Assessing Unconventional Shale Gas Plays in New York

·         Identify high gas potential fairways using same geochemical methods applied to the Barnett and other successful shale gas plays.

·         These include TOC, vitrinite reflectance, hydrogen index and transformation ratios.

·         Create new structure and isopach maps of shale formations and potential gas producing intervals.

 

Ordovician Utica Shale 

Selected Figures (1-10) 

	Figure 1. Two similar black shales: Devonian Marcellus and Ordovician Utica. Deposition of both shales followed lithospheric downwarping associated with tectonic loading. Both shales terminated by shallow shelf carbonates. Both shales thicken to the east.
	Figure 2. Trenton Limestone in blue colors is time-equivalent to Utica Shale in brown colors. Primary interest is in Flat Creek and to a lesser extent the Dolgeville Member.
	Figure 3. Utica Shale. East-west cross-section.
	Figure 4. Flat Creek member isopach map. Flat Creek member thickens to the southeast. In the end, this is likely to be the Utica Fairway map.
	Figure 5. Dolgeville isopach map; it thickens to the southeast.
	Figure 6. Utica Shale TOC map. TOC increases to the SE as Utica (Flat Creek and Dolgeville members) also thickens in that direction
	Figure 7. Utica Shale TOC cross-section. TOC increases in Dolgeville and increases more in the Flat Creek Member.
	Figure 8. Flat Creek HI map. Lowest values occur where TOC was highest in Flat Creek and Dolgeville.
	Figure 9. Flat Creek transformation ratio map, with wells with good Utica shows. Inside the blue lines as defined by the transformation ratio might be a productive fairway for Utica Flat Creek prospects.
	Figure 10. Flat Creek isopach map. The Utica fairway is probably best defined by the Flat Creek Member isopach map. All of the Utica is supermature; the Flat Creek had the highest original TOC which drives HI and TR maps.

 

Flat Creek Member

·         Lowermost member of the Utica Formation.

·         K-bentonites and graptolites used to match key successions (Goldman et al., 1994).

·         Dark gray to black, variably calcareous shale with minor thin beds of argillaceous micrite and biomicrite (Lehmann et al. 1995).

·         Bounded by Dolgeville member on top.

 

Dolgeville Member

·         Interpreted as a slope facies peripheral to the Trenton platform.

·         Tabular ribbon limestones and dark gray to black shale beds.

·         Several geochemically correlated K –bentonites.

·         Bounded on top by Thruway unconformity.

·         Slump folds occur immediately below the unconformity.

·         Folds are dominantly asymmetrical with a westward vergence.

 

Indian Castle Member

·         Uppermost member of the Utica Formation blankets all of western NY.

·         Thin layers of fossil debris, phosphatic debris and quartz.

·         Condensed beds.

·         K-bentonites used to match key successions. Sharp contact with underlying Steuben limestone, more subtle contact where it overlies Dolgeville.

·         Divided into the lower and upper sections (Baird and Brett, 2002).

 

Geochemical Study and Gas Production

·         Using geochemistry in an attempt to define a general fairways for exploration in Utica and Marcellus.

·         Using the same Rock-Eval approach Jarvie et al (2005) used for the Barnett Shale.

·         Used cuttings from 31 wells and samples from 12 cores, 5 outcrops.

 

Gas Production from Shales

·         Gas production from tight shales requires maturation and cracking of oil that has been generated from live organic matter -need to have at least 2 percent TOC to begin with.

·         With increasing maturation carbon and hydrogen are lost from shale due to hydrocarbon generation.

·         Increasing thermal maturity therefore leads to decrease in TOC and hydrogen values.

·         Want shales with decent original TOC, with evidence that significant amounts of gas has formed from that TOC during thermal maturation.

 

Geochemical Measurements

·         TOC = Total organic carbon (%).

·         Live carbon including S1 (oil and gas present in shale) and S₂ (remaining kerogen).

·         Tmax= The temperature at peak evolution of S₂ hydrocarbons from Rock Eval.

·         Ro% = Vitrinite Reflectance (calculated from Tmax).

