petrophysics across the petroleum industry from a core to...
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Petrophysics Across the Petroleum Industry from a Core to a CEO
Australian Oil and Gas Exhibition and Conference23 February 2017Andrew Buffin
What is Petrophysics ?
• Google “What is Petrophysics ?” about 256,000 results• petrophysics• pɛtrə(ʊ)ˈfɪzɪks/• noun• The branch of geology concerned with the
physical properties and behaviour of rocks.
• Wikipedia: Petrophysics from the Greek
πέτρα (petra) ‘rock’ φύσις (physis) ‘nature’
• The study of physical and chemical rock properties and their interactions with fluids
• The description of oil and/or gas distributions and production flow capacity of reservoirs, from interpretations of pore systems and fluid interactions using all available downhole data.
A Brief History of Petrophysics
Shell (Interpreted Log Data – Petrophysics)• Archie, G.E. (1942). "The electrical resistivity log as an aid in
determining some reservoir characteristics". Petroleum Transactions of AIME. 146: 54–62.
• An empirical quantitative relationship between porosity, electrical conductivity, and brine saturation of rocks.
• Laid the foundation for modern well log interpretation• Pickett Plot – A graphical representation of Archie Equation
• MH Waxman- LJM Smits (1968). “Electrical Conductivities in Oil-Bearing Shaly Sands” SPE Journal
• An equation that relates the electrical conductivity of a water-saturated shaly sand
Service companies (Acquired Log Data)• Schlumberger founded in 1926 by brothers Conrad and
Marcel Schlumberger and recorded the first-ever electrical resistivity well log in 1927
• Halliburton, Baker Hughes, Weatherford• Typical logging combo 1936/1950s: SP-short normal-long
normal-lateral log resistivity.• 1950s/60s: GR/Neutron, Electric Log, Lateralog, Microlog• 1970s/80s: GR/BHC Sonic/Dual Laterologs/Micro-laterologs
& GR/Neutron-density, Fluid sampling, Digital data recording to tape, Data transmission started
• 1990-Today: LWD as part or whole substitute for wire-line, GR/Density-Neutron/resistivity) single run, Modular formation testers & Down-hole fluid typing, Additional logs NMR, Array sonic etc., Data transmission commonplace
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The Petrophysicists Contribution
• More of the parameters used in the calculation of STOIIP are provided by Petrophysics than any other discipline!
Where, STOIIP = Stock tank oil initially in placeGRV = Gross rock volumeNet = Net ReservoirGross = Gross ReservoirØ = PorositySw = Water SaturationB0 = Formation Volume Factor
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Geophysicist
Geologist
Reservoir Engineer
Petrophysicist
The Basic Role of Petrophysics
• Permeability derived empirically using relationships of log data with core permeability.
• Environment of Deposition
• Lithology• Volume of Shale• Depth and depth of formations• Porosity• Net Sand / Net Pay• Fluid phase, gas, oil, water• Fluid saturations Sw, So, Sg• Moveable Hydrocarbons• Subsurface Pressures• Temperature• Velocity/Time• Seismic responses• Correlation with other wells
Petrophysics – The Tools of the Trade
• Where am I in the Exploitation Phase?• What’s the reservoir? Lithology, High
Temperature High Pressure (HTHP), geological depositional environment
• Wireline Logs (Open Hole / Cased Hole)• Logging While Drilling (LWD) Logs• Core data and / or Percussion and Cored
Sidewall Samples• Downhole Pressure Measurements and
Fluid Samples • Drilling Cuttings• Hydrocarbon Shows (Gas & Florescence)• Rate of Penetration• Drilling Data
Tools include:Gamma Ray / Spectral Gamma Ray
Spontaneous PotentialTemperature
CalliperResistivity
Density-NeutronSonic
Nuclear Magnetic ResonanceGeochemical
DielectricImage (Resistivity / Sonic)
Carbon – OxygenProduction Logging Tools (Spinners)
The Thin Bed Problem and Solution
• Heterogeneity is common in the rock column
• In rock beds less than 2 feet thick, log resolution is impacted by being strongly influenced by adjacent beds.
