Neotectonic Controls on Petroleum Accumulations, Offshore China

Abstract

Tectonic activity offshore China during the Late Miocene and Quaternary (“neotectonism”) generated unconformities, resulted in depocentre migration, created new faults and initiated earthquake activity. This episode of structural disturbance, which occurred during post‐rift thermal subsidence, modified pre‐existing hydrocarbon accumulations and formed new pools. Constructive effects of neotectonism occurred in the Bozhong Depression, Zhu #2 Depression and the Yinggehai Basin. These effects included the formation of new structural traps, migration routes and source kitchens. Destructive effects occurred in the Xihu Depression where oil/gas fields were partially breached by post‐trap peneplanation and faulting. There are pools with active gas leakage through neotectonic faults and this seems to suggest a dynamic balance between outboard leakage of gas and inboard migration of hydrocarbons. This paper summarizes understanding of the past 15 years of offshore exploration in China which has primarily focused on Neogene reservoirs. Data used for this report include extensive coverage of conventional P‐wave and multi‐component 2D and 3D seismic data, drilling results and extensive geochemical and geological analyses.

Tectonic controls on fault zone flow pathways in the Rio Grande rift, New Mexico, USA

“…Understanding basin-scale subsurface fluid flow is critical to petroleum exploration (e.g., Bethke et al, 1991;Gong et al, 2011), geological CO 2 sequestration (e.g., Birkholzer et al, 2009;Person et al, 2010), and contaminant transport modeling (e.g., Carle et al, 2006). In rift basins, factors affecting regional flow patterns include variations in sediment type (Person and Garven, 1994;Mailloux et al, 1999), basin subsidence and/ or compaction (Cathles and Smith, 1983;Cartwright, 1994), and hydrothermal circulation (Person and Garven, 1992;Simms and Garven, 2004).…”

Revitalization of a mature oil-bearing basin by a paradigm shift in the exploration concept. A case history of Bohai Bay, Offshore China

“…This was especially the case during the Pliocene, when the depression experienced another episode of structural disturbance along the Tanlu Fault (Gong, 2004). The fault is a transtensional fault extending over 400 km offshore from Liaodong Bay in the north to the Liaozhou Bay in the south.…”

“…These explorationists, based on the common association of source rock presence with high rates of subsidence in the onshore depressions, speculated that rapid Neogene subsidence could have generated a new suite of source potential previously ignored and that recent fault movements along the Tanlu Fault could have provided needed conduits for upward hydrocarbon migration into Neogene reservoirs (Zhu and Wang, 2000;Gong and Wang, 2001;Gong, 2004). Sequence stratigraphic studies showed fluvial systems drained toward the depression center, where the predicted lacustrine environments could provide the needed regional top seals (Mi, 2001).…”

“…2 for field locations). These fields, which were filled to their spill points, appear to be in a dynamic balance between hydrocarbon escape and charge (Gong and Wang, 2001;Gong, 2004). To maintain such a balance requires sufficient hydrocarbon generation, efficient migration pathways capable of providing rapid charges and a regional cap.…”

“…Paleogene faults occur basin wide and are mostly syn-sedimentary with over a thousand meters of throw and several kilometers of extension. They often offset preTertiary basement and provide the principal vertical migration pathways for the oil generated in the Eocene and Oligocene source rocks (Gong, 2004). Neogene fault movements, on the other hand, appear to have been more active offshore than onshore.…”