The New Albany shale (Upper Devonian) in the Illinois basin is the primary hydrocarbon source rock for the basin's nearly 4 billion bbl of oil production to date, and for an undetermined volume of gas, nearly all of which is produced from traditional carbonate and clastic reservoirs (Fig. 1).
Mean estimated total recoverable hydrocarbons1 are some 214 million bbl of oil. Resources from the New Albany are estimated at a mean 3.79 tcf of gas for undiscovered, technically recoverable gas.
In situ shale gas reservoirs in the New Albany are commercially established in just two areas in Illinois, at Russellville gas field in Lawrence County and in one or two wells along the Clay City anticline in Clay and Jasper counties (Fig. 2).
The gas play is well-established in Indiana and western Kentucky. One in situ oil producing well was reported in a multiply completed well in the New Albany at Johnsonville field in Wayne County, Ill., but this has not been confirmed. Two shut-in gas wells are located in Clark County, Ill. Shows of oil and gas in the New Albany have been widely observed in drilling reports over much of the basin in Illinois.
Microbial (biogenic) gas from very shallow depths has been produced for over 100 years in areas near the subcrop/erosional limit of the New Albany shale in Harrison County, Ind., and southwards across the Ohio River in Meade County, Ky.
In more recent years, the New Albany shale gas play in Indiana has developed in more deeply buried rocks, along a broad trend in western Indiana, ranging from Clay County in the north, southwards to Spencer County in the south. New Albany gas wells in Kentucky are scattered along the margins of the Rough Creek graben faults as well as within the Moorman syncline/Reelfoot rift and along the Pennyrile Fault System in the south.
The New Albany has widespread distribution throughout much of Illinois, Indiana, and western Kentucky, achieving its greatest thickness in southeastern Illinois and western Kentucky, where it is over 450 ft thick (Fig. 3). The New Albany is greater than 150 ft thick in most of Illinois and is organically rich over much of Illinois (commonly containing "excellent" total organic carbon in the range of 6-10% in its Grassy Creek member).
A vitrinite reflectance maturity map of the New Albany2 shows that a large portion of central and southern Illinois lies within the 0.6% reflectance contour, interpreted as the approximate onset of oil generation by thermogenic processes (Fig. 4). More intense generation occurs in extreme southeastern Illinois, in the area centered on Hardin County, Ill. Later work on maturity indicators from Rock-Eval pyrolysis analysis generally follows this original interpretation area, with modifications.3-5 The oil and gas wells producing from the New Albany in Illinois, Indiana, and Kentucky as of February 2010 are posted on this maturity base map.
Indiana gas wells are shown to lie outside the 0.6% vitrinite reflectance contour, and the gas from these wells is generally interpreted to be of microbial or mixed microbial and thermogenic origin.6
The Illinois gas and oil wells at Russellville, in Lawrence County, are closely associated with the 0.6% reflectance contour, which suggests a higher level of thermal maturity in this area. Two wells along the Clay City anticline, in Jasper and Clay counties, Ill., are closely associated with the higher vitrinite reflectance maturity contour of 0.7%.
The source rock has been well-studied in a traditional geological and geochemical sense. A short summary of some important work follows; this article merely summarizes highlights from the vast body of research that has been conducted on the New Albany. A reference list of publications will be provided upon request to the authors.
New Albany research
The thickness, organic-richness, geochemistry, and geomechanical properties were studied in detail in the late 1970s through US Department of Energy-funded work conducted in Illinois by Cluff, Barrows, Frost, Bauer, Reinbold, Lineback, and others in the Eastern Gas Shale Projects; similar work was done in Indiana and Kentucky.
In the 1990s, the Gas Research Institute funded the Illinois Basin Consortium, made up of the state surveys of Illinois, Indiana, and Kentucky, in its study of the New Albany shale as the unconventional, in situ shale hydrocarbon play was starting to develop. The principal investigators, Hasenmueller and Comer of the Indiana Geological Survey, were supported by coauthor geoscientists at the Illinois State Geological Survey (Frankie, Morse) and Kentucky Survey (Hamilton-Smith).
A follow-up effort by these researchers in 2000, funded by the organization now known as the Gas Technology Institute, updated the emerging gas play and presented the data from previous work in a Geographic Information Systems context, which included maps and assessments using ARC map to display the work.
