Paleo-environmental Reconstruction and Analysis (Paleogeography, Paleoclimate, Paleo-oceanography, Paleobiology) as part of Integrated Source Rock Prediction
Authors: Bohacs Kevin , Fraticelli Carmen 
Published: November 2008

Innovations in paleo-environmental reconstructions can play an important part in the exploration needed to meet the world's growing demand for sufficient and reliable energy. We have developed new technology which integrates the complex interactions among numerous paleoenvironmental controls to predict the occurrence, quality, and distribution of source rocks at a basin-scale. A key element of the analysis is the determination of the impact of paleogeography and paleo-earth systems on the production, preservation, and concentration of organic-matter-rich strata.

Paleo-environmental conditions include all aspects of paleogeography, paleoclimate, paleo-oceanography, and paleobiology. They play an important part in controlling the distribution of lithofacies in sedimentary basins through their proximate, derivative controls on such key parameters as accommodation, sediment supply, hydrology, and fluvial discharge. These proximate controls are complex, and commonly convergent, combinations of first-order, ultimate controls such as tectonics, climate, and biological evolution. Robust predictions of lithofacies and play-element character require detailed consideration of governing processes and key contingencies. For each play element, we therefore used paleo-environmental reconstructions to provide input on process parameters and contingent conditions to the appropriate depositional models.

The accumulation of organic matter in marine depositional environments is controlled by complex, non-linear interactions of three main processes: rates of dilution, production, and destruction. Significant enrichment of organic matter occurs where dilution by clastic or biogenic material is optimized, organic-matter production is maximized, and destruction is minimized. Details of paleogeography (topography, bathymetry, drainage networks, etc.) significantly condition the response of the source rock system to the three key processes. For example, the development of clastic fairways across a shelf allows bypass of coarse clastic sediments into deeper water without adversely affecting the source-accumulation potential of large portions of the shelf.

INTRODUCTION

Complex interactions among numerous paleoenvironmental factors and contingencies control the occurrence, quality, and distribution of hydrocarbon play elements at a basin-scale. Paleogeography and paleo-earth systems (climate, oceanography, fauna, flora) have particularly strong influences on the production, preservation, and concentration of organic matter in strata that form potential hydrocarbon source rocks. This paper first discusses these controls in the context of genetic basin analysis and its place in exploration. It then turns to the role of paleo-environmental reconstructions in genetic basin analysis: what we need to know, how well we need to know it, and the challenges of knowing in terms of processes and contingencies. We then demonstrate the application of paleo-environmental reconstructions and modeling to the prediction of hydrocarbon source rocks. We conclude with a summary of the key considerations for prediction of hydrocarbon play elements.