Eocene to Miocene Composite Total Petroleum System, Irrawaddy-Andaman and North Burma Geologic Provinces, Myanmar
By C.J. Wandrey Petroleum Systems and Related Geologic Studies in Region 8, South Asia Edited by Craig J. Wandrey
U.S. Geological Survey Bulletin 2208–E
U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior Gale A. Norton, Secretary U.S. Geological Survey P. Patrick Leahy, Acting Director
U.S. Geological Survey, Reston, Virginia: 2006
Posted online February 2006 Version 1.0 This publication is only available online at http://www.usgs.gov/bul/2208/E/ For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS
Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report.
Suggested citation: Wandrey, C.J., 2006, Eocene to Miocene Composite Total Petroleum System, Irrawaddy-Andaman and North Burma Geologic Provinces, Myanmar, Chapter E in Wandrey, C.J., ed., Petroleum systems and related geologic studies in Region 8, South Asia: U.S. Geological Survey Bulletin 2208-E, 26 p. iii
Foreword
This report describing the petroleum resources within a total petroleum system in Myan- mar was prepared as part of the World Energy Assessment Project of the U.S. Geological Survey. For this project, the world was divided into 8 regions and 937 geologic provinces, which were then ranked according to the discovered oil and gas volumes within each (Klett and others, 1997). Of these, 76 “priority” provinces (exclusive of the United States and chosen for their high ranking) and 26 “boutique” provinces (exclusive of the United States and chosen for their anticipated petroleum richness or special regional economic importance) were selected for assessment of oil and gas resources. The petroleum geology of these priority and boutique provinces is described in this series of reports. The purpose of the World Energy Project is to assess the quantities of oil, gas, and natural gas liquids that have the potential to be added to reserves within the next 30 years. These volumes either reside in undiscovered fields whose sizes exceed the stated minimum-field- size cutoff value for the assessment unit (variable, but must be at least 1 million barrels of oil equivalent) or occur as reserve growth of fields already discovered. The total petroleum system constitutes the basic geologic unit of the oil and gas assess- ment. The total petroleum system includes all genetically related petroleum that occurs in shows and accumulations (discovered and undiscovered) and that (1) has been generated by a pod or by closely related pods of mature source rock, and (2) exists within a limited map- pable geologic space, along with the other essential, mappable geologic elements (reservoir, seal, and overburden rocks) that control the fundamental processes of generation, expulsion, migration, entrapment, and preservation of petroleum. The minimum petroleum system is that part of a total petroleum system encompassing discovered shows and accumulations along with the geologic space in which the various essential elements have been proved by these discoveries. An assessment unit is a mappable part of a total petroleum system in which discov- ered and undiscovered fields constitute a single, relatively homogeneous population such that the chosen methodology of resource assessment based on estimation of the number and sizes of undiscovered fields is applicable. A total petroleum system may equate to a single assessment unit, or it may be subdivided into two or more assessment units if each unit is sufficiently homogeneous in terms of geology, exploration considerations, and risk to assess individually. A graphical depiction of the elements of a total petroleum system is provided in the form of an events chart that shows the times of (1) deposition of essential rock units; (2) trap forma- tion; (3) generation, migration, and accumulation of hydrocarbons; and (4) preservation of hydrocarbons. A numeric code identifies each region, province, total petroleum system, and assessment unit; these codes are uniform throughout the project and will identify the same type of entity in any of the publications. The code is as follows:
Example Region, single digit 2 Province, three digits to the right of region code 2004 Total Petroleum System, two digits to the right of province code 200401 Assessment Unit, two digits to the right of petroleum system code 20040101 The codes for the regions and provinces are listed in Klett and others (1997). Oil and gas reserves quoted in this report are derived from Petroconsultants’ Petroleum Exploration and Production database (Petroconsultants, 1996) and other area reports from Petroconsultants, Inc., unless otherwise noted. iv
Figures in this report that show boundaries of the total petroleum system(s), assessment units, and pods of active source rocks were compiled using geographic information system (GIS) software. Political boundaries and cartographic representations were taken, with permis- sion, from Environmental Systems Research Institute’s ArcWorld 1:3 million digital coverage (1992), have no political significance, and are displayed for general reference only. Oil and gas field centerpoints shown on these figures are reproduced, with permission, from Petroconsul- tants (1996).
Contents
Foreword...... iii Abstract...... 1 Introduction...... 2 Acknowledgments...... 2 Geologic and Tectonic History...... 2 Stratigraphy...... 9 Exploration and Production...... 11 Total Petroleum System...... 17 Source Rocks...... 17 Source Rock Richness...... 18 Maturation...... 18 Generation and Migration...... 18 Reservoir Rocks...... 18 Traps and Seals...... 19 Assessment Units...... 19 Cumulative Production Data...... 22 Assessment Comparisons...... 22 Summary...... 22 Selected References...... 24
Figures
1–3. Maps showing: 1. Location of Irrawaddy-Andaman (8048) and North Burma (8035) geologic provinces...... 3 2. Geologic province and total petroleum system boundaries...... 4 3. Generalized geology and geologic province boundaries...... 5 4. Tectonic map of Myanmar and Andaman Basin...... 6 5. Generalized stratigraphic column of Central Burma Basin, Myanmar...... 7 6–11. Paleogeographic maps from perspective of study region, showing: 6. Middle Jurassic (approximately 166 Ma)...... 8 7. Early Cretaceous (approximately 130 Ma)...... 9 8. Late Cretaceous (approximately 94 Ma)...... 10 9. Latest Cretaceous (approximately 69 Ma)...... 11 10. Middle Eocene (approximately 50 Ma)...... 12 11. Late Oligocene (approximately 27 Ma)...... 13 12. Maps showing generalized early and late Eocene paleogeography and associated cross sections...... 14 13. Maps showing generalized early Miocene and Pliocene paleogeography and recent cross section...... 15 14. Map showing generalized geology and some oil and gas fields...... 16 vi
15–19. Graphs of data for the Irrawaddy-Andaman geologic province, showing: 15. Cumulative number of new-field wildcat wells versus completion year...... 17 16. Known oil and gas field sizes grouped in thirds by discovery date and ranked by size...... 18 17. Cumulative number of oil and gas fields versus discovery year...... 19 18. Cumulative known (cumulative production plus reserves) oil and gas volumes versus discovery year...... 20 19. Reservoir depth versus field discovery year for oil and gas...... 21 20. Diagram showing mean vitrinite reflectance of rock samples in Gulf of Martaban...... 22 21. Pie diagram showing temporal distribution of producing reservoirs by youngest age...... 22 22. Pie diagram showing distribution of trap type...... 24 23. Events chart summarizing stratigraphy, source rocks, reservoirs, seals, traps, timing, and petroleum information for the Eocene to Miocene Composite Total Petroleum System...... 24
