North East Java Basin

 Basin shows the isochrone contours in Two-Way-Time. The map shows the position of oil and gas fields relative to the depocenters (Darman & Yuliong, 2020)

Some seismic expression of geological features in NE Java Basin, a back arc basin offshore East Java with significant strike-slip fault system, and horst-graben features.

Fold features in the south of Madura Island. The fold in the centre is not a simple anticline, as it may be cut by faults. (Source: Fugro)

Bright amplitude in the centre are related to topographical high, may indicate carbonate build-ups. The sequences are pinching out to the right, and truncated by a shallower unconformity. (Source: Fugro)

The centre part of the faulted anticline feature is slightly thicker compare to the flank, as several sedimentary packages developed towards the core of the anticline. This indicate that the central of the anticline was a sedimentary pocket, probably created by the fault on the left. At later stage these depocentres were uplifted. (Source: Fugro)

Carbonate features of Kujung Formation (Source: Fugro)

Slightly rotated faulted blocks at the basin margin (Source: Fugro)

Steep-dipping Kujung carbonate reef flanks, indicated by arrows. (Source: PGS)
Time slice at 0.15s TWT showing complex meandering channel system. Horizontal scale scale is about 15 km. (Long and Johansen, 2003; data source: PGS)

Time slice at 1.0 s TWT showing the carbonate features. The diameter of the karst feature is probably less than 1 km. (Long and Johansen, 2003; data source: PGS)









3D perspective of the Top Kujung surface about 1.0 s TWT, revelas the density and complex distribution of carbonates throughout the HDMC3D survey area. (Long and Johansen, 2003; data source: PGS)

Arafura Sea

Arafura seismic section (PGS)

A major unconformity in Arafura Sea is shown on PGS seismic line. 

Arafura seismic section (ION)

ION deep seismic (~40 km) indicated a deep feature below a relatively flat and shallow bathymetry in Arafura Sea.




Australian Sector of Arafura Sea

Stratigraphy of Arafura Sea (Source:
Goverment of Australia, Geoscience Asutralia)

Sediment thickness map of the Australian sector of Arafura Sea
(Source: Goverment of Australia, Geoscience Asutralia)

There are probably more seismic and wells in the Australian sector of Arafura Sea. Based on the well data, the Australian Goverment - Geoscience Ausralia has prepared a stratigraphic scheme of the Arafura Sea.

The interpretation of these seismic lines indicated Paleozoic to Proterozoic interval of stratigraphy.

Baram & Sabah Basin

Fig. 1. Geological provinces in NW Borneo region

The Northwest Borneo region is devided into Baram & Sabah Basin to the north and Luconia Basins to the south. These two region is separated by a structural lineament so called the West Baram line.

The Baram Basin is located in the northeast of Borneo, partly in Malaysia and the majority of Brunei offshore. Three major fields were discovered in the shallow water and onshore part of this basin called Champion, SW Ampa and Seria.

Fig. 2. Linked shelf and deepwater structural domains of 
the Baram Basin (Cullen, 2010).

Cullen (2011) has devided the Baram & Sabah region into several structural segments. Segment A, B and C are parts of Baram basin and D is under Sabah basin.

The hinterland of the Baram Basin consists of two contrasting types of bedrock. The hinterland of the southwest part of the basin is dominated by the shales of the Setap and Temburong Formations; whereas the hinterland of the northeast part of the basin is dominated by sandstones of the Crocker Formation. These relationships suggest that the large drainage systems of the Baram and Padas Rivers represent mud-dominated vs. sand-dominated delivery systems to the basin.

Along strike (SW to NE) differences in the structural style of both the shelf and deepwater areas of NW Borneo define four transverse structural domains in the Baram Basin. The B-C and C-D domain boundaries appear to be basement controlled, whereas the A-B boundary is interpreted to reflect differences between the Baram and the Padas- Champion depositional systems (Cullen, 2011). The deepwater structures in Domain A are characterized by high amplitude, symmetric, detached folds (Figure 3). The deepwater parts of Domains B and C are dominated by asymmetric fault-propagation folds that ultimately root into a common detachment level (Figure 4). The structural style of Domain A likely reflects the presence of low strength, possibly overpressured, mud-rich rocks that deform by penetrative bed-parallel slip (Erslev and Hennings, 2003), which is consistent with a provenance of the shale-prone hinterland for the Baram Delta.

