Abstract: Methane clumped-isotope compositions provide a new approach to understanding the formational conditions of methane from both biogenic and thermogenic sources. Under some conditions, these compositions can be used to reconstruct the formational temperatures of the gas, and this capability can be applied to common subsets of both biogenic and thermogenic systems. Additionally, there are examples in which clumped-isotope compositions do not reflect gas-formation temperatures but instead mixing effects and kinetic phenomena; such kinetic effects also occur in common and recognizable subtypes of biogenic and thermogenic gases. Here we review the use of methane clumped-isotope measurements for understanding the origin of methane in the subsurface. We review methane clumped-isotope measurements from numerous biogenic and thermogenic natural gas reservoirs. We then place these measurements in the context of common frameworks for identifying the formational conditions of methane including the use of methane δ 13 C and δD values and C 1 /C 2–3 ratios. Finally, we propose a framework for how methane clumped isotopes can be used to identify the origin of methane accumulations.

Abstract Widely distributed deep-water fan sandstones of early Tertiary age form the reservoir for one of the most successful and prolific plays in the North Sea and NE Atlantic margin. Stratigraphic interpretation of a large well database provides the basis for mapping sand distribution and depositional environments in these two hydrocarbon provinces. Sand thickness maps for five Paleocene–Lower Eocene plays illustrate the intimate relationship between pre-existing structural features and sand distribution and facies in the North Sea. Large-scale depositional environment mapping gives an insight into the similarities and differences between basin evolution and sand distribution in North Sea and NE Atlantic margin basins. Both provinces were affected by the same succession of pre-break-up and syn-break-up tectonic and magmatic events that led to early Eocene continental separation and the formation of the NE Atlantic. The impact of these events was muted within the North Sea, which was protected from Paleocene rifting on the NE Atlantic margin by the Scotland–Shetland hinterland and from Paleocene–early Eocene volcanism by its more distant location. However, it was the combination of tectonic and thermal uplift of this clastic source area that contributed the large volumes of sand that accumulated in both these provinces.

Convergent orogenic systems pose challenges for the prospector seeking to predict oil and gas reservoirs, as these regions are often data poor. Explorationists, therefore, must often rely on conceptual models to predict the occurrence of oil and gas, and to choose the most favorable exploration areas. This paper examines how different conceptual models of hinterland evolution can influence predictions of hydrocarbon systems in an adjacent foreland. A one-dimensional (1-D) method was developed for assessing incremental hydrocarbon yield during progressive fold-belt deformation and source rock burial and maturation. This method was employed to evaluate the way in which hydrocarbon yield is affected by two different scenarios for the timing of uplift of the Puna Plateau and subsequent burial of the adjacent Metán region of northwestern Argentina. In the first scenario, plateau growth and burial of the Metán region begin in the early Miocene and progress to the present day. In the second scenario, plateau growth and basin formation occur predominantly in the Eocene, with minor deformation from middle Miocene to present. The later load timing decreases the relative volume of liquid hydrocarbons available to fill structural traps. The differences in charge volume and timing between the two scenarios are enhanced in this region as a result of thinned crust and relatively high heat flow that linger from a Cretaceous rifting event. The results of the study provide an example of how boundary conditions obtained from studies of an orogenic hinterland can be used to calculate risk for exploring a potential play within a basin where data are incomplete or inconclusive. They also yield general insights on the use of regional genetic concepts to predict thermal history and source rock maturation and yield in data-poor areas.

Abstract The intracratonic, supra-subduction zone setting of the Thailand rift basins caused the rifts to evolve in several ways differently from other intracratonic rifts. Key differences include: widespread occurrence of low-angle normal faults; basin inversion alternating with rifting; diachronous initiation and cessation of rifting; rapid post-rift subsidence; and extensive, low-displacement post-rift faults. These characteristics are related to hot, weak continental lithosphere, rapid evolution of the plate boundaries and stresses during the Cenozoic, and the history of subduction and accretion. Low-angle normal faults impacted the Sirikit Field by controlling the location of fluvio-deltaic reservoirs interfingering lacustrine shales (source and seal). Basin inversion alternating with syn-rift section is detrimental to prospectivity of the southern half of the Phitsanulok Basin by destroying syn-rift structure, and halting hydrocarbon maturation early in the basin history. The diachronous timing of basin development resulted in large, gas-dominated hydrocarbon accumulations in the eastern Gulf of Thailand basins, but was detrimental for younger basins that lack the post-rift section, and the greater variety of petroleum systems and traps that post-rift basins offer. The extensive low displacement–length ratio post-rift faults form significant hydrocarbon traps in the Pattani and North Malay basins. They represent a structural style not usually found in post-rift basins.