scholarly journals Overpressures in the central Otway Basin: the result of rapid Pliocene–Recent sedimentation?

2011 ◽  
Vol 51 (1) ◽  
pp. 439 ◽  
Author(s):  
David Tassone ◽  
Simon Holford ◽  
Mark Tingay ◽  
Adrian Tuitt ◽  
Martyn Stoker ◽  
...  
Keyword(s):  
Late Miocene ◽  
Upper Cretaceous ◽  
Source Rocks ◽  
Hydrocarbon Generation ◽  
Key Factors ◽  
Submarine Channels ◽  
Early Pliocene ◽  
Pore Pressures ◽  
Clastic Sediments ◽  
Drilling Data

This paper reports the first evidence for significant overpressures in the Otway Basin, southern Australia, where most previous studies have assumed near-hydrostatic pore pressures. Overpressures are observed in the Upper Cretaceous Shipwreck supersequence in several wells in the Voluta Trough, such as Bridgewater Bay–1, Normanby–1 and Callister–1. One of these wells penetrated successions of Pliocene-Recent marine clastic sediments nearly 700 m thick that were deposited rapidly in submarine channels and that were probably carved during the late-Miocene to early-Pliocene. Wireline and drilling data suggest that overpressures present in Upper Cretaceous shales and sandstones in the Belfast Mudstone and Flaxman and Waarre formations developed either due to disequilibrium compaction—where there is no evidence of hydrocarbon generation and thick Pliocene stratigraphy is present—or due to fluid expansion where there is evidence of hydrocarbon generation and the Pliocene stratigraphy is thin to absent. The two key factors that may indicate abnormal pore pressures in Upper Cretaceous sediments in the central Otway Basin are the thickness of Pliocene stratigraphy and whether or not hydrocarbons are actively generating from source rocks.

ELEVATED MID-CRETACEOUS PALAEOTEMPERATURES IN THE WESTERN OTWAY BASIN: CONSEQUENCES FOR HYDROCARBON GENERATION MODELS

1997 ◽  
Vol 37 (1) ◽  
pp. 505 ◽  
Author(s):  
M.M. Mitchell
Keyword(s):  
Upper Cretaceous ◽  
Vitrinite Reflectance ◽  
Geothermal Gradient ◽  
Hydrocarbon Generation ◽  
Key Factors ◽  
Factors Affecting ◽  
Early Maturation ◽  
Maximum Temperatures ◽  
Hydrocarbon Preservation ◽  
Uplift And Erosion

The Otway Basin formed during the Mesozoic separation of Antarctica and Australia. A study of apatite fission track (FT) analysis and vitrinite reflectance (VR) data from borehole samples in the western Otway Basin was initiated to elucidate some of the thermal and structural complexities of this region.Interpretation of results suggest that some areas experienced regionally elevated palaeotemperatures, however, much of the region is at present-day maximum temperatures. Where cooling from maximum palaeotemperatures is observed, the timing may be grouped over three main intervals as follows; mid-Cretaceous, Late Cretaceous to Early Tertiary, and Tertiary. Cooling was facilitated by a decline in geothermal gradient, uplift and erosion, or both. Evidence for a decline in geothermal gradient from values >55°C/km in the mid- Cretaceous is recognised in several wells. Elevated mid- Cretaceous palaeogeothermal gradients (50−60°C/km) have been reported for the eastern Otway Basin, suggesting that these high temperatures were a regional phenomena. Cooling by uplift and erosion at this time was minimal throughout the western Otway Basin in contrast to the kilometre scale uplift and erosion reported for the eastern Otway Basin and adjacent basement inland of this section of the rift.The relative early maturation of the Otway Supergroup during mid-Cretaceous regionally elevated geothermal gradients, and subsequent basin restructuring, are key factors affecting hydrocarbon preservation in the western Otway Basin. Strategies for identification of prospective areas include identification of regions that have remained at moderate temperatures during the Early Cretaceous, and have not undergone burial under a thick Upper Cretaceous to Tertiary section.

