Abstract The Tanintharyi offshore region as designated by the government is shown in Figure 8.1a. It is subdivided into two broadly north–south-trending structural elements: the Tanintharyi Shelf on which the small Tanintharyi and North and South Mali basins are also present, and the distal, southern, part of the Martaban Basin. The Tanintharyi Shelf (also known as the Mergui Shelf or Mergui Terrace) forms the eastern part of the region and mainly overlies a basement of Palaeozoic–Mesozoic indurated sediments intruded by granites of the Phuket-Slate Belt terrane (see Chapter 2). Its western boundary is marked by the dextral Shan Fault (also known as the Mergui Fault in Thailand), and the shelf is located in an overall back-arc setting on continental crust. This shelf area is designated as shallow-water licence blocks M12 and M13 in the north to M18 in the south. The sediments on this shelf were sourced during much of the Early and Middle Miocene from the Thai-Myanmar Peninsula in the east, and the succession thickens westwards. During the Late Miocene–Pleistocene, sediment input from the north became more dominant representing the distal portion of the Thanlwin/Ayeyarwady depositional system. The Yetagun Field and associated discoveries in and around the SE corner of Block M12 (Fig. 8.1a, b) are close to the present-day shelf edge, which coincides approximately with the more gradational western boundary of the Tanintharyi Shelf. Several early wells in the northern half of the shelf area had hydrocarbon shows, but the structures were generally small and partially breached. In the eastern part of the Tanintharyi Shelf a number of small rift basins are present: the Tanintharyi Basin (or Rift) in which the Zagawa and Kinmon wells were drilled (Fig. 8.1b), while inshore of this are the North and South Mali basins, discussed below.

Abstract Rakhine (formerly Arakan) is the name of the Myanmar state that extends almost the whole length of the Bay of Bengal coast from the Bangladesh border south to about latitude 17°30′, and inland to the watershed of the Indo-Burman Ranges. The Myanmar government adopted the name for the northernmost of its offshore petroleum regions, and their Rakhine Region comprises the offshore blocks A1–A7 and deep-water blocks AD1–AD16 (Fig. 9.1). Much of that offshore region is occupied by the Rakhine Basin which also extends onshore beneath the Rakhine Coastal Lowlands, and this chapter discusses the petroleum geology of both the Rakhine Region (i.e. offshore) in which the Shwe gas field is located and the Rakhine Coastal Lowlands (onshore) in which a number of small oil discoveries have been made. The Rakhine Coastal Lowlands represents the southwards extension of the hydrocarbon-bearing regions of Assam and eastern Bangladesh. The offshore Rakhine Region covers an area of 170 000 km 2 and has a Tertiary clastic sedimentary fill of several kilometres. The Rakhine Basin is subdivided into: (1) a structurally complex onshore and offshore shelf area; and (2) a poorly structured deep-water area. The two are separated by a dextral trench-parallel shear fault system which represents the boundary between the India Plate in the west and the Burma Platelet in the east. Several tectonic and geological models have been suggested for this area, for example, Curray et al. (1979), Bender (1983), Hutchison (1989), Mitchell (1993), Curray et al. (2003), Mitchell et al. (2010), Rangin (2012) and Rangin et al. (2013).

Abstract While the focus of this volume is Myanmar, some of the basins that are the subject of earlier chapters extend into adjoining countries or their offshore exclusive economic zones (EEZs). In this chapter we look briefly at the progress of exploration in adjoining areas of India (the Andaman Islands), Bangladesh and Thailand. We see that success has so far eluded exploration in Thailand’s EEZ and that of the Andaman Islands, despite seismic and drilling activities over several decades. On the other hand, north from Myanmar’s Rakhine Basin (offshore and onshore) in Bangladesh, substantial gas reserves have been discovered and developed. The stratigraphy and petroleum-system elements for Bangladesh are summarized in Figure 10.1. Proven source rocks occur through the Eocene–Pliocene succession and include the Tura, Sylhet, Kopili, Jenum and Bhuban formations. Miocene sandstone reservoirs comprise the Bhuban and Boka Bil formations (sealed by the Upper Manna Shale) and the Pliocene sandstones of the Tipam Formation are sealed by the Girujan Formation shales. The producing fields are predominantly gas and are onshore, the main exception being the offshore Sangu Field which is closest to the northern Rakhine discoveries of Myanmar. The Hatia Trough–Tripura Foldbelt in SE Bangladesh is the NW continuation of Myanmar’s offshore Rakhine Basin. This foredeep basin lies in the main depocentre of the Bengal Fan (Curray et al. 2003). The Sangu Field lies in very shallow water at the head of the Bay of Bengal, some 45 km southwest of Chittagong. It was discovered by Cairn in 1996 and brought on stream in 1998.