Figure 3. Seismic section across Domain A.

 The deepwater sediments in Domains B and C are derived primarily from the Padas River catchment where the bedrock geology is dominated by sandy turbidites of the Crocker Formation. The fault propagation folds in the deepwater area of Domains B and C suggest a stronger mechanical stratigraphy than in the detached folds of Domain A, which is consistent with a higher percentage of sandstones in Domains B and C owing to a provenance in the Padas River catchment. Although differences in the total amount of strain in different domains of the NW Borneo fold and thrust belt may account for some of the differences in the structural styles between domains, lithology and layering represent more fundamental controls on such interrelated variables such as the strength of basal detachment, the coefficient of internal friction and the critical taper angle.

Figure 4. Seismic section across Domain B, clearly
showing sediment transport from the right of the section.

Thus, differences in the sand to shale ratios in the hinterland of the NW Borneo fold and thrust belt fold thrust belt potentially offers an example of hinterland control on the structural style of deepwater fold and thrust belts.

To southwest the Baram Basin is bounded by West Baram Line, to the north by Northwest Sabah Trough and to the east by the Sabah Inboard.

Seismic lines from structural Domains A and B illustrating the different structural styles in the deepwater fold and thrust belts of those domains. MMU is a Middle Miocene unconformity above which a regional detachment level appears to represent a mechanically weak decollement (Cullen, 2011).

Fig, 5. Seismic section and interpretation across some key fields
in the southwest of Baram Basin (Modified from Sandal, 1996 by Tromp)

Regional seismic cross section in the southwestern part of Baram Basin. SW Ampa Field is shown on the seismic section as a large anticline (Fig. 5). A large down-to-basin fault developed in the west of Gannet well. Merpati is a gas discovery in the deep water play of Baram Basin. Several other large anticlininal features developed in the slope of part of the Baram Basin, mainly consists of deep water deposits. 
. 

Fig. 6. Regional seismic line in the northeastern part of Baram Basin.

Regional seismic section in the eastern part of Baram Basin (Fig. 6) with Champion Field on the right of the section, located on a large structural high. Frigate counter regional fault developed almost at the center of the cross section. Large anticlinal features developed in the west at the slope part of the Baram Basin. The basinal part of the basin has less structure. See Figure 7 for a close-up seismic section of the Champion Field section.

Fig. 7 Seismic section across Champion Field 

A close up seismic section of the east regional seismic section, showing some detail of the Champion Field. There are two down-to basin growth fault in this area, so called Sliver Fault and Champion Growth Fault. Poorer seismic image beneath the Champion structural high is interpreted as a shale diapir. Recent data, however, give better imaging on the deeper part of this section.

Fig. 8. Two large anticlinal feature in the deepwater part of Baram Basin.
A hydrocarbon indicator / flat spot is shown in the anticline on the right.
(Source: PGS)

Detail seismic section of anticlinal features which formed by thrust faults (toe-thurst anticlines) in the deeper water part of Baram Basin. The structure on the left has a flat spot which indicate some hydrocarbon content.

The section also show a relatively shallow unconformity below the sea bottom. A shale dominated transparant zone draped over the two anticlines. 

Fig. 9. Time slace of a 3D Seismic data offshore Brunei (Source: PGS)

Fig. 10. Time slace of a 3D Seismic data offshore Brunei at
shallower lever compare to Fig. 9 (Source: PGS)

Time slice of the deeper water part of the Baram Basin. The anticlines are clearly shown as oval features. The transparant part are the shale dominated interval at the shallower section of the anticlines.



