Malay Basin — NW–SE Transect

Tectonic Phases · 4 Acts

• L. Eoc.Syn-rift — Group L/M lacustrine fill, source rocks deposited
• E. Mio.Transition / sag — Group K, J, I fluvial-deltaic
• M–L. Mio.Inversion — normal faults reverse, anticlines form
• Plio–Rec.Post-inversion — regional subsidence, marine transgression

Reservoir Quality · Group A→M

• Group D: Claystone, sandstone, coal · Deltaic · Excellent
• Group E: Sandstone (Dulang field) · Excellent
• Group F: Sandstone, claystone, coal · Good + regional seal
• Group H: Lower coastal plain · Excellent–Good
• Group I: Siltstone (Angsi, Sotong) · Good
• Group K: Coarse sandstone · Deep play · Fair
• Porosity: 12–28% · Perm: 10–1000 mD

Founder Wells (4) · Plays Tested

• LEBAH EMAS-1 — Western Hinge · 2025 · first well in the play; fairway unproven
• BEKANTAN-1 — Central basin · 2018 · shallowest oil
• BUNGA TASBIH-1 — Angsi flank · 2020 · MBR+ 2024 award
• PUTERI BASEMENT-1 — Eastern flank · 2020 · fractured granite

Settled · Open · What Would Decide It

• Settled: failed rift (Late Eocene–Oligocene extension) with Miocene inversion making the anticlines (Tjia 1989; Madon 2013) · fill >14 km in the deepest centre (Madon 2021) · two overpressure compartments — basin centre top-OP 1,900–2,000 m sealed by Group F shale, basin flank 2,600–3,000 m sealed by Group L shale (Madon 2004, SPE 88455)
• Open: Western Hinge fairway — one well (2025), not a fairway yet · basement play — one well (Puteri Basement-1, 2020) · deep syn-rift K/L/M play — Group K is both reservoir and source, so charge risk drops while seal risk rises; reservoir below ~3,000 m is compaction-degraded · remaining potential ~2 bboe needs new play concepts (Madon 2021)
• Would decide it: 3D seismic over the Western Hinge · a deep well into K/L/M below ~3,000 m · flank pressure data against the 2,600–3,000 m Group L seal prediction · AVO validation of the deep-Group-M Class III anomaly (currently a low-confidence hypothesis)

Basin in numbers: ~500 × 200 km · ~80,000 km² · fill >14 km · >700 exploration wells · ~40% of Malaysia's hydrocarbon resources (Madon 2021).

Licensing 2026: MTJDA Block A-18-01 PSC — 35-year term effective 1 January 2026, awarded to PC JDA Ltd + PTTEP JDX (50/50); exchanged 14 September 2026 at Gastech, Bangkok (Reuters · The Star · NST, 2026-09-14). The effective date precedes the ceremony.

Provenance · Group A→M

• Stratigraphy: Madon 2013, Ishlah 2015, PETRONAS convention
• Tectonics: Tjia 1989 (inversion), Madon 2013 (sag)
• Plays: Scherer 2018 (anticline), PETRONAS MPM 2024 (MBR+)
• Source rock: Group K source facies TOC 0.35–2.0 wt% (mixed Type II/III); Group L best source, HI 300–400 (Madon 2010, GSM). Drawn TOC ranges are regional synthesis values, not single-well measurements.
• Nomenclature: Group labels follow PETRONAS / Madon 2013; other schemes omit Group C (EPMI) or insert Group G (marine transition) — labels are convention, not load-bearing
• Machine layer: geox://basins/malay-basin/profile · geox://literature/GSM-MADON-2021-MALAY-BASIN (Madon 2021, GSM Bull. 72, doi:10.7186/bgsm72202106)
• Wells: /earth/data/wells.json (sovereign canon, F10)
• F7 humility: body shapes are schematics, well positions are basin-level not step-out