AAPG Annual Convention and Exhibition

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The Prediction of Basement Composition and Radiogenic Heat-Flow Contribution for Petroleum System Modelling in Deep-Water Frontier Exploration

Abstract

The thickness and composition of crustal basement are critical elements in the control of hydrocarbon maturation in deep-water rifted continental margin settings. Radiogenic heat-productivity within continental basement contributes significantly to hydrocarbon maturation; in contrast oceanic crust or exhumed mantle contributes very little. Consequently, knowledge of the ocean-continent-transition crustal structure, continent-ocean-boundary location and magmatic type are of critical importance for predicting heat-flow history and for evaluating petroleum systems in deep-water frontier exploration. We have developed quantitative analytical methodologies and an integrated workflow to help constrain the prediction of basement composition and the contribution of radiogenic heat-flow as input to petroleum-system modelling in deep-water frontier exploration. The work-flow and analytical techniques consist of: – Gravity anomaly inversion, incorporating a lithosphere thermal gravity anomaly correction, which is used to determine Moho depth, crustal basement thickness and continental lithosphere thinning. - Residual depth anomaly (RDA) analysis which is used to investigate OCT bathymetric anomalies with respect to expected oceanic values. This includes flexural backstripping to produce bathymetry corrected for sediment loading. - Subsidence analysis which is used to determine the distribution of continental lithosphere thinning. The combined interpretation of these independent quantitative measurements is used to determine crustal thickness and composition across the ocean-continent-transition. This integrated approach has been validated on the Iberian margin where ODP drilling provides ground-truth of ocean-continent-transition crustal structure, continent-ocean-boundary location and magmatic type. In addition, a new joint inversion technique, using deep seismic reflection and gravity anomaly data, has been developed and may be used to help constrain crustal thickness and basement type. The joint inversion method determines the lateral variations in crustal basement density and velocity, and may be used to validate crustal basement thickness determined from deep long-offset seismic reflection data. Deep-water rifted margin examples of the application of this integrated quantitative analysis will be shown.