Abstract Unconventional resources comprise shale gas, shale oil, coal-bed methane, tight gas/oil sands and heavy oil. There is currently no commercial exploitation of unconventional hydrocarbon resources in Myanmar and this side of the industry is very much in its infancy; see Table 11.1 for a summary. Gas shales are thermally mature, organic-rich, source rocks in which gas is held in natural fractures within some pore spaces and also adsorbed onto the organic material. Areas of focus comprise the Tertiary in the Hukaung, Chindwin, Salin, Pyay, Ayeyarwady, Shwebo-Monywa, Myitkyina-Katha, Bago Yoma and Sittaung basins or areas and the Silurian–Devonian in the Lashio and Kalaw areas (Northern Shan State). The best studied of these is the western flank of the Sailin Basin where the source parameters shown in Table 11.2 are noted (after Lynn Myint 2014). Possible shale gas resources for the Upper Eocene Yaw Formation are 3.3 and 13.9 Tcf for the Middle Eocene Tabyin Formation according to the North Petro-Chem Corporation Myanmar (NPCCM). Maturity data from the Ngahlaingdwin-5 well on the west side of the Salin Basin shows a vitrinite reflectance of 0.4 at 2000 m and 0.6 R 0 at 2430 m. If this is correct then top-wet-gas level would be excessively deep at c. 4300 m. The top-oil window in the Sailin Basin is c. 3000 m and top-gas window is c. 6700 m. Tight gas potential may exist in sandstones of the Pondaung and Tabyin formations in the deeper parts of the basin, while some coals in the Yaw formation may have coal-bed methane potential.

Abstract Before the birth of the modern, mechanized, petroleum industry, Myanmar (formerly Burma) was an exporter of oil products from its hand-dug wells in the centre of the country. It is now an important exporter again, but of gas from its offshore fields, and the international petroleum companies are keen to obtain acreage both onshore and offshore; in the lead-up to the 2013 offshore round no fewer than 60 companies pre-qualified with the Ministry of Energy of the Myanmar government. It was not until the incorporation of Burma into British India in 1885 that extensive geological research was initiated in the country, with many of these articles (up to independence in 1948) being published in reports of the Geological Survey of India. Historically important publications by their geologists included a study of the all-important Tertiary rocks by Noetling (1895) followed by his account of the country’s petroleum occurrences (Noetling 1897). A more detailed study followed, covering the core petroleum-bearing area (what we now call the Salin Basin in the Central Burma Depression, Fig. 1.1) by Grimes (1898). As a modern petroleum industry became established following the formation of the Burmah Oil Company in 1886, the Geological Survey of India (Pascoe 1912) published a major update of what the author described had become ‘… .one of the most important industries of the Indian Empire.’ Accounts of the oil fields by industry geologists included those by Stamp (1927), Evans (1941) and Tainsh (1950); meanwhile, a major study of the wider geology of Burma was published by Chhibber (1934 a ) and of its mineral resources by the same author (Chhibber 1934 b ).

