Forest City Basin

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Introduction

The Forest City Basin is a primarily sedimentary basin located in eastern Kansas, northwestern Missouri, and parts of northern Oklahoma.[1] The basin covers a large amount of ground spanning two hundred and forty miles long and one hundred and ninety five miles wide. Hydrocarbons were first discovered in 1860, however when drilling began in the Forest City Basin, results were not immediately seen. It was not until twelve years of petroleum exploration were accomplished that a substantial hydrocarbon discovery was made in Miami County, Kansas in 1882. From there, drilling continued and expanded to over ten thousand wells drilled and twenty one oil fields discovered, each netting over one million barrels of oil equivalent. The Forest City Basin basin has had a fairly productive history that has gradually decreased over time.[2]

[3]Outline of the Forest City Basin
Better view of the stratigraphy of the Forest City Basin[4]

Geologic History

The Forest City Basin is a relatively shallow basin consisting of a large make up of Pre Cambrian granite, gneiss, and schist that in most areas was exposed at one point. Many of these areas have now been covered by several layers of sedimentary depositions of limestone, sandstone, and then later shale. It is believed that the basin was formed during the Middle Ordovician period where the Earth saw an increase in sea floor spreading and ocean current changes. (Lee, 3)[2] The deepest point of the basin is formed by faults exhibiting a fairly strong downward displacement along the Nemaha Anticline which is one of the more famous geologic structures found in Kansas.[2]

Source Rock

TOC and HI Index Table From the Kansas Geological Survey.[5]

The United States Geological Survey and the Kansas Geological Survey have worked together to take samples and analyze source rock samples from throughout the Forest City Basin. During their study the groups were able to pull 123 samples of potential hydrocarbon source rock.[6] Sidewall cores, strip mines, and well cuttings were among the methods used to obtain these samples. Many of the samples gathered consisted primarily of marine black shales that were dispersed evenly across the area searched. Out of the samples taken and analyzed, most were found with a median hydrogen index of around 250-300 mg/g with some samples being as low as 13mg/g and some as high as 1,160mg/g. (Hatch, Newell, 1)[6] In total 18 samples out of 103 taken throughout the Forest City Basin were found to have a total organic carbon percentage greater than one percent. Total organic carbon or TOC is the carbon content in a specific source rock that is expressed in a weight percentage.

Porosity and Permeability

Porosity and permeability are important when looking at the characteristics of a basin and its source rock. Porosity is the amount of free space between rock particles that can hold a liquid. Permeability is the rate at which liquid can flow through rock particles. During a porosity study done by the Kansas geological survey, core samples taken were found to contain sandstone from the St. Peter Sandstone. The St. Peter Sandstone is an Ordovician age structure that extends through most of the central United States, and is made of finely sorted sand and quartz.[7] Porosity values were taken from the St Peter Sandstone cores at 15% for a shallow sample and 9% for the deeper sample indicating a high porosity at depth for a large part of the Forest City Basin that contains this type of sandstone. Because of the well rounded nature of the St Peter Sandstone, a higher permeability can be observed. A permeability study done by the United States Geological Survey showed that the basin had a horizontal flow due to contrast with the overlying shales. (Burrows, 18)[8]

Traps

Because the Forest City Basin covers a lot of ground there is space for multiple traps. Most of the traps identified however are stratigraphic.[2] Stratigraphic traps are hydrocarbon rich source rocks that are sealed by changes in porosity of the rock that surrounds them. In the case of the Forest City Basin, much of the source rock consists of pre-Pennsylvanian limestones that were weathered to be more porous and eventually covered with less porous shale and sand formations. Even with the observable stratigraphic traps in the basin, structural traps such as conventional anticline reservoirs have been the main hydrocarbon producer. [9]Source rock from the Mississippian age was deposited on a northwestward slope and eventually covered by less porous Pennsylvanian age rock which caused further folding contributing to the formation of the Nemaha Anticline. The Nemaha Anticline is where the majority of hydrocarbon production has occurred in the basin.[2]

Closer look at the layering of the Nemaha Anticline. [10]

Production

Production in the Forest City Basin began when hydrocarbons were discovered in the Paola field over one hundred and fifty years ago in 1860. Additional oil discoveries were made in the Nemaha anticline. The Nemaha anticline would be the spot where around 97% of the basin's hydrocarbon production would occur. Ordovician sandstones, Viola Limestone, and Silurian-Devonian dolomites would serve as the primary source rock for this area. (Burrows, 5)[8] Production continued all the way into the late 1980's when most of the conventional oil and gas reserves were found to be depleted. In 1989 when almost all operations had halted, cumulative oil production had reached 2.9 billion barrels with remaining recoverable oil and gas content estimated to be around 140 million barrels. (Burrows, 6)[8] There are numerous coal deposits throughout the basin as seen in the stratigraphic column shown.[11] The coal deposits are mostly located in areas too thin and too deep to be mined through conventional methods. (Bostic, 1)[12]

Future Production

Stratigraphic Map of the Forest City Basin From the Kansas Geological Survey.[13]

