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.

DG

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

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Why high-angle and horizontal formation evaluation?

Geometry effects are more

common in HaHz wells than

vertical wells

Ignoring results in significant

interpretation errors

Correct for geometric effects use

data for quantitative

Petrophysics

Add value to LWD logs