Table
1. USGS estimates of undiscovered oil and gas resources by assessment unit and aggregated for the total petroleum system (Wandrey and others, 2000)...... 23 Eocene to Miocene Composite Total Petroleum System, Irrawaddy-Andaman and North Burma Geologic Provinces, Myanmar
By C.J. Wandrey
Abstract stratigraphic traps have been discovered, potential for more discoveries exists in the deltaic sequences. There is also poten- The Eocene-Miocene Composite Total Petroleum System tial for growth-fault related traps and in the offshore fans. (804801) was divided into two units for the purpose of assess- The Central Burma Basin Assessment Unit (80480101) ment, the Central Burma Basin Assessment Unit (80480101) is located in the north and central basins of Myanmar. It is an and Irrawaddy-Andaman (80480102) Assessment Unit. oil-prone onshore basin developed parallel to the converging The Irrawaddy-Andaman (80480102) Assessment continental and marine plate boundaries. The rocks that com- Unit is located in the southern central basin of Myanmar, pose this assessment unit include the Eocene Laungshe Shale, the Irrawaddy Delta, and Andaman Basin. It is a gas-prone Tilin and Pondaung Sandstones, and the Oligocene-Miocene onshore and offshore basin developed subparallel to the con- Pegu Group, the thickness of which exceeds 6,500 meters. verging continental and marine plate boundaries. The rocks This group includes interbedded sandstones, shales, and coals that compose this assessment unit include Eocene sandstones of deltaic to fluvial facies, and shallow marine shales, lime- and shales and the Oligocene-Miocene Pegu Group, which in stones, and sandstones. places exceeds 6,500 meters in thickness. This group is made Source rocks include the upper Eocene–lower Oligocene up of interbedded, shallow marine shales, limestones, and shales of the Yaw, Shwezetaw, and Okhmintaung Formations. sandstones, and the sandstones, shales, and coals of deltaic Total organic content is generally low where sampled (>1.7 and lagoonal facies. percent). Organic content is primarily terrestrially sourced Source rocks include the lower Oligocene shales of the type III kerogens. Maturities are generally low, from R0 0.2 Yaw, Shwezetaw, and Okhmintaung Formations and shales of to 1.5 percent where sampled outside of this assessment unit the Pegu Group. Total organic carbon percent is generally low to the south in the Gulf of Martaban. The onset of generation (<1.75 percent) where sampled. Organic material is primarily probably occurred in late Miocene. Migration is primarily terrestrially derived type III kerogen. Maturities are generally short updip and vertical through fault and fracture systems low, from R 0.2 to 1.5 percent where sampled in the Gulf of 0 associated with the plate collision. These fault systems have Martaban. Maturities are likely higher in areas of the basin been periodically reactivated through the present. where burial depths are greater. Interbedded sandstones of the Pegu Group are the pri- Significant generation commenced during the Pliocene. mary reservoirs. Permeability ranges from less than 32 mD Migration is primarily vertical through fault and fracture sys- tems associated with the plate collision. These fault systems to as high as 3,200 mD. Porosity ranges from less than 20 have been periodically reactivated through the present. Short percent to 30 percent. The Eocene Pondaung and Tilin sand- updip migration along the flanks of the basin is also likely. stones may also have reservoir potential and have a combined Primary reservoir rocks are interbedded sandstones of the thickness of as much as 3,500 meters, including the interbed- Pegu Group. Permeability ranges from less than 32 millidar- ded shales. cies (mD) to as high as 3,200 mD. Porosity ranges from less Traps include anticlines, faulted anticlines, fault trunca- than 20 percent to 30 percent. Reservoir quality is fracture tions, and stratigraphic traps. Seals include interbedded Oli- enhanced in many cases. gocene and Miocene shales and clays, and the thick clays of Traps include anticlines, faulted anticlines, and a few the upper Miocene and Pliocene Irrawaddy Group. Structures stratigraphic traps. Seals include interbedded Oligocene in the Chindwin Basin area and stratigraphic traps developed and Miocene shales and clays, and the thick clays of the in alluvial and deltaic systems have been only lightly explored upper Miocene−Pliocene Irrawaddy Group. Although few and may have significant potential. Petroleum Systems and Related Geologic Studies in Region 8, South Asia
Introduction Acknowledgments
Among the 26 boutique provinces identified for the U.S. The author thanks Hugh Balkwell and technical reviewers Geological Survey World Energy Assessment (2000) was the D.K. Higley and R.R. Charpentier for their valuable sugges- Irrawaddy-Andaman geologic province (8048) (fig. 1). The tions and insight. Eocene to Miocene Composite Total Petroleum System (TPS) (804801) (fig. 2), as defined for this assessment, extends north and also encompasses most of the North Burma geologic prov- Geologic and Tectonic History ince (8035); therefore, that province is also included in this report. Located in central Myanmar, Gulf of Martaban, and The total petroleum system (TPS) and assessment units the Andaman Sea, it is an onshore and offshore TPS covering (AU) discussed herein owe their primary structural and strati- approximately 800,000 km2 (fig. 3). graphic features to a series of plate tectonic events dating from The North Burma and Irrawaddy-Andaman geologic latest Paleozoic time to the present. The continental plates that provinces are bounded on the north and west by the Indo- were involved in the development of present-day Myanmar are Burman and Arakan Yoma Mountain Ranges and on the east the Indian and Eurasian plates and the Burma or Sunda micro- by the Sino-Burman Ranges, Shan Plateau, and Tenasserim plate or fore-arc sliver. The Burma plate has been described Ranges. The area includes the Chindwin Basin, Salin Basin, as a micro-plate or fore-arc sliver bounded on the west by a Prome Embayment, Irrawaddy River Delta, Gulf of Marta- subduction zone, on the east by a strike-slip fault, on the south ban, and the Andaman Sea east of the Andaman Islands. The by a spreading center, and on the north by a compressional area described is essentially a complex back-arc/fore-arc plate boundary (Curray and others, 1979; Pivnik and others, basin (fig. 4), with portions of, or the entire onshore part 1998). This sliver or micro-plate has also been described as being variously referred to as, the Central Basin, Central an accretionary prism that consists of sedimentary, meta-sedi- Burma Basin, Inner or Central Burma Tertiary Basin, and mentary, intrusive, and volcanic rocks (Curray and others, Central Burma Tertiary Geosyncline. In