• Thinly laminated sand-shale sequences can have clean sands, which are not resolved
• Over thin–bedded and shale intervals, horizontal resistivity is heavily biased toward low–resistivity shale and is less sensitive to the hydrocarbon-bearing sandstone resistivity
• Supressed resistivity data and ‘high’ shale volume result in ‘missed’ hydrocarbons
• An accurate evaluation of low-resistivity pay in thinly bedded or laminated reservoirs, requires an additional vertical resistivity measurement
• This provides much better sensitivity to the presence of hydrocarbons.
• The resistivity is measured in three dimensions and calculates both vertical and horizontal resistivity (Rv and Rh, respectively) from direct induction
• This leads to reliable identification and accurate petrophysical evaluation of low-resistivity pay by determining the Rv, Rh sand fraction and porosity
GR Res
GR Rh Rv
The Shale Problem and Solution
• The negatively charged clay surface provides an additional conductive path reduces the resistivity of the formation.
• If this effect is not taken into account this has the effect of increasing the calculated water saturation above it’s real value.
• Shaly sand interpretation corrects for this effect to calculate Sw.
• Laminated Sand with Shale Reduces Net volume
• Sand with Structural Shale Interclasts Clay primarily in structural (load supporting) positions in rock framework
• Dispersed Clay primarily occupies sand pore space and destroys porosity
The Complex Lithology Problem and Solution
Probabilistic petrophysics:• Run in complex reservoirs with a variable and mixed mineralogy • Used to solve for multiple clay minerals within the reservoir• To ‘constrain’ the result to a specific outcome, this may be determined from
petrology studies, core analysis, XRD etc.• Solves for volumetric fractions and defines bulk mineralogy, grain matrix density,
porosity and fluid saturations• There is not one unique solution
Pyritic Sand:• High PEF• High Density• High Grain Density• Suppressed Resistivity
Results in:• If D-N log used a high Vsh• Low porosity• High Water Saturation• Potentially “Missed” pay
Unconventional & Tight Gas Petrophysics
• A typical logging programme for shale gas and / or tight gas might include 1• Basic logs provide input into the resource calculations 1• NMR provides data on porosity and fluid typing 1• Spectral Gamma Ray and geochemical logging tool are used to aid source rock typing 2• TOC from the Geochemical Log data 2• Rock typing can be determined from cluster analysis of the log data 2• Mineralogy used to correlate rock typing 2• Acoustic, density and image petrophysical data are used as input into the mechanical
properties and hydraulic fracture design 3• A Fracture Index is calculated as a function of the Young's modulus and Poisson's Ratio –
calibrated to core 3• Fracture propagator, fracture attenuator and barriers are determined 3
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3
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Where (do) the Petrophysicists sit (?)
Geologist• Static model input• Porosity &
Permeability• Saturation Height• Net Sand & Pay• Shale volume• Fluid contacts
Commercial (Reserves)• Porosity• Water Saturation• Net Pay
Geophysics• Rock Physics• Gassmann Substitution
Reservoir Engineer• Dynamic model input• Relative Permeability• Saturation Height
Drilling• Pore Pressure• Bit Selection• Lithology
Geomechanics• Core Analysis• Sonic / Density• Rock Strength
Production Technologists• Porosity &
Permeability • Fluid Analysis• Test depths• Perforation Depths Petrophysicist
Service Providers• Data, data and • More Data
Petrophysics from a Core to a CEO
A Core
An Ex-CEO
Petrophysics – State of the Art
The highest level of general development, as of a device, technique, or scientific field achieved at a particular time
• Petrophysical data is used across all the subsurface disciplines – how it’s used is important.
• Are you answering the right questions?• Design your evaluation programme to answer the subsurface
challenges• Data QC & QA with appropriate data editing and corrections• Petrophysical data acquired to identify ‘hidden reserves’ or
‘missed pay’• Petrophysical techniques and tools developed with demand
from the industry
Petrophysics – The Future
• Artificial Intelligence?
“AI allows a computer to make all the mistakes that humans make –only faster”
Attributed to E. R. (Ross) Crain, a retired Consulting Petrophysicist taken from his web site: Crain's Petrophysical Handbook
• Technology changes in the next few years• Down hole reservoir
engineering laboratory • Down hole core laboratory• Nano-technology• Robotics on fully automated
oil and gas fields• Direct measurement of
permeability• 4 D real time-reservoir
monitoring• Data integration and
interpretation