·         HI= Hydrogen Index (S₂ x 100)/ TOC

·         TR= Transformation or conversion ratio calculated from hydrogen index (HI)

 

Geochemical TOC Data

·         Indian Castle < .5%

·         Dolgeville .5 -1.5%

·         Flat Creek 1.5 -3%

 

In Jarvie et al., 2005 study, TOC from cuttings were 2.36 times lower than samples from core; therefore this same dilution effect would be seen in other geochemical parameters.

 

Productive shales are generally >2% TOC.

 

Utica Tmax and Vitrinite reflectance (Ro)

·         Tmax is the temperature where S₂ peaks.

·         Because >95% of the S₂values in the Utica are too low and/or < S₁, the Tmax values are unreliable in the Utica Shale.

·         Tmax can be used in some cases to obtain a calculated value for vitirinite reflectance (Ro) by the formula Ro=0.0180*Tmax-7.16.

·         Because Tmax is unreliable in the Utica, it is not possible to calculate reliable values for Ro.

 

Hydrogen Index

·         Hydrogen Index (HI) is a calculation to determine the amount of hydrogen remaining in the shale.

·         HI = (S₂*100)/TOC.

·         HI decreases as thermal maturity increases because S₂ goes down.

·         Again, S₂ is uniformly very, very low in Utica so the HI values largely driven by TOC –

·         Lower values are generally thought to be better in Utica as they represent higher original TOC

 

Transformation Ratio

·         Evaluates the conversion directly by measuring changes in the kerogen (organic matter) yields.

·         In order to calculate this ratio, you need the present day Hydrogen index (HI_pd) and original Hydrogen index (HI_o) (see Jarvie et al., 2007 for formula).

·         Areas with highest potential for production have values approaching 1, lower values = lower potential.

 

Devonian Marcellus Shale 

Selected Figures (Figures 11-22) 

	Figure 11. Marcellus Shale stratigraphic diagram. Interest primarily in Union Springs Member and lowermost Oakta Creek Member.
	Figure 12. Marcellus isopach map. Marcellus thickens to the east.
	Figure 13. Marcellus TOC map. TOC is much higher in Marcellus than in Utica (up to 12%). TOC values are highest in central part of state and decrease to the east.
	Figure 14. TOC map for Union Springs Member. TOC increases from the western part of NY to the central eastern side of NY.
	Figure 15. TOC map for Oatka Creek Member. TOC increases to the northeast and west-northwest.
	Figure 16. Tmax map, Marcellus Shale. About half of the S2values in the Marcellus can be trusted for Tmax values; using these, Tmax increases to the east as would be expected.
	Figure 17. Ro% map for Union Springs Member. Optimum Ro% is in the central and eastern New York.
	Figure 18. Ro% map for Oatka Creek Member. Ro% for OatkaCreek is in eastern side of basin –based on this it is best to avoid western half of state.
	Figure 19. Union Springs HI map, showing eastern decrease.
	Figure 20. Oatka Creek HI map, with eastern decrease.
	Figure 21. Union Springs transformation ratio map.
	Figure 22. Oatka Creek transformation ratio map.

 

 

Union Springs Member

·         Organic-rich thinly bedded blackish grey to black shale with thin silt bands.

·         The member is between the Cherry Valley and Onondaga Limestone.

·         Characterized as  pyritiferous; farther east the Union Springs becomes the Bakoven Member that becomes darker, less organic and has few limestone members.

·         Lenses in and out in localities in far Western New York.

 

Cherry Valley Member

·         Consists of skeletal limestones and shaly intervals.

·         Westward thinning of the Marcellus Formation in western and central New York leads to the condensation and union of the Cherry Valley limestones with limestones in the upper part of the Union Springs.

 

Oatka Creek

·         Upper member of the Marcellus Formation in Western and central New York.

·         Becomes Cardiff and Chittenango members in Central and Eastern New York.

·         Is confined in Western New York by Stafford and Onondaga limestones.

·         Farther east it is between the Stafford and Cherry Valley limestones where it is present.