scholarly journals Source rock potential of the Late Miocene Metochia formation of Gavdos Island, Greece

2017 ◽  
Vol 47 (2) ◽  
pp. 871
Author(s):  
I. Pyliotis ◽  
A. Zelilidis ◽  
N. Pasadakis ◽  
G. Panagopoulos ◽  
E. Manoutsoglou
Keyword(s):  
Organic Matter ◽  
Source Rock ◽  
Late Miocene ◽  
Source Rocks ◽  
Hydrocarbon Generation ◽  
Low Oxygen ◽  
Crete Island ◽  
Good Potential ◽  
The Rich ◽  
Rock Eval

Rock-Eval method was used to analyze 53 samples from late Miocene Metochia Formation of Gavdos Island (south of Crete Island) in order to characterize the contained organic matter and to evaluate its potential as source rock. The samples were collected from Metochia Section which consists of about 100 m thick marlssapropels alternations. Organic matter analysis showed that the studied succession could be subdivided into two parts. The lower one, which is generally rich in organic matter and the upper one, which is poor. In the lower part the rich horizons in organic matter are characterized by Kerogen type II, III and IV, with low oxygen content, and with fair to very good potential for gas and/or oil hydrocarbon generation. Additionally, the studied samples are thermally immature. Taking into account that the studied area has never been buried in such a depth to reach conditions of maturation, as well as, that the studied section in Gavdos is connected with Messara basin located in the northeastern and, finally, that the main part of Gavdos basin, which is situated between Gavdos and Crete islands, has continuously encountered subsidence, we could conclude that sediments of Metochia Formation could act as source rocks but in the more deep central part of the Gavdos basin.

GIFFSLAND HYDROCARBONS - A PERSPECTIVE FROM THE BASIN EDGE

1984 ◽  
Vol 24 (1) ◽  
pp. 91 ◽  
Author(s):  
J. G. Stainforth
Keyword(s):  
Heat Flow ◽  
Upper Cretaceous ◽  
Oil And Gas ◽  
Source Rocks ◽  
Hydrocarbon Generation ◽  
Lower Tertiary ◽  
Late Tertiary ◽  
Carbonaceous Shales ◽  
Basin Edge ◽  
Gippsland Basin

Permit VIC/P19 lies palaeogeographically seaward of the main producing part of the Gippsland Basin. Deposition of the Latrobe Group commenced with volcanics and continental 'rift-stage' sediments during the Late Cretaceous. This phase was succeeded first by paludal sedimentation in the failed rift during the Campanian and Maastrichtian, and then by cyclic paralic sedimentation during the Paleocene and Eocene.Analysis of the hydrocarbons recovered during recent exploration of permit VIC/P19 shows that they were sourced from moderately mature coals and carbonaceous shales in the Campanian/-Maastrichtian paludal sequence.A maturation model that assumes elevated but decreasing heat flow, related to sea-floor spreading, produces an excellent fit to the observed maturity data and predicts a long history of hydrocarbon generation during the Tertiary. The maturity of the Upper Cretaceous source sequence depends more on the thickness of the overlying Lower Tertiary clastic Latrobe sediments than on the thickness of the Upper Tertiary carbonate wedge. The Late Tertiary phase of burial had relatively little effect on maturation because of its rapidity and the lower heat flow and higher thermal conductivities of the deeper sequence at the time. Overpressures in mature Upper Cretaceous source rocks, resulting from hydrocarbon generation, have driven pore fluids, including hydrocarbons, laterally up-dip into normally pressured reservoirs.The main oil province of the Gippsland Basin has a greater thickness of Lower Tertiary than has VIC/P19. As a result, source rocks are more mature there, and became wholly so by the end of deposition of the Latrobe Group. This facilitated charge of traps at the top of the Latrobe Group, which contain most of the oil and gas discovered to date in the Basin.

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