremely shaly, excepting the southwest part of the field. Its development, estimated at only 50 acres, will produce approximately 6,000 barrels. Six Devonian wells on the structure have produced only 1,100 barrels of oil. However, potential production from the Devonian can not be ignored at this time. The total accumulated production of the Mattoon field on September 1, 1947, is 6,280,000 barrels. End_of_Article - Last_Page 302------------

Geology of Uniontown Pool, Union County, Kentucky: ABSTRACT

The Uniontown pool in northern Union County, Kentucky, discovered in September, 1942, produces mainly from the Waltersburg, Tar Springs, and Cypress sandstones of the Chester series, Upper Mississippian system. It produces in a minor way from a sandstone of Pennsylvanian age and from the Palestine and Hardinsburg sandstones and the Menard limestone of the Chester series. The structure consists of an elongate dome, the western side of which is closed against the upthrown side of a normal fault. There are 229 producing wells in the field, which had produced 8,600,000 barrels of oil to October 1, 1947. The producing area covers approximately 2,000 acres. End_of_Article - Last_Page 304------------

Subsurface Geology of Chester Series in Illinois

The Chester series underlies most of the southern half of Illinois east of East St. Louis. Except where they have been removed by post-Chester erosion, all of the formations in the standard Chester section can be identified in the area. Producing formations are the Cypress and Bethel sandstones, both of which are in the lower part of the Chester series. The maximum known thickness is 1,450 feet at a point in the most southerly part of the area. Because of northward thinning of individual formations, the original thickness of the entire section in the northern part of the area was probably half of this. Uplift, warping, and peneplanation previous to the deposition of Pennsylvanian sediments caused truncation of the series throughout the basin and scalping of local structur s. The isopach map indicates two major pre-Pennsylvanian anticlinal areas in which are located a large proportion of the Illinois oil fields, one the LaSalle anticline, and the other an uplift extending southeast from the region of Sorento.

Geology of Basin Fields in Southeastern Illinois

The Basin fields of southeastern Illinois are so named because of being located near the center of the Illinois basin. Production has so far been obtained in Wayne, Clay, and Richland counties in a series of fields extending 45 miles in a general north-south direction. It is highly improbable that the producing areas will be found to connect. Production was discovered in March, and active development was started in May, 1937. The production from the area to July 1, 1939, was 18,159,275 barrels from 692 wells. Daily average production at that time was 57 barrels per well. Large initial productions are common, and decline is rapid for the first few months. Twenty-acre spacing is prevalent. Production is from oolitic limestone of the Ste. Genevieve formation (McClosky) except in the North Noble field, where it is from the Cypress (Weiler) sandstone, the former being in the upper part of the Lower Mississippian and the latter in the lower part of the Chester series. The Cypress is a widespread sandstone but locally subject to lensing into beds of sands and shales. It is believed that Chester sandstone production will become more important as development extends northward. The oolitic character of the Ste. Genevieve is persistent in the area; however, porosity occurs in lenses of variable proportions laterally and vertically. Approximately 10 per cent of the holes drilled within the limits of production are dry because of lack of porosity in the limestone. Porosity is more persistent on the structures than in the synclines. Most of the McClosky porosity is believed to be primary in origin. All except the Flora field are associated with a general north-south anticline, which has a slight southward plunge into the deeper part of the basin. Accumulation has for the most part been on local closures along the axis, but some production has been obtained from noses and terraces on the flanks on the main feature. Little is known of the pre-Mississippian structural history. The known period of major deformation was post-Mississippian-pre-Pennsylvanian, but subsequent to this there was recurrent folding. The relation of the contact of the Ste. Genevieve to the overlying Chester is controversial. However, the data do not indicate an angular unconformity at this contact in the deeper part of the basin. Small production has been obtained from pre-Mississippian beds on the east and west flanks of the basin; however, since no test below the Mississippian has so far been drilled on structure in the area under consideration, the possibilities for deeper production are highly speculative.

Some Issues in Chester Stratigraphy in Kentucky and Illinois

This paper is a contribution toward the settlement of a long-standing controversy concerning certain points in Chester stratigraphy in Kentucky and Illinois. The late Professor Weller correlated the Renault formation of Randolph County, Illinois, with both the upper part of the Ohara limestone and the lower part of the Gasper limestone, and also correlated the Bethel sandstone of western Kentucky with the Sample sandstone of Breckinridge County, Kentucky. He and his son, Dr. Marvin Weller, denied the validity of the name Gasper and used, instead, the hyphenated designation Renault-Paint-Creek. Professor Weller also questioned the suitability of the name Bethel for the sandstone unit so named. The present paper presents concrete evidence tending to disprove the views of the Wellers on the points mentioned. Certain characteristic species of fossils mark the lower part of the Gasper beneath the Sample sandstone and the same assemblage occurs in Christian and Caldwell counties, Kentucky, in the lower part of the typical "Tribune" limestone of Ulrich (for which the name Gasper was substituted), and above the Bethel sandstone and hence above the Ohara limestone which immediately underlies the Bethel sandstone in western Kentucky. Not one of the characteristic members of this fauna has ever been found in the Ohara limestone or below the horizon of the Bethel sandstone. From this it follows that the Bethel and Sample sandstones are not the same. Therefore the Renault formation cannot be the equivalent of both the Ohara, which is below the Bethel, and the "lower Gasper," which is above the Bethel. As it is admitted by the Wellers that the Gasper is an indivisible unit equivalent to the Renault and Paint Creek, and as the name is applied in accordance with the customary modern practice of giving a new name to two or more combined units, its validity cannot be fairly questioned. In regard to the name Bethel, it is shown that the sandstone near Bethel school, now Crittenden Springs school, which Weller thought to be the lower part of the Cypress sandstone, is directly underlain by the Ohara limestone and therefore clearly Bethel, so that the name is entirely appropriate.