Abstract The geology of the petroleum-bearing parts of Myanmar (essentially the western part of the country) is dominated by the oblique collision between the fixed Sunda Plate in the east (itself a mosaic of Gondwana-derived blocks, and since the Mesozoic a part of the much larger Asian or Eurasian Plate; Fig. 2.1) and the north-moving India Plate (e.g. Curray et al. 1979; Mitchell 1993; Curray 2005; Socquet et al. 2006; Steckler et al. 2008; Hall 2012; Rangin et al. 2013). Before considering the origin of the component parts of Myanmar it is necessary to identify the main structural units that now comprise the western part of the country. Figure 2.1 shows the importance of the Sagaing Fault and its possible offshore continuation in separating the Burma Platelet from the Sunda Plate to its east. Here we follow the terminology of Rangin et al. (2013) in choosing to call this the Burma Platelet, although earlier it was called the Burma Plate by Curray et al. (1979), the Indo-Burma-Andaman Block by Acharyya (1998) and the West Burma Plate by others (e.g. Hall 2012; Metcalfe 2013). The platelet is complex and is discussed further below, but one of its obvious features is the discontinuous belt of dormant volcanoes and granitoid intrusions running down the Central Burma Depression and dividing that major downwarp into forearc and back-arc tectonic domains (Wang et al. 2014). The cones of Mount Popa and Mount Taungthonlon (Fig. 2.1) are among Myanmar’s highest peaks, and the volcanic arc reappears in the Indian sector of the Andaman Sea as the active strato-valcanoes of Narcondam and Barren islands (Bandopadhya et al. 2014) before joining the volcanic arc of Sumatra.

Abstract Oil has been produced in Myanmar for well over 200 years, and a detailed account of the earliest history of the industry to 1914 is contained in the excellent work by Longmuir (2001). It could reasonably be argued that a commercially driven oil industry in what was then Burma 1 predated the oft-quoted 1859 birth of the industry at Titusville, Pennsylvania when Edwin L. Drake drilled his first well, by at least a century. Similarly, Hallett et al. (1985) claimed Scotland was the birthplace of the oil industry, pointing out that oil-shale distillation commenced on an industrial scale in 1865 and reached 2.1 million barrels per year (almost 6000 b/d) in the First World War. As discussed below however, such claims fail to recognize the earlier importance of Burma’s oil industry. Following the relocation of the seat of government from Pegu (now Bago) to Upper Burma in 1635, a procession of British soldier-diplomats made their way up the Irrawaddy (now Ayeyarwady) River to the court of the reigning king, from time to time at Amarapura (now subsumed within southern Mandalay) or Shwebo. Ports of call on this arduous journey included Yenangyaung and some of those early travellers made significant observations on the oil-production industry they found there. Yenangyaung (or Yenan Chaung) can be translated as ‘creek of stinking water’ and the fact that ‘ yenan ’ became the Burmese word for ‘oil’ gives a clue to what those early travellers witnessed. In 1755 George Baker and John North en route to King Alaungpaya’s capital, Shwebo, found ‘about 200 families who are chiefly employed in getting Earth-oil out of Pitts (sic)’.

Abstract All of Myanmar’s commercial onshore oil- and gas fields occur in Cenozoic sedimentary rocks in the Central Burma Depression. The state oil company, Myanmar Oil and Gas Enterprise (MOGE), and most observers divide this very large Cenozoic downwarp into at least seven basins (Fig. 4.1), which is the scheme adopted here for descriptive purposes; others prefer to refer to these seven basins as sub-basins. They can be grouped under two main headings: a northern pair of basins (Chindwin and Shwebo-Monywa basins) in which a few discoveries have been made (in the former) but from which there is no commercial production at present; and a southern region which contains all of the currently producing fields. The boundary between southern and northern regions is at about the latitude of Mandalay, c. 22°N (Fig. 4.1), where there is a slight east–­west structural arch which marks the southern boundary of the Chindwin and Shwebo-Monywa basins. An alternative classification is along plate-tectonic lines, the forearc domain comprising the Chindwin, Salin, Pyay and less certainly the Hukawng basins, and the back-arc domain comprising the Shwebo-Monywa, Bago Yoma and Sittaung basins. The drawbacks of this scheme are that: (1) it is not clear into which domain the Hukawng Basin should be placed; and (2) the Ayeyarwady Delta Basin straddles the buried magmatic arc and so is in both the forearc and back-arc domains. Because of the contentious plate-tectonic categorization of the Hukawng Basin and its frontier exploration status, we have chosen to describe it separately (in Chapter 5) from the basins which lie clearly in the Central Burma Depression.

