Malay Basin Exploration and Geology

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Questions and Answers

What significant environmental transition occurred in the Malay Basin from the Oligocene to the Miocene periods?

The transition shifted from mainly nonmarine environments to increasingly marine environments.

Identify the two main areas where the Malay Basin receives sediment deposits.

The northeastern and southwestern flanks.

What are two giant oil fields located in the southern part of the Malay Basin?

Seligi and Tapis.

Explain how the geographic and stratigraphic distribution of hydrocarbons in the Malay Basin is controlled.

It is primarily controlled by basin morphology. Signup and view all the answers

What is the primary source rock type found in the northern province of the Malay Basin?

Coaly source rocks. Signup and view all the answers

What structural factors determine the distribution of oil and gas in the Malay Basin?

Source-rock quality, maturity, and the timing of generation and structuration. Signup and view all the answers

Describe the main structural trap styles present in the Malay Basin.

The main trap styles are compressional anticlines and fault dip closures. Signup and view all the answers

How does the timing of structuration affect hydrocarbon migration in the Malay Basin?

Early structuration in the south allowed for oil trapping, while late structuration in the north resulted in more gas being trapped. Signup and view all the answers

What geographic area does the Malay Basin cover?

The Malay Basin covers an area of 80,000 km². Signup and view all the answers

When did petroleum exploration in the Malay Basin begin?

Petroleum exploration in the Malay Basin began in 1968. Signup and view all the answers

What significant discoveries were made during the early exploration of the Malay Basin?

Significant discoveries included the Seligi and Bekok oil fields. Signup and view all the answers

Which company drilled the first well in the Malay Basin and what was its name?

Esso drilled the first well named Tapis-1. Signup and view all the answers

What geological features separate the Malay Basin from the Penyu and Pattani Basins?

The Tenggol Arch separates it from the Penyu Basin and the Narathiwat High separates it from the Pattani Basin. Signup and view all the answers

What is the believed age of the formation of the Malay Basin?

The Malay Basin is believed to have formed during the early Tertiary. Signup and view all the answers

What was the nature of the basement rocks underlying the Malay Basin?

The basement rocks are composed of metamorphic, igneous, and sedimentary rocks. Signup and view all the answers

How many exploration wells had been drilled in the Malay Basin by the end of 1997?

By the end of 1997, approximately 330 exploration wells had been drilled. Signup and view all the answers

What are the structural closures formed by basement mounds on the Tenggol Arch when Tertiary sediments are draped over them?

Isolated basement mounds acting as traps for hydrocarbons. Signup and view all the answers

From which group are the shallow marine sandstones that contain oil in the Malong structure sourced?

Group J shallow marine sandstones. Signup and view all the answers

What is the maximum migration distance of hydrocarbons to the Malong structure?

10 km. Signup and view all the answers

Why must the migration model in Tenggol Arch be revised?

Some basement structures were tested and found dry. Signup and view all the answers

What type of traps have been discovered in the northeastern flank of the Malay Basin?

Subtle stratigraphic/fault traps. Signup and view all the answers

What provides the top seal for the hydrocarbon traps in the NE Ramp Margin Play?

Interbedded shale. Signup and view all the answers

What examples of oilfields are found in the PM3 CAA area within the NE Ramp Margin Play?

Bunga Orkid, Bunga Kekwa, and Bunga Raya oilfields. Signup and view all the answers

Which group of shales is primarily responsible for sourcing hydrocarbons via long-range migration in the NE Ramp Margin Play?

Group K and L shales. Signup and view all the answers

What are the geographical features bounding the Malay Basin?

The Malay Basin is bounded by the Terengganu Platform and Tenggol Arch to the southwest, the Narathiwat High to the northwest, and the Con Son Swell to the northeast. Signup and view all the answers

What tectonic characteristics are observed in the Malay Basin based on geophysical data?

The Malay Basin exhibits a complex rift composed of numerous extensional grabens, which indicate great depths that have not been penetrated by drilling. Signup and view all the answers

According to the model by Tjia, how was the Malay Basin formed?

The Malay Basin, along with the Penyu and West Natuna basins, formed as failed rift arms of a triple junction above a Late Cretaceous thermal dome. Signup and view all the answers

What is the role of the mantle plume in the formation of the Malay Dome?

The mantle plume is presumed to create a 'circular regional uplift' known as the Malay Dome, contributing to the tectonic features of the basin. Signup and view all the answers

How did tectonic deformation and uplift affect the pre-Tertiary basement of the Malay Basin?

Late Middle Miocene tectonic deformation and uplift caused the pre-Tertiary basement to shallow to the southeast, resulting in numerous compressional anticlines. Signup and view all the answers

What is the significance of the seismostratigraphic units in the Malay Basin?