this report the entire 1979; Bender, 1983) (fig. 4). Studies of the eastern part of the onshore part will be referred to by the most commonly used Indian plate suggest alternatively that the Burma plate may term—the Central Burma Basin. have been located north of the Indian plate prior to collision, In the Central Burma Basin, the Cretaceous Kabaw and then underwent extrusion and 90° of clockwise rotation to Group (fig. 5) or younger rocks rest on the marine basement reach its present position (Tapponnier and others, 1982; Besse in the western basin and on continental basement rocks in and Courtillot, 1984; LeDain and others, 1984; Everett and the eastern basin. In the ranges to the west, sedimentary and others, 1990). Lee and Lawver (1995) and Pivnik and others metamorphic rocks as old as Early Triassic have been identi- (1998) suggested that the Burma plate originated as a part of fied. East of the Central Burma Basin, rocks younger than the early Tertiary continental shelf of southeast Asia located Cretaceous were not deposited or were almost completely southeast of its present location. removed by erosion, leaving a nearly continuous strati- From Permian through Middle Jurassic time, the Eurasian graphic section from Cambrian to Lower Cretaceous. The plate (or plates) and probably the Burma plate extended just offshore portion of the TPS consists of Eocene and younger south of the equator. The Indian plate was located farther to rocks (Curray and others, 1979; Pivnik and others, 1998). the southwest, between the African, Antarctic, and Australian Structurally, the TPS consists of a north-south-trending plates, making up part of southern Gondwana (fig. 6). During trough or fore-arc/back-arc basin that developed as a result of the Late Jurassic and Early Cretaceous, Southeast Asia and the Eocene oblique multi-plate collision. area of the Burma plate moved northward across the equator to The Eocene-Miocene Composite TPS was further divided between lat 10° and 20° N. into two assessment units (AU) (fig. 2). These AUs are the During the Cretaceous, the Indian plate continued to drift Irrawaddy-Andaman AU (80480102) and the Central Burma northward toward the Burma and Eurasian plates (figs. 7 and Basin AU (80480101). The Irrawaddy-Andaman AU is located 8), and by latest Cretaceous time the sea floor of the Bengal in the southern part of the Central Burma Basin of Myanmar, Basin began to form (Scotese and others, 1988). Along the the Irrawaddy Delta and Andaman Basin. It is a gas-prone Ninety East Ridge a transform fault became active (fig. 9), basin, developed both on and offshore subparallel to the con- and in the Assam area, a southeasterly dipping block-faulted verging continental and marine plate boundaries. The Central shelf developed. Counterclockwise rotation of the Indian plate Burma Basin AU is located in the northern and central part began, and the western part of the Indian plate that is now the of the Central Burma Basin of Myanmar. It is an oil-prone, Seychelles began to break away from the Indian plate (Waples onshore area, and it also developed parallel to the converging and Hegarty, 1999) (fig. 9). During Paleocene time, oceanic continental and marine plate boundaries. plate subduction occurred along the west edge of the Burma 60°E 70°E 80°E 90°E 100°E 8001 Southeast Afghanistan 40° 8002 Himalayan Region 3 8003 Indian Shield Region 1 8004 Sri Lanka 8005 Indo-Burman 8006 Tenasserim-Shan 8023 8021 Makran 8002 8001 8026 8022 Baluchistan Region 2 8024 8023 Central Afghanistan 8022 8024 Afghan 30° 8025 North Burma 8025 Sulaiman-Kirthar 8026 Kohat-Potwar 8028 Himalayan Foreland 8021 8028 8042 8034 8035 8030 Chindwara 8031 Satpura-Brahmani 8031 8032 8030 8032 Damodar 8033 Pranhita-Godavari Eocene to Miocene Composite Total Petroleum System, Myanmar 8006 8034 Assam 20° 8043 8033 8047 8046 8035 North Burma Arabian 8003 8042 Indus Sea 8043 Bombay 8045 8044 Cauvery Bay 8045 Krishna-Godavari of Bengal 8046 Mahanadi 8048 8047 Ganges-Brahmaputra Delta 8048 Irrawaddy-Andaman 8062 10° 8044 8005 8061 Maldives 8062 Lakshadweep 8063 8004 8063 Konkan Irrawaddy- Andaman
8061 Indian Ocean 0°
Figure 1. Location of Irrawaddy-Andaman (8048)and North Burma (8035) geologic provinces shown in green; other assessed provinces in region 8 shown in yellow. Petroleum Systems and Related Geologic Studies in Region 8, South Asia
85°E 90°E 95°E 100°E 105°E INDEX MAP People’s Republic of ÚÊ China India 8035 25° Bangladesh
Mandalay
Myanmar 20°
Thailand Rangoon
15°
8048 Indian Ocean
10°
0 500 1,000 KILOMETERS
EXPLANATION Eocene to Miocene Composite Total Petroleum System 804801 Irrawaddy Province 8048 Other province boundary Irrawaddy-Andaman Assessment Unit 80480102 Central Burma Basin Assessment Unit 80480101 Gas field Oil field
Figure 2. Geologic province and total petroleum system boundaries. Eocene to Miocene Composite Total Petroleum System, Myanmar 5
Osm Mzim Osm Pz Mzim Pzu Pz Pzu Mzim EXPLANATION Mzim Mzim pe Trms Pzu Cs dms MzPz Pr MzPz Geologic province boundary Pzu Mzim Q Pr Ts pe Trms Geologic contact TrmsPr Jd JTr Ts pe Mzim Jd N Pr Evident fault Pz Pr MzPz Trms MzPz Pz Trms Inferred fault Jms Pzu
MzPz pe N Ts pe Trms Ti Mzim e Pr River Pz p Q Trms Ts TKim Cs Pr Water depth contour Pz MzPz Osm pe MzPz Assam Pr pe MzPz Ts N OsmPr Q - Quaternary sediments pe Osm CsPr pe N Pg Cs N N - Neogene sedimentary rocks N pe Ts Q Pr India Cs pe pe Ts Q Q Pg Pg Pg - Paleogene sedimentary rocks Cmsm Ts Osm N pe N Pg pe pe Ts N Ts People’s Ts - Tertiary sedimentary rocks pe Tv Ts TKimTs Pg Pg Pg Republic of Mzim Ti - Tertiary igneous rocks Pg Ts TiQ Ts Q Ks China Tv - Tertiary volcanic rocks N Pg Ts Mzim pe TKim Q N Ts TKim - Tertiary and Cretaceous igneous and metamorphic rocks Pr N Pr TrmsPz N S Q Ts Tv Q Q Pr Ts Pr S Mzim - Mesozoic intrusive and metamorphic rocks Pz Bangladesh Q Ks Pr N Ks - Cretaceous sedimentary rocks Pg Pz Q Jms dms pe Jms - Jurassic metamorphic and sedimentary rocks Pg Cs Chindwin Basin Pr N Cs CsCs Jms Jms Jd- Jurassic and Triassic rocks Ts Pg Q N Pg Pzl Jms JmsTs dms - Triassic metamorphic and sedimentary rocks Pzl Pzu Q Pg N Q Pzl N pe MzPz - Mesozoic and Paleozoic undivided
Shwebo Basin N Pzu Ti Mzim dCs - Lower Triassic to Upper Carboniferous rocks N Q Mzim Q Pzl Pzl Jms Pg Cs N Pzu Cs Q Q Indo-Burman Ranges pe Pz- Paleozoic rocks Q pe pe Pg Pzu Jms Pzu Pz Ts Mandalay N Pz Cs Pzu - Upper Paleozoic rocks Pg pe Q QQ Ks Pg Q N Pzl Q Pzu Pzi Pzl - Lower Paleozoic rocks Q N Q Shan Pzu pe Pzi Q Pzi Pr TrPr Q pe S Pzi - Paleozoic igneous rocks pe Ts Jms Plateau Trms Tv Mt Popa Q Mzim Q Cs Cs - Carboniferous sedimentary rocks Jms Jms S N Pz Arakan Salin Basin TsMzim pe Jms Pr S - Undivided Silurian rocks Pg N N Pzi Pr Pr Q S Pr Osm - Ordovician sedimentary and metamorphic rocks N TKim pe TKimS TKim Pzl S emsm - Cambrian sedimentary and metamorphic rocks
Myanmar Y Pg N N pe oma pe - Undivided Precambrian rocks
T dms I - Undivided igneous rocks pe enasserimTrCs Ranges Pg N Pzi Surface water Pg TrCs Bay Prome Embayment Ks Unmapped area
Pegu of N
Y Q N Q oma Bengal Pzl
Pzu pe Thailand Pg Pzu Yangoon Q 0 500 1,000
S N Q Pzu Q Gulf Q S Pzl of KILOMETERS Martaban Ti Irrawaddy S Pzl Jms N Delta Ti Figure 3. Generalized geology and geologic province boundaries Q (Wandrey and Law, 1999).
