Hydrocarbon systems of northeastern Venezuela:plate through molecular scale-analysis of the genesis and evolution of the Eastern Venezuela Basin

摘要

The prolific,oil-bearing basins of eastern Venezuela developed through an unusual confluence of Atlantic,Caribbean and Pacific plate tectonic events.mesozoic rifting and passive margin development created ideal conditions for the deposition of world-class hydrocarbon source rocks.In the Cenozoic,transpressive,west-to-east movement of the Caribbean plate along the northern margin of Venezuela led to the maturation of those source rocks in several extended pulses,directly attributable to regional tectonic events.The combination of these elements with well-developed structural and stratigraphic fairways resulted in remarkably efficient mogration of large volumes of oil and gas,which accumulated along the flanks of thick sedimentary depocenters.At least four proven adn potential hydrocarbon source rocks contribute to oil and gas accumulations.Cretaceous oil-prone,marine source rocks,and Miocene oil- and gas-prone,paralic source rocks are well documented.We used reservoired oils,seeps,organic-rich rocks,and fluid inclusions to identify probable Jurassic hypersoline-lacustrine,and Albian carbonate source rocks.Hydrocarbon maturation began during te Early Miocene in the present-day Serraina del Interior,as the Caribbean plate movel eastward relative to South America.Large volumes of hydroarbons expelled during this period were lost due to lack of effective traps and seals.By the Middle Miocene,however,when source rocks from the more recent foredeeps began to mature,reservoir,migration pathways,and topseal were in place.Rapid,tectonically driven burial created the opportunity for unusually efficient migratio and trapping of these later-expelled hydrocarbons.The generally eastward migratio of broad depocenters across Venezuela was supplemented by local,tectonically induced subsidene.These subsidence patterns and later migration resulted in the mixing of hydrocarbons from different source rocks,and in a complex map pattern of variable oil quality that was further modified by biodegradation,lats gas migration,water washing,and subsequent burial.The integratin of plate tectonic reconstructions with the history of source rock deposition and maturation provides significant insights into the genesis,evolution,alteration,and demise of Eastern Venezuela hydrocarbon systems.We used this analysis to identify additional play potential associated with probable Jurassic and Albian hydrocarbon source rocks,ofthe overlooked in discussions of Venezuela.The results suggest that oils associated with likely Jurassic source rocks originated in restricted rift-controlled depressions lying at high angles to the eventual margins of the South Atlantic,and that Albian oils are likely related to carbonate depositio along these margins,post-continental break up.In terms of tectonic history,the inferred Mesozoic rift system is the eastern continuation of hte Espino Graben,whose remnant structures underlie both te Serrania del Interior ad the Gulf of Paria,where thick evaporite sections have been penetrated.The pattern of basin structure and associated mesozoic deposition as depicated in teh model has important implications for the Mesozoic paleogeography of northern South Americal and Africa,Cuba and the yucatan and associated new play potntial.