chapter 3 interpretation 3.1 interpretation
TRANSCRIPT
CHAPTER 3
INTERPRETATION
3.1 Interpretation
Depositional environment can be interpreted from many factors such as
sedimentary geometry, lithology, sedimentary structure, paleocurrent and fossils. In
this study, the net to gross (NTG), log shape, log characteristic from wells logs were
used to interpreted the facies type. The NTG maps are very useful for describing the
sedimentary distribution and geometry wherever possible. The facies types are plotted
on the NTG maps to help in interpreting their relationship and extent of the facies.
3.1.1 Net to gross (NTG) map and sedimentary facies interpretation
The NTG values are plotted on the map for each reservoir unit and computer-
contoured. Definite pattern of depositional environment cannot be observed from the
results. To aid in further interpretation, the dominant facies type of each sub-reservoir
unit are plotted on the NTG maps and interpreted. This information is used to
delineate the relationship and extent of each facies type. The result of these exercise
are shown the example in Figure 3.1
There is a trend of the depositional pattern with respect to the facies
development through time in the area and this is described from oldest to youngest,
from Lower Intermediates Seal (LIS) to L4-L3.3, suggest deposition on the delta
31
front. Bird foot shape delta of 1-2 km wide and 2-4 km long are observed. The feeder
fluvial source, some 100-200 m wide is oriented from NNW to SSE (Figures 3.2 and
3.3).
During the L3.2 - L2.3, the area is covered by fluvial channels and crevasses
as regression took place. The channels are mainly oriented NNW-SSE. They are 100-
300 m wide. The crevasses are less extensive, some 500 m - 1 km wide and long
(Figures 3.4, 3.5, 3.6 and 3.7).
By L2.2 to L2 time, bird foot deltas of similar dimension as seen previously
appeared in the area, suggesting a transgressive phase. However, the channel
directions changed from NNE-SSW in the older sequence to NNW-SSE in the
younger sequence (Figures 3.8, 3.9 and 3.10).
During the L1.2 to L1 time, isolated bars populated in the area. They range in
size from 1-2 km long and 100 m -1 km wide with the long axis oriented in E-W
direction. However, in L1, the bars seem to be amalgamated into a single body form,
3.5 km to 4 km long and 1.5 km to 2 km wide (Figures 3.11, 3.12 and 3.13).
Generally, this period culminated in a major drowning of the area that caused
the deposition of Upper Intermediate Seal (UIS).
A regression followed the UIS during the K4.3 to K3.3. This was manifested
in the development of bars of similar size and orientation to those seen in L1.2-L1
(Figures 3.14, 3.15, 3.16, 3.17 and 3.18).
Further regression continued into K3.2-K3.1, exposed the presence of bird foot
deltas of similar dimensions as in L. This time the fluvial channel was coming in from
NNW to SSE (Figures 3.19 and 3.20).
32
In K3-K2.3 times, the area was subjected to transgression as bars were
developed. The bars were of similar dimension and orientation to those seen in L
(Figures 3.21, 3.22 and 3.23).
During K2.2 –K1.1 period, the area experienced a regression as bird foot delta
emerged. The fluvial source flowed in NNW-SSE to N-S directions. The extent of
delta trends to diminish as it gets younger suggesting a transgressive phase (Figures
3.24, 3.25, 3.26, 3.27 and 3.28).
By K1 time, transgression dominated the area as observed by small isolated
bars which measured 100-200 m long and 100-200 m. wide. This phase passed in to
the next major flooding surface which will cause deposition of Main seal (MS)
(Figure 3.29).
It proposes that, K horizons and L horizons in Lan Krabu Formation in this
studies area, experienced regression and transgression in a single cycle twice: First
Cycle- Lower Intermediate Seal (LIS) to Upper Intermediate Seal (UIS) and Second
Cycle- Upper Intermediate Seal (UIS) to Main Seal (MS). Accordingly, in the First
Cycle, the environment changed from Open Lacutrine (LIS) Delta Fluvial
Delta Open Lacustrine (UIS) and in the Second Cycle from Open Lacustrine
(UIS) Delta Lacustrine (MS) (table 3.1). This study conforms to those of Gerard
et al. (1997).
33
Figure 3.1 Result of the interpretation map example in horizon L2.
L2 Facies Map (with NTG values)
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
N
34
Figure 3.2 Facies map with NTG value of sub reservoir horizon L4.
L4 Facies Map (with NTG values)
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
N
35
Figure 3.3 Facies map with NTG value of sub reservoir horizon L3.3.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
L3.3 Facies Map (with NTG values)
N
36
Figure 3.4 Facies map with NTG value of sub reservoir horizon L3.2.
L3.2 Facies Map (with NTG values)
Channel sand (finning upward)
Crevasses (coarsening upward)
Shale
N
37
Figure 3.5 Facies map with NTG value of sub reservoir horizon L3.1.
Channel sand (finning upward)
Crevasses (coarsening upward)
Shale
L3.1 Facies Map (with NTG values)
N
38
Figure 3.6 Facies map with NTG value of sub reservoir horizon L3.
