Presentation Identifier (Title or Location), Month 00, 2008

Petrophysical Characterization of the

Marcellus & Other Gas Shales

Daniel J. Soeder, NETL, Morgantown, WVPresentation for PTTC/DOE/RSPEA Gas Shales Workshop, 28 Sep. 2011

AAPG Eastern Section Meeting, Arlington, Virginia

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Petrophysics• Physical properties of rocks

• Wireline well log measurements

– radioactivity, density, conductivity, sonic velocity

– links between well logs and geology

• Measurement of reservoir rock and fluid transport

properties (core analysis)

– porosity, pore volume compressibility, capillary entry

pressure, pore size distribution

– permeability/relative permeability, flowpath aperture,

flowpath tortuosity, reaction to stress

– links between core analysis and petrography

– classically designed for conventional reservoirs;

added challenge in shale.

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Gas Shale Geology Sedimentary rock formed from mud

Composed of fine-grained material: clay,

quartz, organic matter, and other minerals.

Clay-rich shales are fissile: split into thin sheets

Shale can be silty or calcareous, and grade into

other lithologies (siltstone/limestone)

Shale types: organic-rich (black) and organic

lean (gray or red)

Shale porosity ~ 10%, permeability is very low.

Pore spaces between grains are small.

Gas occurs in fractures, in pores and adsorbed

or dissolved onto organic materials and clays.

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Marcellus Shale in Hanson Quarry, NY

Oatka Creek Member

Cherry Valley LS

Union Springs Member

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WV 6 7355.2 Organic-rich black shale100 µm

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Woody

organic

10 µm

Pyrite >

Parallel clay flakes

Microfracture

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Nanoporosity in Shale

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Petrophysics of Shale• Shale grain size is very small: silt sized quartz grains,

clay flakes, organic matter. Small grains = small pores

• Pores in shale are flat, slot-like structures, supported

by asperities or surface roughness, versus triangular

pores supported by round grains.

• Small pores are easily plugged by liquids held under

high capillary pressures

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Pore Geometry and Drawdown Stress• The linear shape of slot pores is more strongly

affected by narrowing under stress than

triangular pores.

• Asperities in slot pores are easily crushed

during high net stress excursions, and do not

recover the pore shape, resulting in

hysteresis.

• Slot pore behavior under increased net stress:

– greater mean aperture (smaller pores closed)

– greater flowpath tortuosity (loss of inter-connectivity)

– result: lower permeability

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DOE Eastern Gas Shales Project 1976-1992

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EGSP Cored Well Locations38 total, including 3 wells in the Antrim

Shale of the Michigan Basin, and one

well in the New Albany Shale of the

Illinois Basin

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Appalachian Basin Stratigraphy

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IGT Core Analysis 1982-89• Institute of Gas Technology in Chicago (now GTI) had a

contract to perform tight sand core analyses for DOE

Multiwell Experiment (MWX) in Colorado.

• A high-precision, steady-state gas permeameter and

porosimeter was developed for this work, called the

Computer Operated Rock Analysis Lab, or CORAL

• The CORAL used temperature control to produce a gas

reference pressure stable to ~1 part in 500,000

• Gas flow through cores was measured by differential

pressure build-up in calibrated downstream volumes

• Actual flow sensitivity was as low as 10-6 standard cm3

per second

• Pore volumes under net stress were measured using

Boyles Law to an accuracy of 0.01 cm3

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IGT Core Apparatus (CORAL)

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Permeability

• Henry Darcy: 19th Century French hydrologist defined the basic

parameters for water; some modifications needed for gas

• Flow is controlled by permeability of the porous medium, x-s area,

pressure drop, fluid viscosity and flowpath length:

Q = kA (ΔP/µ L); to solve for permeability: k = µ L (QA/ΔP)

In the lab, L and A are properties of the sample, µ is a property of the

measuring fluid, ΔP is controlled, and we measure Q.

• Akin to electrical conductivity, in that some materials allow fluids

to pass through more easily than others

– Ohm's law: I = U(1/R): current = voltage divided by resistance

• Basic permeability unit: darcy = 1 cp fluid flowing at 1 cm3/sec

under 1 atm ΔP per cm length, through a cross-section of 1 cm2

– millidarcy = 10-3 darcy: conventional oil & gas reservoirs

– microdarcy = 10-6 darcy: tight sands, coal, some shales

– nanodarcy = 10-9 darcy: some coals, many shales

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Pulse versus Steady State• Joel Walls under Amos Nur at Stanford University developed a

pulse technique for low permeability rocks

– Stanford Rock Physics Project in 1982

– Used decay of pressure pulse to calculate permeability

– Fast, commercial technique, currently in use

• Phil Randolph at IGT stood by a modification to the steady

state technique for research purposes

– Temperature control gave stable reference pressure

– Adjustments to stress, fluid redistribution, adsorption and other

subtle phenomena could be measured over time

– Slow technique; days to weeks to collect data

• Side by side comparison for GRI showed similar performance

on dry rock

– Steady state more accurate for relative permeability to gas under

partial liquid saturations

– Pulse technique much faster

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IGT CORAL Operations

Modification of CORAL for Devonian shale analyses:

1) Reconfigured air circulation for better temperature stability

2) Improved digitizing resolution with new data logger

3) New temperature control algorithm to minimize overshooting

the desired setpoint.