The strata of the Malay Basin are subdivided into informal seismostratigraphic units, each designated alphabetically from A to M, indicating a chronological order of deposition. Signup and view all the answers

Describe the tectonic model that suggests how basin grabens are formed.

In plate tectonic theory, T-shaped rift arms can spread out to produce ocean basins, and in the case of the Malay Basin, these grabens radiate from the triple junction, forming depocenters for sediment deposition. Signup and view all the answers

What was inferred about the tectonic model based on diastrophic activities in the region?

Diastrophic activities suggest that a hot spot located at the triple junction influenced the tectonic evolution of the Malay Basin and related basins. Signup and view all the answers

What type of rock formations predominantly host hydrocarbons in the Malay Basin?

Sandstone reservoirs from Groups D to K mainly host hydrocarbons. Signup and view all the answers

Describe the primary source rock types involved in hydrocarbon formation in the Malay Basin.

The primary source rock types are lacustrine shales rich in algal components and fluviodeltaic coastal plain shales. Signup and view all the answers

What is the estimated total gas reserve in place for the Malay Basin?

The total gas reserve in place is estimated to exceed 60 TSCF. Signup and view all the answers

Which reservoirs were successfully penetrated by the Bergading Deep-1 well?

The Bergading Deep-1 well successfully penetrated reservoirs in Group F. Signup and view all the answers

What characterizes the main gas and condensate findings in the Bergading-1 well?

Bergading-1 well found gas in Groups B, D, and E reservoirs. Signup and view all the answers

Explain the depositional environment of reservoir rocks in the older groups K, L, and M.

Reservoir rocks in older groups K, L, and M are primarily formed in fluvial channels within a nonmarine-lacustrine setting. Signup and view all the answers

Identify two main depositional settings indicated for source rocks in the Malay Basin.

The two main depositional settings for source rocks are lacustrine and fluviodeltaic. Signup and view all the answers

What is the significance of effective source rocks in the Malay Basin's oil and gas reserves?

Effective source rocks are crucial as they contribute to the substantial oil and gas reserves in the basin. Signup and view all the answers

Study Notes

Introduction: Malay Basin

Located in the southern Gulf of Thailand between Vietnam and Peninsular Malaysia
Covers 80,000 km² with 14 km thick sediment
Continues northwest to Thailand’s Pattani Trough and southeast to Indonesia’s West Natuna Basin
First oil and gas discoveries in 1968

Exploration History

The initial exploration and production rights in the Malay Basin were granted to major oil companies Esso and Conoco in 1968, marking a significant step in the development of the region's oil and gas industry.
Esso operated north of 5°N latitude, Conoco operated south which includes the Penyu Basin
Starting in 1974, exploration was under production-sharing contracts
Esso drilled Tapis-1 in 1969 (found gas in sandstones) and Tapis-2 in 1974 (found oil)

Tectonic Framework

Located at the center of Sundaland
One of the deepest continental extensional basins in the region
Formed during the early Tertiary
Tenggol Arch separates the Malay Basin from the Penyu Basin
The Narathiwat High separates it from the Pattani Basin
Elongate NW-SE trending basin with pre-Tertiary basement of metamorphic, igneous, and sedimentary rocks
Basement rocks are the offshore continuation of eastern Peninsular Malaysia geology
Bounded by relatively shallow (<1.5 km) basement areas:
- Terengganu Platform and Tenggol Arch to the southwest
- The Narathiwat High to the northwest
- Con Son Swell to the northeast
Complex rift composed of numerous extensional grabens interpreted from geophysics data
Some smaller grabens identified on the west-central margin from seismic mapping
Pre-Tertiary basement shallows southeastwards due to late Middle Miocene tectonic deformation and uplift
Various tectonic models proposed for the origin of the Malay Basin
Tjia’s (199) triple junction model explains the formation of the Malay Basin, Penyu, and West Natuna basins as failed arms of a triple junction over a Late Cretaceous thermal dome
This model suggests a hot spot at the triple junction of the three basins based on diastrophic activities onshore and offshore Peninsular Malaysia
This hot spot (mantle plume) developed a circular regional uplift (Malay Dome)
The T-shaped rift arms spread forming regional grabens radiating from the triple junction and became depocenters for sediment deposition

Stratigraphy

Malay Basin strata subdivided informally into seismostratigraphic units called Groups
Groups are designated alphabetically (A-M) in order of increasing age
Reconstruction of the basin’s palaeogeographic development shows a progression from mainly nonmarine environments during the Oligocene (Groups L and M - synrift basin development phase) to increasingly marine environments (Miocene and later Groups K to A/B)
Malay Basin was a narrow seaway or gulf that received sediment from its northeastern and southwestern flanks

