Passive margin evolution and its controls on natural gas leakage in the southern Orange Basin, blocks 3/4, offshore South Africa

Evidence of a widespread paleo-pockmarked field in the Orange Basin: An indication of an early Eocene massive fluid escape event offshore South Africa

“…The main phase of petroleum generation is proposed to have occurred during the Cenomanian to Campanian period, followed by a minor generation phase during the late Cretaceous/ early Cenozoic, driven by rapid shelf progradation due to margin tilting, erosion and possibly increased heat-flow due to volcanism. A similar process has been proposed by Kuhlmann et al (2010Kuhlmann et al ( , 2011 and Paton et al (2007), for present-day gas leakage features observed in the southern basin, which would result from ongoing petroleum generation in the Cenozoic depocenters.…”

“…The sedimentary succession of the basin consists of 8 km thick synrift and drift sequences related to the continental break-up of Gondwana and the opening of the South Atlantic, taking place during the late Jurassic (Gerrard and Smith, 1982). The margin evolution and basin structure have been documented based on exploration seismic datasets and well reports (Gerrard and Smith, 1982;Dingle et al, 1983;Paton et al, 2008;de Vera et al, 2010;Kuhlmann et al, 2010). Muntingh and Brown (1993) and Brown et al (1995) provided the sequence stratigraphic framework of the late Jurassic and Cretaceous used in this study (Fig.…”

“…Thermal maturity decreases to wet-gas and oil window maturity towards the west and southwest of the shelf break, in the area of the Cenozoic sediment wedge (van der Spuy, 2003;Paton et al, 2007;Kuhlmann et al, 2011). Their present-day maturity below the Cenozoic shelf-break of the northern Orange Basin is expected to be within the wet-gas to dry-gas range (van der Spuy, 2003;Kuhlmann et al, 2010Kuhlmann et al, , 2011. Some authors propose a main phase of hydrocarbon generation from this source rock during the Campanian due to rapid burial, and a second ongoing generation phase in the southern Orange Basin due to the progradation of the thick (more than 2000 m) Cenozoic wedge (Paton et al, 2007;Kuhlmann et al, 2011).…”

“…Fluid and gas escape features and associated seismic anomalies, such as bottom simulating reflectors (BSR), chimney and pipe structures have been identified and characterized in various marine environments around the world (Berndt et al, 2004;Haacke et al, 2007;Judd and Hovland, 2007, and references within;Cartwright et al, 2007;Løseth et al, 2009;Westbrook et al, 2009;Løseth et al, 2011) and specifically in the South Atlantic margin (Cartwright et al, 2007;Gay et al, 2007;Pilcher and Argent, 2007;Swart, 2009;Moss and Cartwright, 2010;. Evidence of fluid and gas leakage processes, such as "sniffer" anomalies near the seafloor (Jungslager, 1999), also mud diapirs (Ben-Avraham et al, 2002;Viola, et al, 2005), pockmarks and seismic chimneys (Ben-Avraham et al, 2002;Paton et al, 2007;Kuhlmann et al, 2010;Boyd et al, 2011), have previously been identified on 2D seismic surveys in the Orange Basin, offshore South Africa. They have been related, by means of numerical modeling, to the underlying petroleum system (Paton et al, 2007;Kuhlmann et al, 2011).…”

Reconstruction of the southwestern African continental margin by backward modeling

“…A non-exhaustive list comprises: (1) seismic investigations (e.g. Bauer et al, 2000;Bauer et al, 2003;Fern andez et al, 2010;Gladczenko et al, 1998;Hartwig et al, 2012;Koopmann et al, 2013;Kuhlmann et al, 2010;Weigelt and Uenzelmann-Neben, 2007), (2) potential field modeling (Hirsch et al, 2007(Hirsch et al, , 2009; Maystrenko et al, 2013;Stewart et al, 2000), (3) dating of vertical movements by sequence stratigraphy and geochemical dating methods (Broad et al, 2006;Brown et al, 1995;Holtar and Forsberg, 2000;Kuhlmann et al, 2011;Light et al, 1993;McMillan, 2003;Paton et al, 2007;Trumbull et al, 2007), (4) kinematic analysis or (5) a combination of several techniques (e.g. : Hirsch et al, 2010;Paton et al, 2008).…”