Another sample of time slice at shallower level is shown in Fig. 10. This section goes across the transparent interval, which mainly composed of deepwater shale.

The transparant interval is a shale formation, often called the 'transparant shale' sequence.









Potential hydrocarbon indicator at the core of the anticline. (Seismic courtesy: PGS)

Sabah deepwater - Dudar (Source: Ngah, 1994)

2 seismic sections displayed
by Ngah, 1994

Additional sections are included in Ngah (1994) article. Two sections from Sabah Basin are displayed here. Sabah deepwater seismic section has a steep deeping bathymetry. The young transparent section which is a shale dominated section is similar to those found in Baram Basin. Young faults are expressed well at sea bottom.

Sabah - Tenbungo (Source: Ngah, 1994)

The seismic profile in Tenbungo area has more relief on the sea bottom, formed by young faults and erosion

Jong et al., (2015) have put a number of seismic sections around Borneo basins and put them in the same scale. This exercise give a good picture of the basin features and their magnitudes.  In the index map, section 2, 3, 4 and 5 are located in Baram-Sabah basin.

Reference:
Cullen, A., 2011, Influence of Hinterland Bedrock Lithologies on Aspect of Borneo's Deepwater Fold and Thrust Belt, Berita Sedimentologi #22 (link_*)

Jong, J., Barker, S. M., & Kessler, F., L., 2015, A Comparison of Fold-Thrust Belts in Eastern Sundaland: Structural Commonalities and Differences on the Circum-Broneo Margin, IPA 39th Annual Convention and Exhibition.

Ngah, K., 1994, Malaysia's Gas Resources, AAPG Search and Discovery, Vol. 1, #97001 (link_**)

Tarakan Basin

Geographic Location: Northeast of Borneo Island

Water depth: Partly onshore, down to more than 3000 m

Hydrocarbon potential: Gas and Oil

Main reservoir target: Tarakan and Bunyu Formation (Pliocene and Upper Miocene interval)Main reservoir facies: Deltaic setting

Main source rock: Type III source rock in the Miocene and older interval

Significant geological features in the basin:

1. Tarakan Arches
2. Paleo Tarakan Delta Foresets







1. The Tarakan arches

The Tarakan arches are the most outstanding structural features in the western part of Tarakan Basin. Petroleum accumulations occur in these arches.

Each of the arches are named after the islands formed on the surface: Tarakan, Bunyu and Ahus anticlines. Sebatik anticline in the north is not covered by this seismic section. Oil and gas accumulation occur in the Tarakan and Bunyu Island

A quick look at these arches on seismic will give the impression that these arches are a series of simple anticlines and synclines. Detail evaluation indicate strong strike-slip components in these structural features.





Source: Lentini, M. & Darman, H., 1997; Wight, A., 1995







2. Paleo Tarakan Delta Foresets

Foresets are clearly seen on seismic section for Pleistocene to Upper Miocene sections. In some sections there are carbonate layers close to the top of the sand sequence, indicating the end of sand supply on that interval.


This seismic section is about WE orientation in the southern part of Tarakan Basin shelf. The yellow units are sand dominated sequence and the blue units are carbonate layers.

The faults are dipping towards the west and the fault system on the right are counter regional faults.

Source: Lentini, M. & Darman, H., 1997

Kutei Basin

Geographic Location: East of Borneo Island

Water depth: Partly onshore, down to more than 3000 m. The deeper water part is also known as the Makassar Strait basin.

Hydrocarbon potential: Gas and Oil

Main reservoir target: Balikpapan Formation (Pliocene and Upper Miocene interval)

Main reservoir facies: Deltaic setting

Main source rock: Type III source rock in the Miocene and older interval

Significant geological features in the basin:
1. Samarinda Anticlinorium onshore
2. Paleo Mahakam Delta Foresets offshore.








Samarinda anticlinorium map, showing the NNE-SSW trend anticlines and structures in dashed red line. The location of the seismic line across this area is shown in black line.













