mk-trmb08 - subsurface mapping
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Further Reading
Jahn, F., et al, 2003, “Hydrocarbon Exploration and Production” - pp 136 – 157
Tearpock, D.J., and R.E. Bischke, 2003, “Applied Subsurface Geological Mapping – With Structural Methods” 2nd Edition
Chapter 8: Structure Maps
Chapter 14: Isochore and Isopach Maps
Data Type for Reservoir Geology
Data pertains to the reservoir rock and its
extent:
Geologic and Seismic Data
Well Log and Well test Data
Core Data
Visualized using Cross Sections
and Maps
A Map is planar projection (bird’s eye view) of a feature
Therefore a map is two dimensional representation of three dimensional object
Contour spacing reflects the slope
Equal spacing – a constant slope
Closer spacing – a steeper slope
Types of Subsurface Maps
Structure Top or Base Formation
Top or Base Pay (Porous Zone)
Unconformity
Fault Surface
Properties Gross Sand Thickness (isochore/isopach)
Net to Gross Ratio
Net HC Thickness
And so on.........
A Few Rules (Remaining Rules Pls Chk the Text Book)
Circles of contours indicate a High
A closed depression should be marked with hachures
Formation Top Vs Porosity Top
Usually formation tops (stratigraphic markers) are recognizable by seismic, therefore geophysicists tend to map on the top of formation
Development geologists should phantom-down the map to the Porosity top
Formation top
Porosity top
Datumed at a stratigraphic
marker
8
Blackshale Coal 240 ms
Base Permian 150 ms
Eakring Village (projected)
Near Top Dinantian
500 ms
Potential reservoir interval
Tw
o W
ay
Tim
e (T
WT
)
in S
eco
nd
s Well tie to seismic
0.1
0.2
0.3
0.4
0.5
1.0
0.0
-0.1
-0.2
Eakring Village (projected)
Base Permian 150 ms
Blackshale Coal 240 ms
Seismic
horizons picked
based on
velocity contrast
Often some
distance from
reservoirs
How to Phantom Down
Formation Top =
Seismic Marker
Reservoir Top
Phantoming (Isopach) Down
Convert seismic time map to depth map on top of Formation
Generate isopach (isochore) map from Formation Top to Reservoir Top
Cross contour the two maps - add values of the crossing contours and post them onto the map
Draw contour lines based on the posted values
Depth Structure On Formation Top
Formation Top
Reservoir Top
Elevation at point X = 1093 m
Isochore Map – Formation Top to Reservoir Top
Formation Top
Reservoir Top
Thickness at point X = 298 m
Predict Reservoir Top at Point X
Repeat this process till sufficient
map coverage
By using cross contouring
technique - one can calculate
Reservoir Top at any given point
Hence – one can generate
Structure Map on Top of
Reservoir with greater
confidence
The technique can easily be
performed using computer
mapping software
This technique may avoid two
horizons crossing each other if
gridding performed
independently
Horizons Crossing on Extrapolation
A Gap at Normal Faults
Downthrown side should be marked
Fault location shifted for next lower sections
Fault
Construction
on Map
Applying Correct Geometry on Map
Net Sand Isochore Map
Special technique required for Net Pay Construction
Porosity Map
Bottom and Edge Water
Bottom Water Edge Water
Pay attention to geometry differences
Bottom Water
Key Components:
• Structure map on top
• Oil Water Contact
Net Pay Map Construction
Very simple task:
• Substract contour values
with OWC number
• Adjust to net values
Edge Water Reservoir
Key Components:
• Structure on top
• Structure on base
• Oil water contact
• Net sand thickness
Key Components:
• Structure on top
• Structure on base
• Oil water contact
• Net sand thickness
Edge Water
Edge Water
Important aspects:
• OWC on top – marks
outer limit of oil - blue line
• OWC on base – marks
inner limit of water –
inside this line:
net sand = net pay – red line
Edge Water - Detail Procedure-1
1. Draw depth structure
map on top reservoir –
mark OWC – blue line 2. Draw depth structure
map on base reservoir
– mark OWC – red line
3. Take net sand isochore
map – draw OWC on
base (red line)
4. Remove contour
outside the circle
5. Draw OWC on top
(blue line)
Edge Water - Detail Procedure-2
Edge Water - Detail Procedure-3
6. Connect contour
lines – start from
thickest part
7. Complete the
contour lines as
necessary
8. Planimeter the map
to calculate net oil
sand volume
Edge Water Reservoir – Oil and Gas
GAS GAS / OIL
CONTACT
Key Components:
• Structure on top
• Structure on base
• Oil water contact
• Gas oil contact
• Net sand thickness
1. Draw depth structure map
on top reservoir – mark
OWC – blue line and GOC
– red line
2. Draw depth structure map
on base reservoir – mark
OWC – green line and
GOC – brown line
Edge Water Reservoir – Oil and Gas:
Detail Procedure-1
Edge Water Reservoir – Oil and Gas:
Detail Procedure-2
3. Take net sand isochore
map – draw GOC on base
4. Remove contour outside
the circle
5. Draw GOC on top
6. Connect contour lines –
start from thickest part
7. Complete the contour lines
as necessary
8. Net gas pay map done
Edge Water Reservoir – Oil and Gas:
Detail Procedure-3
9.Draw:
OWC on top (blue),
OWC on base (green),
GOC on top (red),
GOC on base (brown)
Note:
• area between OWC
on base and GOC on
top – full net sand
thickness
• Area inside GOC on
base – no oil zone
10. A) Overlay Net
Sand Map
Edge Water Reservoir – Oil and Gas:
Detail Procedure-4
10. B) Remove contour
lines outside full net
sand thickness
Edge Water Reservoir – Oil and Gas:
Detail Procedure-5
Edge Water Reservoir – Oil and Gas:
Detail Procedure-6
11. Complete contour
lines as necessary
Final products:
• Net gas pay
• Net oil pay
Calculate Rock Volume Slice (Vb)
Trapezoidal
Pyramidal
Where:
• An = area of one contour
• An+1 = area of the next contour
• h = contour interval
Note: if An/An+1 > 0.5 use Trapezoidal
Calculate Reservoir Volume
• Add all slices from
bottom up
• Never miss the
volume of crestal
point
Initial Hydrocarbon In Place
Symbol Remarks
IHCIP Initial hydrocarbon in place
Resv Volume Reservoir volume
Ф Porosity
(1 – Sw) Hydrocarbon saturation
Formation Volume Factor
Ratio of HC in reservoir vs at surface
Thanks for your kind attention
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