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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.
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What is the primary source rock type found in the northern province of the Malay Basin?
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What structural factors determine the distribution of oil and gas in the Malay Basin?
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Describe the main structural trap styles present in the Malay Basin.
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How does the timing of structuration affect hydrocarbon migration in the Malay Basin?
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What geographic area does the Malay Basin cover?
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When did petroleum exploration in the Malay Basin begin?
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What significant discoveries were made during the early exploration of the Malay Basin?
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Which company drilled the first well in the Malay Basin and what was its name?
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What geological features separate the Malay Basin from the Penyu and Pattani Basins?
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What is the believed age of the formation of the Malay Basin?
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What was the nature of the basement rocks underlying the Malay Basin?
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How many exploration wells had been drilled in the Malay Basin by the end of 1997?
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What are the structural closures formed by basement mounds on the Tenggol Arch when Tertiary sediments are draped over them?
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From which group are the shallow marine sandstones that contain oil in the Malong structure sourced?
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What is the maximum migration distance of hydrocarbons to the Malong structure?
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Why must the migration model in Tenggol Arch be revised?
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What type of traps have been discovered in the northeastern flank of the Malay Basin?
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What provides the top seal for the hydrocarbon traps in the NE Ramp Margin Play?
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What examples of oilfields are found in the PM3 CAA area within the NE Ramp Margin Play?
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Which group of shales is primarily responsible for sourcing hydrocarbons via long-range migration in the NE Ramp Margin Play?
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What are the geographical features bounding the Malay Basin?
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What tectonic characteristics are observed in the Malay Basin based on geophysical data?
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According to the model by Tjia, how was the Malay Basin formed?
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What is the role of the mantle plume in the formation of the Malay Dome?
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How did tectonic deformation and uplift affect the pre-Tertiary basement of the Malay Basin?
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What is the significance of the seismostratigraphic units in the Malay Basin?
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Describe the tectonic model that suggests how basin grabens are formed.
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What was inferred about the tectonic model based on diastrophic activities in the region?
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What type of rock formations predominantly host hydrocarbons in the Malay Basin?
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Describe the primary source rock types involved in hydrocarbon formation in the Malay Basin.
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What is the estimated total gas reserve in place for the Malay Basin?
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Which reservoirs were successfully penetrated by the Bergading Deep-1 well?
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What characterizes the main gas and condensate findings in the Bergading-1 well?
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Explain the depositional environment of reservoir rocks in the older groups K, L, and M.
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Identify two main depositional settings indicated for source rocks in the Malay Basin.
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What is the significance of effective source rocks in the Malay Basin's oil and gas reserves?
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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.