Abstract The Myanmar Ministry of Energy has identified as prospective the three basins discussed here, but they have seen little exploration activity. Arguably the Hukawng Basin is distinct from the others insofar as exploration drilling has been carried out, and a potentially prospective stratigraphic succession has been encountered. Moreover, this basin lies on trend with the petroliferous basins of the Central Myanmar Depression. But it would be hard to argue that it is anything other than a frontier basin, and for that reason it is included here. For various reasons we consider the other basins discussed here to carry higher risk. The Ministry’s onshore map accompanying the details of the 2013 bidding round included two blocks on the western flank of the Shan Plateau in what MOGE calls the Kalaw Basin: Blocks PSC-U and PSC-V. These blocks, which lie NE and east of the capital Naypyidaw (see Chapter 4, Fig. 4.2), were not however included in their list of blocks on offer. It is an area of complex folding (e.g. Garson et al. 1976), much affected by NNW–SSE faults of which some (such as the Panlaung Fault) are considered by Ridd & Watkinson (2013) to have had a history of dextral strike-slip movement during the Late Cretaceous–Palaeogene. The western part of the two blocks (i.e. west of the Panlaung Fault) exposes Palaeozoic sediments of the Slate Belt intruded by granites (Mitchell et al. 2007), and is considered to have no petroleum potential. The eastern part of the blocks is more difficult to assess. Above the ubiquitous Permian–Triassic Plateau Limestone (=Shan Dolomite), Triassic flysch (Shweminbon Formation) passes up into non-marine younger Mesozoic rocks including red beds and coal-bearing intervals.

Abstract Licensed and available exploration acreage offshore Myanmar covers an area of c. 178 969 km 2 which is equivalent to the total area of the North Sea. The main offshore regions defined by Myanma Oil and Gas Enterprise (MOGE) are the Rakhine, Moattama and Tanintharyi regions with areas of 170 000, 140 000 and 156 000 km 2 respectively, each of which has been subdivided into a number of licence blocks by MOGE as shown in Figure 6.1. It is these block numbers to which we frequently refer when discussing the petroleum geology in the following chapters. The deep-water Neogene offshore and the Middle Miocene and older section in the shallow water are both virtually unexplored, with exploration drilling activity to date mainly restricted to water depths <200 m. This has arguably been due to the imposition of economic sanctions, which have limited the involvement of western companies and the use of the most modern technology and equipment. The offshore Myanmar basins are dominantly gas-prone, and current remaining recoverable-reserves estimates for the main discoveries based on Wood Mackenzie are Zawtika 2.05 Tcf, Shwe/ShwePhyu/Mya 4.09 Tcf, Yadana 2.89 Tcf and Yetagun with 1.5 Tcf and 41 MMbbls condensate (for field locations see Fig. 6.2). Offshore exploration started with seismic acquisition in 1966 followed by the first well in 1972. Between 1972 and 1976 some 30 offshore wells (8 in the Rakhine and 22 in the Moattama regions) were drilled without any commercial success; drilling was then suspended from 1976 to 1982. The earliest offshore exploration wells were drilled by the Myanmar Oil Company (MOC) which subsequently became MOGE in the shallow-water northern Moattama Basin, with three wells drilled in 1972: 6CC-1 (aka MOC-1), drilled on the M3 Block to a depth of 4224 m, tested gas from tight sands at 3679–3684 m but with low flow rates; 9GC-1 (aka MOC-2), drilled on the M4 Block to 3973 m, tested gas at 2905 m; and 3CA-1(aka MOC-3), drilled on the M6 Block to 1127 m, resulted in a major blow-out and the loss of the rig.

