Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
The Importance of Upwelling Along the Californian Margin with Links to Sequence Stratigraphy and Petroleum Significance
(1) Neftex Petroleum Consultants Ltd, Abingdon, United Kingdom.
The Minerals Management Services estimates that the Pacific outer continental shelf contains undiscovered technically recoverable resources of 10.43 billion barrels of oil and 13.79 billion barrels of oil-equivalent natural gas. To glean new insight into the petroleum systems and key play elements of the region we have conducted a biostratigraphically constrained, sequence stratigraphic analysis of available published well and outcrop data covering both platformal and basinal stratigraphy. The study focuses on the Miocene Monterey Formation - a recognised upwelling-related source rock.
The relationship between upwelling and high TOC sediments is recognized globally and is well established. Deposition of organic-rich facies is accepted during the transgressive systems tract and the maximum marine transgression. However the sequence stratigraphic analysis of sediments along the Californian margin identified facies of high TOC with oil prone kerogen deposited during the lowstand systems tract. Support for this interpretation comes from sediment cores along the west coast of Africa which demonstrate organic-enrichment during the last glacial (lowstand) periods.
The recognition of world class LST source rocks in California creates a potential analogue for deep water exploration globally by extending source rock deposition distal of TST and MFS source rocks without the need of an ocean anoxic event. The occurrence of LST upwelling source rocks is governed by global climate, continental configuration and local depositional environments. Local climate, structure and shelf width need to be understood to predict the development of lowstand deltas. These control where sediment is transported off the shelf, therefore where clastic dilution can destroy upwelling source rock potential. Conversely subsequent delta switching allows the burial and thermal maturation of LST source rocks.
Our global palaeogeographic and palinspastic mapping allows an understanding of upwelling patterns through time, enabling the prediction of potential LST source rock development. The risks associated with local development of these source rocks such as areal and temporal extent of upwelling, preservation of oil prone facies and the impact of LST sediment input can be assessed through a regional palaeogeographic understanding. This allows prediction of the occurrence, thickness and potential maturity of these source rocks which can be assessed within a genetic model.