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SUBSURFACE INTERPRETATION

Well Data Interpretation
Reservoir Identification
•Gamma Ray (GR) log analysis
–High GR è shale
–Low GR è sandstone or limestone
•Spontaneous Potential (SP) log analysis
–Monotonous è shale
–Deflection è sandstone or limestone

Correlation
•Using Sequence Stratigraphic model:
•Assumption:
–Deterministic model
–Sedimentary architecture controlled by: Relative change of sea level
–Relative change of sea level controlled by Eustatic and Tectonic
•Eustatic global of sea level in sinusoidal form (Harmonic wave)
•Tectonic movement relatively constant
  è Rising and falling of sea level can be identified in log     record
  è Represent time boundaries
  è Good Correlation marker

Correlation
•Sequence Stratrigraphy Hierarchies
–Sequence
–System Tract
–Para sequence
–Bed set
•One Sequence can be bounded by :
–SB and SB
–MFS and MFS
Schematic dip profile illustrate the key sequence stratigraphic surface-sequence boundaries, and maximum flooding surfaces, and their stratigraphic expression. These surfaces serve to subdivide stratigraphic sections into sequences and systems tracts.
Schematic dip profile illustrate the key sequence stratigraphic surface-sequence boundaries, and maximum flooding surfaces, and their stratigraphic expression. These surfaces serve to subdivide stratigraphic sections into sequences and systems tracts


•Within one sequence theoretically can be divided into three system tracts:
–Lowstand system tract (LST)
–Transgressive system tract (TST)
–Highstand system tract (HST)

One system tract can be divided into several parasequences.
Each parasequence bounded by Flooding Surface (FS).
FS  time boundary good marker for correlation.
One parasequence can contain several beds or several facies.

Petrophysic Analysis
Gross thickness
Net thickness
Net to Gross
Water saturation (Sw)
Pay thickness
Hydrocarbon contacts (OWC, GOC, GWC, etc)

Gross Thickness
Define qualitatively by:
GR log 
SP log
Guided by Flooding Surface 
Measure in TVD
Gross thickness = bottom - top

Net Reservoir Thickness
Guided by Gross thickness 
Applied Vshale Cut Off
Applied porosity Cut Off
Vshale using GR
Vshale = (GR-GRmin)/(GRmax-GRmin)
Note:
GR = GR at cut off
GRmin = Minimum GR reading
GRmax = Maximum GR reading

Net Reservoir Thickness
Vshale using SP
Vshale = (SSP – PSP) / SSP Archie Formula (default)
Swn= (a x Rw) / (Fm x Rt)  
Shaly sand reservoir:
Simandoux
Poupon/Indonesia
Note:
SSP = the deflection from the shale line to clean line
PSP = the deflection from the shale line to the curve reading   at zone of interest
Net to Gross Ratio
NTG = Net thickness / Gross interval

Water Saturation (Sw)

Pay Thickness
Vshale cut off
Porosity cut off
Sw cut off

Hydrocarbon Contact
Based on log analysis
Based on Flat spot
Based on RFT plot
Based on DST

Well and Seismic Integration
Depth Structure Map
Gross Reservoir Map
Iso-porosity Map
Iso-saturation Map

Depth Structure Map
Well reservoir picking 
Seismic to well tie
Seismic horizon picking
Time structure map
Depth structure map

Gross Reservoir Map
Gross thickness from well data
Cross correlation between well thickness and Attribute Map
Generate formula transferring Attribute  Map to Gross Map based on cross plot
Generate Gross Map

Iso-porosity Map
Value from well data
Cross correlation between well porosity and AI seismic map
Generate formula transferring AI Map to Porosity Map based on cross plot
Generate Porosity Map

Iso-saturation Map
Iso-saturation from well data
Cross correlation between well Sw and AI seismic map
Generate formula transferring AI Map to Sw Map based on cross plot
Generate Sw Map

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