Given the low remaining reserves and high cost of recovery and discovery future production in the Forest City Basin is going to continue becoming more limited than it already is. Most companies when evaluating a basin for drilling potential are going to look at many of the risks and uncertainties that come with this basin as not worth the time and effort. The coal deposits found within the basin do show potential to produce methane that if economic to extract could potentially be worth pursuing. (Bostic, 1)[12] In the past the basin was seen as a valuable asset with rich resources that was absolutely worth further exploration and production, but now that these resources have been largely recovered it is likely going to see little to no future production.[14]

Drilling Risks

The primary drilling risks associated with the Forest City Basin will be found in the basin's history. The extensive drilling and exploration efforts since the basin's discovery over 150 years ago have exhausted the majority of hydrocarbons remaining in the basin. During the source rock deposition stage of its lifecycle the Forest City Basin experienced heavy erosion in the limestone and sandstone source rock that would later be covered by the Pennsylvanian shale previously discussed.[8] The erosion is thought to not have an affect on the porosity and migration of the source rock however, it makes oil and gas content more difficult to locate through conventional means. The primary risks with drilling in the basin are all going to center around the low remaining hydrocarbon content and the difficulty and expense of locating new reserves in a volume worth extracting

Further Reading

https://www.kgs.ku.edu/Publications/Bulletins/51/02_intro.html

https://mospace.umsystem.edu/xmlui/bitstream/handle/10355/33126/research.pdf?sequence=2

https://www.kgs.ku.edu/Publications/Bulletins/TS13/

References

  1. Fracking in Missouri. Ballotpedia. (n.d.). Retrieved April 27, 2022, from https://ballotpedia.org/Fracking_in_Missouri
  2. 2.0 2.1 2.2 2.3 2.4 Stratigraphic Architecture of Lower to Middle Pennsylvanian Coal-beds in the Forest City Basin of Northeastern Kansas. Stratigraphic architecture of lower to Middle Pennsylvanian coal-beds in the forest city basin of Northeastern Kansas. (n.d.). Retrieved April 27, 2022, from https://www.kgs.ku.edu/PRS/AAPG2005/forestcity/p1-02.html
  3. Chavez, C. (n.d.). Province 5056 forest city basin oil and gas assessment. Province 5056 Forest City Basin Oil and Gas Assessment | U.S. Geological Survey. Retrieved April 27, 2022, from https://www.usgs.gov/media/images/province-5056-forest-city-basin-oil-and-gas-assessment
  4. GROUND WATER ATLAS of the UNITED STATES. HA 730-J regional summary text. (n.d.). Retrieved April 27, 2022, from https://pubs.usgs.gov/ha/ha730/ch_j/J-text1.html
  5. https://www.kgs.ku.edu/Publications/Bulletins/TS13/
  6. 6.0 6.1 Hatch, J., & Newell, D. (n.d.). Geochemistry of oils and hydrocarbon source rocks from the Forest City Basin, northeastern Kansas, northwestern Missouri, Southwestern Iowa, and southeastern Nebraska. KGS. Retrieved April 27, 2022, from https://www.kgs.ku.edu/Publications/Bulletins/TS13/
  7. Argeology, & Argeology. (2019, January 25). The St. Peter Sandstone. Arkansas Geological Survey Blog. Retrieved April 27, 2022, from https://arkansasgeological.wordpress.com/2019/01/25/the-st-peter-sandstone/
  8. 8.0 8.1 8.2 8.3 Burrows, C. (n.d.). The Faculty of the Graduate School at the university of ... Retrieved April 27, 2022, from https://mospace.umsystem.edu/xmlui/bitstream/handle/10355/33126/research.pdf?sequence=2
  9. Charpentier, R. (n.d.). Forest City Basin Province (056) - USGS. Retrieved April 27, 2022, from https://certmapper.cr.usgs.gov/data/noga95/prov56/text/prov56.pdf
  10. Joeckel, R.M. & Divine, Dana & Howard, Leslie & Cameron, Kathleen & Waszgis, Michele. (2019). Geology of Southeastern Nebraska.
  11. Banerjee, S., Barker, C., Fite, J., George, S., Guo, G., Johnson, W., Jordan, J., Person, M., Reeves, T. K., Safley, E., Swenson, J. B., Volk, L., & and Erickson, R. (2015, August 14). Reduction of risk in exploration and Prospect Generation through a multidisciplinary basin-analysis program in the south-central mid-continent region. UNT Digital Library. Retrieved April 27, 2022, from https://digital.library.unt.edu/ark:/67531/metadc694051/
  12. 12.0 12.1 Bostic, J. (n.d.). USGS Online Publications Directory. [PARENTDIR]. Retrieved May 11, 2022, [from https://pubs.usgs.gov/of/ from https://pubs.usgs.gov/of/]
  13. https://www.kgs.ku.edu/PRS/AAPG2005/forestcity/p1-02.html
  14. Wells, J. S. (1987, January 1). Petroleum potential of the forest city basin. AAPG Datapages/Archives. Retrieved April 27, 2022, from https://archives.datapages.com/data/tgs/136/136.htm