2. Mini-frac Analysis
Introduction
1. Why is it important ?
2. Current AER Guidelines
3. AER opinions on testing and analysis
4. Analysis Methodologies
5. Recommendations
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3. 1 - Why is it important ?
• Number of breaches in the caprocks, why?
– Breaking caprocks (stress related)
– Pre-existing faults (stress related)
– Other ?
• Stress state of reservoir dictates maximum operating
pressure (MOP) for thermal injection projects
• Mini-fracturing is only direct way to measure the
minimum stress
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4. Initial Stress State is Complicated
• Vertical stratigraphic variation
– Elastic properties change with depth
– Tectonics
• Areal variation
– Faulting
– Karsting
– Influence of rivers/mining
• Deep cuts cause stress relief in lateral direction
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5. Is there this much
heterogeneity?
Can there be closure
stresses above
overburden gradient?
For well 03-23
Test intervals 2
meters apart in same
formation have wildly
different closure
stresses
5
Typical overburden
stress gradient line
Typical horizontal
stress gradient line
Mini-Frac Comparison
Depth versus Closure Stress
6. Personal Observations + Involvement
• Geomechanical modeling
– QA/QC for stress input into geomechanical models
• Concerns
– Types of mini-frac analysis techniques used
– Reported stresses
– Variation in results may be misinterpretation
• Application of scientific method
– Returned to basic principles and reviewed mini-frac theory
– Peer review of new ideas with team
– Publish ideas
– Open to criticism
– Adapt
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7. 2 - Current AER Guidelines
• Draft Caprock Criteria and Information
Requirements for SAGD in the Shallow Thermal
Area (June 2014)
– MOP = 0.8 * Minimum Closure Stress
• Draft Directive xxx (2013)
– All mini-frac reports + digits to be submitted to AER
– Submit within 90 days of test
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8. 3 - AER opinions on testing and analysis
• AER has no preference for tests
– 3 major types of tests are used in industry
• Open hole MDT pump-in/fall-off
• Cased hole pump-in/fall-off
• Cased hole pump-in/flowback
• Analysis techniques
– No opinion
– Industry must sort it out
• Biggest problem in industry – we have not sorted it out
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9. 4 - Analysis Methodologies
1. Nolte Analysis of Closure (1979)
• G Time
• Holistic Method (2007)
– Basis for commercial software
2. AOSTRA Mini-frac Manual Approach (1992)
• Specialized plots
– Not used outside of Canada
3. Pressure Transient Analysis Method (2011)
• Difficulty with special cases
• IMO - Problem resolved in upcoming SPE 174454
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11. Combination G
Function plot
Tight Oil Test (not in Oilsands)
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During Nolte Flow BHP versus
G Time has constant slope
Nolte Flow is sign of an open fracture
12. pfoc = 8400 kPa
Combination G
Function plot
Tight Oil (not in Oilsands) Test
Everyone should agree on this
closure pick
12
Departure from constant slope is
evidence of closure
14. End of HRTS at DT=0.0058 days
P=1708 kPaa
Gradient = 16.9 kPaa/m
Ken Nolte approved method
Concave Up Concave UpConcave Down
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15. Combination G
Function plot
End HRTS at G= 0.88 or DT=0.0058 days
P = 1708 kPaa
Gradient = 16.9 kPaa/m
by ‘holistic method’
same result as Ken Nolte method
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16. End HRTS at G= 0.88 or DT=0.0058 days
P = 1708 kPaa
Gradient = 16.9 kPaa/m
Combination G
Function plot
Some analysts are picking closure stresses
somewhere within ellipse for HRTS behavior
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18. McMurray Test
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dP/dG slope is never constant
No Nolte Flow
How do you pick closure?
Discussed in SPE 174454
June 2015 Heavy Oil Conference
19. Ambiguous as no Nolte Flow
Many analysts would pick
closure at the red circle
G = 0.95
P = 1600 kPa
Gradient = 13.4 kPa/m
This is unjustified
McMurray Test
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Discussed in SPE 174454
June 2015 Heavy Oil Conference
20. ‘The Practice of Reservoir Engineering’
(1994) Laurie Dake
Some time ago the author was confronted by a
university geologist who declared that of all the
subjects he had ever encountered, reservoir
engineering was the one that stood in greatest need of
an "Academic Audit".
In other words, it's about time that somebody stood
up and made a clear pronouncement about what
works and what does not amongst the myriad of
theoretical papers and books on the subject. 20
21. 5 - Recommendations
• Need for an “Academic Audit”
• Only experts who have not done any analysis in the oilsands can act as
auditors
– Ken Nolte (Schlumberger)
– Christine Ehlig-Economides (U of Houston)
– Mike Smith (NSI)
– Larry Britt (NSI)
• Specific tests are picked for analysis
– Vendors/Consultants should be able to help identify appropriate tests
• Reports and presentations given by local analysts in open meeting
• External expert makes recommendations to AER
• AER establishes acceptable interpretation framework
– Framework needs to be adaptable to new ideas/technology
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