·         Dark grey to black organic-rich shale.

 

Vitrinite Reflectance Calculation

·         Vitrinite refelctance(Ro) is a measure of thermal maturity that can be done directly on plant matter.

·         Ro can be estimated from reliable Tmax data using the following calculation.

·         Ro(%)=(0.0180*Tmax)-7.16.

·         The Tmax data in the Marcellus is much better than the Utica –about half the points have useable S₂ values.

 

Vitrinite Reflectance (Ro%) (based on Jarvie et al, 2005

 

Well Cuttings                                                              Core

•Low maturity source rocks 0.0 –0.55%         •Low maturity source rocks 0.0 -0.55%

•Oil window 0.55% -1.0%                              •Oil window 0.55%-1.15%

•Condensate-wet gas window 1.0 %-1.40%  •Condensate–wet gas window 1.15%-1.40%

•Dry gas window > 1.40%                             •Dry gas window > 1.40 %

 

Comments on Marcellus

·         Some wells, such as the Beaver Meadows well, were drilled in what is the geochemical fairway for Marcellus but were not completed and are assumed to be dry holes. Why?

·         Other aspects may be equally important:

                        –completion/frac practices need to be refined.

                        –may need certain silica content.

                        –too much TOC?

                        –Overcooked?

·         More work is needed

 

Future Work

·         Calculate and make maps of original TOC, S₂ and HI.

·         Get analysis of gas samples from newer wells whenever possible.

·         Get mineralogy data for shales.

·         Resample areas where data is questionable or missing and test conclusions with new samples in fairways.

·         See what happens with newer wells in fairways that have new drilling/completion/frac concepts.

 

Conclusions (Figure 23) 

Figure 23. Map of Utica and Marcellus fairways. They overlap in eastern side of basin.

 

·         The Marcellus and Utica Shales both contain fairways that are favorable to gas exploration based on geochemical data.

·         Both fairways occur in overlapping areas in the eastern Southern Tier of the State where there are not many wells drilled to date.

·         Wells with good shows occur in predicted fairways.

·         Within the Utica Shale, the Flat Creek and, to a lesser extent, Dolgeville members, which both thicken to the east and pinch out to the west, have the best potential.

·         In the Marcellus Shale, the Oatka Creek and Union Springs members have the best potential.

·         The Marcellus is organically richer than the Utica.

 

Acknowledgements

·         John Martin for NYSERDA financial support

·         Fortuna Energy

·         EOG Resources

·         Jay Leonard of Platte River Associates for geochemical data on easternmost Utica well cuttings

 

References 

Baird, G.C.,  and C.E. Brett, 2002 Indian Castle Shale: late synorogenic siliciclastic succession in an evolving Middle to Late Ordovician foreland basin, eastern New York State: Physics and Chemistry of the Earth, Parts A/B/C, v. 27, no. 1, p. 203-230.

Goldman, D., C.E. Mitche.., Stig. M. Bergstrom J.W. Delano, and S. Tice, 1994, K-Bentonites and Graptolite Biostratigraphy in the Middle Ordovician of New York State and Quebec: A New Chronostratigraphic Model: Palaios, v. 9, no. 2, p. 12-143.

Jarvie, D.M., 1991, Total organic carbon (TOC) analysis, in R.K. Merrill, ed., Treatise of petroleum geology: Handbook of petroleum geology, source and migration processes and evaluation techniques: AAPG, p. 113-118.

Jarvie, D.M., R.J. Hill, and R.M. Pollastro, 2005, Assessment of the gas potential and yields from shales: The Barnett Shale model, in B.J. Cardott, ed., Unconventional energy resources in the southern Mid-continent, 2004 symposium: Oklahoma Geological Survey Circular 110, p. 37-50.

Jarvis, D.M., R.J. Hill, T.E. Ruble, and R.M. Pollastro, 2007, Unconventional shale-gas systems: The Mississippian Barnett Shale of north-central Texas as one model for thermogenic shale-gas assessment: AAPG Bulletin, v. 91, p. 475-499.

Lehmann et al. 1995