Hydrocarbon Occurrences

Southern part of the basin contains most oil reserves (Seligi and Tapis)
Hydrocarbons occur in reservoirs from Group L to D
Groups E, I, J, and K are the most prolific
Two provinces:
- Northern gas-prone
- Southern oil-prone (exceptions exist)
Regional oil and gas distribution controlled by basin morphology
Semi-regional factors controlling oil and gas distribution:
- Source rock quality and maturity
- Timing of generation and structuration
Source rocks:
- Coaly in the north (mainly Group I)
- Lacustrine in the south (Groups K, L, and M)
Timing between structuration and hydrocarbon migration varies south to north
- Structures formed earlier in the south trapping oil
- Later structuration in the north resulted in more gas being trapped

Hydrocarbon Plays and Trap Styles

Trap styles mostly compressional anticlines and fault dip closures
Trap styles and hydrocarbon plays categorized by:
- Structural features
- Geographic and stratigraphic distribution
- Source-reservoir relationships

Tenggol Arch Plays

Relatively featureless except for isolated basement mounds, forming structural closures when Tertiary sediments drape over them
Basement drapes form a unique trap style with oil discovered in one of the structures at Malong (Group J shallow marine sandstones)
Hydrocarbons at Malong probably charged from Group K or older lacustrine shales across the Tenggol Fault, migrating up-dip onto the Tenggol Arch
Interbedded shales provide the top seal for drape structures
Sedimentary succession on the Tenggol Arch is generally less than 1500 m thick, making any potential rock immature. This means Malong oil may have come from deeper half-grabens to the northeast of the Tenggol Fault
Migration distance to Malong is at most 10 km
Malong discovery sparked interest in other basement structures on the arch, assuming oil migrated over long distances (30-60 km) from the Malay Basin
However, some of the basement structures were tested and found dry, requiring revisions of the migration model

NE Ramp Margin Play

19 oil and 15 gas discoveries made on the northeastern flank of the Malay Basin
Major trap styles:
- Subtle stratigraphic/fault traps in Groups I, J, and K (Larut and Bunga Raya fields)
- Faulted anticlinal traps in Groups I, J, and K reservoirs (northeastern and eastern parts)
Lateral seal provided by sand-shale juxtaposition
Top seal provided by interbedded shales
Hydrocarbons sourced from:
- In situ interbedded source beds
- Beds down-dip (Groups K and L shales) via long-range migration
Examples:
- Bunga Orkid, Bunga Kekwa, Bunga Raya oilfields (PM3 CAA area)
- Lerek, Pantai, Lumut, East Belumut, Larut, Abu oilfields in PM5 and PM8
Other trap styles:
- Basement drapes (similar to Tenggol Arch - South Raya Field)
- Stratigraphic channel plays (Bindu discovery)
- Stratigraphic pinch-out traps
- Onlap traps

Deep Reservoir Play

Play involves reservoirs within or below the overpressured zone beneath existing discoveries/fields
Bergading structure (N-trending anticline) in the northern part of the basin near JDA
Bergading-1 well found gas in Groups B, D, and E
Bergading Deep-1 well drilled to 3100 m (penetrated Group F overpressured zone)
Substantial amounts of gas and condensate found in Groups H and I reservoirs

Reservoir Rocks

Hydrocarbons found in sandstone reservoirs (Group D down to K)
Depositional environments vary with stratigraphy
Older groups (K, L, M) reservoirs formed as mainly fluvial channels in a nonmarine-lacustrine setting
In J and younger groups, sandstones are predominantly shoreface and subtidal shelf sands (esp in J) and fluvial-deltaic to estuarine channel complexes (I group and younger)

Source Rocks

Abundant oil and gas reserves in the Malay Basin indicate the presence of effective source rocks
Two main depositional settings for source rocks:
- Lacustrine
- Fluviodeltaic
Lacustrine source rocks (Oligocene/Early Miocene K, L, M, and pre-M/synrift groups):
- Shales rich in algal components
- Only penetrated at shallow depths on the basin flanks
Fluviodeltaic source rocks (Lower-Middle Miocene I and E groups):
- Coastal plain shales and coal/carbonaceous shales
- Encountered in the basin center

Natural Gas

The Malay Basin is not purely an oil province, containing several large gas accumulations
Natural gas estimated to be more than half of the hydrocarbon reserves of the basin
Total gas reserves in place estimated to exceed 60 TSCF
Large proportion of the reserve in the Jernih, Lawit, Duyong, and Seligi fields

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Description

This quiz covers the key aspects of the Malay Basin, including its location, exploration history, and tectonic framework. Delve into the geological formation and significant discoveries that have shaped this crucial area between Vietnam and Peninsular Malaysia.