Ti N Ti Q I Ti Pzl
Pg Ti
Pzl Pzl Pzl
Pg Ks Q Pzl Pzl Ti
Pzl
Ks Pzl Pg Andaman Pzl Pzl Ts Pg Cs Pz Pg Sea Ks Pzl Pzl Pz Ks
Andaman Islands
Pg Pzl Pzl
Q
Pzl
Ti
Pg Petroleum Systems and Related Geologic Studies in Region 8, South Asia
96°E Southern Tethys suture
^ Foredeep (Indonesian-
S ^ Andaman trench= ^ H ^ I M A L A Y A ^ subduction zone) ^ ^
^ ^ ^ ^
^ ^ ^ ^ Inner volcanic arc
^ ^
^ ( Cenozoic volcanoes)
ER ^
PP M^
U SA
^
S S
A lls ^ i
H ^ a
u g
ea a Major fault zones t N I
S la ^ hillong P ^
S
N ^ E 24° G
N
A
s
R O l l i
H
n
i
h C
a N Ga Delt nges A P | S
M | l
R a h
|
U | t a l B l Shan boundary fault zone B e | n l
| a l O
| u U
D | ^ Thrust complexes N
I ^
|
a |
m R
o | Oceanic spreading ridge
Y | n
Bay a
| k
M
a |
r A
of |
| Bengal YANGOON A 16°
N 0 100 500 KM Gulf of Martaban
Narcondam R Island BANGKOK Andaman A Barren Island N Gulf of Islands
Thailand G Andaman
Sea E S 8° Ninety East Ridge
Figure 4. Tectonic map of Myanmar and Andaman Basin (modified from Bender, 1983). Eocene to Miocene Composite Total Petroleum System, Myanmar
Southwest Irrawaddy Prome Salin Chindwin Delta Embayment Basin Basin FORMATION PERIOD EPOCH GROUP
Pleist- ocene Plio- cene
Mingin Kaungton Irrawaddy
Kathabung
Miocene Obogon Shwethamin Kwingyaung Kyaukkok Kyaukkok Natma Pegu Tumyaung Pyawbwe Pyawbwe
Letkat
Okhmintaung Okhmintaung Oligocene
Tertiary Padaung/Tiyo Padaung/Tiyo
Shwezetaw/ Shwezetaw/ Kyaukpon Kyaukpon EXPLANATION
Yaw/Nakyila Unconformity Yaw Yaw Pondaung Oil production Pondaung Pondaung Taunggale Gas production Taunggale Tabyin/Tilin Tabyin Eocene Laungshe Laungshe Source rocks Jaintia Paunggyi Paunggyi Shale
Kanbala Kanbala Sandstone Siltstone, shale, and sandstone
Kabaw Shale, siltstone,
Paleocene Group and sandstone
Kabaw Limestone
Kabaw Group Volcanics Cretaceous
Figure 5. Generalized stratigraphy of Central Burma Basin, Myanmar (modified from Stamp, 1927; Khin and Win, 1969; and Bender, 1983). 8 Petroleum Systems and Related Geologic Studies in Region 8, South Asia
EURASIAN PLATES
BURMA PLATE
AFRICAN INDIAN PLATE PLATE AUSTRALIAN PLATE
Marine ANTARCTIC Shelf PLATE Lowlands Mountains
Figure 6. Middle Jurassic (approximately 166 Ma). Perspective lat 20° S., long 68° E. (modified from Scotese and others, 1988, and Scotese, 1997). plate (Pivnik and others, 1998). Paleocene oblique subduction faults and north-south elongate anticlinal features such as the of the oceanic plate may have also detached the Burma plate Pegu Yoma (fig. 3). The Pegu Yoma rose 900–1,200 m in the from the Eurasian plate. Initial collision of the northeastern middle of the Central Burma Basin, dividing it into east and Indian and Burma plates occurred during the Eocene, possibly west subbasins. During the Pliocene, Mount Popa and other resulting in the coupling of the plates and accelerating the volcanoes along the volcanic arc to the south became more northward movement of the Burma plate (Pivnik and others, active, depositing volcanic mud and ash. The proto-Chind- 1998). From Eocene to early Miocene time, tectonic activity win, Irrawaddy, and Sittang drainage systems developed. increased due to plate collision and rotation (figs. 10 and 11). East-west uplift and faulting occurred near Mandalay, caus- During the Miocene, faulting, sedimentation, and the opening ing the Irrawaddy River to turn abruptly west and capture the of the Andaman Sea were controlled primarily by northwest- Chindwin River. By Holocene time, anticlinal ridges in the southeast extension and rifting. Regionally, terrestrial sedi- eastern part of the Central Burma Basin were again uplifted ment influx from the rapidly rising Sino-Burman, Indo-Bur- and 300–450 m of sediments were stripped off. To the west, man, and Himalayan ranges significantly exceeded carbonate 300–900 m of the newly uplifted Pegu Yoma were eroded. accumulation rates on late Miocene platforms (Roychoudhury Myanmar now consists of three primary features; from east to and Deshpande, 1982); and this influx smothered carbonate west these are the Sino-Burman Ranges and Shan Plateau, the reef formation along the shelf areas. The former shelf areas Central Burma Basin, and the Indo-Burman Ranges (fig. 3). along these collision zones were either subducted or became The TPS rests on both marine and continental crusts, and the emergent fluvial-deltaic environments. oceanic-continental plate boundary trends north up through Early Pliocene collision of the Burma plate resulted in the Central Burma Basin and coincides approximately with the southwest-northeast transpressional forces that created reverse northern boundary of the Irrawaddy-Andaman AU. Eocene to Miocene Composite Total Petroleum System, Myanmar
EURASIAN PLATES
BURMA PLATE
AFRICAN PLATE INDIAN PLATE AUSTRALIAN PLATE
Marine ANTARCTIC Shelf PLATE Lowlands Mountains
Figure 7. Early Cretaceous (approximately 130 Ma). Perspective lat 20° S., long 68° E. (modified from Scotese and others, 1988, and Scotese, 1997).
Stratigraphy Upper Jurassic and Cretaceous redbeds of the Hsipaw, Kalaw, Mergui, and Khorat Formations were deposited (Bender, Stratigraphic sequences ranging in age from Cretaceous 1983). Jurassic and Lower Cretaceous rocks are missing or not to Pleistocene are shown in figure 5 for four different parts identified in the Central Burma Basin and in most of the Indo- of the Central Burma Basin. The discussion that follows, Burman Ranges to the west. Following this hiatus, in the area however, includes mention of rocks (mostly older, but some of of the Indo-Burman Ranges, Early Cretaceous volcanic tuffs Cretaceous age and younger) not shown in figure 5; some of and cherts of the Kyauknimaw Formation were deposited. these strata are described from observations within the basin, Throughout the Central Burma Basin, the Albian to Turonian but others are described from exposures elsewhere. age Lower Kabaw Group Paung-Chaung and Ywahaungyi From Carboniferous to Jurassic time, extensive carbon- Formation limestones were deposited. Campanian-age graded ates such as the Plateau Limestone Group and Shan Dolomite volcanoclastics then covered much of the Central Burma Basin Group were deposited in what is now eastern Myanmar, and what are now the Indo-Burman Ranges. Following this including the area of the Shan Plateau and Tenasserim Moun- episode of volcanic activity, extensive limestone reefs such as tain Ranges (Rau and Sethu, 1933; Hobson, 1941; Brunsch- those in the Upper Cretaceous–Paleocene Falam Formation weiler, 1974; Bender, 1983) (fig. 3). were deposited in the area of the Indo-Burman Ranges. The Jurassic Tati Limestone Formation in northeastern Along the eastern portion of the approaching Indian plate, Myanmar and the Shan Plateau and the Kamawkala Lime- Rajmahal Trap volcanics and carbonates of the Bolpur and stone Formation in the east and southeast accumulated in a Ghatal Formations accumulated. Although these carbonates shallow marine environment before a period of uplift that was are recognized today primarily on the eastern and western marked by a regional unconformity. On this unconformity, shelves, they were also likely deposited over much of the 10 Petroleum Systems and Related Geologic Studies in Region 8, South Asia
EURASIAN PLATES
BURMA PLATE
AFRICAN PLATE
INDIAN PLATE
Kerguelen Hot Spot Mascarene AUSTRALIAN Basin PLATE
Marine ANTARCTIC Shelf PLATE Lowlands Mountains
Figure 8. Late Cretaceous (approximately 94 Ma). Perspective lat 20° S., long 68° E. (modified from Scotese and others, 1988, and Scotese, 1997).
