2.determining organic shale from porosity and resistivity

7/31/2019 2.Determining Organic Shale From Porosity and Resistivity

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AVDirect Method for Determining Organic Shale Potential from Porosity and Resistivity Logs to Identify Possible

Resource Plays*

Thomas Bowman1

Search and Discovery Article #110128 (2010)Posted June 14, 2010

*Adapted from oral presentation at session, Genesis of Shale Gas--Physicochemical and Geochemical Constraints Affecting Methane

Adsorption and Desorption, at AAPG Annual Convention, New Orleans, LA, April 11-14, 2010

1Mantle Oil & Gas, LLC ([email protected])

Abstract

Today many geoscientists are faced with identifying possible resource plays throughout the world. Determination of potential organic contentof the shale sections is one of the first estimations that is often made, and time and again there is a lack of information readily andinexpensively available to make these preliminary estimates. As Passey (AAPG, 1990) and others have shown, there are several methods that

can be used to determine the organic content by interpretation of various electric logs. One such method, referred to as the log R technique,used for identifying and calculating total organic carbon in organic-rich rocks can be quickly estimated by the improvement of cross-plotting

sonic logs (DT) and log (natural logarithm) of resistivity data and determining the shale line that can then be used to calculate a pseudo-soniclog that is then displayed over the existing sonic logs to determine the organic shale potential for a zone in an individual well. In water-

saturated, organic-lean rocks, the two curves parallel each other and allow the shale calculation line to be determined. However, in eitherhydrocarbon reservoir rocks or organic-rich shale sections a separation between the curves occur. Using the gamma-ray curve, reservoir

intervals can be identified and eliminated from the analysis. The separation in organic-rich intervals results from two effects: the porosity curve

responds to the presence of low-density, low-velocity kerogen, and the resistivity curve responds to the formation fluid. In mature source rocksthe magnitude of the resistivity increases because of the presence of generated hydrocarbons. By cross-plotting multiple wells this techniquecan provide relative information for an area or entire shale section. This method requires little more than a simple cross-plot and log calculationmathematics to provide a geoscientist sufficient data to easily and quickly determine potential organic shale sections. Across an area, these log

cross-plot displays support the correlation and mapping of organic-rich shale sections and allow the geoscientist to quickly determine highgraded areas of focus for further study. This method allows organic richness to be assessed in a wide variety of lithologies and maturities using

common well logs and has been applied to many of the North American shale plays, such as the Barnett, Woodford, Eagle Ford and Marcellusshales.
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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Meissner, F.F., 1978, Petroleum geology of the Bakken Formation, Williston Basin, North Dakota and Montana in Montana GeologicalSociety, The Economic geology of the Williston Basin; Montana, North Dakota, South Dakota, Saskatchewan, Manitoba, p. 207-227.

Meyer, B.L., and M.H. Nederlof, 1984, Identification of source rocks on wireline logs by density/resistivity and sonic transit/resistivitycrossplots: AAPG Bulletin, v. 68, p. 121-129.

Nixon, R.P., 1973, Oil Source Beds in Cretaceous Mowry Shale of Northwestern Interior United States: AAPG Bulletin, v. 57/1, p. 136-157.

Passey, Q.R., S. Creaney, J.B. Kulla, F.J. Moretti, and J.D. Stroud, 1990, A practical model for organic richness from porosity and resistivity

logs: AAPG Bulletin, v. 74, p. 1777-1794.

Philippi, G. T., 1968, Essentials of the petroleum formation process are organic source material and a subsurface temperature controlledchemical reaction mechanism, in Advances in organic geochemistry: Oxford, Pergamon Press, p. 25-46.

Schmoker, J.W., 1981, Determination of organic-matter content of Appalachian Devonian shales from gamma-ray logs: AAPG Bulletin, v.

65/7, p. 1285-1298.

References


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Theme VIII: Genesis of Shale GasPhysicochemical andGeochemical Constraints Affecting Methane Adsorption and

Desorption

Direct Method for Determining Organic ShalePotential from Porosity and Resistivity Logs to

Identify Possible Resource PlaysT. Bowman

Mantle Oil & Gas, LLC

AAPG

Annual Convention & ExhibitionNew Orleans, April 2010


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Passey, Q. R., S. Creaney, J. B. Kulla, F. J. Morettiand J. D. Stroud, 1990, A practical model fororganic richness from porosity and resistivitylogs:AAPG Bulletin, V. 74, P 1777-1794.

