Abstract Disputed areas of the South China Sea (SCS) can be explored effectively ahead of boundary settlements by using potential fields data coupled with geological literature. Potential fields techniques are uniquely suited to such screening evaluations because the foundation data sets, particularly gravity, are seamless, cover huge areas at low cost, provide basin-scale sedimentation as well as structural information and can identify large targets. When integrated with published knowledge, gravity and magnetics data provide powerful exploration tools; in disputed zones, perhaps the only ones available. The authors used potential fields data processed and displayed by GETECH's proprietary methods to revamp the tectonic interpretation of the SCS, redefine basins and identify new depocenters, structures, and sediment delivery systems. The disputed areas of current oil and gas production will be discussed: the Xisha Trough, southeastern Qiongdongnan Basin, Phu Khanh/Nha Trang Basin, Tu Chinh/Vung May Basin and the carbonate bank regions of the northern and southern margins of the SCS. The Phu Khanh and southern Qiongdongnan basins in particular have been redefined and extended. Hydrocarbon sourcing is a key issue over much of the outboard area due to the thinness of the Cenozoic section outside of the major basins. Indications of hydrocarbons do occur in both the basins and banks areas. Gravity derivatives, a sediment isopach calculated from depth to magnetic basement, and corroboration from the literature provide the basis for mapping depocenters. The depocenters are interpreted as having mainly Cenozoic fill, with inferred Paleogene source rocks, but significant Pre-Tertiary sections and Pre-Tertiary hydrocarbon sources may be a component of some. Thermal maturity will be a key discriminator between oil and gas. Heat flow variations with time will be a major factor in modeling thermal maturity because of differences in the relative timing of tectonic events across the area. Clastic reservoirs are more likely to offer sealed traps than the numerous reefs and carbonate banks, which often grow to the seafloor. The synrift section offers the best chance of sandstone reservoirs, sealed by post-rift deepwater mudstones. Gravity attribute and derivative image interpretation indicates that the more established sediment delivery systems did not reach most of this area. A few speculative canyon systems are mapped outboard of the Northwest Palawan Basin, but nearly all channel signatures are short, discontinuous, local features. Structures are present in all basins. Fault-related highs between the grabens/half-grabens should provide structural targets in the marginal banks areas. Given the resolution of the gravity data used by the authors (approximately 6–8 km), mappable structures are large. Large targets are an economic necessity because most of the outboard disputed zones are in water depths greater than 1000 m. The deep water, combined with boundary issues, will delay seismic exploration and drilling, but potential fields interpretation indicates areas worth further investigation. Political progress is being made in addressing disputed zones in the SCS. Perhaps we will yet see some of these areas thoroughly tested. Presented at: 2005 South East Asia Petroleum Exploration Society (SEAPEX) Conference, Singapore, 2003
Abstract A new long-offset, long-record crustal-scale seismic survey of 9600 km called JavaSPAN was acquired in the Java Sea and Makassar Strait. The East Java Sea is underlain by continental basement with a prolonged multiphase history of deposition punctuated by extensional and compressional events. This East Java Terrane is a major component of SE Sundaland lying between the Meratus suture, the contemporary Java arc, and the west Sulawesi orogenic belt, but is poorly constrained on the north under the North Makassar Basin and in Kalimantan. A Precambrian to Permo-Triassic sedimentary section up to some 8.5 km in thickness overlies crystalline basement in a number of fault blocks and synformal structures below a strong angular unconformity. A thin overlap assemblage of Cretaceous to early Cenozoic sediments overlies that unconformity. Middle Eocene to Neogene clastic and carbonate rocks overlie another angular unconformity that marks the initiation of a well known history of Palaeogene extension, sag, and Neogene inversion. The East Java Terrane rifted from the Bonaparte-Arafura sector of northern Australia in the Jurassic and accreted onto a magmatic arc on the SW flank of what is now Kalimantan in the Cretaceous.
This paper presents the techniques and results of a depth to basement inversion effort over the South China Sea area of Southeast Asia. Integrating the results of the inversions with geoseismic, well and geological data results in an accurate and informative description of the tectonics and structure of the area. Results show that significant packages of sediments of exploration interest exist that have not been exploited. Basin geometry and structure can be derived from the inversion of gravity and magnetic data. Using some newly developed techniques these inversions can also discriminate between different lithologies. Magnetic data can be inverted for magnetic basement and for intermediate layers of volcanic material. Gravity data can be inverted for structures which produce density contrasts in basins. Combining these results, basin structure can be explored to determine depth to basement, to high density structures such as carbonates, and to high susceptibility structures such as volcanics. New high resolution data sets for gravity and magnetic data have been merged and now cover all of greater Southeast Asia. These data allow us to extend our interpretation to all offshore basins and some onshore as well. We use the structural interpretations described above along with enhancements of gravity, magnetic and digital elevation model data. Combining these interpretations and enhancements with published data in a GIS environment allows us to constrain additional interpretations of tectonic development, and sedimentary facies and structures in basins. Examples are shown for basins around the South China Sea. Early results from offshore South America will also be presented.
This paper presents the techniques and results of a depth to basement inversion effort over the South China Sea area of Southeast Asia. Integrating the results of the inversions with geoseismic, well and geological data results in an accurate and informative description of the tectonics and structure of the area. Results show that significant packages of sediments of exploration interest exist that have not been exploited. Basin geometry and structure can be derived from the inversion of gravity and magnetic data. Using some newly developed techniques these inversions can also discriminate between different lithologies. Magnetic data can be inverted for magnetic basement and for intermediate layers of volcanic material. Gravity data can be inverted for structures which produce density contrasts in basins. Combining these results, basin structure can be explored to determine depth to basement, to high density structures such as carbonates, and to high susceptibility structures such as volcanics. New high resolution data sets for gravity and magnetic data have been merged and now cover all of greater Southeast Asia. These data allow us to extend our interpretation to all offshore basins and some onshore as well. We use the structural interpretations described above along with enhancements of gravity, magnetic and digital elevation model data. Combining these interpretations and enhancements with published data in a GIS environment allows us to constrain additional interpretations of tectonic development, and sedimentary facies and structures in basins. Examples are shown for basins around the South China Sea. Early results from offshore South America will also be presented.
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