Abstract The rate of success in drilling for oil and gas in the Gulf of Thailand has been increased in a ratio of one to three since 1977. Two commercially explorable gas-condensate fields of total estimated reserves up to 5 Tcf have been found in Union Oil’s concession Block 12 and Texas Pacific’s concession block 15 and block 16. The Union field is located in the southern Pattani trough and the Texas Pacific field is situated in the northern portion of the Malay basin. Several gas and condensate reservoirs have been identified in lower to middle Miocene deltaic sandstones, ranging in depth from 3,300 to 8,800 ft (1,006-2,682 m) in the Texas-Pacific field and from 5,000 to 8,700 ft (1,524-2,652 m) in the Union field. A 620 km submarine pipeline connecting these fields northward to Sattahip Shore, formed as common carrier for combining gas flow at the daily rate of 500 MMcf, is planned by the Natural Gas Organization of Thailand (NGOT). Initial daily gas production of 150 MMcf from Union field is expected to be on stream by January 1981, to supply electricity for industries and domestic demands in Bangkok and the eastern provinces as a substitute for imported fuel oil. Pre-Tertiary basins in the relinquished areas of the inner Gulf of Thailand are considered to be future petroleum potential basins.

ABSTRACT Texaco Exploration drilled the Mayura #1 well in the southern Pattani Basin of the Gulf of Thailand in the first half of 1994 with partners Fina and Ampolex. The well was drilled on the ramp side of a half-graben and had numerous oil shows in proximal, nonmarine reservoirs within the synrift section. One DST zone flowed oil but the permeability of the reservoir units was compromised by kaolinite in the pore system. High frequency, nonmarine sequence stratigraphy was applied to the wireline log data. Interpretation criteria are outlined suitable for application to proximal stratigraphic positions within alluvial fan to braided plain environments. A typical sequence is composed of stacked, fining-upward parasequence units that aggrade during times of relative base level rise. Each sequence shows the depositional response to factors that reorganize the drainage patterns and/or the delivery system of sediments to the basin. This response records an overall maturing-upward of depositional processes in each sequence through geologic time. Alluvial fan lithologies accumulated near the base of the sequence and braided plain to high energy fluvial sands aggraded in the middle to the top of each sequence. The resulting stratigraphic architecture formed two reservoir plumbing systems that affected the DST results in the Mayura well. Interpretation of seismic data shows that two large-scale movements on the border fault also affected the sediments in this basin. Tectonically-controlled sediment packages formed with rapid deposition into the accommodation created by slip on the border fault. Poorly organized depositional processes dominated at this time. As the accommodation filled, the fluvial plain broadened and a more mature, fluvial plain had time to develop and aggrade. Tectonic control on the sediments reduced and the influence of other factors, like base level, increased causing a stacked sequence architecture. Each rapid slip on the border fault created a low-order, shallowing-upward sediment package. It is also interpreted to be a ‘maturing-upward’ cycle of depositional processes. The low-order tectonic and higher-order sequence stratigraphy in graben settings show a hierarchy of depositional packages that can lead explorationists to greater predictability of reservoirs within nonmarine environments.

Abstract Thailand’s economy was forecast by the World Bank to grow by 5% in 2008 and gas demand was growing at around 3% per year. It is estimated that around 50% of its gas requirement may need to be imported by 2022 and the bulk of this is expected to come from the Thai-Malaysia Joint Development Area (MTJDA) and from Myanmar. Consequently, there is a drive within Thailand to maximize exploration within the country as well as to look at alternative energy sources. Thailand aims to reduce its proportion of energy consumption from oil from 41 to 31% within the next 15 years, substituting this with natural gas from the Gulf of Thailand while increasing the contribution of natural gas from 29 to 38% (S. Polachan pers. comm. 2007) (Fig. 13.1 ). In the main petroleum producing province, the Gulf of Thailand, production of gas, oil and condensate is still increasing (Fig. 13.2 ). Thailand currently has 19 producing gas fields (18 offshore and one onshore) and 22 oil fields (19 onshore and three offshore). The main basin and field locations are shown in Figure 13.3 . Proven, probable and possible reserves estimated by the Thai Government’s Division of Mineral Fuels (DMF 2007) are listed in Table 13.1 . For the purposes of this chapter, the petroleum geology of Thailand is divided into four main areas (Fig. 13.3 ) as follows: Gulf of Thailand, Tertiary, non-marine to marine basins (oiland gas-prone); Onshore Northern