unconventional petrophysical analysis in unconventional reservoirs putting the puzzle together in...
TRANSCRIPT
Unconventional Petrophysical Unconventional Petrophysical Analysis in Unconventional Analysis in Unconventional
ReservoirsReservoirsPutting the Puzzle Together in Gas Shales
Lee Utley
“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
“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
Has this happened to you?Has this happened to you?
Somebody just dumped some stuff in your officeLarge stack of logs
Several CDs/DVDs of digital dataCore 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.
General GoalsGeneral Goals
• Areal extent• Thickness• Type of hydrocarbon• Possible production mechanisms• Barriers to economic production
Evaluate the resource
Specific Goals to Achieve Using Specific Goals to Achieve Using Log AnalysisLog Analysis
• Gas Content • Analysis of ‘conventional’ formations• Maturity• Total Organic Content• Porosity• Water saturation• Lithology• Rock Properties• Fracture types
Why is this so hard to do?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
Useful Core DataUseful Core Data
• Geochemical analysis (Ro, TOC, etc…)• Porosity• Water saturation• Gas content (including adsorption isotherm
information)• Mechanical properties
Gas Storage SitesGas 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 can’t be quantified.
Calculation of Gas ContentCalculation of Gas Content
• For sorption, relate TOC to gas content – usually through Langmuir parameters.• Don’t 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.
Why look at ‘conventional’ areasWhy look at ‘conventional’ areas
• Production pathways• ‘Unfavorable’ porosity• Stimulation barriers• Uphole ‘bail-out’ zones
Log Indicators of MaturityLog 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.
Use Old Resistivity Logs TooUse Old Resistivity Logs Too
• Use resistivity inversion modeling to get old ES logs and induction logs up to modern standards – compare apples to apples
1940’s 1980’s Modern
Density – Neutron SeparationDensity – Neutron Separation
Gas Shale Well One Gas Shale Well TwoLower Vitrinite Reflectance Higher Vitrinite Reflectance
Four main methodsFour 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
Standard Porosity TransformStandard 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.
fluidmatrix
matrix
log
Basic Porosity EquationBasic Porosity Equation
fluidmatrix 1log
Rock co
ntributio
n
Fluid contri
bution
Porosity Equation with TOCPorosity Equation with TOC
TOCTOCfluidTOCmatrix VV 1log
Rock co
ntributio
n
Fluid contri
bution
TOC contri
bution
Solved for PorositySolved for Porosity
fluidmatrix
TOC
matrixmatrix TOC
TOC
1log
ccgmto
ccgmto
ccgmto
fluid
TOC
matrix
/0.14.0
/4.13.1
/68.260.2
Two most common methodsTwo most common methods
• Probabilistic methodology• Integrated neural network solution
Use Lithology to Correlate with Use Lithology to Correlate with Rock PropertiesRock Properties
Neural Network of Young’s Modulus in Two Permian Basin wells using a Fort Worth Basin Model
Neural Network Computed Young’s Modulus
Roc
k Pr
oper
ties
Com
pute
d Y
oung
’s M
odul
us
Imaging LogsImaging Logs
• Fracture Size• Direction(s)• Complexity• Open/Closed• Induced fracture direction (stress field)
Core Data AcquiredCore Data Acquired
Conventional and pressure cores – Extensive data suite• Porosity• Water Saturation• TOC• XRD• Canister desorption• Adsorption isotherms• Capillary pressures• CEC
Integrate Core DataIntegrate Core Data
Quartz Plagioclase Calcite Dolomite Apatite Pyrite Total Total Organic Porosity Water Bulk Volume Bulk Volume
Clays Carbon Saturation Water Hydrocarbon
34 1 10 6 0 0 35 6 8 54 4 4
37 4 13 3 1 0 29 5 7 46 3 4
32 2 20 3 1 0 29 5 8 50 4 4
23 2 46 4 1 1 22 1 0 76 0 0
13 1 41 20 0 0 18 3 4 37 1 2
12 2 61 17 1 1 4 1 2 32 1 1
23 2 33 4 0 0 30 3 4 56 2 2
10 1 74 10 0 0 3 0 1 67 1 0
30 0 26 8 0 0 33 1 3 89 2 0
16 1 23 13 0 0 40 2 5 75 3 1
31 3 11 3 1 0 42 4 5 70 3 1
34 2 17 12 1 1 23 4 5 74 4 1
15 1 15 41 1 1 24 1 1 79 1 0
35 5 8 4 1 1 39 5 2 100 2 0
Gas shales can be effectively Gas shales can be effectively analyzedanalyzed
• 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.