Figure 1. Location map of Blocks A-1 and A-3, offshore western Myanmar (Green color represents the original block boundary before relinquishment)

SEAPEX Exploration Conference 2007

Orchard Hotel, Singapore

24th 26th April 2007

A Success of the New Play Concept Offshore Northwestern Myanmar:

Pliocene Deepmarine Turbidites of the Eastern Bengal Fan

Su-Yeong Yang, Michelle Kim Daewoo International Corporation

INTRODUCTION

Daewoo International Corporation acquired

Block A-1 and Block A-3 in 2000 and 2004

respectively offshore northwestern

Myanmar (offshore Rakhine) in the Bay of

Bengal in the Indian Ocean (Figure 1).

There had been exploration activities in this

region in 1970s by several international oil companies, resulting in only minor

hydrocarbon shows in poor reservoirs. Since

then, the region had been barren for more

than twenty years until Daewoo started

exploration in Block A-1 in 2000. A new

concept of deepmarine turbidites play was

introduced by Daewoo and resulted in three

gas discoveries in this area, Shwe and Shwe

Phyu in Block A-1 and Mya in Block A-3.

REGIONCAL GEOLOGY

The offshore Rakhine is located in the

eastern part of the Bengal basin surrounded

by the Indian craton to the west, the

Shillong Plateau to the north, and the Indo-

Burman ranges to the east, but opens to the south, extending into the Bay of Bengal

containing the Bengal deep-sea fan.

The structural architecture of the offshore Rakhine has been controlled by oblique subduction

of the Indian plate beneath the Burman plate (Gani and Alam, 1999). As the Indian plate

subducts beneath the Burman plate, the NW-SE or N-S trending Chittagong-Tripura Fold Belt

(CTFB) and the westward-migrating Neogene accretionary prism complex are developed in

the east of offshore Rakhine (Figure 2) (Curray, 1991). Highly faulted and folded structure,

sometimes related with mud diapirs, are developed nearshore Rakhine. The intensity of

tectonic deformation is relatively severe in the east and gradually diminishes to the west

developing two anticlinal structures in Blocks A-1 and A-3, Ngwe and Shwe in the NNW-SSE

direction. Strike-slip faults with flower structures are observed in the Ngwe anticline and in

the south of the Shwe anticline.

PREVIOUS EXPLORATION

The previous exploration activities were concentrated in structural highs in the shallow-water

areas. A total of seven wells were drilled offshore western Myanmar by international oil

companies in 1970s. The main reservoir objectives were the Miocene and Oligocene sediments transported from inland Myanmar and deposited near the coast of western

Myanmar. The drilling results revealed that these sediments are shale-rich deposits with minor

oil or gas shows. It was concluded that the lack of reservoir was the main reason for failure in

the previous exploration, and there were no exploration activities for more than twenty years

offshore western Myanmar since then.

DEVELOPMENT OF A NEW PLAY CONCEPT

2D Seismic Interpretation

After Daewoo had acquired Block A-1 in 2000, the existing 1,800km of 2D seismic data

acquired in 1970s were reprocessed. The seismic interpretation of the 2D reprocessed data during the Study Period indicated the existence of deepmarine turbidites in the submarine fan

system transported from the northwest to the southeast. New 2D seismic data of 3,800 L-km

Figure 2. Tectonic setting, offshore northwest Myanmar (D.A. et. al., 1988)

were acquired subsequently after entering into the Exploration Period in 2001. The seismic

sequence stratigraphic analysis using the new 2D seismic data suggested that there are two

types of deposition in the late Pliocene, one from the northwest as part of the Bengal fan

(lower G-series sediments) and the other from the northeast inland Myanmar (the D-series

and upper G-series sediments) (Figure 3).

Figure 3. Two types of sediment source in the late Pliocene deposited in Blocks A-1 and A-3

The lower G-series sediments show an elongated mounded shape trending NW-SE direction

(Figure 4a). These sediments are characterized by high-amplitude continuous reflections

which onlap onto a late Pliocene sequence boundary, PLSB2, near the base of the slope and

spread out widely basinward to the southeast (Figure 4b). The seismic facies and the external

form of this deposition represent a basin-floor-fan system containing sand-rich deepmarine

turbidite deposits transported from the northwest. The upper G-series sediments show a

prograding wedge shape in the eastern area of Block A-1, of which sediments were

transported from northeast inland Myanmar and deposited in the slope. This prograding

wedge thins out basinward to the west or southwest.