northern Indian shelf and the area of the Burma plate. This in the Salin Basin (Khin, 1991). Conformably overlying the shelf environment persisted through Late Cretaceous when Pondaung Formation (fig. 5) in the Central Basin, southwest regressive sandstones such as the Tura Formation in the east Chindwin Basin, Prome Embayment, and Thayetmyo area are and Pab Formation in the west were deposited. the shales and sandstones of the middle Eocene Yaw Forma- From Paleocene through middle Eocene time, shales of tion. The eastern portion of the Central Burma Basin, which is the Kanbala and Taunggale Formations were deposited in the part of the Asian plate, was emergent during the early Eocene. Irrawaddy Delta and Prome Embayment areas. Upper Creta- The area south of Mandalay and west of the Irrawaddy River ceous–Paleocene Kabaw Group (the Laungshe Shale of Stamp, was primarily a shallow marine environment, with the excep- 1927) shales, limestones, and sandstones (fig. 5) were depos- tion of the area of the present-day Indo-Burman Ranges (figs. ited in the Salin Basin. The lower Eocene Paunggyi Formation 4 and 12). The area north of Mandalay and in the eastern limestones rest unconformably on the Kabaw Group in the Chindwin Basin was emergent with a shallow marine environ- Salin Basin and conformably in the western Chindwin Basin ment only in the west. (Bender, 1983). Overlying the Paunggyi Formation are the The Eocene to upper Miocene lower Pegu Group in the shales and sandstones of the middle Eocene Laungshe Forma- Salin Basin and Prome Embayment area contains many of the tion of Bender (1983) (a different formation than the Laungshe identified source rocks and reservoirs within the Eocene to of Stamp, 1927). Deposited on the Laungshe are the upper Miocene TPS. For example, upper Eocene–lower Oligocene Eocene shales and sandstones of the Tabyin and Tilin Forma- Shwezetaw or Kyaukpon Formations of the Pegu Group consist tions. Tabyin Formation shales have good source potential of shallow marine interbedded clays, shales, and sandstones. Eocene to Miocene Composite Total Petroleum System, Myanmar 11
EURASIAN PLATES
Tethyan Sea BURMA PLATE AFRICAN PLATE
INDIAN PLATE
Seychelles
Madagascar Mascarene rift basin
Ninety East Ridge
Kerguelen Hot Spot AUSTRALIAN PLATE Marine Shelf ANTARCTIC Lowlands PLATE Mountains
Figure 9. Latest Cretaceous (approximately 69 Ma). Perspective lat 20° S., long 68° E. (modified from Scotese and others, 1988, and Scotese, 1997).
The Shwezetaw and Kyaukpon Formations contain both source Obogon Formation (as much as 1,000 m thick) consists of fine- and productive reservoir rocks, and they are conformably to medium-grained sandstones, sandy shales, and siltstones. overlain by the Padaung Formation (fig. 5) clay and sandstone, The unconformity at the top of the Obogon Formation marks which produces both oil and gas. Upper Eocene–lower Oligo- the top of the Pegu Group. Deposited in alluvial environments, cene rocks were not deposited, or were eroded, in the western on the unconformable top of the Pegu Group, was as much Irrawaddy Delta (Bender, 1983). Following this hiatus, shallow as 3,000 m of nonmarine medium- to coarse-grained massive marine shales, sandstones, and limestones of the upper Oligo- crossbedded sandstones, clays, and conglomerates of the upper cene Tumyaung Formation were deposited in the Irrawaddy Miocene to Quaternary Irrawaddy Group (fig. 13). Delta area. To the north, in the Prome Embayment and Salin Today the total sedimentary column in the Central Basin, the sandstones and limestones of the Okhmintaung Burma Basin exceeds 12,000 m in places, with the greatest Formation accumulated. On an unconformable late Oligocene thickness in the Irrawaddy Delta and the thinnest along the surface marking the top of the Okhmintaung, as much as 1,000 east edge of the basin. m of sandy shales and fine- to medium-grained sandstones of the upper Oligocene−lower Miocene Upper Pegu Group Pyawbwe Formation was deposited. The Pyawbwe sandstones Exploration and Production produce both oil and gas. As much as 1,500 m of sandstones of the lower to middle Miocene upper Pegu Group Kyaukkok Oil seeps and production from hand-dug wells were Formation overlies the Pyawbwe Formation. The Kyaukkok reported in the Yenangyuang area as early as the thirteenth Formation also produces both oil and gas. The middle Miocene century. By 1797 production at Yenangyuang (fig. 14) from 1 Petroleum Systems and Related Geologic Studies in Region 8, South Asia
EURASIAN PLATES
Indus Assam- Shelf Arakan BURMA Shelf Bombay PLATE Shelf INDIAN Bengal Basin AFRICAN PLATE PLATE Somali Basin
Seychelles Mascarene Basin
Madagascar Ninety East Ridge
AUSTRALIAN PLATE Marine
Shelf ANTARCTIC PLATE Lowlands Mountains
Figure 10. Middle Eocene (approximately 50 Ma). Perspective lat 20° S., long 68° E. (modified from Scotese and others, 1988, and Scotese, 1997).
several hundred hand-dug wells on 12.8-m spacing yielded one gas discovery off the Arakan coast, all of the blocks were a total of 200–400 barrels per day. Hand-dug wells were relinquished by 1977. reported as late as 1949, and to be as deep as 120 m. In 1888, Interest in offshore exploration was revived in 1982, the first “drilled” (cable tool) well was brought in, and rotary when Yadana gas field was discovered 70 km offshore in drills were used as early as 1911 (Stamp, 1927). Although the Irrawaddy Delta fan at a water depth of 45 m (fig. 14). the total number of exploratory wells drilled was not large, Reserves are estimated at more than 5 trillion cubic feet of successes continued until World War II, when the petroleum gas (TCFG), with the nearby Sein and Badamyar discoveries industry infrastructure was almost completely destroyed. adding 0.7 TCFG of reserves. Total Myanmar Exploration Following that war, rehabilitation of the industry was slow. In and Production (TMEP), Unocal, Petroleum Authority of 1959, the Payagon oil and gas field was discovered, and the Thailand Exploration and Production International Limited rate of exploration increased (fig. 15). The oil industry was (PTTEP), and Myanma Oil and Gas Enterprise (MOGE), in a nationalized in 1965 and the national oil company Myanma joint venture, began development of the field in 1992, and in Oil Company (MOC) was formed. In 1970 MOC discovered 1998 Yadana field came on line (www.energy.gov.mm/MOGE; Mann oil field, and between 1972 and 1974 MOC drilled 12 accessed 2003). Yetagun gas field, with reserves in excess of wells in the Gulf of Martaban. That drilling effort resulted in 3 TCFG and 80 million barrels (mmb) of condensate, in the several uneconomic gas discoveries. In 1974 MOC invited Taninthayi offshore area of the eastern Andaman Sea (fig. 14), foreign oil companies to bid on offshore blocks. Thirteen was discovered in 1992 (www.energy.gov/mm/MOGE_2.htm; offshore blocks were awarded. After numerous dry holes and accessed 2003). As demand for gas in the region increases and Eocene to Miocene Composite Total Petroleum System, Myanmar 13
EURASIAN PLATES
INDIAN PLATE Myanmar AFRICAN PLATE Somali Basin Seychelles Mascarene Basin
Ninety East Ridge Madagascar
AUSTRALIAN PLATE
Marine
Shelf ANTARCTIC PLATE Lowlands Mountains
Figure 11. Late Oligocene (approximately 27 Ma). Perspective lat 20° S., long 68° E. (modified from Scotese and others, 1988, and Scotese, 1997).
