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Wettability and Rock Diagenesis: Why Microbes are Important

David B. Vance

ARCADIS US, Inc.

Presented at the 20th Annual CO2 Flooding Conference

December 11-12, 2014

Midland, Texas

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Why Oil is in ROZs

• The upstream community has recognized that petroleum in place is biodegraded by anaerobic microbial processes such as sulfate reduction

• Then the question becomes, given geologic time frames, why is there any oil in ROZs

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The Reason there is Oil in ROZs

• There are two dynamic processes that preserve oil in an ROZ

• One is Microbial Self Limitation – Microbial biodegradation daughter products

stop degradation process • The second is the creation of an oil wet

system – Oil is physically retained on mineral surfaces

making it resistant to physical hydraulic flushing

Imagine the result

ROZ Oil Chemistry Biodegradation

Microbial Processes Biodegradation Process

Controls

Active Microbes In Situ ROZ Properties

• Specific degradation pathways can be associated with single or multiple organisms with gene coding that can be turned on/off in response to conditions

• Often degradation sequences require consortia of multiple microbes in cooperating communities

• Hydrocarbon structure has an effect • Biosurfactant production effects

interfacial properties • Degradation by-products like H2S can be

inhibitory to microbes

• Availability of electron acceptors in order of importance: Sulfate; Iron; Bicarbonate; Nitrate; Oxygen

• Salinity/Temperature/Pressure • Porosity/Permeability/Surface Area and

modification by microbial activity • Hydraulic heads and flow rates • Chemistry of the mineral matrix • Water/Petroleum/Gas interfacial forces • Chemical, physical properties and

structure of the petroleum

Microbial Processing of Petroleum with Positive and Negative Feedback Loops

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Modified Activity Diagram – Calcium, Anhydrite, Sulfur

0

1

2

3

4

5

6

0.1 1 10 100 1000

Log

aCa2

+/a2

H+

Hydrogen Sulfide (aq) mg/L

Calcite

Elemental Sulfur Anhydrite

After: Richard et al, 2005, Oil & Gas Sci. and Tech., Vol. 60, No. 2, pp. 275-285

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Microbial Self Limitation

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BTEX Degradation Median Half Lives in

Days

8

Ben

zene

Tolu

ene

Eth

ylB

enze

ne

Xyl

ene

1

10

100

1000

Anaerobic Biodegradation of Organic Chemicals in Groundwater:

A Summary of Field and Laboratory Studies

Prepared by:

Dallas Aronson, Philip H. Howard

Environmental Science Center, Syracuse Research Corporation

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Microbial Self Limitation (MSL)

• With Almost Universal Microbial Activity Associated with ROZs, Transition Zones, and Even Main Pay Zones – Why Does Petroleum Remain in Place over Millions of Years

• The Answer is Microbial Self Limitation (MSL)

Imagine the result

Microbial Self Limitation (MSL) (2) • Dominant in Sour Oil Systems is the Effect of

Hydrogen Sulfide from Sulfate Reduction • In Sweet Oil Systems Inhibition of Methanogenesis is

More Important • The Presence of Iron (Particular in Clastic Systems)

may Limit MSL Effects • Irrespective MSL Governs Residual Oil

Concentrations and the Geometry of ROZs and Transition Zones

• That knowledge may be used as an Assessment and Exploration tool

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Concentration of H2S that Induce Microbial Inhibition

0

200

400

600

800

1000

1200

mg/

L H

ydro

gen

Sulfi

de

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Microbial Self Limitation (MSL) – Consequences

• MSL Governs Residual Oil Concentrations and the Geometry of ROZs and Transition Zones

• MSL Effects Apply to Sour and Sweet Oil Systems, Carbonate and Clastic Geologic Systems

• At this Point it is Dominantly Applicable to Shallow Petroleum Systems that have Temperatures Suitable for Microbial Activity

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Microbial Self Limitation (MSL) – Consequences (2)

• Knowing that MSL is Taking Place can be used as an Assessment and Exploration tool Allowing for Fact Based Economic Decision Making Regarding Targeted ROZs

• The Suite of Available Analytical Tools Includes (but is not limited to): the Physical Chemistry of the Multiphase Oil/Water/Gas System; Specifics of Microbial Populations (using genetic probes for example); Digenetic Processes; Interfacial Chemistry; Physical Hydrodynamics; Geophysical Properties; and ETC

Imagine the result

Phase Distribution of H2S - mg/Kg

0.1

1

10

100

1000

Water Oil Water Oil Gas

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H2S – Phase Distribution Initial Rules of Thumb

• The mass loading of H2S in the petroleum phase will be 3 times higher than the concentration of H2S in water in contact with that petroleum

• The mass loading of H2S in any confined gas phase can be 100 times the concentration of H2S in the petroleum

Imagine the result

Microbial Diagenesis

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Porosity Curve

“Bow” Shaped Character of Porosity Curve Porosity and PhotoElectric Cross section Log A characteristic “bow” shape on logs is generally present in the ROZs with decreasing resistivity and increasing porosity below the oil/water contacts

Imagine the result

Biogeochemical Diagenesis • Sulfate Reduction using Anhydrite of

Gypsum in the Mineral Matrix Produces an Increase in Porosity by Dolomitization – This induces surface effects as well

