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Formation evaluation in high-angle and
horizontal wellsDavid Maggs
Based on:
Rapid and Practical Characterization of Near wellbore Layer Structure and Properties in High-Angle and Horizontal Wells.
Society of Petrophysicists and Well-Log Analysts, Annual Conference 2015, Long Beach, California
Salehi, M. T., Abadie, J., Asif, S., Ito, K., Maggs, D., Morriss, C., … Griffiths, R.
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Outline
High-angle and horizontal well
formation evaluation challenges
Layer based petrophysics
– Global layer models
– New local layer model and workflow
Examples
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Why high-angle and horizontal formation evaluation?
Add value to LWD logs
Geometric effects make it
difficult to use directly for
quantitative Petrophysics
HaHz data often ignored in
models
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High angle challenge
Measurements :
Respond to multiple layers
Show extended bed boundary effects
Complicates log interpretation
Solution – layer based petrophysics
Global layer model:
Laterally extensive layers
Suited for deep reading resistivity
Manually constructed
Based on Geological model
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The 3DP data interpretation workspace
Logs on the top
Model built below:
Existing models
Boundary
crossings
Dips
Local knowledge
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The 3DP model
Objective:
Simplest model
consistent with the
logs
Layer properties
automatically
populated & manually
adjusted by user
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Model-Compare-Update
Initial model
Used resistivity in middle
of bed
Layer model => Shoulder
affect
Adjust geometry & layer
properties
Final model
Match resistivity &
polarization horns
Sand resistivity doubled, water saturation reduced 40%
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Local layer model
Near-wellbore formation model
Model from borehole images
Semi-automatic construction
Suited for shallow reading logs
Efficient workflow for thin bed analysis
Helps define global layer model
geometry
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Local layer model workflow
25m25m
25m
Measured
Density
Image
Modeled
Density
Image
Density
Modeling
Misfit
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Case Study #1
Global model 3 layers
Resistivity modeled
as an anisotropic
layer
Laminations seen on
image, modeled as
local layers
Global & local models
are consistent &
complimentary
GR and Square
Log
Resistivity
Modeled and
Measured
Density and
Square Log
Measured
Density Image
Modeled
Density Image
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Case study #2
75 degree Wellbore, WBM
GR, propagation & laterolog resistivity, density/neutron
“…. differences between the resistivity logs?”
Logs do not “see” laminations clearly visible on the resistivity image
Can we explain the differences and get the right answer?
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#2 – Workflow
Images define
layers & dip
Local & global
models
Model-Compare-
Update to match
log data
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#2 – Modeled logs
Nice Match between the
modeled and measured logs
Some 3D effects ignored on
image
GR/Density/Neutron also, not
shown here
Even Laterolog resistivity
matches!
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#2 – Layer properties
Logs affected by thin beds
in a high angle well bore
Layer properties have
geometric effects removed
and better reflect true
formation properties
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#2 – Petrophysics
Standard evaluation misses
thin layers and averages the
answers
Layer properties evaluation
reflects layers seen in the
image
Impacts net to gross &
volumes
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New local layer model
Defines the formation model near the wellbore
Based on density image
Fast and practical
Complements the global layer model
Corrects measured logs for geometry effects