Figure 4a. Isopach of the G- series sediments showing two types of sedimentation: a submarine fan from the northwest lower G-series) and a prograding wedge from the northeast (upper G-series)

Figure 4b. Seismic section showing the PLSB2 sequence boundary and the lower G-series submarine fan (basin floor fan)

The D-series sediments which overlie the G-series sediments were all transported from the

northeast inland Myanmar and deposited in the slope as prograding wedges (Figure 5a and

Figure 5b). The prograding wedges of the D-series and upper G-series sediments show

generally low-amplitude reflections. Some high-amplitude reflections at the D- and upper G-

series slope sediments were interpreted as shingled turbidites with isolated sand bodies.

Three prospects were generated based on the 2D seismic interpretation in Block A-1: Shwe,

Shwe Phyu and Ngwe which mean Gold, Platinum and Silver in Myanmar respectively. The

lower G-series sediments showing high-amplitude continuous reflections in stratigraphic traps

were the primary exploration objectives, whereas the overlying upper G-series and D-series

Figure 5a. Isopach of the D-series sediments showing prograding wedges from the northeast

Figure 6a. Seismic section correlated with the Shwe-1 and -1A log interpretation of total porosity (left) and gas saturation (right), showing the D1 and D2 formations and the G3.2 and G5.2 gas reservoirs.

sediments showing high-amplitude reflections in structural traps were the secondary

exploration objectives.

Figure 5b. Seismic section flattened to the PLSB2 sequence boundary to show the D-series lowstand prograding wedge

Drilling Result of the First Exploratory Well, Shwe-1/1A

The first exploratory well, Shwe-1, was drilled vertically to penetrate the two objectives in the

D-series sediments (D1 and D2) and an objective in the upper G-series sediments (G1)

located at the structural crest. And then the sidetrack well, Shwe-1A, was drilled to test the

offset G5 objective which could not be reached by the vertical well. Significant gas kicks

were observed in the mud-log data at the D-series objectives where reflections show high

amplitude. However, there are no sand reservoirs in this interval. The high amplitude at the D-

series objectives is due to the minor gas trapped in the shale or siltstone at the crest of the

structural high (Figure 6a).

After the disappointing result with

the poor reservoirs at the first three

objectives from the vertical well,

the sidetrack well, Shwe-1A,

encountered gas-charged sand

reservoirs at the G3.2 and G5

formations (Figure 6a). A massive

turbidite sand unit was discovered

at the high-amplitude continuous

reflection of the G5 objective

which pinchouts toward the

structural high to the east (Figure

6b). The G5 formation was

subdivided later into the G5.1 and

G5.2 formations by detailed 3D

seismic interpretation and log

interpretation. The exploratory

Figure 6b. Perspective view of Amplitude at Top G5 based on 2D seismic interpretation (subdivided into G5.1 and G5.2 later). The Shwe-1A well penetrated the eastern edge of the G5 which pinchouts toward the structural high to the east.

well, Shwe-1A, penetrated the G5.1 sand and the following appraisal wells penetrated the

G5.2 sand. The log interpretation of the Shwe-1A shows that the G5.1 sand has the average

porosity of 24%, the average water saturation of 28% and the net thickness of 20m. A series

of relatively thin sand units of the G3.2 formation, which was subdivided from the G3

formation, also contains gas although there is no high amplitude observed at the top of the

G.3.2 formation and this formation was not an objective. The low amplitude at the gas-bearing

G3.2 formation is caused by tuning effect of thin sand units.

3D Seismic Interpretation

After the Shwe-1/1A was drilled, the 3D seismic data of 1,200 square kilometers were

acquired immediately over the Shwe discovery and the Shwe Phyu and Ngwe prospects to

locate the appraisal wells and additional exploratory wells. The 3D seismic interpretation

confirmed that the lower G-series sediments are a submarine fan system transported from the

northwest. The horizon slice of the 3D seismic data shows a feeder channel coming from the

northwest to develop a submarine fan of the G5.2 reservoir (Figure 7).

Figure 7. Seismic amplitude at Top G5.2 showing the sediments transported from the northwest through a feeder channel and deposited as a fan lobe

Figure 8. Gas discoveries in Blocks A-1 and A-3

Success of the New Play Concept

The drilling result of the exploratory well and the 3D seismic data proved the new play

concept of deepmarine turbidites deposited in the submarine fan system offshore northwestern

Myanmar as part of the eastern Bengal fan.

After the discovery of Shwe, Daewoo have made two more additional discoveries in Blocks

A-1 and A-3 by applying this concept of the deepmarine turbidite play: the Shwe Phyu

discovery in Block A-1 in 2005 and the Mya (which means Emerald in Myanmar) discovery

in Block A-3 in 2006 (Figure 8).

The Daewoos discoveries have awaked interest of international oil companies in exploration in this region. As a result, all of the blocks offshore western Myanmar and some deepwater

blocks in the north have been already awarded to several international oil companies and joint

ventures in last few years.

