Ardmore Woodford Basin

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The Ardmore Basin is located in South-Central Oklahoma between the Criner Hills and the Arbuckle Mountains. Petroleum exploration began over 100 years ago with the discovery of the Healdton Field in 1913. (Healdton Field) This discovery marked the beginning of real oil development in Southern Oklahoma. The primary source rock in the basin is Pennsylvanian and Ordovician sandstones. The hydrocarbons produced are mostly oil with relatively low amounts of gas. Types of oil expected from the area varies from light-sweet crudes to heavy bitumen.

History of The Basin

The SAMEDAN Oil Corporation's first well. Later known as Noble Energy.

The history of the Ardmore basin is quite special for Oklahoma. The Oklahoma land run in 1889 brought with it oil prospectors looking for new oil fields. The Oklahoma territory and Indian Territory were fair game for these wildcats. However, in 1896 the Secretary of the Interior fearful of monopoly ruled "that no person nor company could have under lease in excess of 640 acres of land in Indian Territory." (Society A.G.) Producers went on strike and up to 1900 only 27 wells had been drilled in all of Indian Territory. In the summer of 1904 the ruling was overturned, and mass drilling was resumed. The Plains Development Company's discovery of the Healdton Field started the frenzy of drilling that followed in the Ardmore basin. The basin is made up of 27 fields which have a variety of stratigraphy. Many large businesses found their beginnings in the basin including Noble Energy, and Halliburton. ExxonMobil is the dominant producer with more than 270,000 net acres.

Primary Geologic Risks

The risks involved with the Ardmore basin include very rapid lateral changes in lithology, and lenticular beds that make finding correlations difficult within the basin. Hydrocarbon types can change rapidly across a play in the basin making defining geologic strata difficult. Many areas have not been geologically studied thoroughly with only the logs of wells in areas where known oil production has been positive. This tough geology has quelled many interested parties from continuing exploration in the area.

Petroleum Systems

Seal

The major reservoirs of the Ardmore basin include Ordovician and Pennsylvanian sandstones, with Missourian and Devonian carbonates. The Woodford shale that runs through the majority of the basin acts as the major seal. Faulting has also formed anticlinal and syncline traps that hold much of the regions petroleum. A large Igneous basement encapsulates the basin form the bottom.

Source Rock

Sedimentary deposition in Southern Oklahoma compared to Northern Oklahoma.

The source rock in the Ardmore Basin is unique for Oklahoma as it is a much deeper sedimentary rock deposit than traditional areas in the state. This increase in depth allows many different type of thermal maturity and source rocks to form.

Most common are organic rich sandstones that have high porosity and permeability. They occur at relatively low depths which make them great for conventional drilling. Pennsylvanian sandstones are the most prolific source of petroleum for the area, but rocks of the Simpson and Arbuckle are also significant producers of oil. These are dark black organic rich shales formed during the Mississippian and Ordovician periods when Oklahoma was a shallow sea rich with organic life.

Trap

In the late Paleozoic structural deformation occurred at an extent that caused great change geologically. The common traps are generally structural and stratigraphic types. There are also prominent anticlinal and syncline traps in the area as well.

Migration

The Sho-Vel-Tum oil field shows westward migration from drilling data and well logs. The field shows four vertical faults and two anticlinal folds with the axis pushing hydrocarbons westerly pooling along a horst. (Carpenter) The Loco field was known for its heavy asphaltene oil. Slow moving and structurally in an area with steep angled faulting, the main migration of oil in this area is due to gravity and water. In Carter county the Hewitt oil field sandstone formation shows a series of limestone caps with fine grained sands. The unconformity dips allowing seeping oils to converge in the Desmoinesian lower. (Cook)

Primary and Secondary Reservoirs

The primary reservoirs are sandstones of the Pennsylvanian and carbonates of the Ordovician. They are mainly comprised of oil with little amounts of gas. It is thought the high oil amounts in this area can be attributed to the high amounts of oil prone organics present during deposition. Secondary reservoirs in the area are Mississippian and Ordovician carbonates that are high in oil. Limestone from the Ordovician though more sparse, has in some areas been successful as a secondary reservoir.

HC type / Maturation

Oil and gas production and facilities of Oklahoma. Circle and highlight over the Ardmore Basin.

The hydrocarbons found in the Ardmore basin vary depending on time period of deposition, and area. The basin has many geologic differences from field to field and this has led to major differences in hydrocarbons that can be expected post-production. Mainly an oil producing zone, you could expect depending on area to produce light API gravity oils, with low sulfur contents, to heavy asphaltenes in an adjoining area. The deep sediments in the Ardmore basin allow for ideal thermal maturation which accounts for the large amounts of oil found. This sediment bed is unique for Oklahoma.