Abstract The Moattama Region as defined by the Myanmar government and Myanma Oil and Gas Enterprise (MOGE) comprises a number of different geological elements, but is dominated by the Martaban Basin which lies between the Yadana and M8 highs in the west and the Tanintharyi Shelf in the east (Fig. 7.1). The westernmost margin of the defined region includes the MD-1, MD-2 and MD-3 blocks (Fig. 7.2) which occupy the southwards continuation of the Rakhine Basin (discussed in Chapter 9) and includes the plate boundary between the Indian Plate and the Burma Microplate. The dominantly Late Oligocene–Early Miocene carbonate platform of the Yadana and M8 highs overlies a volcanic basement, and in turn is overlain by a relatively thin succession of Upper Miocene–Recent clastic sediments deposited from the ancestral Ayeyarwady River. Seismic sections over these structural highs show them to have had a complex history of alternating deposition and uplift and, in the case of the narrow M5 basin which separates these highs, there was clearly a phase of structural inversion between the Middle and Late Miocene. Further east in the central part of the Martaban Basin area, a thick clastic succession of ?Early–Late Miocene age is present. This is thought partly to have been deposited from the ancestral Ayeyarwady River and partly from the other major river entering the basin, the Thanlwin River. Sediment from those two sources cannot be distinguished on seismic sections, and in this account we refer to the combined package as the Thanlwin/Ayeyarwady delta system. This Martaban Basin sedimentary sequence then thins eastwards onto the Tanintharyi Shelf (Fig. 7.1).

Abstract With an area of over half a million square kilometres, or roughly that of France, Thailand is second only to Myanmar in size among the countries which make up mainland SE Asia. It lies entirely within the tropics and the distance between its northern point (latitude c. 20°30′N) and its southern point (latitude c. 5°30′N) is a distance of over 1600 km. About four-fifths of the country forms a compact northern land area bordered by Myanmar, Laos and Cambodia. The southern part of the country partly surrounds the Gulf of Thailand (an inlet of the South China Sea), the western arm of this embrace forming the Thai Peninsula which extends south to the border with Malaysia. The western side of the peninsula is partly bordered by southernmost Myanmar and partly by the Andaman Sea.

Abstract The only previous detailed account of the Lower Palaeozoic of Thailand in English is that by Bunopas (1981) which formed part of a wider palaeogeographic study, ostensibly of Western Thailand but in fact embracing the whole country. The regional account by Wongwanich & Burrett (1983) was a briefer summary and it looked in particular at the biostratigraphy. Recent studies concentrating on the Ordovician and Silurian limestones of Thailand have examined the conodont faunas and sedimentary petrology, enabling Agematsu et al. (2008a) to throw important new light on the palaeogeography. Outcrops of undoubted Cambrian to Silurian age occur in Northern, Western and Peninsular Thailand but are absent from the eastern part of Northern Thailand. In NE Thailand the only records of Lower Palaeozoic rocks are of Middle-Upper Silurian faunas described from calcareous mudstone outcropping in the Loei Fold Belt at Ban Nong (Sangkhom District in Nong Khai Province) and Ban Na Tum (Nam Som District in Udon Thani Province) (Fig 3.1 ). They include tabulate and rugose corals, a new trilobite species and strophomenid brachiopods ( Sakagami & Nakornsri 1987 ; Yanagida 1988 ; Kobayashi & Sakagami 1989 ; Fontaine et al. 2005 ). In SE Thailand certain limestone beds are lithologically similar to dated Lower Palaeozoic rocks elsewhere and, although their ages cannot be confirmed, they are considered here also to be Lower Palaeozoic (Fig 3.1 ). The Silurian fossiliferous rocks in the Loei Fold Belt, mentioned above, are the only

Abstract Thailand forms part of the core of SE Asia and, together with the rest of Sundaland, is considered to have formed from continental fragments derived from the break-up of the northern margin of Gondwana, a major Precambrian continent, during the Palaeozoic. Fragments of this continent rifted away and became separated from Gondwana by the development of new oceanic crust, and moved northwards leaving expanding oceans behind them. At the same time oceanic crust lying to the north of these fragments was subducted beneath the southern margin of Asia until, during the Triassic, the fragments collided with and were accreted to Asia. Collision zones between continental fragments are marked by accretionary complexes, belts of serpentinized and highly disrupted oceanic mantle, basaltic crust and ocean-floor sediments forming ophiolites together with thrust and imbricated continental margin sediments; these include mélanges, composed of a variety of blocks of igneous and sedimentary rocks in a fine-grained clay or serpentinous matrix.