Use of Resistivity Logs as a Tool for Estimating Interparticle Porosity - PowerPoint PPT Presentation

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Use of Resistivity Logs as a Tool for Estimating Interparticle Porosity

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Use of Resistivity Logs as a Tool for Estimating Interparticle Porosity Outline of talk A little bit about why How can we do it? A short derivation An example from ... – PowerPoint PPT presentation

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Title: Use of Resistivity Logs as a Tool for Estimating Interparticle Porosity


1
Use of Resistivity Logs as a Tool for Estimating
Interparticle Porosity
2
Outline of talk
  • A little bit about why
  • How can we do it?
  • A short derivation
  • An example from the Clearfork
  • Some caveats
  • Finish it up

3
Setting the stage
  • We can model permeability from interparticle
    porosity and petrophysical class
  • The only tool in current usage to get to
    interparticle porosity is the sonic
  • Sonics are, unfortunately, an uncommon log

4
Setting the stage
  • The resistivity log tends to respond to separate
    vug porosity in much the same fashion as the
    sonic tool
  • It tends to ignore the larger pore bodies we
    refer to as separate vugs

5
How can we do it?
  • We will assume that the interparticle portion of
    the porosity will behave as an Archie type
    rock.
  • This means that we can assume for the
    interparticle porosity that the porosity exponent
    (m) and the saturation exponent (n) are both
    close to 2

6
How can we do it?
  • We will also assume that the ratio water
    saturation provides us with a valid water
    saturation estimation in the interparticle
    porosity.

7
A short derivation
  • Water saturation at some depth in from the
    wellbore, Si, is calculated fromSin
    Frz/Riwhere Si is the water saturation, S, at
    some depth of investigation, i, Ri is the
    associated formation resistivity at that depth, F
    is the formation factor, and rz is the apparent
    water resistivity at that depth of investigation

8
A short derivation
  • Swn Frw / Rt, Sxon Frmf / Rxo
  • (Sw / Sxo)n rw / rmf / Rt / Rxo
  • Sxo Swr
  • (Sw / Swr)n rw / rmf / Rt / Rxo
  • Sw(1 - r)n rw / rmf / Rt / Rxo

Sw rw / rmf / Rt / Rxo 1/((1 r)n)
9
A short derivation
  • Swn Frw / Rt
  • F 1 / fm
  • Swn fm rw / Rt
  • Sw f (Rw / Rt)1/2
  • Sw rw / rmf / Rt / Rxo 1/(2(1 .2))

f (Rmf / Rxo)1/2 (Rt Rmf) / (Rw Rxo)1.25
10
An example from the Clearfork
11
An example from the Clearfork
12
An example from the Clearfork
13
An example from the Clearfork
14
An example from the Clearfork
15
An example from the Clearfork
16
An example from the Clearfork
17
An example from the Clearfork
18
An example from the Clearfork
19
An example from the Clearfork
20
Some pitfalls
  • Technique is sensitive to the ratio of Rmf to Rw
  • Environmental corrections are important
  • Micro-porosity or intra-particle porosity can be
    an issue

21
To finish up
  • We have described a way to enhance the use of
    resistivity logs in characterizing porosity
  • It allows us to not only estimate permeability,
    but allows us to look into water saturation
    variations
  • A good understanding of the rocks is critical to
    making this work
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