Click to view presentation in PDF format (~2.7 mb).

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.