a pipeline system is developed, further exploration and devel- small decrease in field size through time indicates that the opment in the area are likely. Recently a large gas discovery province is still not mature in terms of exploration; a mature has been made off the west coast of Myanmar. province would show a larger decrease in field sizes between Within the Central Burma Basin at least 59 fields were the first and third thirds. The largest fields were found in the discovered between 1864 and 1996 (Petroconsultants, 1996). first and third thirds for oil and the second and third thirds These fields contain at least 76 reservoirs that have produced for gas. Known field size versus discovery year plots (fig. 17) oil, gas, or condensate. The largest fields are Yenangyuang also show that relatively large gas fields are still being found. (>200 mmbo), Yadana (>5 TCFG), and Yetagun (>3 TCFG) The plots of cumulative volume of known (cumulative discovered in 1889, 1983, and 1992, respectively (fig. 14). production plus proven reserves) oil and gas versus the field The plot of cumulative new-field wildcat wells versus discovery year (fig. 18) show recent large increases in cumula- completion year for the Irrawaddy-Andaman geologic prov- tive known volumes. The reservoir depth versus field discovery ince (fig. 15) shows that, although the total number of explo- year plots (fig. 19) indicate that, although generally deeper, in ration wells drilled is low, the rate of exploration increased some cases the reservoirs found later were very shallow. This substantially in the 1960s and the rate has remained relatively may indicate that significant resource is to be found that was constant since the 1970s. previously bypassed. These are also areas where seismic data The plots of known oil and gas fields ranked by size and acquisition and interpretation are difficult. Application of the grouped in thirds by date of discovery do not show a signifi- most recent seismic technology and methods to these areas cant decrease in field size in progressive thirds (fig. 16). The may reveal additional shallow traps. Note that data for gas 1 Petroleum Systems and Related Geologic Studies in Region 8, South Asia
95°E 99°E 95°E 99°E
28° 28° INDIA INDIA
PEOPLE’S PEOPLE’S REPUBLIC REPUBLIC OF CHINA OF CHINA
24° 24°
MYANMAR MYANMAR
20° 20°
THAILAND THAILAND
16° 16° Gulf Gulf of of Martaban Martaban
EXPLANATION
Land area Marine Alluvial/deltaic
WEST EAST WEST EAST
60 Ma 40 Ma
Molasse sediments Flysch sediments
Paleozoic shelf sediments
Granodioritic intrusions
Crystalline Asian plate
Oceanic plate Fault
Figure 12. Generalized early (left) and late (right) Eocene paleogeography (modified from Khin and Win, 1968) and associated cross sections near lat 20° N. (modified from Bannert and Helmcke, 1981). Eocene to Miocene Composite Total Petroleum System, Myanmar 15
95°E 99°E 95°E 99°E
28° 28° INDIA INDIA
PEOPLE’S PEOPLE’S REPUBLIC REPUBLIC OF CHINA OF CHINA
24° 24°
MYANMAR MYANMAR
20° 20°
THAILAND THAILAND
16° 16° Gulf Gulf of of Martaban Martaban
EXPLANATION
Land area Marine Alluvial/deltaic EAST WEST
Molasse sediments Flysch sediments
Paleozoic shelf sediments
Granodioritic intrusions
Crystalline Asian plate
Oceanic plate Fault
Figure 13. Generalized early Miocene (left) and Pliocene (right) paleogeography (modified from Khin and Win, 1968) and recent cross section near lat 20° N. (modified from Bannert and Helmcke, 1981). 16 Petroleum Systems and Related Geologic Studies in Region 8, South Asia
95°E Chindwin River
Mandalay EXPLANATION Quaternary sediments
Neogene sedimentary rocks
X
Yenangyat Shan Plateau Paleogene sedimentary rocks Salin Mt. Chauk Popa 20° Indo-Burman Ranges Tertiary sedimentary rocks
Basin Yenangyuang Tertiary intrusive and extrusive rocks Mann SAGAING FAULT Mesozoic and Paleozoic igneous and
I KAB r Minbu r metamorphic rocks a
w A W a d Cretaceous sedimentary rocks d y T enasserim Ranges Jurassic metamorphic and sedimentary rocks Prome Triassic metamorphic and sedimentary rocks Prome Embayment Lower Triassic to Upper Carboniferous Myanauang
Shwepyitha Mesozoic and Paleozoic intrusive and River metamorphic rocks Undivided Paleozoic rocks Upper Paleozoic rocks Yangoon Syriam Lower Paleozoic rocks Payagon Undivided Permian rocks Gulf of Carboniferous sedimentary rocks Irrawaddy Delta Martaban Undivided Carboniferous to 15° Ordovician rocks Yadana Sein Undivided Silurian rocks
Badamyar T aninthayi Undivided Precambrian rocks Geologic province boundary Yetagun Fault Inferred fault River Andaman Water depth contours Sea Oil field Gas field Oil and gas field Town or city Anticline
Andaman Islands
10° Figure 14. Generalized geology and some oil and gas fields (modified from Khin, 1991, and Wandrey and Law, 1999). Eocene to Miocene Composite Total Petroleum System, Myanmar 17
120 D L E I F
- 100 W E N S L F 80 L O E R W E B
AT 60 M C U D N L I E W V 40 I T A L U 20 M U C 0 1840 1860 1880 1900 1920 1940 1960 1980 2000 2020 YEAR
Figure 15. Cumulative number of new-field wildcat wells versus completion year for the Irrawaddy-Andaman geologic province (Petroconsultants, 1996).
discoveries do indicate a slight trend toward deeper discover- Source Rocks ies. Exploration strategies designed to find larger commercially viable gas fields offshore are driving this trend toward deeper drilling. The primary source rocks identified in the Central Burma Exploration is presently controlled by the limited market Basin are the middle Eocene Tabyin/Tilin, Taunggale, and for gas within Myanmar as well as the neighboring countries Laungshe Formations; upper Eocene Yaw Formation; lower of Thailand and Bangladesh. When gas demand increases, Oligocene Shwezetaw, Padaung, and Okhmintaung Forma- exploration for and development of Myanmar’s gas potential tions (Khin, 1991) (fig. 5). Up to 1,200 m thick, the Tabyin will likely accelerate. Formation consists of weathered clays with coal particles, platy limestone, lignite seams, and thin tuffaceous sandstone layers that increase in number to the north (Cotter, 1914). The Total Petroleum System Yaw Formation consists of as much as 300 to 600 m of shales, The USGS recognizes several petroleum systems within interbedded limestones, and bituminous coal in the Chind- the Irrawaddy-Andaman and North Burma geologic provinces. win Basin (Cotter, 1914). The Yaw Formation was primarily For assessment purposes, however, they were combined into deposited in a marine environment in the western portion of one composite petroleum system, the Eocene to Miocene the Central Burma Basin and lagoonal to alluvial environment Composite Total Petroleum System (804801). This combina- in the eastern portion. The Shwezetaw Formation, as much as tion was made because correlations between source rocks and 1,200 m thick, consists of sandstones (calcareous in the lower reservoir hydrocarbons were available for only the Central part), shales, and thin coal seams deposited in shallow marine Burma Basin at the time of the assessment. Oil analyses indi- to alluvial environments (Vredenburg, 1922). The Padaung cate Eocene and Oligocene–lower Miocene sources (Curiale Formation consists of as much as 1,500 m of marine shales and others, 1994; M.D. Lewan, oral commun., 1998). Multiple with interbedded sandstones that increase in thickness and stacked source and reservoir rocks, connected by extensive frequency near the top of the formation (Bender, 1983). The fault systems, allow mixing of hydrocarbons; this makes iden- Okhmintaung Formation consists of shallow marine sand- tification of distinct TPS difficult. stones, shales, and infrequent limestones. The rocks that compose this TPS are of Eocene through mid- Oligocene and Miocene source and reservoir rocks occur dle Miocene age (fig. 23). These formations include carbonates, along the north, east, and west sides of the Andaman Sea, but shallow marine shales and sandstones, and the sandstones, silt- near the spreading center sediment thickness was probably stones, shales, and coals of deltaic, alluvial, and lagoonal facies. insufficient for generation to occur. 18 Petroleum Systems and Related Geologic Studies in Region 8, South Asia
1,000 Maturation
Burial depths generally increase from north to south in the Central Burma Basin, with the youngest source rocks 100 (Miocene) found in the Gulf of Martaban and northern Anda- man Sea (Matthews and others, 2000). In the Salin Basin (fig. 3) the thermal gradient is low, with mature source rocks at depths of 4 km or greater (Khin, 1991; Curiale and others, 1994). Given the low thermal gradient, upper Eocene and 10 lower Oligocene source rocks are likely to be the youngest mature rocks in the north. Elevated temperatures associated
KNOWN OIL FIELD SIZE (MMB) with the tectonic and volcanic activity are generally local- ized and would have had little effect on regional maturation 1 (Barker and others, 1984). The R0 value versus depth plot 0 10 20 30 40 50 for the Gulf of Martaban indicates that rocks of Miocene OIL FIELD RANK age were sufficiently mature to generate oil and gas (fig. 20) (Bender, 1983). 10,000 Samples taken from depths of 3,048 m in the Salin Basin
have a maturity of 0.5 percent Rm. In order to reach thermal ) F maturities sufficient for generation and expulsion, Khin (1991) C B ( 1,000 suggested, the source must be deeper in the Salin Basin. E Z I Curiale and others (1994) argued that Eocene and lower Oligo- S
D cene source rocks reached the minimum maturity required L E I 100
F for generation. Further burial history data and collection of S
A samples from greater depths may resolve this question. G N
W 10 O N
K Generation and Migration
1 The onset of generation may have been as early as late 0 10 20 30 40 50 Miocene (12 to 8 Ma), and generation is likely continu- GAS FIELD RANK ing today in at least the northern part of the Central Burma Basin. Generation probably occurred first in the Gulf of First third of fields discovered Martaban and Irrawaddy Delta area where burial depths were Second third of fields discovered the greatest. Miocene rocks in the deep basin entered the oil Third third of fields discovered window 8 to 5 Ma, the “gas window” 6.5 to 5 Ma, and the “dry gas window” 6 to 4.5 Ma (Matthews and others, 2000). Figure 16. Known oil and gas field sizes grouped in thirds by Migration is primarily into adjacent reservoirs and vertically discovery date and ranked by size for the Irrawaddy-Andaman through faults that developed during compressional stages geologic province (Petroconsultants, 1996). that created the anticlinal structures present in the Central Burma Basin.