PETROLUEM SYSTEM

Reservoirs

The lower G-series sediments (G5.1, G5.2 and G6.1) of late Pliocene time, transported from

the northwest and deposited in the submarine fan systems as part of the eastern Bengal fan,

provide excellent reservoirs offshore northwestern Myanmar. The G6.1 gas sand of the Mya

discovery shows continuous reflections which extend to the southeast with an elongated shape.

The seismic facies and the Mya-1 well data indicate that the G6.1 sand was deposited in the

channelized fan system. The overlying G5.2 sand in the Shwe discovery is the most

prominent gas reservoirs in this region. A widespread fan lobe, represented by high-amplitude

continuous reflections extending a few tens of kilometers, is developed by a long feeder

channel passing through Block A-1 from the northwest. The G5.2 fan lobe contains massive

turbidite sands in the proximal area, and the turbidites become less sandy in the distal part of

the fan lobe (Figure 9). The G5.1 sand was deposited in a splay lobe and is also an excellent

reservoir in the Shwe discovery.

The upper G-series sediments (G3.2 and G2.2) are mainly channel-levee deposits transported

both from the northwest as part of the Bengal fan and from the northeast inland Myanmar.

The G3.2 sands in the Shwe discovery and in the western part of the Shwe Phyu discovery are

channel-levee deposits or splay lobes trending in the NW-SE direction. Thick, porous sand

units of the G3.2 formation are developed in or near the channels or at the splay lobe, whereas

thin strings of levee sand are deposited in the overbank/levee environment in the Shwe

discovery (Figure 10). The G3.2 formation in the eastern part of the Shwe Phyu discovery is

submarine fan deposits transported from the northeast (Figure 11). The size of the fan lobe

from the northeast is relatively small and reservoir quality of the fan-lobe deposits is not as

good as the one transported from the northwest, indicating that the depositional energy was

relatively low or the sediment source was less sandy. The overlying G2.2 formation in the

Shwe Phyu discovery is channel-levee deposits transported both from northeast and northwest.

Figure 9. Well to seismic correlation in the Shwe discovery: (a) Amplitude map of Top G5.2, (b) Seismic section correlated with log interpretation of total porosity (left) and gas saturation (right)

Figure 10. Well to seismic correlation in the Shwe discovery: (a) Amplitude map of Top G3.2, (b) Seismic section correlated with log interpretation of total porosity (left) and gas saturation (right)

Figure 11. Well to seismic correlation in the Shwe Phyu discovery: (a) Amplitude map of Top G3.2, (b) Seismic section correlated with log interpretation of total porosity (left) and gas saturation (right)

The D-series sediments transported from the northeast and deposited in the slope as

prograding wedges above the G-series sediments do not show good reservoirs in this region.

However, the D-series sediments or overlying sediments may provide good reservoirs when

they are deposited in the basin as submarine fan deposits.

Source

Although no wells have penetrated any source rock offshore Rakhine and source rock is still

unknown, the accumulation of gas in this region already has proved the existence of source

rock. A thick accumulation of the Miocene and Pliocene deepmarine shale in the Bengal fan

which thickens to the west may play as source rock of the gas accumulated offshore Rakhine.

Seals

The turbidite reservoirs are overlain by a thick section of Pliocene deep-marine shale which

makes impermeable top seals.

Traps

All of the discoveries in Blocks A-1 and A-3 are made in the stratigraphic traps developed in

the western flank of the Shwe anticlinal structure. The channel-fill shale in the updip location

is the main trapping mechanism in the Shwe discovery. Strike-slip faults or stratigraphic

pinchouts also act as trapping mechanism in the region.

CONCLUSION

Deepmarine turbidites of the late Pliocene, deposited in the submarine fan or channel-levee

complex systems, were proved to be excellent gas reservoirs offshore northwestern Myanmar.

The Daewoos discoveries with the new play concept have upgraded the potential of the whole offshore western Myanmar. The future exploration in this region needs to be targeted

for deepmarine turbidites in the basinal area.

REFERENCES

Curray, J. R., 1991, Possible greenschist metamorphism at the base of a ~ 22-km sedimentary

section, Bay of Bengal. Geology, v. 19, p. 1097-1100.

D.A. Pivnik et al., 1988, Polyphase deformation in a fore-arc/back-arc basin, Salin subbasin,

Myanmar (Burma). AAPG Bulletin 82, No. 10, 1837~1856

Gani, M. R. and Alam, M. M., 1999, Trench-slope controlled deep-sea clastics in the exposed

lower Surma Group in south-eastern Fold Belt of the Bengal Basin, Bangladesh. Sedimentary

Geology, v. 127, p. 221-236.