Collaborative work by US Geological Survey geologists and state survey geologists examined produced oils and hydrocarbon extract geochemistry.7 Cluff and Byrnes8 modeled maturity, expulsion, and migration using Lopatin analysis method, and Bethke, Reed and Oltz9 evaluated migration routes, in chapters published in AAPG Memoir 51, Interior Cratonic Basins.10
A USGS Open File Report11 discussed and interpreted problems in using vitrinite reflectance for maturity indicators for the New Albany shale in the Illinois basin, where measured vitrinite reflectance (Ro) is suppressed and thus may be mistakenly interpreted if studied in the absence of Rock-Eval pyrolysis maturity evaluation and source rock quality indicators. That study reported that reflectance values, corrected to Rock-Eval measurements, reveal an in-place oil generative region in the Illinois basin that has a greater areal extent than previous studies had indicated.
Further work by USGS geoscientists explored the source rock, analyzing and modeling the New Albany's material balance character, maturity, expulsion, loss, migration to "catchement areas" in a Total Petroleum Systems approach assessing traditional oil reservoirs.4 5
In 2002, then-University of Michigan PhD candidate Jennifer McIntosh, with Lynn Walter and Anna Martini, published "Pleistocene recharge to Midcontinent basins: Effects of salinity structure and microbial gas generation" in Geochimica et Cosmochimica Acta.12 The work examined the regional extent of microbial and thermogenic gas plays in the eastern portion of the Illinois basin by coupling produced gas and water elemental and isotope geochemistry.
The same group investigated hydrogeochemical factors, such as sulfate and chloride concentrations, and meteoric recharge that may limit or enhance microbial methane generation. Sampling in the New Albany shale was limited to productive gas areas in Indiana and Kentucky, where the gas shale play had begun to emerge and develop.
Since at the time the gas shale play had no successful discovery in Illinois, and as a consequence, produced brines from the New Albany in Illinois were unavailable, the study focused on Indiana and Kentucky, where the play was active. Brine samples in some Devonian-Silurian productive areas in Illinois were used as proxy to estimate generalized brine concentrations in the New Albany.
In 2007, the USGS released its assessment of undiscovered, technically recoverable oil and gas resources of the Illinois basin.1 The report considered three "continuous" (source rock and reservoir combined) assessment units for in situ hydrocarbons. The Devonian-Mississippian New Albany Continuous Assessment Unit play had "the greatest potential for undiscovered gas, with an estimated mean resource of 3.79 tcf of undiscovered, technically recoverable gas."
More recent studies
Recent geochemical work on two samples of New Albany gas from producing fields in Indiana13 was published as an abstract and presented at a talk at the AAPG Eastern Section meeting in 2007.
The work describes New Albany shale gas composition and stable isotopes studies from a shallow (1,353 ft) and a deeper (2,722 ft) reservoir in Indiana. The shallow reservoir gas sample is interpreted to be a mixed thermogenic and microbial (biogenic) gas, while the chemical composition, and carbon and hydrogen isotopes of methane in the deeper sample indicated a thermogenic origin for that gas.
These chemical parameters have not been evaluated in a basin-wide approach in Illinois that may lead to further definition of play areas. In addition, no formation water chemistry data have been published for the recently emerging play in Illinois, which may serve to constrain the microbial aspects of the play. Gas analyses from recently drilled Illinois basin New Albany reservoirs are not publicly available at this time.
In March 2008, an AAPG Bulletin paper entitled "Identification of microbial and thermogenic gas components from Upper Devonian black shale cores, Illinois and Michigan Basins"14 evaluated produced gas and water and desorbed gases from crushed core samples from Indiana and Kentucky, key components for the modern assessment of the play and its economic development.
The study, however, did not analyze samples from Illinois, where the New Albany Shale Group is thicker, more widely distributed, and apparently encompasses the potential full range of the microbial and thermogenic play areas. In addition to sampling produced gases, and desorbed gases from crushed core samples, McIntosh and Martini have also recently had success with analyzing mud gases obtained during drilling of fractured shale wells in Indiana to evaluate the origin (thermogenic vs. microbial) of natural gas.15
Mud gases can be collected using an in-line sampling device (Isotubes) developed by ISOTECH Laboratories,15 and analyzed for gas composition and stable isotopes (∆13C of CH4, ∆D of CH4, and ∆13C of CO2).
Ongoing research under a Research Partnership to Secure Energy for America (RPSEA) grant through funding from the US DOE, conducted by a consortium including the GTI and a host of university and industry partners, has been working to address the gas play, natural fracture systematics, stimulation methods, production, and operations strategies in Indiana and western Kentucky.