Source Rock Richness Reservoir Rocks Total organic carbon (TOC) content is generally low where sampled, with a TOC minimum in the Gulf of Martaban Reservoir rocks range through almost the entire strati- of <0.2 percent and a maximum of 1.5 percent. The kerogen is graphic section from Eocene to Miocene (figs. 21 and 23). primarily gas prone, terrestrial, type III in the Gulf of Marta- Primary reservoir rocks include sandstones of the Eocene– ban. API gravities of oils range from 8° to 52°. Sulfur content lower Oligocene Shwezetaw, Padaung, and Okhmintaung ranges from 0.01 to 0.23 percent. Curiale and others (1994) Formations and the Miocene Pyawbwe and Kyaukkok For- and Khin (1991) suggested that only one oil family is present mation sandstones. These reservoir sandstones were depos- in the Central Burma Basin and that variations in chemical ited in alluvial, deltaic, and near-shore marine environments. characteristics of oil samples are due primarily to biodegrada- Reservoir quality within the Pegu Group reservoirs varies tion. Khin (1991) also suggested a possible Mesozoic source throughout the province, with porosity ranging from less than in the Salin Basin, the Cretaceous Paung Chaung Limestone 20 percent to more than 30 percent and permeabilities from Formation of the Kabaw Group (fig. 5). less than 92 millidarcies to more than 3,200 millidarcies. Eocene to Miocene Composite Total Petroleum System, Myanmar 19
16
S 14 D L E I
F 12 L I O
F 10 O R E B 8 M U N
E 6 V I T A
L 4 U M U
C 2
0 1840 1860 1880 1900 1920 1940 1960 1980 2000 FIELD DISCOVERY YEAR
25 S D L E
I 20 F S A G F
O 15 R E B M U
N 10 E V I T A L
U 5 M U C
0 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 FIELD DISCOVERY YEAR
Figure 17. Cumulative number of oil and gas fields versus discovery year for the Irrawaddy-Andaman geologic province (Petroconsultants, 1996).
Traps and Seals Assessment Units
Anticlines, faulted anticlines, fault blocks, and strati- The Eocene to Miocene Composite TPS was subdi- graphic traps are the primary traps (Petroconsultants, 1996) vided into two units for assessment purposes: these are the (fig. 22). Seals include interbedded Oligocene and Miocene Irrawaddy-Andaman (80480102) Assessment Unit (AU) and shales and clays of the Pegu Group and overlying Irrawaddy the Central Burma Basin (80480101) AU (fig. 2). Group. The Irrawaddy-Andaman AU is located in the southern The primary elements of the Eocene to Miocene Com- Central Burma Basin, the Irrawaddy Delta and Andaman posite Total Petroleum System and their relationship to timing Basin. It is a gas-prone onshore and offshore basin developed of events are shown in the events chart (fig. 23). subparallel to the converging continental and marine plate 20 Petroleum Systems and Related Geologic Studies in Region 8, South Asia
800 )
B 700 M M (
E 600 M U L
O 500 V L I O 400 N W O
N 300 K E V I
T 200 A L U
M 100 U C 0 1840 1860 1880 1900 1920 1940 1960 1980 2000 FIELD DISCOVERY YEAR )
F 9,000 C B (
E 8,000 M
U 7,000 L O V 6,000 S A
G 5,000 N
W 4,000 O N
K 3,000 E V I 2,000 T A L 1,000 U M
U 0 C 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 FIELD DISCOVERY YEAR
Figure 18. Cumulative known (cumulative production plus reserves) oil and gas volumes versus discovery year for the Irrawaddy-Andaman geologic province (Petroconsultants, 1996).
boundaries. The rocks that compose this assessment unit Significant generation commenced during the Pliocene. include Eocene sandstones and shales and the Oligocene- Migration is primarily vertical through fault and fracture sys- Miocene Pegu Group, with a thickness exceeding 6,500 m in tems associated with the plate collision. These fault systems places. This group is made up of interbedded, shallow marine have been periodically reactivated through the present. Short shales, limestones, and sandstones, and the sandstones, shales, updip migration along the flanks of the basin is also likely. and coals of deltaic and lagoonal facies. Primary reservoir rocks are interbedded sandstones of Source rocks include the lower Oligocene shales of the the Pegu Group. Reservoir quality is fracture enhanced in Yaw, Shwezetaw, and Okhmintaung Formations and shales many cases. Traps include anticlines, faulted anticlines, and a of the Pegu Group. Total organic content is generally low few stratigraphic traps. Seals include interbedded Oligocene (<1.75 percent) where sampled. Organic material is primarily and Miocene shales and clays, and thick clays of the upper terrestrially derived type III kerogen. Maturities are generally Miocene−Pliocene Irrawaddy Group. Although few strati- low, from R0 0.2 to 1.7 percent where sampled in the Gulf of graphic traps have been discovered, potential exists for more Martaban, but maturities are likely higher in areas of the basin discoveries in the deltaic sequences. There is also potential for where burial depths are greater. growth-fault related traps in the offshore fans. Eocene to Miocene Composite Total Petroleum System, Myanmar 1
0
500
1,000
1,500
2,000
RESERVOIR DEPTH, IN METERS RESERVOIR 2,500
3,000 1840 1860 1880 1900 1920 1940 1960 1980 2000 FIELD DISCOVERY YEAR
0
500
1,000
1,500
2,000 RESERVOIR DEPTH, IN METERS RESERVOIR 2,500
3,000 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 FIELD DISCOVERY YEAR
Figure 19. Reservoir depth versus field discovery year for oil (top) and gas (bottom) in the Irrawaddy- Andaman geologic province (Petroconsultants, 1996).
