Unconventional Petrophysical Analysis in Unconventional Reservoirs

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Unconventional Petrophysical Analysis in
Unconventional Reservoirs

• Putting the Puzzle Together in Gas Shales

Lee Utley
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Intuitively, it is my belief that this magnitude
of money could be better spent on other projects.
Executive with Mitchell Energy in his
recommendation for attempting the first
completion in the Barnett Shale discovery well
(Slay 1) - 1982
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Why are we spending all this money to find out
how much gas is in the Barnett? If we really
want to know what will happen in Johnson County,
we just need to drill some damn wells!
Engineering executive with Mitchell Energy upon
finding out the magnitude of our planned spending
on coring and analysis to reevaluate the gas
content of the Barnett - 1999
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Introduction
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Has this happened to you?

• Somebody just dumped some stuff in your office
• Large stack of logs
• Several CDs/DVDs of digital data
• Core reports
• Several maps and cross-sections
• You are told that your company wants to get into
  this Barnett Shale play everyone is talking about
  so you need to figure this out.

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Problems
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General Goals

• Areal extent
• Thickness
• Type of hydrocarbon
• Possible production mechanisms
• Barriers to economic production

Evaluate the resource
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Specific Goals to Achieve Using Log Analysis

• Gas Content
• Analysis of conventional formations
• Maturity
• Total Organic Content
• Porosity
• Water saturation
• Lithology
• Rock Properties
• Fracture types

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Why is this so hard to do?

• Old logs with limited information
• Little or no core data
• Complex lithologies cause problems with typical
  methods
• TOC calculation is difficult at best
• Porosity determination is complicated by presence
  of TOC

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Useful Core Data

• Geochemical analysis (Ro, TOC, etc)
• Porosity
• Water saturation
• Gas content (including adsorption isotherm
  information)
• Mechanical properties

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Gas Content
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Gas Storage Sites

• Sorption TOC
• Pore space
• Open natural fractures

Most gas is stored in the pore space and the TOC.
Fracture storage is usually minimal and probably
cant be quantified.
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Calculation of Gas Content

• For sorption, relate TOC to gas content usually
  through Langmuir parameters.
• Dont forget about non-methane adsorption
• For pore space, use conventional gas-in-place
  equations.
• TOC and porosity are two of the biggest keys in
  looking at gas shales.

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Conventional Analysis
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Why look at conventional areas

• Production pathways
• Unfavorable porosity
• Stimulation barriers
• Uphole bail-out zones

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Maturity
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Log Indicators of Maturity

• Resistivity
• Density Neutron Separation

Use averages of these values in very well defined
geologically correlative areas to compare to core
vitrinite reflectance data.
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Use resistivity as a predictor
(OGJ Morel 1999)
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Use Old Resistivity Logs Too

• Use resistivity inversion modeling to get old ES
  logs and induction logs up to modern standards
  compare apples to apples

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Density Neutron Separation
Gas Shale Well Two
Gas Shale Well One
Higher Vitrinite Reflectance
Lower Vitrinite Reflectance
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TOC
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Four main methods

• Use average TOC from published accounts and apply
  it to every well
• Density log regression
• Delta log R
• Passey, et al AAPG 1990
• Neural Networks

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Porosity
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Standard Porosity Transform

• Core matrix numbers exclude organic material.
• Normal log presentations show very high apparent
  porosities. These porosities are closer to the
  volume of pore space and organic material
  combined.

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Basic Porosity Equation
Rock contribution
Fluid contribution
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Porosity Equation with TOC
Rock contribution
Fluid contribution
TOC contribution
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Solved for Porosity
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Water Saturation
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What are the correct parameters?
R
?
a

w
S
n
w
f
m
R
t
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Pickett Plot
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Calculate Water Saturation
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Lithology
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Two most common methods

• Probabilistic methodology
• Integrated neural network solution

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Neural Network Solution
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Rock Properties
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Standard Rock Mechanic Equations
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Use Lithology to Correlate with Rock Properties
Neural Network of Youngs Modulus in Two Permian
Basin wells using a Fort Worth Basin Model
Rock Properties Computed Youngs Modulus
Neural Network Computed Youngs Modulus
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Fractures
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Imaging Logs

• Fracture Size
• Direction(s)
• Complexity
• Open/Closed
• Induced fracture direction (stress field)

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Barnett Shale Case Study
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Core Data Acquired

• Conventional and pressure cores Extensive data
  suite
• Porosity
• Water Saturation
• TOC
• XRD
• Canister desorption
• Adsorption isotherms
• Capillary pressures
• CEC

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Integrate Core Data
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Train a Volumetric Neural Network
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Apply integrated solution to all wells
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Fort Worth Model Applied to Permian Basin Well
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Comparison
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Conclusions
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Gas shales can be effectively analyzed

• Maturity, TOC, and porosity are some of the keys
  to gas shale analysis and can be determined from
  logs.
• Even without extensive core data, gas shales can
  still be analyzed, at least in a relative sense.
  
• Other gas shales can be evaluated from log data
  and core data using these techniques. An
  integrated study is required for full evaluation.

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Unconventional Petrophysical Analysis in
Unconventional Reservoirs

• Putting the Puzzle Together in Gas Shales

Lee Utley