chapter 3 interpretation 3.1 interpretation

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