The Central Burma Basin AU is located in the north and Source rocks include the upper Eocene–lower Oligocene central part of the Central Burma Basin of Myanmar. It is an oil- shales of the Yaw, Shwezetaw, and Okhmintaung Formations. prone onshore basin developed parallel to the converging conti- Total organic carbon content, generally low where sampled nental and marine plate boundaries. The rocks that make up this (less than 1.7 percent), is primarily terrestrially sourced type assessment unit include the Eocene Laungshe Shale, Tilin, and II and III kerogens. The onset of generation probably occurred Pondaung Sandstones, and the Oligocene-Miocene Pegu Group, in late Miocene. Migration is primarily over short distances, the latter exceeding 6,500 m in thickness. This group includes updip, and vertically through fault and fracture systems associ- interbedded sandstones, shales, and coals of deltaic to fluvial ated with the plate collision. These fault systems have been facies, and shallow marine shales, limestones, and sandstones. periodically reactivated through the present. Petroleum Systems and Related Geologic Studies in Region 8, South Asia
Depth m 0 Precambrian EXPLANATION 1% Reliable value Paleocene Unreliable value unknown 3% 1% 1,000 Eocene 10%
? ? unconformity
2,000 Late Tertiary samples Miocene Oligocene 55% 30% unconformity 3,000 Lower Cretaceous and Upper Jurassic samples
4,000 0 0.5 1.0 1.5 2.0 MEAN REFLECTANCE (percent Ro) Figure 21. Temporal distribution of producing reservoirs by Figure 20. Mean vitrinite reflectance of rock youngest age. Percentages represent number of reported samples in Gulf of Martaban (modified from occurrences by reservoir (IHS Energy Group, 2001). Bender, 1983).
Interbedded sandstones of the Pegu Group are the pri- Assessment Comparisons mary reservoirs. The Eocene Pondaung and Tilin sandstones may also have reservoir potential and have a combined thick- ness of as much as 3,500 m including the interbedded shales. Kingston (1986) estimated the mode of undiscovered Traps include anticlines, faulted anticlines, fault trunca- petroleum resources in the Irrawaddy basin at 1.1 BBO and at tions, and stratigraphic traps. Seals include interbedded Oli- <2.1 TCFG. Masters and others (1998) estimated the mean for gocene and Miocene shales and clays, and the thick clays of undiscovered petroleum resources at 1.4 BBO for the Burma the upper Miocene and Pliocene Irrawaddy Group. Structures Basin and 6.2 TCFG for the Burma Basin and Andaman Sea. in the Chindwin Basin area and stratigraphic traps devel- In this study mean undiscovered resources were estimated to oped in alluvial and deltaic systems have been only lightly be 725 mmbo and 20.5 TCFG (table 1). explored and may have significant potential. Differences in estimates for undiscovered oil and gas result because the areas assessed are not the same size and significantly more data were available for the most recent assessment. Cumulative Production Data
Based on Petroconsultants International Data Corpora- tion data to 1996, the Irrawaddy Province (8048) was ranked Summary 103rd in the world (including United States provinces). This volume is approximately 0.1 percent of world volume The Eocene-Miocene Composite Total Petroleum System excluding the United States. Known petroleum volumes are has produced the majority of the hydrocarbons in the Central 0.7 billion barrels of oil (BBO) and 10.3 TCFG for a total of Burma Basin and Irrawaddy Delta. Structural traps are pre- 2.5 billion barrels of oil equivalent (BBOE) including natural dominant, but stratigraphic traps are likely to be found in both gas liquids (NGL). ancient and modern delta environments. Eocene to Miocene Composite Total Petroleum System, Myanmar 68 31 99 94 593 686 162 623 785 Mean 73 171 244 242 413 1,327 1,569 1,399 1,813 F5 55 26 81 74 513 587 130 539 669 F50 NGL (MMBNGL) NGL 9 4 13 11 20 125 136 129 149 F95 874 1,134 2,008 1,563 2,697 fields, all liquids are included under the NGL (natural gas liquids) 16,949 18,512 17,824 20,521 Mean 2,751 2,011 4,763 3,903 6,654 36,669 40,572 38,680 45,334 F5 951 759 Gas (BCFG) Gas 1,709 1,285 2,235 14,982 16,266 15,740 17,976 F50 Undiscovered Resources similarly. similarly. Fractiles are additive under the assumption of perfect positive correlation. Shading indicates 158 133 291 197 356 3,710 3,908 3,843 4,199 F95 516 516 209 209 724 724 Mean 498 498 1,192 1,192 1,690 1,690 F5 446 446 177 177 624 624 Oil (MMBO) F50 75 75 27 27 102 102 F95 1.00 1.00 1.00 1.00 1.00 1.00 (0-1) Prob. 1 6 1 6 MFS Central BurmaAssessment Basin Unit Irrawaddy-AndamanAssessment Unit EoceneTotal: to Miocene Composite Petroleum Total System Total Total Total USGS estimates of undiscovered oil and gas resources by assessment unit and aggregated for the total petroleum system (Wandrey and others, 2000). USGS estimates of undiscovered oil and gas resources by assessment unit aggregated for the total petroleum system (Wandrey Oil Fields Oil Fields Oil Fields Oil Type Code Gas Fields Gas Fields Gas Fields Gas and Field Table 1. Table geologic and accessibility probabilities) of at least one field equal to or greater than the MFS. Results shown are fully risked estimates. For gas category. F95 representscategory. a 95 percent chance of at least the amount tabulated. Other fractiles are defined not applicable] 80480101 80480102 804801 [MMBO, million barrels of oil. BCFG, billion cubic feet of gas. MMBNGL, million barrels of natural gas liquids. MFS, minimum field size assessed (MMBO or BCFG). Prob., probability (including both Petroleum Systems and Related Geologic Studies in Region 8, South Asia
Favorable elements of this petroleum province are suit- able organic material, sufficient maturation, ongoing charging of reservoirs, short near-vertical migration paths, and early Fault block Fault trap formation. Draping structure 3% 1% Facies change 1% 1% Dome Regional arch 4% 5% Selected References Fold nose 3% Monoclinal fold Bannert, D., and Helmcke, D., 1981, The evolution of the 1% Asian plate in Burma: Geologische Rundschau, v. 70, no. 2, Asymmetric anticline p. 446–458. 12% Anticline Barker, C.E., and Pawlewicz, M.J., 1987, The effects of igne- 69% ous intrusions and higher heat flow on the thermal maturity of Leonardian and younger rocks, western Delaware Basin, Texas, in Cromwell, D.W., and Mazzullo, L., eds., The Leonardian facies in W. Texas and S.E. New Mexico and Guidebook to the Glass Mountains, West Texas: Midland, Tex., Permian Basin Section−SEPM Publication 87-27, p. 69–83.
Bender, F., 1983, The geology of Burma, in Bender, F., Figure 22. Distribution of trap type. Percentages represent Jacobshagen, V., de Jong, J.D., and Luttig, G., eds., Beitrage number of reported occurrences (IHS Energy Group, 2001). zur Regionalen Geologie der Erde: Berlin, p. 298.
75 60 45 30 15 GEOLOGIC MESOZOIC CENOZOIC TIME SCALE Cretaceous Paleocene Eocene Oligocene Miocene Pliocene PETROLEUM Lower Pegu Gp. Upper Pegu Gp. SYSTEM EVENTS
Shwezetaw Fm Shwezetaw
Paunggyi Cngl Paunggyi Tabyin Clay Tabyin Cl Padaung Ss Okhmintaung Ss Pyawbwe
Yaw Fm Yaw Laungshe Sh Laungshe Ss Tiln Ss Pondaung Ss Kyaukkok Obogon Fm Obogon Irrawaddy Group Rock unit
Source rock Reservoir rock Seal rock Overburden rock Trap formation Accumulation Migration Generation Preservation Unconformity Unconformity Unconformity
Figure 23. Events chart summarizing stratigraphy, source rocks, reservoirs, seals, traps, timing, and petroleum information for the Eocene to Miocene Composite Total Petroleum System. Selected References
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