A highly squeezed regional seismic line (40 km long), crossing four major aniclines within the Samarinda Anticlinoium. In the absence of palaeontlogical data correlation across these anticlines is very difficult (dips vary from 0-75 degrees). Cores of anticlines appear to be chaotic on seismic (1) and bounding faults (2) are difficult to pick. Also visible are down-to-basin syn-depositional faults (3), west-to-east progradational downlaps (4) and evidence of syn-depositional structuring (5) indicating that uplift was occuring at the end of the Early Miocene (from Carter and Morley, 1996).


A detail seismic section across Separi anticline with detail seismis character of the structure. Note the higher topographical relief at the core of the anticline, indicating the location of outcrops. The outcrops are dominated by deltaic sandstone-shale facies and limestones beds.

North Sumatra Basin

OFFSHORE

Figure 1.

Location of offshore North Sumatra Basin and seismic lines shown on this page (after Tsukada et al 1996).


General information:

Geographic location: North of Sumatra Island
Water depth: 20 to 500 meters
Hydrocarbon potential: proven oil and gas basin with predominantly gas.
Largest field in the basin: Arun Field (Discovery: 197?)
Main reservoir target: Peutu, Baong and Keutapang Formations
Main reservoir facies: Miocene carbonate reef / build up.
Main source rock: Bampo Formation









Figure 2.

Geoseismic Line BLD-JAU showing northwesterly dipping half grabens filled by the Late Oligocene sediments that underlie the P22 SB. The P22 SB represents a boundary of major shift in depositional environments from a fluvial setting below the SB to a bathyal setting above the SB (Tsukada et al. 1996).














Figure 3.

Geoseismic Line ITU-BLD showing a young overthrust front (see annotation) located in the deepwater offshore North Sumatra. The syn-rift megasequence was deposited above half grabens and tilted fault blocks as shown below approximately 4 s (overlain by the P22 SB). Evidence of tectonic inversion is shown by the folding of the P22 SB, N14 SB and other younger reflectors that was controlled by the half graben (after Tsukada et al. 1996).









Figure 4.

Geoseismic Line ITU-JAU shows Jambu Aye Utara Ridge (JAU Ridge) located on the northeastern side and the NW extension of the North Lho Shukon Deep (Tsukada et al. 1996). The Lho Shukon Deep is the main source rock kitchen that supplies gas to the surrounding major fields such as the Arun Field.

Sample seismic reflection image acquired in the North Sumatra Basin, Indonesia. The folded sediments, which appear as dark and white lines, are deformed by a deeper fault. The magnitude of deformation decreases upward, indicating that these sediments were deposited while deformation was occurring (past 20 million years). As a consequence, the units at the surface appear nearly flat, despite the large fault that lies beneath (Shaw et al, 1997)






PGS in cooperation with MIGAS, has acquired 7,756 line km of MultiClient 2D (NS-06 & AS-08 MC2D) data, located in the North Sumatra Basin, Offshore Indonesia. Most of the area covered by the survey is largely under-explored, except for the platform areas to the east over the NSO block and the near coastal areas. The water depth ranges from very shallow in the coastal areas to deeper than 1,000 m in the central parts of the basin. The detail is available here.

ONSHORE
Onshore North Sumatra has one of the longest petroleum history. A number of fields were discovered and the basin is considered mature from exploration perspective. Lion Energy has published a map which shows the main fields and prospects. Some seismic sections were compiled in this chapter.








1. Alur Siwah Field

In 2013, Maranu et al, published an article related to the reservoir characterization of Alur Siwah field. Several seismic sections were published in this article. Two of them have clearly shown a carbonate build up feature.

Strong reflector has significantly form an envelop of the carbonate unit. The reflectors above it shows onlaping feature towards the carbonate structure.

The section below shows the absolute AI section through AS-7a line. The red color in this section shows the carbonate build up.







2. Amanah Prospect

Peak Oil has proposed a prospect to be drilled, called Amanah Timur-1. The detail of the prospect is available in their brochure with the following link.