Channel sand (finning upward)
Crevasses (coarsening upward)
Shale
L3 Facies Map (with NTG values)
N
39
Figure 3.7 Facies map with NTG value of sub reservoir horizon L2.3.
Channel sand (finning upward)
Crevasses (coarsening upward)
Shale
L2.3 Facies Map (with NTG values)
N
40
Figure 3.8 Facies map with NTG value of sub reservoir horizon L2.2.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
L2.2 Facies Map (with NTG values)
N
41
Figure 3.9 Facies map with NTG value of sub reservoir horizon L2.1.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
L2.1 Facies Map (with NTG values)
N
42
Figure 3.10 Facies map with NTG value of sub reservoir horizon L2.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
L2 Facies Map (with NTG values)
N
43
Figure 3.11 Facies map with NTG value of sub reservoir horizon L1.2.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
L1.2 Facies Map (with NTG values)
N
44
Figure 3.12 Facies map with NTG value of sub reservoir horizon L1.1.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
L1.1 Facies Map (with NTG values)
N
45
Figure 3.13 Facies map with NTG value of sub reservoir horizon L1.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
L1 Facies Map (with NTG values)
N
46
Figure 3.14 Facies map with NTG value of sub reservoir horizon K4.3.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
K4.3 Facies Map (with NTG values)
N
47
Figure 3.15 Facies map with NTG value of sub reservoir horizon K4.2.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
K4.2 Facies Map (with NTG values)
N
48
Figure 3.16 Facies map with NTG value of sub reservoir horizon K4.1.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
K4.1 Facies Map (with NTG values)
N
49
Figure 3.17 Facies map with NTG value of sub reservoir horizon K4.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
K4 Facies Map (with NTG values)
N
50
Figure 3.18 Facies map with NTG value of sub reservoir horizon K3.3.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
K3.3 Facies Map (with NTG values)
N
51
Figure 3.19 Facies map with NTG value of sub reservoir horizon K3.2.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
K3.2 Facies Map (with NTG values)
N
52
Figure 3.20 Facies map with NTG value of sub reservoir horizon K3.1.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
K3.1 Facies Map (with NTG values)
N
53
Figure 3.21 Facies map with NTG value of sub reservoir horizon K3.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
K3 Facies Map (with NTG values)
N
54
Figure 3.22 Facies map with NTG value of sub reservoir horizon K2.4.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
K2.4 Facies Map (with NTG values)
N
55
Figure 3.23 Facies map with NTG value of sub reservoir horizon K2.3.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
K2.3 Facies Map (with NTG values)
N
56
Figure 3.24 Facies map with NTG value of sub reservoir horizon K2.2.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
K2.2 Facies Map (with NTG values)
N
57
Figure 3.25 Facies map with NTG value of sub reservoir horizon K2.1.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
K2.1 Facies Map (with NTG values)
N
58
Figure 3.26 Facies map with NTG value of sub reservoir horizon K2.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
K2 Facies Map (with NTG values)
N
59
Figure 3.27 Facies map with NTG value of sub reservoir horizon K1.2.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
K1.2 Facies Map (with NTG values)
N
60
Figure 3.28 Facies map with NTG value of sub reservoir horizon K1.1.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
K1.1 Facies Map (with NTG values)
N
61
Figure 3.29 Facies map with NTG value of sub reservoir horizon K1.
Channel sand (finning upward)
Bar sand (coarsening upward)
Shale
K1 Facies Map (with NTG values)
N
62
Reservoir Sub reservoir Depositional Environment
K1 Delta-Front K1.1 Bird-Foot Delta, Mouth bar K1 K1.2 Bird-Foot Delta, Mouth bar K2 Bird-Foot Delta, Mouth bar
K2.1 Bird-Foot Delta, Mouth bar K2.2 Bird-Foot Delta, Mouth bar K2.3 Delta-Front
K2
K2.4 Delta-Front K3 Delta-Front
K3.1 Bird-Foot Delta, Mouth bar K3.2 Bird-Foot Delta, Mouth bar
K3
K3.3 Delta-Front K4 Delta-Front
K4.1 Delta-Front K4.2 Delta-Front
K4
K4.3 Delta-Front UIS UIS Lacustrine
L1 Delta-Front L1.1 Delta-Front L1 L1.2 Delta-Front L2 Bird-Foot Delta, Mouth bar
L2.1 Bird-Foot Delta, Mouth bar L2.2 Bird-Foot Delta, Mouth bar
L2
L2.3 Fluvial Channel, Floodplain L3 Fluvial Channel, Floodplain
L3.1 Fluvial Channel, Floodplain L3.2 Fluvial Channel, Floodplain
L3
L3.3 Bird-Foot Delta, Mouth bar L4 Bird-Foot Delta, Mouth bar L4
L4.1 Bird-Foot Delta, Mouth bar LIS LIS Lacustrine
Table 3.1 Depositional environment of sub reservoir horizon.
2nd CYCLE
1st CYCLE