Abstract

The NE Natuna Production Sharing Contract (PSC) is an offshore block located on the northernmost part of the Indonesian territory, 300 km. NNE of Natuna Island. It lies within the East Natuna Basin where Esso's supergiant "D-Alpha" gas field, 100 km. to the SSE, and the 1978 oil discovery well, Bursa-1X (3,020 BOPD), 30 km. to the SSE, are situated. BP's LanTay and Lan Do gas fields and the Dua oil and gas discovery (1,514 BOPD, 625 BCPD and 18 MMCFGPD) in the South Con Son Basin of southern Vietnam are approximately 85 km. to the north and 95 km. to the WNW, respectively. ()

Five prospects and leads have been identified within the block (). Potential unrisked upside reserves for each of these five features range from 1,436 to 4,716 MMBO, indicating that the arithmetic total upside potential of the block could be at least 14,730 MMBO. Seismic lines in (Prospect A: 1,436 MMBO) and (Prospect B: 1,843 MMBO) illustrate the major plays in the block. These plays are analogous to producing fields in the region and with their enormous reserve potential, they make the NE Natuna PSC as one of the most technically and commercially attractive areas in Asia.

Titan's evaluation of the block, which included petrophysics, biostratigraphy, geochemistry, sequence stratigraphy, AVO analysis and prospect assessment indicates that there is indeed a potential, major, operative petroleum system in the area. The stratigraphy and the components of the petroleum system of the East Natuna Basin is shown in . Previous unsuccessful wells in or near the area were mainly focused on Miocene carbonates and did not test any objective in the hydrocarbon window. The prospects and leads mapped by Titan have sub-carbonate sandstone closures within the hydrocarbon window as primary objectives. Seismic within the block consist of vintage 1970 (AGIP) and 1996–1998 (GFB) data, plus the 2004 TSG-Nopec spec shooting.

Seismic sequence stratigraphy points to the widespread presence within the block of a major lacustrine sequence in the Oligocene Gabus Formation (please refer to and ). Similar sequences are the major petroleum source rocks for giant fields in several SE Asian basins. Lopatin modeling shows that this lacustrine sequence within the block is currently in the oil/gas window or past thermal maturity assuring maximum generation of hydrocarbons (). This interpretation is supported by the geochemical analysis results that the oil at the Bursa-1X well was sourced from a horizon with abundant liptinitic (cuticles/spores/algae) kerogen, in a state of full thermal maturity for heavy to medium oil generation and which comprises mainly waxy hydrocarbons containing abundant higher-plant derived biomarkers typical of a terrestrial source. Several other potential, high frequency, lacustrine source rock intervals are present in the Arang Formation.

The main reservoir objectives of the prospects and leads within the block are the fluvio-deltaic sandstones of the Oligocene-Early Miocene Gabus and Arang formations. These sandstones reach individual thicknesses in excess of 30 meters and exhibit average porosity of nearly 20%. The reservoirs of the Dua discovery well () and several giant oil and gas fields in the greater Sarawak, West Natuna, Con Son, Brunei and Sabah basins are similar to these Gabus-Arang reservoirs. Previous wells in the basin targeted the Miocene Terumbu carbonates sealed by thick marine claystones of the Muda Formation. Average porosities of these carbonates reach as high as 31%. These are the reservoirs at D-Alpha, Bursa, Lan Tay and Lan Do.

The NE Natuna PSC was originally awarded by Pertamina to P.T. Binatek Reka Natuna and GFB Resources (Natuna) Limited on May 25, 1997. The contract area currently measures 1,460 sq. km. after modification due to the Indonesia-Vietnam boundary resolution on 26 June 2003. Water depths within the block range from 130–900 meters. The NE Natuna PSC has "frontier" and "deep water (>200 meters)" terms, providing the contractor a production share of up to 62.5% and 71.4286% for oil and gas, respectively.

Esso drilled one well, Durian Besar-1, in 1998 as part of their farm-in to the block. The well only tested the top of a large, shallow Late Miocene reef and was abandoned as dry. Esso withdrew after this drilling and the operatorship was transferred back to GFB Resources. Titan Resources (Natuna) Indonesia Limited acquired 85% of the block and is currently the operator. A substantial participating interest is available to farminee/s in exchange for seismic and/or the drilling of one well.

For further information, please contact Arturo Morado, Jr. in Manila, Philippines (Email: [email protected], [email protected]).

Presented at: 2005 South East Asia Petroleum Exploration Society (SEAPEX) Conference, Singapore, 2005