Meyer, B. L., andM. H. Nederlof, 1984,

Identification of source rocks on wireline logs bydensity/resistivity and sonic transit/resistivitycrossplots:AAPG Bulletin, V. 68, P 121-129.

Methods - References


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MATRIX

W

ATER

NON-SOURCE

SOLID

MATRIX

W

ATER

IMMATURESOURCE

SOLID ORGANIC

MATTER

MATRIX

WATE

R

MATURESOURCE

SOLID ORGANIC

MATTER

Mature Source Rocks As a Source Rock Matures, a portion ofthe solid organic matter is transformed to liquid or gaseoushydrocarbons which move into the pore space, displacing theformation water.*

*After Philippi (1968), Nixon (1973) and Meissner (1978)

Source Rock Composition


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Source Rocks - shales and lime-mudstones containing

significant amounts of organic matter.

Non-Source Rocks - also contain small amounts of organicmatter (< 1 wt. %).

Organic-rich sediments have a higher resistivity thanorganic-lean sediments

Organic-rich rocks - increase in sonic transit time and anincrease in resistivity

Organic-rich rocks can be relatively highly radioactive(higher gamma-ray reading than ordinary shales and

limestones) Schmoker, 1981

Hypothesis


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After Passey et al. (1990)

Schematic guide for

the interpretationof a wide variety offeatures observedon log R overlays

Schematic of log R Response

100

log R0 1

T (sec/ft)

log R

WATER

WATER

GASOR

OIL


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Passey Method In Practice

SP-100 40.0

GR0.00 150

ILD(AIT90)0.20 2000

6600

6700

6800

6900

7000

7100

7200

7300

7400

7500

5.5

-61 29 4 03 MB LF

-65 04 3 54 BR NT

-5800.00

-5900.00

-6000.00

-6100.00

-6200.00

-6300.00

-6400.00

-6500.00

-6600.00

-6700.00

-6800.00

-5800.000

-5900.000

-6000.000

-6100.000

-6200.000

-6300.000

-6400.000

-6500.000

-6600.000

-6700.000

-6800.000

MINT CREEK 2H424393097700

-5800.00

-5900.00

-6000.00

-6100.00

-6200.00

-6300.00

-6400.00

-6500.00

-6600.00

-6700.00

-6800.00

DT

120 20.0

5.5

6129 403MBLF

6504 354BRNT

-5800.00

-5900.00

-6000.00

-6100.00

-6200.00

-6300.00

-6400.00

-6500.00

-6600.00

-6700.00

-6800.00

-5800.000

-5900.000

-6000.000

-6100.000

-6200.000

-6300.000

-6400.000

-6500.000

-6600.000

-6700.000

-6800.000

MINTCREEK 2H424393097700

-5800.00

-5900.00

-6000.00

-6100.00

-6200.00

-6300.00

-6400.00

-6500.00

-6600.00

-6700.00

-6800.00

10 100 90 40

Scale Sonic and Resistivitywhere 50 sec/ft equal to 1decade Resistivity (ohm-m) log R


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Modified Procedure

1. Calculate LogR of all Resistivity logs2. Cross-Plot LogR vs Sonic (DT)*3. Determine low Resistivity Shale line

4. Calculate new Sonic (pseudo-sonicDtR) from Shale line [DtR=b-m*LogR]

5. Overlay pseudo-sonic (DtR) over sonic6. Highlight cross over of pseudo-sonic

with DT7. Interpret Organic shale section

*Use Porosity log in place of DT


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-1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4

54

63

72

81

90

99

108

117

126

135

LOGR

DT

Log Data: MINT REEK(2H), ntitle 1: DT vs. L R

DT = 100.538828 - 25.1536122*LOGR

Log R

DT

Shale Line

DtR=105-25*LogR

Shale Play

Cross Plot AnalysisBarnett Core (Mississippian)

Fort Worth Basin

Carbonates

1 DecadeResistivity

50sec/ft

Passey

Log RSlope


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Conclusions

1. Organic-rich sediments have ahigher resistivity than organic-lean sediments

2. Organic-rich rocks - increase insonic transit time and anincrease in resistivity

3. Organic-rich rocks can berelatively highly radioactive(higher gamma-ray readingthan ordinary shales andlimestones)

4. The LogR cross plot is a quickand easy determination ofresource

5. Word of Warning


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Thank You

2.determining organic shale from porosity and resistivity

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