Yet to date the basin in Illinois has been sparsely explored in this in situ unconventional play. The play, which began with gas exploration, has grown to include in situ oil exploration. However, in Illinois, where the source rock is thicker, organic-rich, more widely distributed, and is the site of the vast volume of Illinois basin oil and gas production, the play remains underexplored and wildcat in character.
Illinois drilling
Today, only one field, Russellville, in eastern Lawrence County, has established commercial production in the New Albany in Illinois (Fig. 5).
New Albany gas and oil production was first discovered there by Hux Oil in the late 1980s and confirmed by additional drilling, but the wells were shut in due to lack of gas collection infrastructure and ultimately plugged. Recent drilling, in both vertical and horizontal wells, has reestablished commercial production and expanded the gas field, located on the crest of an unnamed anticline of regional extent.
Gas in the New Albany at Russellville is closely associated with structural closure on the unnamed anticline that trends NW to SE and parallels the LaSalle anticlinorium, located about 8 miles west. The LaSalle anticlinorium structure is a major oil trap for Illinois basin oil and gas. Russellville oil and gas field also produces oil and gas from Mississippian and Pennsylvanian strata. Reports of initial production of New Albany gas at Russellville range from 38 Mcfd to 450 Mcfd.
One or two wells along the Clay City anticline reportedly produce gas commingled with oil from well-established Mississippian zones. Unverified reports indicate that approximately 20 Mcfd/well was or is commercially produced from the New Albany on the Clay City anticline.
Main Consolidated oil field (Fig. 2) in Crawford County, Ill., along the flanks of the LaSalle anticlinorium, has a recent test that is reportedly temporarily abandoned as a gas well after incomplete testing of 350 Mcfd. The well, originally drilled as a vertical well, was reworked and completed as a horizontal well, but ISGS records and communications with the original operator suggest that the well has not yet been completed or put on production.
Several other areas in Illinois have been tested; shows of gas and oil are established; some wells are shut in, temporarily abandoned, or plugged.
Two wildcat wells with gas shows were drilled in recent years in southern Saline County, where the New Albany is relatively deeply buried and close to faults associated with the Fluorspar District. They are located near the western flank of the Hicks Dome intrusion, a local magmatic heat source and the center of greatest thermal maturity in the New Albany in the Illinois basin. The Saline County wells currently have temporarily abandoned and observation status, and have undergone a change in operators.
Inhibiting factors
Factors that inhibit the in situ hydrocarbon play in Illinois may include:
• Access to pipeline infrastructure.
• Problems with nitrogen in some wells.
• Water encroachment from strata below and above.
• Water associated with faults.
• Lack of data and understanding of natural fracture systems.
• Uncertainties in best practices for stimulation and well treatment.
• Problems associated with obtaining mineral rights in heavily drilled areas.
• Economic factors related to the fluctuations in gas prices.
In addition, geological factors, primarily the lack of high levels of thermal maturity (and low reservoir pressures and unknowns about permeability), make the New Albany in Illinois perhaps less attractive as a thermogenic gas target than other shale gas plays in other, more thermally mature basins.
However, basin modeling work and Rock-Eval analysis suggest that the New Albany sources, expels, and presumably may reservoir oil and gas at all stages of its maturity history within the oil and gas window, and therefore, this extremely rich, oil prone source rock may remain a successful target for exploration and production.
Due to its lower level of maturity, and coupled with its kerogen type being more oil prone than gas prone, the thermogenic play may not be as prolific as other in situ gas plays, yet the New Albany in Illinois may be an in situ hydrocarbon play waiting to emerge.
Lack of data on the brine geochemistry of the New Albany in the western, southern, and central regions in Illinois where the shale is submature to early mature opens the possibility for a new microbial (biogenic) gas wildcat play comparable with the east side to the basin. This area is wide open, with relatively sparse acreage held by production.
In summary, many factors, from lack of data to market economics, make the New Albany unconventional, in situ source rock/reservoir play an enigma. Is the play emerging, or is the New Albany a world-class oil source for conventional reservoirs only? It remains to be seen.
Acknowledgments
The authors acknowledge the many colleagues and researchers that have contributed to the vast body of scientific work on the New Albany shale in the Illinois basin. This article appears courtesy of the Illinois State Geological Survey, Institute of Natural Resource Sustainability, University of Illinois at Urbana-Champaign. Publication authorized by the director, ISGS. Beverly Seyler and Zak Lasemi, ISGS, provided technical reviews.
The authors
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