utica shale gas-yulini

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Shale Gas Resource Evaluation and Its Geochemistry Application

By : Yulini Arediningsih

A Case Study of Utica Gas Shale in Quebec, Canada

Daniel Acker/GettyImage

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Fast facts Characteristics of gas shales ChallengesApplication of Geochemistry Utica Shale Gas System, Quebec, CanadaConclusions

Outline

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Shale is the most common sedimentary rocks having very low permeability. Gas shale plays triple functions as gas self-producer, trap and storage, with lack of migration Shale gas becomes an alternative gas supply to substitute conventional gas whose production has recently declined. Currently, Montney Fm. and Horn River Basin in Western Canada have produced 1 Bcf of their total 240 Tcf recoverable resource. Other potential gas shale plays i.e. Colorado Group (AB, SK), Utica Group (QC) and Horton Bluff Group (NB).

Fast Facts

Due to its huge volume and very low permeability, shale gas extraction processes become complex requiring enormous advanced stimulation techniques such as hydrofracturing, steam injection and etc. to improve their fracture system so they can flow at commercial rate.

Source www.bbc.co.uk

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Low matrix permeability < 0.01md, low matrix porosity <9%. Types of gas produced can be biogenic, thermogenic gas and mixed gas.Gas generated in shale is stored as :

predominantly sorbed gas in organic fraction or kerogen; free gas within micro (<2nm) to meso-sized(2-50nm) pore spaces and shale fractures; and dissolved gas in formation water natural pores and fractures of shale.

Characteristics of Gas Shales

To enable shale producing gas, favorable conditions needed are :

High gas generation that are governed by : geochemical characteristics of the shale such as

maturity, organic content,

High gas preservation, that are controlled by rock properties of the shale such as

large volume with sufficient thickness; extensive natural or induced fracture permeability and porosity with sufficient gas saturation;lithological heterogeneity within the shale interval providing internal source – storage rock with good sealing

Source : Bustin and Clarkson, 1998

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Application of Geochemistry

What can be solved by applying Geochemistry studies :

Characterization of shale source rocks including thermal maturity, source rock richness and kerogen typing based on

plots of TOC and data from Rock-Eval Pyrolysis analysis

direct visual kerogen characterization

vitrinite reflectance

Sorption/desorption characteristics

Geochemical modeling of hydrocarbon generation and preservation

Gas play type (biogenic, thermogenic or mixed)

Carbon isotopes analysis for maturity and gas potential

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GIP estimation of shale gas resources is difficult mainly because of complex nature of gas storage between free gas and sorbed gas in nano to micro scale shale porosity Mass balance calculation to estimate GIP needs careful consideration Understanding the geochemistry of stored gas will make better approach in estimating economic of shale gas potential Poor understanding on how organic geochemical characteristics (such as TOC, organic material, vitrinite content) controls gas adsorption/sorption capacity in the shale kerogen However we have better knowledge on

vitrinite content and methane adsorption capacity showing positive correlation (Bustin and Clarkson, 1998)methane adsorption capacity can be controlled by increase in micro porosity due to thermal maturity (Levy et al, 2007)Shales with higher maturity, their maceral compositions tend to give a significant impact on methane adsorption capacity (Chalmers and Bustin, 2007).

Challenges

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Utica Shale Gas Play, Quebec, Canada

STATUS UPDATE : (Summarized from Lavoie et al (2011)) :

Located in St. Lawrence Lowlands, southern of QuebecExploration started in April 2008 so far 30 wells have been drilledThe main target :

interval depth 1000-2000m of medium to deep thermogenic shale gas play (zone #2)calcareous and organic-rich Middle Ordovician Utica shale

OGIP estimates : 120 -160 Bcf/section, overall giving significant Tcf amount of its total GIP accumulation. Factors of gas quality, the shale fracture network that can be hydrofractured, its strategic location and high gas demand have elevated the prospective status play to contingent resources/reserves.

(Lavoie et al, 2011)

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GEOLOGY AND STRATIGRAPHYThe Utica shales is typically calcareous and rich in organic materials deposited in

marine environment overlying the massive Trenton limestone during the Taconic Orogeny.Complex monoclinal and SW/NE trending normal fault system surrounding the potential

area appears to have created favorable fracture network to ease hydro-fracturing process.

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GEOCHEMISTRY STUDIESSamples analysed are from low maturity Utica shales to provide an estimation of TOCoriginal for transformation ratio (TR) and kerogen type estimation (see next figure)

Thermal maturity, measured in reflectometry-vitriniteequivalence (Ro eq.), varies between 1 and 4% from the northwest toward the southeast.

TOCpresent day : 1 and 6% (samples from the south to northeast of the Utica shale play) suggesting a mature to dry natural gas and condensate type.