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Shale Petrophysics in the 1980s

• Only 5 cores out of 38 EGSP wells penetrated to the

Marcellus Shale

• DOE funded EGSP core analysis at the Institute of

Gas Technology (now GTI) in Chicago 1982-84

• EGSP cores had deteriorated, leading to challenging

sample selection

• Samples analyzed were 7 Ohio Shale cores, and 1

Marcellus

– Ohio Shale contained oil; difficult gas measurements

– Marcellus Shale had strong sensitivity to net stress

– Marcellus had very strong adsorbed gas component

– Permeability of all shales very low, but measureable

• New analyses planned to follow up on earlier results

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EGSP WV-6 Well and Core (MERC#1) Photographed in 2011

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Ohio Shale Gas Permeability

100 nanodarcies >

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Marcellus Shale Gas Permeability

• Gas slippage in tight rocks.

• Klinkenberg correction:

– K = k∞ x 1+b/P

– where b is the Klinkenberg

coefficient (slope)

• Effect of net stress: 2x net

stress = 2/3 reduction in

permeability (19.6 µd at 3000

psi net PC; 6 µd at 6000 psi net PC

• Derived parameters:

– Flowpath aperture

– Flowpath tortuosity

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Gas Pore Volume in Marcellus

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Gas Content of Marcellus Shale

1980 NPC estimates for shale: 0.1 to 0.6 scf

gas/ft3

1988: IGT core analysis: 26.5 SCF/ft3 at

3500 psi reservoir pressure; GIP= 3693

TCF; 10% recoverable = 369 TCF

2002: USGS Open-File Report 2006-1237:

Marcellus has 2 TCF of recoverable gas.

2008: Engelder and Lash: Marcellus has

500 TCF of GIP, with 50 TCF recoverable.

2009: Engelder revised this to 363 TCF

recoverable.

2011: USDOE - Energy Information

Administration using 410 TCF recoverable.

USGS estimate is 84 TCF recoverable.

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IGT Data - Circa 1988

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Marcellus Gas Production

• Mitchell Energy adapted new technology for

economic production of shale gas in the 1990s

– directional drilling, laterals & light sand fracs

– Barnett Shale in Ft. Worth Basin, Texas

• Range Resources, Renz #1 well, October

2004, Washington County, PA;

– Trenton-Black River Limestone original target

– recompleted vertically in Marcellus Shale

– light sand frac; IP 300 MCFD

• Range Resources, Gulla #9 well, 2005

– "Barnett" type - drilled horizontally

– slickwater frac completion; IP 4 MMCFD

• 3157 Marcellus Shale wells drilled in PA

between January 2008 and June 2011

• Energy value of U.S. natural gas may equal

twice the oil in Saudi Arabia.

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NETL Petrophysical Analyses

• Precision Petrophysical Analysis Laboratory (PPAL)

• Constructed in a lab at the Petroleum and Natural Gas

Engineering Department at West Virginia University

– Student access (esp. international students)

– PNGE expertise to analyze and model the data

– Facilities accessible for 24-hour operations

• Based on IGT's CORAL design, but smaller footprint

with improved sensor electronics, greater degree of

computer control, and only 2 coreholders instead of 4.

• Design capabilities of 10,000 psi confining pressure,

1500 psi pore pressure, and 30 psi differential pressure

– Flow differential pressure sensors 0.5 psid full scale

– Porosimetery differential sensor 0.5 psid; displacement volume

calibrated to 0.7 mL per turn, readable to ± 0.003 mL.

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PPAL under construction

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Coreholders

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Flow Measurement System

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Pore Volume Measurement

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Plug Samples

Samples obtained from Facies 2 (shaly limestone),

Facies 4 (noncalcareous black shale) and Facies 5

(silty gray shale) for initial comparisons.

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Lithofacies in the Marcellus Shale

Facies 1: gray, calcareous shale

Facies 2: shaly limestoneFacies 3: black, calcareous shale

Walker-Milani, Margaret E., 2011, Outcrop lithostratigraphy and petrophysics of the Middle Devonian

Marcellus Shale in West Virginia and adjacent states: M.S. thesis, West Virginia University, July 2011.

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Lithofacies in the Marcellus Shale

< Facies 6: volcanic ash (Tioga)

Facies 4: black, non-calcareous shale Facies 5: dark gray, silty shale

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NETL Research Directions

• Forge links between physical rock behavior and geology (facies

and depositional environments)

– 3-D spatial variation of rock properties - EarthVision framework model

– link physical properties to geology through sedimentary lithofacies

– improved predictability of behavior

• Investigate net stress effects and hysteresis

– loss of gas production under drawdown

– ability to "re-inflate" shales in the future for CO2 sequestration

• Multiphase flow in shale

– pore scale interaction of gas, water and oil

– ability of shale to act as a caprock or seal

– effects of retrograde condensate

– gas potential in gray shales

• Behavior of different gases in black shale

– organics, clays and adsorption potential of CH4 versus CO2

– reaction of these gases to the presence of oil or water

– net stress, permeability and gas type

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Daniel J. Soeder

USDOE/NETL

3610 Collins Ferry Road

P.O. Box 880

Morgantown, WV 26507

(304) 285-5258

Daniel.Soeder@netl.doe.gov

http://www/netl.doe.gov

Questions?

Websites for additional information:

NETL Oil & Gas Technologies Reference Shelf (reports):

http://www.netl.doe.gov/technologies/oil-

gas/ReferenceShelf/index.html

Society of Core Analysts: http://www.scaweb.org/

Research Partnership to Secure Energy for America

(RPSEA): http://www.rpsea.org/

Marcellus Shale Coalition (industry site):

http://marcelluscoalition.org/