• In Clastic Systems the Reduction of

Ferric Iron Oxides to Produce Soluble Ferrous Iron can Increase Porosity in General as well as Preferentially Enlarge Pore Throats

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Biogeochemical Diagenesis (2) • Biogenic Mineral Products such as

Dolomite are Often Generated as Nano-Scale Crystallites – that Impacts other Physical/Chemical Process by Influencing Interfacial Chemistry and Chemical Reaction Rates

• That in Turn Induces Oil Wet Conditions – An oil wet system is resistant to physical

hydraulic sweeping over geologic time frames

Imagine the result

Dolomitization in ROZs – Biogeochemical Effects

• Sulfate Reduction Converts Gypsum to Limestone and Then Dolomite

• The Cell Walls of Active Microbes and Extracellular Polysaccharides Have Points of Negative Charge and Scavenge Magnesium for the Water Environment to meet Metabolic Needs

Imagine the result

Changes in Molar Volume

0

10

20

30

40

50

60

70

80

Gypsum Anhydrite Calcite Dolomite

Normalized Molar Volume cm3/Mole

Imagine the result

Diagenesis in Clastics • With iron oxide cements: • Conversion to ferrous iron

increases porosity and opens pore throats

• It may free fines • It may generate colloidal

ferric iron oxides

Imagine the result

Wettability

Imagine the result

Calcite 9.5

pH Point of Mineral Surface Zero Charge Sulfur

2.3 Fe Oxide 8.5

Quartz 2.0

Clays 2.5

Feldspars 2.0

Dolomite 8.0

Gypsum 10.3

14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

pH

Incr

easi

ng a

cidi

ty

+ + -

- -

+

Red = Positive Charge on Mineral Surface; Blue = Negative Charge

+ +

+

+

+ - -

-

-

-

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Anaerobic Benzene Degradation Detailed Pathway with Examples of Carboxyl Groups on Intermediate's

Microbial Biotechnology Volume 4, Issue 6, pages 710-724, 30 MAR 2011 DOI: 10.1111/j.1751-7915.2011.00260.x http://onlinelibrary.wiley.com/doi/10.1111/j.1751-7915.2011.00260.x/full#f2

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Surface Area vs. Crystal Size

0

500

1000

1500

2000

2500

1.00E-091.00E-081.00E-071.00E-061.00E-051.00E-041.00E-03

Surf

ace

Area

Met

ers p

er G

ram

Crystal Diameter Meters Millimeter Micron Nano Meter

Imagine the result

Nano Scale Effects

• Surface area per unit mass increases • The number of crystal planes, edges, and

defects increase • Those features enhance the potential for

surface attachment • The process creates roughness and nano

to micro channels which increases capillarity forces

Imagine the result

After Brown 2001 Science Vol. 294 pp. 67-70

Water Wet Mineral Surface

Imagine the result

There are Complex Interfacial Forces at Work

• Smaller and lighter molecules at any given temperature have a higher velocity than larger molecules or agglomeration of molecules

• Petroleum biodegradation generates small soluble charged and polar molecules

• Higher physical kinetic velocities contribute to migration to a mineral surface

Imagine the result

Becoming Oil Wet

Carbonate Mineral With Positive Surface

Charge

+ +

+ +

+

+

+

Petroleum

Petroleum

Petroleum

Petroleum

Imagine the result

Becoming Oil Wet Biodegradation & Biogenic

Products

Carbonate Mineral With Positive Surface

Charge

+ +

+ +

+

+

+

Biodegraded Petroleum

Biodegraded Petroleum

Biodegraded Petroleum

Small Soluble Alcohols, Ketones and Carboxylic Acids – Polar and Charged

Imagine the result

Petroleum

Becoming Oil Wet Attachment of Small Soluble Charged and Polar Species – Degradation and Biogenic

Carbonate Mineral With Positive Surface

Charge

+ +

+ +

+

+

+ Biodegraded Petroleum

Biodegraded Petroleum

+ -

Surface Conditioning

Film

Imagine the result

Petroleum

Becoming Oil Wet Co-Adsorption and Agglomeration on Non-

Polar Liquid Hydrocarbon

Carbonate Mineral With Positive Surface

Charge

+ +

+ +

+

+

+ Biodegraded Petroleum

Biodegraded Petroleum

+ -

Imagine the result

( o r g a n i c )

S t a g n a n t f l u i d

M o b i l e f l u i d

S o i l o r r o c k m a t r i x

Carbonate

Wettability - Adhesion and Cohesion

Adhesion Cohesion

Imagine the result

Summary The Role of Microbial Biogeochemistry

– Enhanced porosity driven by biogenic changes in carbonate mineral suites

– Chemical composition of the petroleum • Hydrocarbons are consumed and graded by sulfate

reducing microbes • That process generates hydrogen sulfide that

inhibits microbial activity at concentrations over 100 to 200 mg/L – That prevents total hydrocarbon consumption

– The production of small soluble charged and polar species by biodegradation initiates the oil wet process • Charged/Polar species attach • Non-polar and liquid petroleum then adsorb and

agglomerate

Imagine the result

dvance@arcadis-us.com