Petroleum & Facility Engineering

The Ardmore basin has historically had plentiful oil and easy drilling. With oil reserves in the area declining and production falling, engineers have had to adapt to continue to find success. Water flood projects are one of the most common forms of gaining additional recovery in these semi depleted oil and gas fields. Placing injector wells around a recovery well and pushing the oil to the correct area is an important task. By failing to predict where oil will be pushed or where water will flow, there is a risk of missing oil or pushing it in the wrong direction. Geologists and engineers work side by side to complete the recovery operations. Water recycle and disposal units are built to keep the operation moving and need to be tuned to the right amount of flow rate. Producers believe this type of recovery process poses the best low cost high return scenario to operate in some areas of the Ardmore Basin.

Analysis of Geologic Uncertainties

The Ardmore basin is comprised of 27 individual fields. These fields all have different geologic makeups due to the major structural deformation during the Paleozoic era. This has been the biggest grievance of the basin as producers look for new prospects. The geology from area to area is so different that it poses an extreme geologic challenge for companies that present many uncertainties.

Primary Drive Mechanisms

The primary drive forces for oil extraction in the Ardmore Basin include dissolution, gravity, water drive, and gas drive. Most commonly used are dissolution and gravity. In certain areas along a river especially in Love county, water drive and dissolution are the primary drive mechanisms. Due to the large variance in the lithology of the basin many different drive factors are used in areas of close proximity of one another depending on what is needed.

Current and Future Assessment of the Basin

Currently the Ardmore basin is still being developed. The basin's development was expected to increase dramatically from drilling by ExxonMobil between the years of 2013-2017. Unfortunately low oil prices curbed the development in the basin from 14 rigs running continually in the Ardmore basin in 2013 to 2 rigs by the end of 2015. Small private conventional producers are the main companies that are still operating in the area. Water flooding projects and re-entry operations have allowed new previously not captured oil to be recovered from the basin.

References

1. Information about the Oklahoma Liquids Plays. (n.d.). Retrieved November 14, 2020, from https://www.naturalgasintel.com/information-about-the-oklahoma-liquids-plays/

2. Henry, M. E., & Hester, T. C. (n.d.). Southern Oklahoma Province 061. Retrieved November 13, 2020, from https://certmapper.cr.usgs.gov/data/noga95/prov61/text/prov61.pdf

3. Healdton Field: The Encyclopedia of Oklahoma History and Culture. (n.d.). Retrieved November 14, 2020, from https://www.okhistory.org/publications/enc/entry.php?entry=HE003

4. Boyd, D. T. (n.d.). Oklahoma Oil: Past, Present, Future. Retrieved November 13, 2020, from http://www.ogs.ou.edu/fossilfuels/pdf/OKOilNotesPDF.pdf

5. Wavrek, D. A. (n.d.). Characterization of Oil Types in the Ardmore and a Marietta Basins, Southern Oklahoma Aulacogen. Retrieved November 13, 2020, from https://static1.squarespace.com/static/55565c13e4b0d497d6e374d6/t/5581c5bfe4b09b87d6d7cf16/1434568127681/Wavrek+1992.pdf

6. Cardott, B. C. (n.d.). Oklahoma Shale Resource Plays. Retrieved November 13, 2020, from http://ogs.ou.edu/docs/geologynotes/GN-V76N2P21-30.pdf

7. Society, A. G. (1959). Petroleum geology of southern Oklahoma. Tulsa, OK, OK: The American Association of Petroleum Geologists. (Book)

8. Carpenter, M., & Tapp, B. (n.d.). Structural analysis of Sho-Vel-Tum using balanced cross sections. Retrieved from http://ogs.ou.edu/docs/guidebooks/GB38PIIRP11.pdf

9. Cook, J. M. (2010). STRATIGRAPHY, DEPOSITIONAL ENVIRONMENTS AND RESERVOIR DESCRIPTION OF THE TUSSY (DESMOINESIAN) SANDSTONES, SOUTHEAST JOINER CITY FIELD, LOVE AND CARTER COUNTIES, OKLAHOMA. Retrieved December 7, 2020, from https://shareok.org/bitstream/handle/11244/14046/Cook_okstate_0664M_12115.pdf?sequence=1

10. Our Beginnings. (n.d.). Retrieved December 09, 2020, from https://www.nblenergy.com/node/203