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1 Omegalink International, Ltd., 2382 Rt. 118, Dorchester, New Hampshire 03266; omegalink{at}juno.com
2 Surface Geochemical Services AS, P.O. Box 5740, 7437 Trondheim, Norway; malvin{at}geolabnor.no
3 Omegalink International, Ltd., 2382 Rt. 118, Dorchester, New Hampshire 03266; omegalink{at}juno.com
4 Geolab Nor AS, P.O. Box 5740, 7437 Trondheim, Norway; iafe{at}geolabnor.no
Gary holds a Ph.D. from Columbia University under M. G. Langseth (Heat Flow Department), Lamont-Doherty Earth Observatory. He spent 6 years at Gulf Research and Development (Harmarville Lab), where he studied measurement and modeling of hydrocarbon thermal regimes. He continued this work at Brookhaven National Laboratory as visiting research associate at Lamont-Doherty and (1989–present) as a director at Omegalink International Ltd.
Malvin Bjorøy, a graduate of organic chemistry from the University of Bergen, spent 8 years at the Norwegian Continental Shelf Institute, where he established the surface geochemistry group and became head of the department, establishing Geolab Nor AS in 1985. Malvin has directed more than 70 surface geochemical surveys, mainly in the Norwegian, North, and Barents Seas and in the Far East. Malvin has published more than 80 articles in international journals.
Robyn holds a B.S. degree from the Virginia Polytechnic Institute and State University, with graduate studies at Virginia Commonwealth University. She began working with Omegalink International, Ltd., in 1980 and has since participated in numerous marine and land-based heat-flow and geochemical data acquisition programs. This includes data reporting and publication in international journals. Robyn currently serves Omegalink as a director specializing in field operations.
Ian is a graduate of geology from Imperial College, London, United Kingdom. Besides routine well geochemistry and visual kerogen microscopy, Ian's work has included numerous regional well projects and surface geochemical surveys worldwide. Ian is currently laboratory manager at Geolab Nor AS, Trondheim, Norway, having been involved with more than 20 articles in international journals.
Simultaneous heat flow and geochemical gravity coring data from 186 sites on the Brunei margin reveal abundant thermogenic hydrocarbons in the landward half of our study area, where the mean heat flow is 83.7 ± 66.5 mW/m2. Seaward, the mean heat flow is 59.0 ± 22.6 mW/m2, and surface thermogenic hydrocarbons are largely absent. In accord with active accretionary complexes, the low-heat-flow zone coincides with the Palawan (northwest Borneo, Nansha) Trough paleosubduction zone. The high-heat-flow zone of hydrothermal convection and hydrocarbon seepage coincides with the landward, land-derived Baram delta sediments, constituting a pseudo–accretionary prism. The transition from oil to gas production with increasing geothermal gradient, observed in well data, appears to be reflected in our surface data. Equality of Brunei and China margin heat flow predicts a common thermotectonic origin that predates by less than or equal to 5 m.y., the oldest (32 Ma) magnetic lineations in the South China Sea Basin. Thermal effects of prior active subduction, if any, have dissipated, and Brunei margin heat flow has rebounded to theoretical passive-margin values.
A single megaseep exhibits maximum heat flow (604 mW/m2) coincident with anomalous thermogenic hydrocarbons. Vertical fluid flow at 1.7 cm/yr (0.67 in./yr) (5.5 x 10–10 m/s; 1.80 x 10–11 ft/s) from 6 km (3.7 mi) depth, implying greater than 30 times focusing of flow, can account for this heat flow and provide hydrocarbon transport from potential sources. A 42 times higher flow rate via bubble ascent or continuous gas-phase flow can also account for our data. Simple models of fluid flow around fault-bounded sediment troughs reproduce the observed heat flow. These models predict that measurements confined to trough interiors, where heat flow is uniform, seriously underestimate mean regional heat flow (23–80%) and thermal maturation; whereas heat flow at all geochemical coring sites yields reliable means.
Megaseep data reveal systematic changes in thermogenic hydrocarbons and heat flow with distance from the seep axis. A simple diffusion model represents these changes in terms of bulk near-surface processes. A simple thermogenic model also simulates gas data; however, thermal-maturation parameters indicate no causal connection between megaseep heat flow and thermogenesis. Invariant parameters, less affected by migration, fractionation, mixing, and biodegradation, remain anomalous more than 250 m (800 ft) from the megaseep axis, encompassing all four high-heat-flow sites. This constitutes a significantly greater aperture for identifying seeps in coring data compared with headspace gases, found anomalous at one site only. Like heat flow, invariant parameters that are extreme at the megaseep may particularly reflect more active seepage, where hydrocarbons are less altered and more closely reflect their sources. Regional data covering 10,000 km2 (3600 mi2) largely reflect the same near-surface processes occurring within 500 m (1600 ft) of the megaseep. Consequently, distances from regional seeps and paleoheat flow can be inferred.
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  M. R. P. Tingay, R. R. Hillis, R. E. Swarbrick, C. K. Morley, and A. R. Damit Origin of overpressure and pore-pressure prediction in the Baram province, Brunei AAPG Bulletin, January 1, 2009; 93(1): 51 - 74. [Abstract] [Full Text] [PDF]
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