Shales with TOC of 4 and 6% have a lower maturity level (between 0.5 to 1.0% Ro eq.)

The Utica shales are type II based on data of maturity (%Ro) and HI

TR is estimated to be 75% (1% TOCpresentday over 4% TOCoriginal) signifying that large quantities of natural gas in the system have been generated from the kerogen.

This good TR estimate may provide confidence in applying the mass-balance approach for the calculation of OGIP.

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GAS GEOCHEMISTRY

Overall, gas type in the St. Lawrence Lowlands range from low maturity (wet) to high-maturity (dry) thermogenic gas.

GC analysis of main target zone (medium to deep thermogenic play) contains gas with 95% methane. Toward shallower thermogenic zone located on the north shore of the St. Lawrence River, the gas become less mature containing higher ethane and propane.

Data of ethane carbon isotopes and gas wetness from the Utica shale gas wells are plotted within a isotope rollover anomaly zone as represented by data from the Barnett, Haynesville, and Marcellus prolific gas shales. This signifies promising future potential of the Utica gas shale.

The isotopic data from the Utica shale gas wells also suggest that :

all gas encountered is thermogenic generated from the same source rock,

Indication of increasing maturity trend

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Understanding the geochemistry of stored gas will make better approach in estimating economic of shale gas potential

GIP estimation of shale gas resources is difficult mainly because of complex nature of gas storage between free gas and sorbed gas in nano to micro scale shale porosity

Application of geochemical techniques and analyses such as kerogen typing (S2 vs TOC plot) and ethane isotopes, in the Utica Shale gas data provides positive contribution on understanding the gas resources in the Utica Shale. The results suggest the shale contain a mature to dry natural gas and condensate type.

More importantly, good estimate of TR value from TOCpresent day vs TOCoriginal data provide confidence in applying the mass-balance approach for the calculation of OGIP.

Conclusions

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Cited ReferencesAllen, N., Aplin, A.C., Thomas, M., 2010, Organic geochemical controls on shale gas storage, a conference poster at www.ceg.ncl.ac.ukBustin, M. R., Bustin, A., Ross, D., Chalmers, G., Murthy, V., Laxmi, C., Cui, X., 2008. Shale Gas Opportunities and Challenges. Search and Discovery

Articles #40382 (2009). Adapted from oral presentation at AAPG Annual Convention, San Antonio, Texas, April 20-23. Bustin, R.M. and Clarkson, C.R., 1998: "Geological Controls on Coalbed Methane Reservoir Capacity and Gas Content"; The International Journal of

Coal Geology, V. 38, p.3-26.Bustin, A.M.M., Bustin, R.M. and Cui, X., 2008, Importance of fabric on the production of gas shales; Unconventional Gas Conference, Keystone,

Colorado, February 10–12, 2008, Society of Petroleum Engineers, SPE 114167Bustin, R.M. 2005. Gas Shale Tapped for Big Pay. AAPG Explorer, February 2005Chalmers GLR and Bustin RM, 2007, The organic matter distribution and methane capacity of the Lower Cretaceous strata of Northeastern British

Columbia, Canada, International Journal of Coal Geology, 70, 223-239 Shale Gas consortium Curtis, J.B., 2002, Fractured shale-gas systems, AAPG Bulletin, v. 86, no. 11 (November 2002), pp. 1921–1938Kuuskraa V.A. and Stevens, S.H., 2009, Worldwide Gas Shales and Unconventional gas: A Status Report, Worldwide Gas Shales and Unconventional

GasLavoie, J.Y. , Marcil, J.S., Dorrins, P.K., Lavoie, J., and Aguilera, R., 2011 Natural-Gas Potential in the St. Lawrence Lowlands of Québec: A Case

Study, Journal of Canadian Petroleum Technology, p.72-82 Levy JH., Day SJ., Killingley J.S, 1997, Methane capacities of Bowen Basin coals related to coal properties, Fuel, 76(9), 813- 819Passey, Q.R., Bohacs, K.M., Esch, W.L., Klimentidis, R., and Sinha, S, 2010, From Oil-Prone Source Rock to Gas-Producing Shale Reservoir –

Geologic and PetrophysicalCharacterization of Unconventional Shale-Gas Reservoirs, SPE 131350Pittsburgh, C.B., Kieschnick, RSr., Lewis, R.E., Waters, G., 2006, Producing Gas from Its Source, Oilfield Review, Autumn, p.36-49http://www.neb.gc.ca/clf-nsi/rnrgynfmtn/nrgyrprt/ntrlgs/prmrndrstndngshlgs2009/prmrndrstndngshlgs2009nrgbrf-eng.htmlTalukdar, S.C, 2009, Application of Geochemistry for Shale Gas Assessment, Baseline Resolution, Weatherford

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