Atterberg Limit Tests Indicate Physical Properties in ... · Atterberg Limit Tests Indicate ......

Atterberg Limit Tests Indicate Physical Properties in Caprock:A Low Cost Screening Tool for Caprock Integrity Evaluation

Michelle Uwiera‐Gartner Gartner Works Ltd.Mike R. Carlson Applied Reservoir EnterprisesMing Lui & Peter Cooper Big Guns Energy Services Inc.

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Outline

• Basic objectives» Better characterization» Contain costs

• What are Atterberg Limits?» History» How are they done

• Do they work?• What do they identify?

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Basic objective – Strength characterization

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$$$$$

Screening tool – test where it matters

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$Triaxial test critical area

* Approximately one tenth the cost

Screen with cheap test

Atterberg Limits: Background• HISTORIC:

– Developed early 1900s Swedish soil scientist• Originally ceramic industry• Describes plasticity of clay for bricks • Avoid shrinkage and cracking when fired

– Only 2 parameters needed:» Upper and lower plasticity limits

• TODAY:– Behavior of clay– Classifying soils– Correlate engineering properties

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Transition in Soil Behavior• Measure of critical water

contents in a fine‐grained, soil. – Impacts shear strength

• Shrink Limit (SL)– Water content between the

solid and semi‐solid states.• Liquid Limit (LL)

– Water content between semi‐liquid and plastic state

• Plastic Limit (PL)– Water Content between plastic

and semi‐solid state• Calculated: Plasticity Index (PI)

– Range of water content where a soil behaves plastically.

– PI = LL ‐ PL

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Water Contents where the soil behaviour changes

Core Preparation, Logging, Testing

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Everything you need to know you learned in Kindergarten ….

8(after Practical caprock analysis Carlson et al.)

Just how are Atterberg Limit

tests performed???

Sample Preparation Materials• core• cheese grater• blender• distilled Water• No# 40 sieve (425 μm)

• Modified‐ASTM #D4318

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Laboratory Testing

Liquid Limit

Plastic Limit

10(after Practical caprock analysis Carlson et al.)

Casagrande’s Plasticity ChartSoil Classification

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Comparison to Stress‐Strain Response

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Water content where the soilbehaviour changes

As water content increases, soilchanges from a brittle solid, toplastic solid, to viscous liquid

Correlations to Mohr‐Coulomb

13Practical caprock analysis Carlson et al.

Atterberg Limits: Observed Trends in the Athabasca Oil Sands

• High Smectite content results in higher PI and LL.• Low Smectite content results in lower PI and LL.

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Minerology – Friction Angle

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Summary of XRD AnalysisSAMPLE TYPE WEIGHT Total

ID. OF ANALYSIS % Smec Clay

BULK FRACTION: 83 11 23SAMPLE CLAY FRACTION: 17 69 94

BULK & CLAY 100 21 36BULK FRACTION: 79 7 29

SAMPLE CLAY FRACTION: 21 57 92BULK & CLAY 100 18 43









SAMPLE CLAY FRACTION: 24 46 95






Trends in Athabasca Caprock

• Type and amount of clay affect shear strength.• Smectite clay > ~ 40%, high PI, low φ˚• Smectite clay < ~ 20%, low PI, high φ˚

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< 20% Smectite

> 40% Smectite

Advantages of Atterberg Limit Tests

• Long‐term use in civil engineering

• Fast and low cost $$• Identify weaker caprock• Locate samples for triaxialtesting

• Integrated, site‐specific description

• Regulatory and safety requirement

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AER Requirements

• Document RC‐02 – Caprock Criteria and Information Requirements• Geologic Characterization:

– Lithology– Depth and Structure

• Physical Properties– Permeability– Mechanical Testing

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CODE TITLE

RC‐01 Summary of Conclusions from Reservoir Containment Project

RC‐02 Caprock Criteria and Information Requirements

RC‐03 Development of the Maximum Operating PressureFormula *

RC‐04 Limitations of Geomechanical Models

RC‐05 Monitoring Reservoir Containment in Thermal EOR

Only Part of Caprock Integrity Evaluations

• Caprock core evaluation– Lithologic heterogeneity, continuity– Structure contacts– Unit thickness

• Thin section analysis• XRD• Triaxial testing

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Summary

• Atterberg Limit tests are fast & cost effective for assessing caprock properties:– Long history of use in other engineering fields– Screening method for selecting triaxial sample locations

– Identify potential weaker areas– Insight into possible clay type

• Used with other index tests.• Assist with developing site‐specific, correlations for evaluating delineation wells.

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QUESTIONS ??

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